Art Morrison IRS vs DSE Quadralink

[jtwoods4]

Hey guys, I am trying to learn what the difference is in handling characteristics between the new Art Morrison IRS and the Detroit Speed Quadralink. Is anyone using the AME IRS setup? It looks awesome. When I talk about handling I mean full on road racing at professional tracks. Planning on installing in a 70 Firebird.

https://www.pro-touring.com/attachment.php?attachmentid=107418&stc=1

107419

[dhutton]

Mary Pozzi is using the AME IRS:

https://www.pro-touring.com/threads/110184-Art-Morrison-IRS-install-67-Camaro?highlight=Art+Morrison

https://www.pro-touring.com/threads/104678-New-Art-Morrison-IRS/page6?highlight=Art+Morrison post 107

http://www.lateral-g.net/forums/showthread.php4?t=45908&highlight=art+morrison

Don

[dontlifttoshift]

That same argument was used in support of leaf springs as well.

[dhutton]

That same argument was used in support of leaf springs as well.

True but there is not going to be a lot of comparable data points for the AME IRS for a while compared to the quadralink. Especially in all out road racing.

Don

[Schwartz Performance]

There are so many variables to the "versus" arguments.
IRS is heavier but is well engineered. You have a lot of features in an IRS that you can't with a solid axle, like toe and camber for instance. You can get these built into a solid axle housing but there are drawbacks and expenses there as well since it's more permanent.

We also have a full chassis that shaves weight off of the factory setup... Our Raybestos 1971 Camaro weighed in at 3350 with fuel in it. We primarily use a triangulated 4-link and have great results. Placed first and second 2013/2014 in the PHR/Car Craft Muscle Car Of The Year on our 2nd gen chassis, for what it's worth.

-Dale

[Carl @ Chassisworks]

If you are actually going to be racing I would think that the rule book will probably make the decision for you. If you're doing Pro-Touring/HPD events then there are a lot of factors to consider. There are some trick parts coming down the pipeline for your car. That's all I can really say at the moment.

[wiedemab]

That same argument was used in support of leaf springs as well.

True-dat! I've been looking for where I can buy me some driver skills............. ;)

[dontlifttoshift]

Brandon, driver skills are cheap and can be bought here. http://evoschool.com/

This isn't really a question of these parts against these parts, you are comparing two completely different types of suspension.

Using internet wisdom and conventional theory the IRS should
-Ride better
-Handle better on uneven pavement, ie jumping curbs to straighten out a chicane
-Allow for easy adjustment of caster/camber/toe
-Allow for more tuning and setup options
-Have less unsprung weight

The solid rear axle should
-Handle more power reliably and consistently and do a better job of putting it to the ground
-Require less maintenance through less moving parts
-Be easier to set up and tune
-Cost less
-Weigh less overall

There are exceptions to everyone of those points above, for example cost. I can very easily put together a 9"/ four link package that will cost much more than the price of the Morrison IRS.

What the OP needs to define is
-His usage more specifically, I have my doubts about "all out road racing"
-His skillset and knowledge, can you handle the install, are you writing a check, is someone else doing it and are they capable?
-His budget
-How willing he may be to actually go through the testing process to get the parts truly optimized for his application. All the adjustment in the world is useless if you are not willing to crawl under the car and turn wrenches between sessions.

Where the hell is Ron Sutton?

[jtwoods4]

If you are actually going to be racing I would think that the rule book will probably make the decision for you. If you're doing Pro-Touring/HPD events then there are a lot of factors to consider. There are some trick parts coming down the pipeline for your car. That's all I can really say at the moment.

Hey Carl,

I do pro touring, PDX, and HPDE events. HPDE and PDX events at the level 4 is extremely competitive even though it is not licensed competition racing. licensed competition racing takes it to another level and I don't plan on doing that.

I currently participate in these events in my Pro Touring 1970 Trans Am. however since it is original Trans Am I was limited on the types of chassis and suspension I could use without cutting the original car up. I also cannot install a cage in this car because it would destroy the original body of the 1970 Trans Am and I just couldn't bring myself to do that.

my new build is based on a 1970 Firebird Esprit which has no pedigree or intrinsic value compared to the Trans Am so I'm pretty wide open on the modifications I can do to this car.

[jtwoods4]

What the OP needs to define is
-His usage more specifically, I have my doubts about "all out road racing"
-His skillset and knowledge, can you handle the install, are you writing a check, is someone else doing it and are they capable?
-His budget
-How willing he may be to actually go through the testing process to get the parts truly optimized for his application. All the adjustment in the world is useless if you are not willing to crawl under the car and turn wrenches between sessions.


Hey Donny Thanks for the feedback, I will try to answer your questions.

My usage will be Pro Touring events, NASA HPDE and SCCA PDX. I am not sure if you have experienced DE or PDX at the level 4 but it is very competitive and we are definitely racing, even though it is not official. Yes, the licensed competition racing takes it to another level but DE and PDX events at Level 4 are plenty competitive and we are definitely "road racing", we are pushing our cars to the limits.

Regarding my skillset, I am an engineer by trade and my current car will be my 3rd build. I build my cars myself in my 2 car garage. I will probably outsource the sheet metal and fabrication work to install the rear end suspension... sheet metal work is not something I have done.

I am very willing to go through the testing process. I spent several months tuning and tweaking my last build (1970 Pro Touring Trans Am). I spent a lot of time under my car and in the garage so I am a competent mechanic.

Regarding budget... When I build a car I start by listing all the components I would like to put on the car. Suspension, engine, transmission, wheels, etc... I then total up the cost and if I feel the cost is unreasonable I will then tweak my build. Right now I am trying to determine if a DSE or IRS rear end will work well with a stock front subframe (with modified suspension geometry of course).

For example, if the DSE or IRS system cannot be fully utilized without also using an aftermarket front clip then the budget completely changes on this build. However, if the DSE or IRS can make a big difference even with a modified stock front sub frame then the budget changes again.

[Cdog]

Hey guys, I am trying to learn what the difference is in handling characteristics between the new Art Morrison IRS and the Detroit Speed Quadralink. Is anyone using the AME IRS setup? It looks awesome. When I talk about handling I mean full on road racing at professional tracks. Planning on installing in a 70 Firebird.

https://www.pro-touring.com/attachment.php?attachmentid=107418&stc=1

https://www.pro-touring.com/attachment.php?attachmentid=107419&stc=1

If you’re leaning in the IFS direction but still not sure if you want to make the financial commitment why not do the AM Tri-4 link set up? Get the car done, test, tune find your and the cars limits. You can add the AM IFS to the AM Tri-4 frame later if you choose.


I’ve raced in a F2000 series and have been through the driving schools as a young kid while racing Karts. Road racing is a skill set that a person generally has a talent for to stay in it. It’s not like any other type of racing in that regard. I’ve seen several guys go through the motions but where scared ****less when the flag dropped. You should make sure you’re comfortable and capable before throwing 100k at a car.

[jtwoods4]

If you’re leaning in the IFS direction but still not sure if you want to make the financial commitment why not do the AM Tri-4 link set up? Get the car done, test, tune find your and the cars limits. You can add the AM IFS to the AM Tri-4 frame later if you choose.



Thank you cdog. I was unaware that the AM Tri-4 could be upgraded to the IRS later. For the other guys following this thread here is the Tri-4. Looks like it is a setup that competes with the DSE Quadralink.

107513

[badazz81z28]

A IRS would be nice, but I think that is a different league in terms of cost and performance. Heck you could buy the quadra link and pay to have it installed than what the IRS cost alone. You don't gain enough to justify the money unless you compete. How much are those 1/10ths worth to you? If I was going to spend that much on a car to get it to that level, I would consider a new corvette or Camaro. I would seriously consider what the plan is for the car and be prepared to spend $$$$$

Besides, like people always tell me, just because the car can handle well, doesn't mean it will with me behind the wheel. A lot of the performance in cars like Mary's has a lot to do with her experience. The car with leafs performed just as well. So don't get too caught up with that and I also think she's sponsored by AME, so there may be some bias opinions.

[Cdog]

Thank you cdog. I was unaware that the AM Tri-4 could be upgraded to the IRS later. For the other guys following this thread here is the Tri-4. Looks like it is a setup that competes with the DSE Quadralink.

107513

To back that up. We’re a AM dealer at Starlite. We’ve installed the AM Tri-4 on my personal 69. I’ve spoke to the tech guy’s over at AM. The frame section is the same between the two. There will be some mods to convert. Tabs etc.....

Best of luck.

[jtwoods4]

A IRS would be nice, but I think that is a different league in terms of cost and performance. Heck you could buy the quadra link and pay to have it installed than what the IRS cost alone. You don't gain enough to justify the money unless you compete. How much are those 1/10ths worth to you? If I was going to spend that much on a car to get it to that level, I would consider a new corvette or Camaro. I would seriously consider what the plan is for the car and be prepared to spend $$$$$

Besides, like people always tell me, just because the car can handle well, doesn't mean it will with me behind the wheel. A lot of the performance in cars like Mary's has a lot to do with her experience. The car with leafs performed just as well. So don't get too caught up with that and I also think she's sponsored by AME, so there may be some bias opinions.

those are some good points. Thank you. I'm leaning towards the Art Morrison tri-4 at this point. looks like a very nice piece.

[Ron Sutton]

Using internet wisdom and conventional theory the IRS should
-Ride better
-Handle better on uneven pavement, ie jumping curbs to straighten out a chicane
-Allow for easy adjustment of caster/camber/toe
-Allow for more tuning and setup options
-Have less unsprung weight

The solid rear axle should
-Handle more power reliably and consistently and do a better job of putting it to the ground
-Require less maintenance through less moving parts
-Be easier to set up and tune
-Cost less
-Weigh less overall

There are exceptions to everyone of those points above, for example cost. I can very easily put together a 9"/ four link package that will cost much more than the price of the Morrison IRS.

What the OP needs to define is
-His usage more specifically, I have my doubts about "all out road racing"
-His skillset and knowledge, can you handle the install, are you writing a check, is someone else doing it and are they capable?
-His budget
-How willing he may be to actually go through the testing process to get the parts truly optimized for his application. All the adjustment in the world is useless if you are not willing to crawl under the car and turn wrenches between sessions.

Where the hell is Ron Sutton?


LOL. Hey Donny ! Here's my 2¢
First, everything Donny said above is excellent. So I'm just adding points of interest.

Key Goals & Objectives for Track Car Rear Suspensions ... just for educational sake:
With a few minor exceptions, the rear suspension design has no impact on mid-corner "roll through zone" grip or corner speed capability.
I just heard a lot people say, "What?" :seizure:

The factors that DO play a role on mid-corner "roll through zone" grip & corner speed capability are:

CG, Roll Center & Track Width
Mechanical Roll Resistance: Spring & Sway Bar Rates
Shock Valving

Whether you have a 3-link, 4-link, 196-link, IRS, torque arm, truck arm, etc ... is irrelevant to mid-corner "roll through zone" grip & corner speed capability … because there is no torque (engine or braking) being put through the rear suspension during the mid-corner "roll through zone." The few minor exceptions to this, are if the rear tires have camber, toe or rear steer from the rear suspension design. Those items can & do affect mid-corner "roll through zone" grip & corner speed capability. Another exception is rear suspension bind … which can have an obvious, negative effect on handling. But frankly, all of these … camber, toe and/or rear steer … and even suspension bind … are possible with most rear suspension designs.

So why do we care what rear suspension design we run?
Corner entry & corner exit. The choice of rear suspension design … and the key details in the rear suspension design … all play a role in how much rear grip the car has on corner entry (turn-in & braking) and corner exit (steering unwind & throttle roll on).

While there are a lot of details (18 to be exact) in optimizing a rear suspension, the biggies during design, or purchase selection, are:
1. Articulation
2. Torque Distribution
3. Instant Center
4. Packaging
5. Pinion Angle Change
6. Rear Roll Center
7. Rear Steer
8. Camber
9. Toe
10. Tuning Adjustability

Articulation is the amount of angle differential the housing can achieve from the chassis. Maybe not so obvious ... but we need the rear housing to articulate at least as far as the chassis needs to roll. This matters more if you're running a conventional suspension strategy that rolls 3° or more. This is less of an issue if you're running a modern low roll suspension strategy that rolls around 1°. With the solid mounted Diff of IRS, this is a non-issue.

Torque Distribution is most critical & not understood by most. We've been trained (wrongly) to just look at anti-squat for our rear tire loading geometry. But when you attach suspension link brackets to a live axle with torque coming through it ... the link brackets become levers ... and the length & location of these levers completely affect how much of the torque is pushing the lower links & car forward ... and how much of the torque is lifting the chassis & loading the rear tires for grip. This is CRITICAL for optimum forward bite on corner exit ... especially with harder TW200, short sidewall, radial tires.

“Most” rear suspensions designed for ProTouring cars do NOT have enough torque “lifting & loading” because there is not enough room for long top link brackets to fit under the factory floors of the cars we’re building here. In oval & road racing, if you pay attention, you’ll notice the top links are mounted higher on the housing. This provides more leverage (more torque) for the top link(s) pulling, lifting the chassis & planting the rear tires. As a side note, you’ll notice at the top levels in door slammer drag racing … Pro/Stock, Pro/Mod, etc. with 1500-2500+ HP & tall, soft sidewall slicks … they place the top links lower (closer to the axle centerline) to reduce the violence on launch that causes tire shake. We don’t have that concern with 600-1000 hp & our tires. 3-links & 4-links ... if room above the housing allows the brackets to be tall ... allow optimum torque distribution for grip.

With IRS the diff is solid mounted to the chassis, so the torque distribution is always 50/50. This is better than a lot of ProTouring rear suspensions with short top link brackets. But it’s not “optimum” for every application. Obviously, with solid mounted IRS, the torque distribution is not adjustable for tuning.

While we're on torque distribution, almost all rear suspension designs load the LR tire more under hard acceleration. This is amplified with higher power engines. This causes the car to have more rear grip on the exit of LH corners & less grip on the exit of RH corners. Only Offset 3-links & Torque Arms allow optimum torque distribution side-to-side ... for zero torque steer ... allowing equal handling on LH & RH corners. The Offset, Decoupled 3-link … my personal favorite for race & track cars … offers separate & optimum tuning for corner entry & corner exit grip. Decoupled Torque Arms also allows separate tuning to optimize the grip on corner entry & corner exit ... but the tuning is limited. The Offset, Decoupled 3-link is the ultimate track car rear suspension. All other rear suspension designs have you tuning for the best compromise.

The Instant Center is your rear suspension pivot point as well as the point it picks up on the chassis to load the tires (except torque arms). Where it is in relation to the CG is very important. Too far behind the CG & the car will lose traction late on corner exit. Too far ahead of the CG and the car will spin the tires upon initial throttle roll on. This needs to be tunable & optimized to your car. I typically start with it under the CG & fine tune for track conditions.

This is very tunable with 3-link & 4-link suspensions … as long as you utilize brackets with slots or multiple holes to make it adjustable. The way to adjust this on torque arms is to have multiple length torque arms & the mounting points built into the chassis to change torque arms. This takes longer to adjust at the track than simply adjusting the link heights with a 3 or 4 link.

The instant center of IRS is determined by the control arm angles. Commonly connected to anti-squat, but I caution you not to make decisions by anti-squat percentages alone. You can achieve the same anti-squat number with a lot of different control arm angles … and they will not handle the same. The instant center location & anti-squat need to be worked out together. Unfortunately tuning the instant center location on IRS is NOT quick, nor easy. So we can say it is tunable, but the amount of work & time required makes it not practical to tune the instant center/anti-squat at the track.

Packaging in the PT world is probably at the top of the list. When someone is asking for my recommendation for their car ... the first I ask is, "Are you keeping the rear seat?" If the answer is yes, we should eliminate all three versions of the 3-link ... because where they really need to mount conflicts with the rear seat. Frankly so do parallel 4-links, unless the top links are ridiculously low & short. If the back seat stays ... IRS (some fit with a back seat & some don’t) Triangulated 4-link & Torque Arm suspensions are the best of what will fit & allow a back seat.

If the back seat goes & we can remodel the sheet metal in the rear floor & trunk area... it's wide open. 3-links & 4-links allow optimum torque distribution for grip. 3-Links offer the most articulation. Offset 3-links allow optimum torque distribution for zero torque steer ... allowing equal handling on LH & RH corners. The Offset, Decoupled 3-link offers separate & optimum tuning ... for the ultimate grip on corner entry & corner exit.

Pinion Angle Change happens greater when the top links & lower links (of a 3 or 4 link) are short or have a large difference in length. It also happens with weak/soft leaf springs & lots of power. It's not the end of the world. You just have to plan & deal with it. Obviously no pinion angle change with IRS.

Rear Roll Center adjustment ... to me, from my experience, for track tuning ... is one of the easiest, more predictable tuning devices you can ever have to help balance & neutralize the handling of the car. It's simple. Raise it to free the rear end up. Lower it for more rear grip. Don't go outside the sweet spots. Having a rear suspension with no adjustment for the rear roll center really ties your hands. It eliminates one of the best tuning devices out of your tool box. You can run a double adjustable panhard bar or adjustable Watts link with any suspension but IRS. Yes ... even leafs & triangulated 4-links.

To me, this is the biggest draw back/weakness to IRS. You have to adjust the rear control arm mounts to move the roll center in IRS. Just like the instant center/anti-squat … it is adjustable … but the time & work required make tuning it at the track impractical for most guys. Pro road race teams will do it, but they have built the car to make adjustment quicker, have worked out their set-ups in advance & have multi-person crews to get’er done.

Rear Steer
First, I’d better clarify that all cars have rear steer when driven to the car & tire’s limits, because the slip angle of the rear tires (contact patch) is pointing toward the outside of the corner. We don’t accurately know what the slip angle of your tires are. But for instance, let’s say the tires you run achieve optimum grip at an 8° slip angle … the rear of your car has 8° of rear steer to start with.

Rear steer from the suspension … also known as roll steer … is when the rear wheels change direction (relative to chassis centerline) during body/chassis roll while cornering. Positive rear steer is when the rear wheels shift direction slightly to point towards the outside of the corner. This “steers” the tires further outward at the rear of the car, increasing our degree of rear steer & frees up the car. If we add 1° of positive rear steer, we end up with a total of 9° rear steer. Negative rear steer is when the rear wheels shift direction slightly to point towards the inside of the corner. This “steers” the tires inward at the rear of the car, reducing our degree of rear steer & tightens up the car. If we add 1° of negative rear steer, we end up with a total of 7° rear steer.

Rear steer can be achieved in 3-link, 4-link & torque arm rear suspensions by setting the angle of the lower links. If you run the lower links level, you have no rear steer. If you raise the front of the lower link mounting points, so the links run uphill to the front, you are adding positive rear steer. If you lower the front of the lower link mounting points, so the links run downhill to the front, you are adding negative rear steer. With IRS suspensions, positive or negative rear steer is achieved with the toe rod … similar to a tie rod in a front suspension, except the inner pivot mounts to the chassis.

Rear Camber
Negative camber of the rear tires … in small amounts … helps the outside rear tire run with a flatter contact patch, giving it more grip. Just as in the front end, camber helps the contact patch of the outside tire & hurts the contact patch of the inside tire, by tipping it the wrong direction. But the loss is not a “1-for-1” kind of thing.

The outside rear tire is loaded more, so it “rolls under” more than the inside rear tire. If you add a small amount of negative camber (0.5°-1.5°) to the rear tires to optimize the outside rear tire’s contact patch … you will hurt the contact patch & grip of the inside rear tire … but not very much. The gain in grip on the outside rear tire will exceed the loss of grip on the inside rear tire, netting an overall grip increase. Besides … you need to disengage the inside rear tire to a degree anyway, to get the car to turn. Just don’t get carried away … or the loss of grip on the inside rear tire will make the car loose.

This makes sense, providing you feel you need more rear tire grip. In my experience, with adjustable rear suspensions, I’ve never been in a situation where I couldn’t get all the rear grip we needed. We don’t want more rear grip than front grip … and front grip is the limiting factor. So the question is not will it help rear grip … it will. The question is … do we need more rear grip in the corner … or more front grip?

In my experience, the times where we need more rear grip is we have a road course Track Car, AutoX or Race Car with MORE weight bias in rear than front. Like Formula Fords, Porsche 911/930/935 & other rear engine exotics. Frankly, very few PT cars achieve a significantly higher rear weight bias.

Rear Toe
Toe-in of the rear tires ... takes the outside rear tire & toes it "inward" increasing slip angle & reducing rear steer. This makes the outside rear tire have grip sooner & respond quicker on corner entry. This is quite common in road racing, as it builds confidence in the driver. But there are many negative side effects. In my opinion, the side effects are not worth it.

Side effects:
a. The outside rear tire gets to the optimum slip angle at a lower corner speed, reducing that tire's ultimate corner speed capability.
b. The toe-in of the two rear tires ... say 1° each for a total of 2° toe-in ... creates unwanted scrubbing of the rear tires. This builds heat, misleading the crew into thinking they're working the rear tires better.
c. The poor inside rear tire is turned the opposite direction for optimum slip angle, and therefore has less grip throughout every section of the corner.
d. Toe-in of the rear tires reduces the rear steer effect of slip angle. That rear steer effect is needed to offset the counter steer effect the slip angle produces in the front end. So we end up with a tighter race car … prone to pushing & understeer.
IMHO, I feel rear toe-in is a band-aid for old design, tall sidewall tires and/or cars with a rear heavy weight bias that need additional grip on corner entry

Toe-out of the rear tires ... takes the outside rear tire & turns it "outward" to reduce slip angle. This makes the outside rear tire have grip later & respond later … so the car may feel loose on entry. But the outside rear tire gets to the optimum slip angle at a higher corner speed, increasing that tire's ultimate corner speed capability. The inside rear tire is turned the correct direction for optimum slip angle, and therefore has more grip throughout every section of the corner. Now both tires have more grip & the capability for the back end of the car to carry more corner speed … if the front is also capable. But the biggest effect toe-out of the rear tires produces … is increased rear steer effect of slip angle. This increased rear steer effect makes the car turn better … to help offset the counter steer effect the slip angle produces in the front end.

Tuning Adjustability is KING for track cars.
Knowing that front tire grip is the highest priority, we tune the rear grip up or down to make the handling neutral & balanced for optimum performance, fastest lap times, ease of drivability & highest degree of fun & driver enjoyment.

But if you can not adjust your rear suspension, how do you optimize the car for track conditions or driver preference? IMHO, having the rear suspension easily adjustable is key. Each rear suspension has different key areas that are quick & easy to adjust or hard & time consuming to adjust. I should say here, that these don’t apply, if you buy & install a non-adjustable suspension.

In addition to Donny’s list, here is a PDF chart showing pros & cons … what is & isn’t changeable during design & installation … along with what is quick & easy to adjust at the track … and what is not. 107514

My Opinion & Preference:
First I have to share an analogy. When I raced Karts we ran 2-strokes which LOVE to be rich on the bottom end of the RPM range coming off corners. If you got the carb rich enough for optimum corner exit power in the 10,000-12,000 rpm range … the engine would go too rich & burble somewhere above 12,000 rpm and fall on its face. The slang term was 4-cycling when the engine went too rich. I got a special set-up that allowed me to lean the carb with a lever on the steering wheel. The lever was green, so when guys asked me what it was, I told them it was a weed whacker lever to mow the grass when I went off track. :rotfl:

Eventually I told them it was a “Lean Lever” that let me lean the carb on the top end (12,000-14,500 rpm). They couldn’t understand why I wanted the top end leaner than could be achieved through jetting. I didn’t. I wanted the low end much richer off the corner … and just used the lean lever to get the overly richened carb back to where the A/F ratio was happy above 12,000 rpm. So in other words, I used a lean lever as a different approach to the goal of running the low end richer.

I think of IRS the same way. Some people will say IRS has more grip than solid axle rear suspensions. That’s not accurate. IRS allows us to achieve negative camber & therefore better grip on the outside rear tire & less grip on the inside rear tire (through camber the opposite direction) when cornering. This allows us to run softer spring & sway bar packages in the rear to increase rear grip. Like the lean lever allowed me to run the low end richer … the lower mid-corner grip of IRS allows us to add grip to help the entry & exit. It is just another approach to skin the cat. But like anything, you had better know how to tune it.

For the type of cars we run here in Autocross & on Road Course Track Days … I prefer solid axle rear suspensions. Assuming we have enough suspension travel to get the rear of the car to roll .35°-.40° more than the front … to achieve the optimum diagonal roll the car needs. If so, I can always disengage the inside rear tire of a solid axle rear suspension … to the optimum degree … just as well as an IRS. To achieve this consistently, requires an adjustable rear roll center via a Watt’s link or panhard bar.

I prefer a solid axle rear suspension when:
• The car is front engine, front weight biased or somewhere around 50/50 weight biased.
• The ride height rules … or the conditions we place on ourselves (like the need to drive over speed bumps) … require the car to be 2.5” or more off the ground.
• Because in this case, I know front grip is the limiting factor & I have enough suspension travel to create an optimum handling result.

For solid axle rear suspensions:
1. The highest performer for track purposes is the Offset, Decoupled 3-Link.
2. Next would be the Offset 3-Link.
3. Next would be a regular centered 3-Link or 4-link (as long as articulation is not an issue).
4. None of these will fit well under a seat, unless the top links are super short (not recommended).
5. The best that fit under the seat are triangulated 4-links & torque arms.
6. Regardless of choice ... make them adjustable ... as well as the rear roll center.

I prefer IRS when factors make it difficult to disengage the inside rear tire:
The car is mid or rear engine, with substantially more weight on the rear tires (54%+).
The ride height rules place the car very close to the ground (under 2”), limiting suspension travel.
Because in this case, I know rear grip is the limiting factor & I have do not have enough suspension travel to create an optimum handling result.


Summary:
Frankly, at this level of competition, I think we can make most rear suspension packages work well if we get them set-up right & dial them in through tuning. Each of these rear suspension styles has pros & cons. So pick your poison & get after it. ALL rear suspensions have strengths & weaknesses. My advice is to pick the version that best suits your usage, priorities & goals. Then do your best to design it, set it up & tune it to optimum performance for your usage.


:cheers:

[jtwoods4]

Now that's what I'm talking about! What an amazing response. You da man Ron!

[Ron Sutton]

Now that's what I'm talking about! What an amazing response. You da man Ron!

You're welcome John. Best wishes with your project!


:cheers:

[ace_xp2]

What about roll axis control? When both front and rear suspensions move the roll center as the suspension moves, you can keep closer to the original roll axis as the suspension moves which should improve predictability/feel. Not worth it?
IIRC you can also play with rear steer and suffer less wander in single wheel bump. Also, multi links can get really funky with when,how much, and which way they apply steer or toe throughout the range of travel (though I don't think you can tune this without a rework, not sure).

[David Pozzi]

We are very pleased with the Art Morrison IRS. Mary has done very well with it. It isn't as tuneable for roll center or anti-squat as a 3 link, but the lower unsprung weight makes the car much more stable & the negative camber gain increases cornering grip, plus it's the strongest IRS I've seen, which was important to me.

[Ron Sutton]

What about roll axis control? When both front and rear suspensions move the roll center as the suspension moves, you can keep closer to the original roll axis as the suspension moves which should improve predictability/feel. Not worth it?
IIRC you can also play with rear steer and suffer less wander in single wheel bump. Also, multi links can get really funky with when,how much, and which way they apply steer or toe throughout the range of travel (though I don't think you can tune this without a rework, not sure).

Ace, I didn't understand your question. Since no one else chimed in to answer ... if you can restate it ... I may be able to answer your question.

[Ron Sutton]

We are very pleased with the Art Morrison IRS. Mary has done very well with it. It isn't as tuneable for roll center or anti-squat as a 3 link, but the lower unsprung weight makes the car much more stable & the negative camber gain increases cornering grip, plus it's the strongest IRS I've seen, which was important to me.

Hey David,

Mary told me she LOVED the new Art Morrison IRS when I talked to her at Scottsdale. She said originally it was set up with too much rear steer & tuned "some" of it back out. Then it was perfect. It was sure fun to watch her run that car in the final 4. Of which should be mentioned 3 of the fastest 4 were utilizing IRS.

I've recently designed a car for a client with IRS. I sure do like the aluminum D60 Morrsion uses. But my client went the C6 route with the trans in the rear also, for even better front/rear weight distribution.

:cheers:

[ace_xp2]

What I was getting at is that when an independent suspension rolls the roll center moves, and that if both ends are independent you can have both roll centers move in similar ways, better maintaining roll axis which I would think should feel more predictable (maybe there's a better term?) as then both ends will experience a similar change in rc to cg position.

[David Pozzi]

Hey David,

Mary told me she LOVED the new Art Morrison IRS when I talked to her at Scottsdale. She said originally it was set up with too much rear steer & tuned "some" of it back out. Then it was perfect. It was sure fun to watch her run that car in the final 4. Of which should be mentioned 3 of the fastest 4 were utilizing IRS.

I've recently designed a car for a client with IRS. I sure do like the aluminum D60 Morrsion uses. But my client went the C6 route with the trans in the rear also, for even better front/rear weight distribution.

:cheers:




Ron,
After installing the IRS I did the first alignment & added more negative camber, I didn't think of it at the time but this changed the rear caster setting which is difficult to measure because it requires a flat spot to put a gauge on. The caster setting is critical on this suspension because it establishes the toe link height. So- we actually had a lot of toe-in gain under roll and bump which caused the rear to feel unsettled at corner exit. I made "tuning" adjustments to the toe cams but my baseline was way off. I finally did some dynamic toe (bumpsteer) checking and found the problem. After all the work to install the IRS, I was pretty behind on other things and with new front and rear suspension, it took me till mid-season to get back on it and verify rear toe change.

Matt at Art Morrison came up with a caster number that their outer hubs need to be set to and I set it to that. We currently are not using much toe-out gain, I think it's at .020" per inch bump but we need to do more testing. I think at our HP and traction levels we won't be able to use much more but time will tell.
Matt made the comment the roll center is very stable, but I don't recall the static RC height.

I was seriously considering a Corvette transaxle for my 67 Camaro. The main drawbacks were the time it would take me to design mounts and install it, dealing with the torque tube, exhaust passage past it, plus would it be strong enough. It was looking like I could be spending an extra year in the shop fussing with it compared to just doing a 3 link (the way I work). I had decided to just design my own 3 link & dream on about an IRS, - then I got a ride in the Morrison 69 Camaro and I was hooked... My Camaro was my first car and I'm the original owner, so I want to drive it on the street a fair amount in addition to doing track and autocross events. The IRS makes the car ride so much better it was a no-brainer for me.

[Ron Sutton]

What I was getting at is that when an independent suspension rolls the roll center moves, and that if both ends are independent you can have both roll centers move in similar ways, better maintaining roll axis which I would think should feel more predictable (maybe there's a better term?) as then both ends will experience a similar change in rc to cg position.

Now I understand what you're saying. Other than the RC migrating side to side, IRS RC movement is similar to solid axle RC movement, but not necessarily linear.

[Ron Sutton]

Ron,
After installing the IRS I did the first alignment & added more negative camber, I didn't think of it at the time but this changed the rear caster setting which is difficult to measure because it requires a flat spot to put a gauge on. The caster setting is critical on this suspension because it establishes the toe link height. So- we actually had a lot of toe-in gain under roll and bump which caused the rear to feel unsettled at corner exit. I made "tuning" adjustments to the toe cams but my baseline was way off. I finally did some dynamic toe (bumpsteer) checking and found the problem. After all the work to install the IRS, I was pretty behind on other things and with new front and rear suspension, it took me till mid-season to get back on it and verify rear toe change.

Matt at Art Morrison came up with a caster number that their outer hubs need to be set to and I set it to that. We currently are not using much toe-out gain, I think it's at .020" per inch bump but we need to do more testing. I think at our HP and traction levels we won't be able to use much more but time will tell.
Matt made the comment the roll center is very stable, but I don't recall the static RC height.

I was seriously considering a Corvette transaxle for my 67 Camaro. The main drawbacks were the time it would take me to design mounts and install it, dealing with the torque tube, exhaust passage past it, plus would it be strong enough. It was looking like I could be spending an extra year in the shop fussing with it compared to just doing a 3 link (the way I work). I had decided to just design my own 3 link & dream on about an IRS, - then I got a ride in the Morrison 69 Camaro and I was hooked... My Camaro was my first car and I'm the original owner, so I want to drive it on the street a fair amount in addition to doing track and autocross events. The IRS makes the car ride so much better it was a no-brainer for me.

Hey David,

Thanks for sharing some set-up & tuning info!

I find it interesting you & Mary ended up with toe-out. When we build solid rear axle suspensions ... with floater hubs & cambered ends (typically 9" Ford) I run a little toe-out too, as long as the driver has some experience & skills. Rookies really want the rear end "under them" so I don't run toe-out with rookies. But I run a little toe out with my veteran road race drivers. With the IRS stuff I design ... same thing ... if they're a rookie ... we start with neutral toe. But if they have skills & experience, I run some toe out.

Thanks again for sharing !

[Cdog]

Ron,
After installing the IRS I did the first alignment & added more negative camber, I didn't think of it at the time but this changed the rear caster setting which is difficult to measure because it requires a flat spot to put a gauge on. The caster setting is critical on this suspension because it establishes the toe link height. So- we actually had a lot of toe-in gain under roll and bump which caused the rear to feel unsettled at corner exit. I made "tuning" adjustments to the toe cams but my baseline was way off. I finally did some dynamic toe (bumpsteer) checking and found the problem. After all the work to install the IRS, I was pretty behind on other things and with new front and rear suspension, it took me till mid-season to get back on it and verify rear toe change.



Matt at Art Morrison came up with a caster number that their outer hubs need to be set to and I set it to that. We currently are not using much toe-out gain, I think it's at .020" per inch bump but we need to do more testing. I think at our HP and traction levels we won't be able to use much more but time will tell.
Matt made the comment the roll center is very stable, but I don't recall the static RC height.

I was seriously considering a Corvette transaxle for my 67 Camaro. The main drawbacks were the time it would take me to design mounts and install it, dealing with the torque tube, exhaust passage past it, plus would it be strong enough. It was looking like I could be spending an extra year in the shop fussing with it compared to just doing a 3 link (the way I work). I had decided to just design my own 3 link & dream on about an IRS, - then I got a ride in the Morrison 69 Camaro and I was hooked... My Camaro was my first car and I'm the original owner, so I want to drive it on the street a fair amount in addition to doing track and autocross events. The IRS makes the car ride so much better it was a no-brainer for me.




David, How did the car scale/weight after the IRS install? Did you install a AM G-frame on the front end of your or Mary’s car?

Thanks in advance, Corey

[ace_xp2]

Now I understand what you're saying. Other than the RC migrating side to side, IRS RC movement is similar to solid axle RC movement, but not necessarily linear.

A solid axle has no virtually no RC movement with a watts though, and very little movement with a panhard, neither of which would mimic the way the RC moves in a typical IFS. Whereas with a IRS back there those movements could be made to keep closer to one another front to back, linear or not. In that way, both suspensions would experience relatively the same change and so have a more linear response from both ends no?
I suppose it's probably more useful with something closer to a factory vehicle which rolls a fair bit, as you'll then have more IFS RC migration (and so a change roll stiffness) which will then make the comparative lack thereof at the rear lead to a change in the cars handling as the vehicle rolls (though of course, that change could be favorable).

[Ron Sutton]

Hi Ace!


A solid axle has no virtually no RC movement with a watts though, and very little movement with a panhard, neither of which would mimic the way the RC moves in a typical IFS. Whereas with a IRS back there those movements could be made to keep closer to one another front to back, linear or not. In that way, both suspensions would experience relatively the same change and so have a more linear response from both ends no?
I suppose it's probably more useful with something closer to a factory vehicle which rolls a fair bit, as you'll then have more IFS RC migration (and so a change roll stiffness) which will then make the comparative lack thereof at the rear lead to a change in the cars handling as the vehicle rolls (though of course, that change could be favorable).

Ah ... now I understand why we're on different pages. You're thinking about a Watt's link with the bell crank mounted on the housing ... and I never run them that way. I either run a panhard bar or Watt's links with the bell crank mounted to the frame structure.

For anyone following along with our conversation ...
A. For a Watt's link with the bell crank mount on the housing, the rear roll center stays at the same height more or less. It raises or lowers only with tire squish & extension.
B. For a Watt's link with the bell crank mount on the frame, the rear roll center raises or lowers equally as the frame does.
C. For a panhard bar, which must be mounted to the frame on one side only, the rear roll center raises or lowers half as much as the frame does.
D. For an IRS suspension, the rear roll center raises or lowers based on the angles & intersections of the control arms. How much varies with the geometry.

For example, if the rear of the car rises an 1" on braking or squats 1" on acceleration ...
A ... may only rise or squat 1/8"-1/4"
B ... would rise or squat the same 1"
C ... would rise or squat 1/2"
D ... the amount per inch varies.*
* I have 2 recent IRS designs for clients that vary a lot. The rear RC in #1 changes 1.1" per inch of chassis rise or squat. The rear RC in #2 only changes .4" per per inch of chassis rise or squat.

Back at the ranch ...
Ace, my thinking was the frame mounted bell crank Watts is similar to my #1 IRS example. And a panhard bar is similar to my #2 IRS example. And you referenced, the housing mounted bell crank Watts doesn't move like these three do. But none of them truly mimic an IRS. As the RC migrates left or right during roll with an IRS, which doesn't happen with a Watts or PHB.

:cheers:

[David Pozzi]

David, How did the car scale/weight after the IRS install? Did you install a AM G-frame on the front end of your or Mary’s car?

Thanks in advance, Corey

I guess I started a trend. I bought a front sub for my 67 from Art Morrison, then Mary and James saw it in my shop, we discussed the pros and cons, etc. Then Mary and James had new engine installs coming up. No better time to swap subs than while the engine is already out... So they both changed.
We gained a little rear weight, something like 50 lbs. Went from 52% front to 51%.

[Rod]

I think were comparing apples to oranges....
leafs springs 500 bucks, four link with coil overs 2500 bucks, IRS 10,000+ bucks!!.....

I stated 6 years ago IRS and full independent suspended cars were the way to go and will dominate the sport.....but you cant slap IRS in everything and it will be great...the car balance, roll centers, scrub, width, weight transfer on the car has to be balanced, matched front to rear, other wise the car will actually drive worse, pitching and rolling all over with two different targets (front and back) never intersecting for greater than a moment

just my two cents

[nokones]

Very good article in Super Chevy

[Cobra 498]

I think were comparing apples to oranges....
leafs springs 500 bucks, four link with coil overs 2500 bucks, IRS 10,000+ bucks!!.....

I stated 6 years ago IRS and full independent suspended cars were the way to go and will dominate the sport.....but you cant slap IRS in everything and it will be great...the car balance, roll centers, scrub, width, weight transfer on the car has to be balanced, matched front to rear, other wise the car will actually drive worse, pitching and rolling all over with two different targets (front and back) never intersecting for greater than a moment

just my two cents

Right on the money, the whole package and how it works as a unit, the front and rear suspensions need to be designed to work together.

[dhutton]

I think were comparing apples to oranges....
leafs springs 500 bucks, four link with coil overs 2500 bucks, IRS 10,000+ bucks!!.....

I stated 6 years ago IRS and full independent suspended cars were the way to go and will dominate the sport.....but you cant slap IRS in everything and it will be great...the car balance, roll centers, scrub, width, weight transfer on the car has to be balanced, matched front to rear, other wise the car will actually drive worse, pitching and rolling all over with two different targets (front and back) never intersecting for greater than a moment

just my two cents

Keep in mind the IRS includes the differential and brakes. Add those to a Quadralink and the gap narrows. Still significant but not $7500.

[ace_xp2]

Oh yeah, had completely forgot about the two different styles of watts linkage, Oops!

[David Pozzi]

I think were comparing apples to oranges....
leafs springs 500 bucks, four link with coil overs 2500 bucks, IRS 10,000+ bucks!!.....

I stated 6 years ago IRS and full independent suspended cars were the way to go and will dominate the sport.....but you cant slap IRS in everything and it will be great...the car balance, roll centers, scrub, width, weight transfer on the car has to be balanced, matched front to rear, other wise the car will actually drive worse, pitching and rolling all over with two different targets (front and back) never intersecting for greater than a moment

just my two cents

Rodney, One thing that kept nagging me was the success Newman guys were having with their C4 stuff. Also that they don't like to alter the suspension. It was an eye-opener to see how well they were doing with that stuff.

If you refer back to the original post of this thread, the question asked was about differences between a DSE 4 link and IRS like the Art Morrison.

I'm going to bring up some extra info here that may help someone in their build. It includes leaf springs and a little bit on the AME front sub we use.

The First Gen Camaro subframe is very limiting to getting wide tires up front, the AME sub has 2.5" more room to the frame rail per side, so getting more rubber on the front is easier. A 275/18 is the most I've heard of on a stock sub. I think turn radius will suffer at that point. It did on the One Lap Camaro when we put 275's on it. The AME sub is stiffer in torsion than a stock sub plus there is weight savings. The weight savings is mostly all in the unsprung suspension, - the knuckles and A arms which is the best place to be light. The rack is nice for a little more direct feel, but most racks are based on Fox body Mustang valving which is not very firm at all. The Mustang Cobra R was a good rack, but they are out of stock. The access to the engine & extra space to run dry sump hoses, etc is excellent. Shock and spring access is excellent for tuning/swapping. 3 hole adjustable front sway bars with rod ends, plus the sway bar arms are longer so they don't bind at the limit like a stock sub.

On the rear, aftermarket leaf springs are a quick and easy way to go fast. They do a lot & properly installed and supported (shackles) they do amazingly well. The downfall is extra unsprung weight and there is inter-leaf friction that is an unknown. Twisting of the leaf in roll can happen and add extra rear roll stiffness during corner exit. I think there is an upper horsepower limit to leaf springs where they will not perform well without being even heavier/stiffer or adding extra linkage to handle the extra loads. I wouldn't want to put 600, 700, or 800+ hp through them. Tuning them is very very limited.

3 or 4 link suspension greatly improves the ride with less unsprung weight, better rear axle location and along with it increased ability of the rear suspension to deal with bumps and undulations. Some have tuneability of geometry for anti-squat/dive, also roll center with a Panhard bar or Watts link, ease of changing spring rates or ride height. From what I've seen of the DSE 4 link, it's not tuneable for geometry which is probably a good thing for most of their customers & I'm sure they have a good setting & their cars and customers do well with their stuff. The sway bar is adjustable and the usual coil overs. I think the shocks are a bit short on their first gen kit so they probably have a smaller sweet spot for ride height than their second gen 4 link. If you want a super-low ride height, the shocks may bottom out. I would find out the design height they recommend and see if that matches what you want for your car. I think you can be low, you just can't be super-low. This is a good idea to check out when considering any suspension, also don't go so low you are bottoming out or you will never get the suspension to work right.

On a second gen Camaro, to take full advantage of a Mini-Tub, the leaf springs have to be relocated inboard, and a shock crossmember added to relocate them inboard. It makes a lot more sense to go to a link suspension or IRS than spend money relocating leaf springs.

[David Pozzi]

Keep in mind the IRS includes the differential and brakes. Add those to a Quadralink and the gap narrows. Still significant but not $7500.


Here's pricing info from AME:
Ok, so going back through this thread, the one thing I wanted to address is the pricing. When Super Chevy did the story on Matt's car, it was in the advanced prototype stage and we had no clue as to what the price was going to be, so with a best guess I put a number together. Please keep in mind that that also included the entire rear weld-in subframe for a 1st Gen car as well.

So, for what we have available now here is the pricing and component breakdown:
IRS Cradle
Strange S60 differential
Upper control arms
Front lower control arms (with Johnny Joints)
Rear lower control arms (with Johnny Joints)
Toe link kit
5th Gen Camaro knuckles machined to accept C6 hubs
C6 30-spline hubs
5th Gen Camaro parking brake kit
Two-piece adjustable sway bar
Cradle bushing kit
Driveshaft Shop 30 spline axle package w/ 930 CV joints
JRI non-adjustable monotube coil-overs
5th gen Camaro disc brake kit 12.4" rotor

This package (which is rated at 1400+ RWHP) is priced at $11,500
This IRS package can be added to any rear subframe or chassis in our line-up. We also have sold a number of these packages with loose brackets so customers can graft it into existing chassis and subframes. There are also numerous options available on the shocks and brakes.


The two biggest pricing factors in this IRS is the Strange S60 center and high HP Driveshaft Shop axles with the 930 CV's. We are going to be offering a package very shortly with a few different options for OE Camaro diffs as well as a more affordable axle package from Driveshaft Shop - power rating should still be in the 700-800 RWHP range.

Hope this answered a few questions regarding the pricing... Any more please let me know.


Here is their lower cost unit:
OK, so we finally have pricing on a more budget friendly IRS package:

So, this package includes the GM diff and GM axles and GM brakes, here is the pricing and component breakdown:
IRS Cradle
GM 5th Gen differential 3.27 gear ratio
Upper control arms
Front lower control arms (with Johnny Joints)
Rear lower control arms (with Johnny Joints)
Toe link kit
5th Gen Camaro knuckles machined to accept C6 hubs
C6 30-spline hubs
5th Gen Camaro parking brake kit
Two-piece adjustable sway bar
Cradle bushing kit
GM 5th gen axle package narrowed by The Driveshaft Shop
JRI non-adjustable monotube coil-overs
5th gen Camaro disc brake kit 12.4" rotor

This package will sell for $9865.00. We also have a 3.45 GM differential and a 3.91 GM differential also available.

I think a Currie Ford 9" rear with Baer floater is $6000. with brakes: http://scandc.com/new/node/924
Then you need to buy suspension.

[Rod]

Rodney, One thing that kept nagging me was the success Newman guys were having with their C4 stuff. Also that they don't like to alter the suspension. It was an eye-opener to see how well they were doing with that stuff.



I have spent many nights around the campfire with Paul Newman discussing that very subject, and the reasons he has stayed with C4 design...and their chassis is the complete deal...it is just many customers want the latest, greatest, c5,c6,c7, to sum it up, Paul basically states that the pivot points/arm widths and track width of the c4 is better suited to the narrow muscle cars we stuff the chassis under, with c5,c6,c7 it was designed for wider track width and many just narrow the track width to fit under the muscle cars and never change the pivot points so instead of those pivot points intersecting and working together, now they cross over each other and the suspension fights there natural path, affecting the handling..........you had a great write up David...good thing I wasn't out there still Mary would have kicked us out of the house because we would have talked about this one for hours

[Cdog]

I guess I started a trend. I bought a front sub for my 67 from Art Morrison, then Mary and James saw it in my shop, we discussed the pros and cons, etc. Then Mary and James had new engine installs coming up. No better time to swap subs than while the engine is already out... So they both changed.
Corey, We gained a little rear weight, something like 50 lbs. Went from 52% front to 51%.

Thanks for revising to cover the subframe. I have the AME sub on both of my cars. We’re pushing to get the 69 done first. I noticed you did some customizing on James uprights for his AME suspension. I have plans to buy you a beer and discuss one of these days. I’m in process of moving back to Orange County to be closer to the shop and get more involved.

Jack & I are getting close to getting the 69 on the ground again. AME 69 Camaro with a LSA/T56 mag.:cheers: