Specs on subframes?

[JamesJ]

Tom, there are some people that will disagree with your statement that a rear leaf spring car is bad, or not desirable. The person(s) will probably not say anything since it has been said and if people don’t listen the first time then who is to say they will listen the second, third, and so on. My opinion is not involved here.

[nancejd]

I'm not sure it would be suicide except for one manufacturer. Some people are going to want handling at the expense of everything else. Some people just want wide tires, but want the cushiest ride they can get. Don't forget that the Camaro subframe was designed to provide "big car feel" originally. There is just no information out there. Maybe what the performance parts industry needs is to have some enthusiasts start a Consumer Reports type of magazine. Use the subscription money to buy one of each frame, test independently, and report the results.

[touring67]

I have read some good things about leaf rear suspension on here and have heard that it can be made to work quite well. The reasons I can see myself using rear leafs would be that: I didn't want to cut into the floor or trunk, its cheaper to leave them as they are with some mods like DSE offers, and they are relatively simple to tune or rather not tune than other higher dollar rear suspensions and can 'apparently' (I don't know because I don't have that experience) work quite well in a good handling car.

As far as I am concerned about the rear I would like whatever worked best in my application. BUT since I can't EVER stop upgrading I think it would be in my favor (my wallet namely) to do it 'right' the first time. Once I find out what the limit (best) is for my purposes I will go with that. But for now I am concerned with the front as that is what I have disassembled at this time.

And as far as suicide for those companies, I say good. I think that is exactly what they need, otherwise how will they get any better? I think capitalism and competition should be put to work here...

[justanova]

For starters it would be nice to see more of what Pozzi has done, publish your numbers and tell everyone how you got there.

I think the subframe manufacturers should provide the info like camber curves, etc... and let the consumer do their research on front suspension design by using many of the books/suspension programs that the suspension guru's on here recommend, herb adams chassis engineering comes to mind. and let the consumer choose whats best for thier application/budget and then its up to the consumer to tune spring rates and shock valving etc...

my .02

[Fuelie Fan]

I can't believe the C6 Corvette still uses a leaf spring. My Camaro's just a had an all poly rear end fitted, it's still crap.

It's not like the C6 is using the leaf springs for "geometry". They are being used solely as a spring. Completely different.


Here comes my off-the-cuff reasoning for why the corvette uses it.

A cantilever beam produces a basically linear deflection vs load, so in theory it should be at least as effective as standard coil spring. You also don't have issues of coil bind. When made of composite, I believe there's a solid weight savings to be had. you can also get the pickup point way out at the upright which has two benefits. First, you don't have to build the lower a-arm to be strong enough to support the spring loads, which means less weight, some of which is unsprung to boot. Second, the spring doesn't have to be as stiff, which means it can be further reduced in size for weight savings.

I'm sure some of these can be refuted as I'm not a suspension expert, and there are certainly advantages to coils, but It's not the surprise of the century that they use it, and it's hardly a complete pile of crap as you suggest. It cracks me up, in fact, that you would make such a statement, as if the corvette engineers are complete numbskulls that only design suspensions in between debates about whether the world is round and staring in awe at the mysterious substance the wise man on the hill calls "fire".

[Salt Racer]

Would'nt a well tuned and set up front suspension keep a certin degree of castor and camber all throught it's travel? If so it seems you could test that on a allighnment rack...

I think the subframe manufacturers should provide the info like camber curves, etc... then its up to the consumer to tune spring rates and shock valving etc...

Static testing probably would give you a rough idea of how well the car would stick during steady-state cornering. But that's not all there's to suspension design. Stuff like RC migration characteristic is tough to determine w/o computer aid (or at least scaled drawing), and those invisible stuff has major influence on transient characteristic.

As for manufacturers publishing simple date like bumpsteer, camber curve, etc, the danger is it could become just another one of marketing hypes. With enough reading of books and info available on net these days, it's pretty easy to get rough ideas of what is ideal. You can easily publish those numbers without actually measuring anything.

It is true that no matter how well the system is engineered, you will have to fine-tune stuff on your end. Look at all the Camaros on this site - how many Camaros do you see that have exact same combination of parts? Also driver ability/preference play major role in suspension tuning. However, ALL suspension manufacturers, especially the ones specializing in specific car model(s), need to be able to provide baseline setting for their own products. If a manufacturer failed to do so, personally I'd be skeptical of their knowledge and experience.

...Now you could also put too big of tires in the front and scrub too much speed in the corners. Or too big of rear tires and have severe under steer. Seems to me there probably is a magic number most race car builders look for when making their suspensions...

This is very true. Unfortunately, because of the nature of this hobby, too many people opt for the biggest tires they can fit without taking balance into account. Try 225/335 combo on a nose heavy car and go around a track, and you'll hear overheated 225s screaming for mercy while 335s on rear are barely getting hot. You may be able to balance out handling by increasing rear roll rate, but that would not make good roll rate distribution. With extra rotating/unsprung mass and stiffer than ideal roll rate, rear end would not be able to maintain road contact as well as a more balanced combo of narrower tires & ideal roll rate. Bigger rear tire is not always better when you're very limited in front tire size.

Of course, if aesthetics is the priority as in case of street rodders and cruiser type people, Bigger is always better. 335s would make nice conversation pieces at car shows.


I've already rumbled enough about leaf springs in other threads. Fuelie Fan is correct that leaf springs on C4/C5/C6 has nothing to do with suspension kinematics. As long as their rates are linear (or close to it), they'd work just as well as metal springs. As for the typical leaf spring setup as on Camaros, it has much better kinematics than a poorly-executed link suspension.

Think of leaf setup as a carburetor, and the link setup as fuel injection. A properly calibrated carburetor would make just as much power as a good MAP injection, even though the carburetor may not be as efficient. This is like a comparison between leaf and a good 3-link - leaf setup is capable of just as much cornering traction as 3-link, but it will fall behind in some other areas. The same carburetor would outperform an alpha-N system that has not been calibrated with flying color - this analogy is like well-setup leaf vs. drag race ladder bars for cornering applications. Not all fuel injections/link suspensions are created and calibrated equally.

Leaf setup should not be overlooked if rear seats and stock floor are to be retained in the original locations.

[touring67]

I guess since we are somewhat debating leaf springs I will say that my biggest gripe with the 67 leaf setup is the monos with non staggered shocks and their inability to control wheelhop and spin. I'm sure some measured spin will always occur on a street car with 17 inch rims and DOT street radials but it could be lessened with a different proper setup. I'm sure they can handle corners, but can they handle a dragstrip better than a well setup 3 link? Nevermind that one could use ladder bars and a 4 link...as I'm sure we can all understand the limited ability of those setups (especially the 4 link) to take hard fast corners and they do often have limited street life due to bind.

[MuscleRodz]

Vette Brake Products offers a composite mono leaf spring for the 67-69 Camaros that is suppose to eliminate wheel hop. They also claim they can tune them spefically to you car and they are good to a fairly high hp #. They are not cheap though. Combine that with some Caltrac bars and I think you would be impressed.

Mike

[Cdog]

Salt Racer,
I really enjoy reading your posts. You seem to be very educated by books and real world experiance. As this conversation goes on about what suspension really works we seem to be adding alot of ego, bling bling and theory to this subject. I personally feel that the C4 & C5 a-arms and knuckel componets are great matches for a performance platform suspension. They're light, strong and look good. It just makes sense to use them just like it makes sense to use a quality tool over a made in china tool.The mustang 2 stuff might work as well but how do we know? My train of thought on this subject is that if I spend 6-7'Gs on a subframe it better do more than look pretty. I won't be buyin one with out proof of it out performing a stock subframe or it's compitition. Right now these products are in their infancy of production and testing. I think in the future we can expect some real testing now that alot of us are asking the right questions instead of drooling on these subframe's like their a set of DD cups. If not I will probably just go to a race car chassis builder and have them build me one. So in your opinion would you feel better about say the 21st century frame over the Wayne D, Do to the fact that 21'st actualy builds race car chassis? Then secondly what rear suspension has the best amout of compromise for track and street. So far I like the Tri 4 link like the mule, the art morrison tri-4 and the truck arm. Having some kind or rear seat would be nice but not manditory. What do you think?

[touring67]

If you are going to use a Tri 4 link you would have to move the seat. It is up to you if you want to delete it entirely but you dont have to. You would have to move it forward if you wanted to keep it and a Morrison Tri 4 bar without a housing would run you up to almost 3k for the parts alone plus install. This is the system used on Arts 55 Belair that pulled .94g on the skidpad though so it does corner well and it acts like a 4 link so it will control axle twist as well. I think you would like a tri 4 bar for your setup as you seem to be alright with the option of moving/deleting the seat and you want street and track action which I think it offers. Mind you, I may not be the best opinion to take but that's up to you.

And as far as subframes go I am still trying to weigh the benefits of going either way. It would be easier if someone knew all the specs but so far not much has surfaced. It may be too soon to get a lot of info on them but I think sometime info will start to come out.

[Salt Racer]

Cdog,
Thanks for the kind words. I also would have appreciated some visual aids of a set of DD cups ;-)

I do agree that '88-'96 C4 and C5 parts are excellent, but like I said in other threads, the pickup points (aka pivot points) need to be arranged right.

MII-based IFS can be made to work reasonably well, though there are some limitations. If you give a set of MII spindles and a set of C4/C5 knuckles to a suspension engineer, there's no doubt he'll be able to make better suspension using Corvette stuff. But a good engineer can design a better suspension using MII spindles than a Corvette-based system designed by an intern. It's just like my leaf vs. link analogy.

Here's a real world example. Art Morrison's 55 has MII-based IFS. It put down pretty good numbers during testing conducted by SuperChevy. They also tested the '56 roadster w/ C5 running gear owned by Chris Titus on the same day. The car didn't fare as well as Morrison's 55. I'm not sure about the geometry of Mr. Titus' suspension, but Art Morrison told me the '56 roadster didn't even have sta bars (aka swaybars) and had leaky shocks at the time of testing. It's quite apparent that tuning and preparation played a big role. If you ever run into Mr. Titus, ask him about Morrison's 55. He got to ride shotgun in it on slalom course.

Major kudos to SC staff and Mr. Titus for publishing the actual testing data - they could have covered up the poor performance of C5-based '56 Chevy or not even publish it. Most people get lots of info from magazines - informing the truth is the only way this customer-driven industry can move forward.

As far as which subframe is best...I will have to leave the decisions up to you. I work for one of street rod companies, so it's not appropriate for me to sway your decisions towards one company or the other.

I think one of the members here has Morrison Tri. 4-bar setup in a Camaro. IIRC, his screen name is 70t/a or something. You may want to ask him about rear seat issue. If you don't mind using split rear seats like on a late model Camaro, 3-link with central UCA is also a possibility. The link can be covered up with elbow-height console or something if you're so inclined.

[Tom Nickols]

[QUOTE= It cracks me up, in fact, that you would make such a statement, as if the corvette engineers are complete numbskulls that only design suspensions in between debates about whether the world is round and staring in awe at the mysterious substance the wise man on the hill calls "fire".[/QUOTE]
It still cracks me up that the American public are still being ripped of with old technology that is 50 years old (30 if we're talking composite spring) whilst the rest of the world has moved on along time ago. Now I'm not sugesting the Corvette is not a world class product. Just it could be kicking averbody elses butt if the engineers we're alowed to design something better.

Have you ever watched a corvette running down the freeway? the rear tires are chopping and skipping at every bump. Did you ever see a leafspring on a modern LOTUS, Ferarri, Porsche, Lamborgini or Masarati? The only excuse for using a leaf spring is COST. And no, it appears you don't know anything about suspension.

[Cdog]

[QUOTE=Tom Nickols]

It still cracks me up that the American public are still being ripped of with old technology that is 50 years old (30 if we're talking composite spring) whilst the rest of the world has moved on along time ago. Now I'm not sugesting the Corvette is not a world class product. Just it could be kicking averbody elses butt if the engineers we're alowed to design something better.

Have you ever watched a corvette running down the freeway? the rear tires are chopping and skipping at every bump. Did you ever see a leafspring on a modern LOTUS, Ferarri, Porsche, Lamborgini or Masarati? The only excuse for using a leaf spring is COST. And no, it appears you don't know anything about suspension.

To be honest I don't think the american public cares. That's what makes a corvette a 50 thousand dollar car and a ferarri a 150 thousand car. The cool thing about a vette is that you can get 90% of the performance of a Ferarri at 1/3 of the Ferarri price. I've seen leaf spring cars on 10 inch tires do 9 sec. in the quarter mile. Seems to me you can get them to work great in specific applications.

[Salt Racer]

...Have you ever watched a corvette running down the freeway? the rear tires are chopping and skipping at every bump...

Uh, I don't mean to get in between you two and I admit Fuelie Fan could have said it in a less-offsensive way, but chopping and skipping are shock valving problems. The shocks are too stiff in jounce and/or rebound at high piston velocity.

I respect your opinion, and it's totally fine by me if you think leaf springs suck. But saying something like that just b/c they are products of old technology doesn't sound right. That makes SLA suspension, coil sprung link suspension, and even reciprocating engines also should be considered obsolete. I know '49 Ford had SLA IFS, and perhaps even earlier models too. Late '40s GM had coil sprung link rear suspension that is kind of a derivative of truck arms, and Model T's had reciprocating engines (flathead four bangers).

All of european sports cars you listed still have SLA suspension and reciprocating engines. They are much improved but the basic configurations are still the same, and there are more efficient alternatives (Wankel, turbine engine, etc).

As for the leaf springs on Corvette, it's hard to believe composite springs are cheaper than simple wound steel wires. I would imagine main reasons to be packaging, better fatigue characteristic and reduction in unsprung mass. Coil overs are very nice, but those small 3.5" diameter (typical O.D.) steel springs won't last too long on a 3000+lb car that sees regular street duties. I believe this is the primary reason why springs on all mass-produced vehicles are much larger in diameter to handle stress. Larger mean diameter also allows the increase in wire diameter to maintain the same spring rate (for a given number of coils), which further increases fatigue life.

OK, I'm done.

[touring67]

No offense intended Salt Racer but I thought you would know if Morrison's Tri 4 bar would need relocating of the seat. Either way, I spoke to Brock from Morrison today and inquired about it and he was quite sure that the seat would at least have to be moved forward some and depending on other mods might just have to be removed.

With that situation covered I will also post back here to cover some specs on the Morrison IFS. I'm sure 'some' people may know these specs already but for the sake of this thread I will post them when I get them tomorrow. As far as other frames and mods go I am still checking into these and hopefully will have more info tomorrow....if possible..

[Salt Racer]

Actually, I don't know (no offense taken at all BTW). I don't own a Camaro, and as far as I know, Morrison changes kickup height of rear rails depending on the ride height and tire height customers want so I don't think they can draw out a set rule.

For example, you may be able to save the rear seats if you want 25" tall rear tires and 9" ride height at rocker panel, but I'm almost certain the seats would have to be modified if you want tall 29" tires and drop the car down to 4" (which I think is physically impossible w/o gutting trunk and wheel tubs).

[Fuelie Fan]

Sorry if I got under your skin, Tom, but the parallel you tried to draw between first-gen camaro leafs and corvette leafs seemed completely illogical, and that got me fired up.

I will also point out that despite my apparent complete lack of suspension knowledge, you chose not to disprove a single one of my points. If you can, by all means do, I'm here to learn as is everyone else. If any of my points were incorrect, please inform us. I have no problem being proven wrong, but just calling me dumb is grade-school immaturity, and I have no interest in getting into a name-calling contest.

Salt Racer, I will second CDog, unlike myself and others you are always very grounded, unemotional, and informative!

[Salt Racer]

Not always, but I try.

[Tom Nickols]

Ok to loose the emotion, my was only setting out to question the logic of spending lots of cash on the front end when it's basically ok, and leaving the rear end alone. To me this doesn't sound right. We cant proove easily that the new front end works, you're replacing like for like. But on the back, if you spent your cash there you could really make the difference, and a measureable one too.

No problem Fulie, I'm an engineer in the IRL, a Chevy fan and English. I just wish the imposible - Quad cams and coils springs!!!

[touring67]

Ok, so I have SOME info on a few parts but not much, however I will have more come Monday as most people close their doors for the weekend. Here are some specs on the DSE UCA's without the coilover kit. They offer 4-5 degrees of caster with caster lugs to easily adjust this while maintaining the same camber. Apparently these adusters keep the camber and caster settings seperate. The camber curve is LESS POSITIVE but not negative and not neutral. Apparently no one's bolt-on arms will bring the curve into the negatives. With just the UCA there should be no re-locating of the UCA mount and is not recommended for use with the Guldstrand mod. SECONDLY, if the coilover kit is purchased one will see 'improved' RCH but the actual spec is confidential. The camber curve will also become LESS POSITIVE, but not negative and getting closer to neutral. The coilover kit also IMPROVES bumpsteer but does not bring it to zero. However this can be adjusted with the steering kit. With this kit it is acceptable to lower the car without hampering the spring travel as it was designed for that. The price for kit 2 which is up to the coilover kit with arms etc is 2395. For full details check out their site. Ok enough with DS&E for now. Please, if anyone finds any discrepancies IN ANY of this please feel free to bring it up.

Since I didn't get the chance to talk to too many people I only have Art Morrison's IFS to talk about briefly as I don't know all the specs on it yet. It is lighter and quite strong but not really intended for road racing. This kit does offer zero bumpsteer and RCH is above ground but actual spec I won't know till Monday if not confidential. The caster is 2-3 degrees built in. As for the camber curve I don't know yet as its actual spec, along with RCH, is not available right now. ALSO, if anyone is interested these specs will be the same as on the Wayne Due frame. Wayne's frame is narrowed 3 inches however, so 275 mm tires shouldnt be a problem in the front and it weighs approximately 200 lbs less.

As for right now I don't think I know anymore but I will keep checking. I intend to check out 21st century, Alston, Fatman and some other aftermarket UCA makers. As for Corvette I don't know of anyone that uses it directly on a frame and I'm sure that everything would change if mounting points were changed so finding the specs might not be feasible. AND I know I forgot a bunch but that's all I can remember right now.

Bottom line...it will take a lot more than some simple bolt-ons to get perfect or even anywhere near perfect geometry.