Specs on subframes?

[David Pozzi]

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

Sorry I haven't contributed before now, I've been buisy.

I'm a ways from getting my Camaro running but let me offer a fiew observations on suspension.

THE WHOLE PACKAGE:
The whole driver/car combination is critical to accomplishing a performance goal or benchmark, if any one thing is deficent, the goal won't be met. You can have a killer car but if the driver can't handle it, nothing is accomplished, likewise a poor tire or spring choice will shoot down an otherwise good car from setting a good time, etc.

SUBFRAME
It must have good torsional rigidity, - at least as good as the factory sub. Some of the aftermarket subs look rather flexable in this respect. At least GM put some thought and engineering into trying to make the sub rigid. The geometry sucks but can be fixed, how good is perfect geometry if the subframe is wanking around?

SUBFRAME WEIGHT SAVINGS
I hear different claims of saving weight from the factory sub.
Here's what a GM sub weighs:
SUBFRAME WEIGHT additon list
Bare sub 110
knuckle assys 92
springs 22
A arms - upper 20
A arms - lower 22
Shocks 6
Ctr link and tie rods 17
Trans Crossmember 10
Sub total 299

PS box, hoses, pump 44
TOTAL 343
================================================== ======
SUBFRAME WEIGHT additon list
Bare sub 110
knuckle assys 92
springs 22
A arms - upper 20
A arms - lower 22
Shocks 6
Ctr link and tie rods 17
Trans Crossmember 10
Sub total 299

man steering box 16.5
TOTAL 315.5
=================================
A fiew lbs can be saved over stock, but not hundreds of pounds in my opinion.

I like Rack and Pinion steering, if I got a sub as light and stiff (or stiffer) as stock and it had a front steer power rack, low scrub radius, good neg camber gain, lots of pos caster, zero bumpsteer, good brakes, I'd be pretty happy with it. But it seems there can be lots of little things that can creep in to cause extra or unexpected problems. Most aftermarket subs don't have as much neg camber gain as a stock Camaro with Guldstrand mod. My experience has shown you need -2 to -2.5 deg neg camber static setting even with the Guldstrand mod on an open track Camaro. One thing that helps the late vettes get by with less neg camber gain is very very low chassis roll and high amounts of positive caster.

REAR SUSPENSION
I've been told by Herb Adams personally and read in several books that the multi-leaf spring layout as used in a Camaro is pretty darn good, (not the springs themselves but the overall design). Is there better? Sure, but how much better, and did you do the "better" system properly or is the better suspension have some geometry errors hurting it's performance?

There are most likely certain conditions where one suspension might do better than another, I think on a pretty smooth surface like Laguna Seca, there would be little to gain from a three lnk rear, but on a rougher surface it might do better.

I'ts important when comparing to compare best to best, and the best leaf setup I suspect is the Global West Cat 5 leafs. It is the most free from bind and I'm guessing the rate and design are good for handling and pretty much eliminate wheel hop. I haven't tried these leaf's but the design looks good to me. I don't know the best three link design geometry but some of the books have starting suggestions.

There was mention of Corvette composite leaf designs. The major benefit of this design was isolating the wheel vibrations from the chassis and convienient packaging, - coil springs take up room, require extra chassis bracing, and make the CGH slightly higher, but the leaf springs can be slung underneath where there is more strength in the chassis down low. The chassis is probably easier to make or assemble too. I've had a couple of C3's with rising rate multi-leaf rear cross springs, and they rode terrible in the rear, and they had lots of drivetrain and wheel noise. GM put composite rear springs on them in 80 or 81, and it was an improvement in ride quality. From a handling perspective, the chassis really doesn't know if the spring is a coil or leaf the way the C4 or C5 vette suspension has them connected. Race Corvettes are converted to coils because they are easer to change to different rates.

I have read several posts of the Vette Brakes fiberglass Camaro springs breaking, also of wheel hop problems. If the horsepower is low, they seem to work OK but when you get close to 400hp, they don't work.

TESTING/COMPARING
I guess I'm a bit too skeptical to believe it can be done well enough to be of use to "us". As Salt Racer more-or-less said, it only takes one thing amiss and the car won't do well. The car or cars would have to be well developed, not just a subframe thrown on and timed in a slalom, etc. Most guys who have bought aftermarket subs say they are great but say they are not experienced in suspension tuning or mods.

I would like to see comparisons of chassis stiffness in ftlbs per degree for each subframe system. Comparison of neg camber gain, roll center height and movement, SVSA, FVSA, bumpsteer weight added or saved, F/R weight changes, rear RCH, and movement, rear anti-squat/anti-dive.

Things that stick out in my memory:
I attended a road race at Laguna Seca in the early 90's, I saw a worn out looking 69 Camaro in vintage TA configuration running in second place with a bunch of tube-framed plastic bodies GT1 Corvettes and Camaros! The leader Corvette fell out with mech problems and the 69 was LEADING THE RACE!

After a fiew laps, he got in a little over his head at turn 9, and spun off while leading all the other guys. This car had LEAF SPRINGS but it must have had a pretty good overall package! ;)
The guy found the car parked by a garage, bought it, and threw an engine in it, hopped in and just flew! The car was previously owned by a very successful local racer who parked it long ago.

My point here is, sometimes a simple plain combo that is well sorted will win over another car that is much more exotic. I stress the "sometimes" part!

A plain "stick" rear axle has lots of benefits when putting the power down when exiting a corner, leaf or coil/three leaf, it compares very well to an independent rear axle if the pavement is smooth.

I'm going with rear leaf on mine so I can get my car going in my lifetime... I have lots of other projects. I'm going to count on driver talent and a superoir driver/car package to get me by others on the track. If the talent thing doesn't work out well, I'll try other rear setups if I can find the time to do so.

For those who want to try a three link, I think there is a little to be gained, maybe a little better feel powering out of a turn, - stability kinds of things. More traction? - maybe, faster track time? could be a tenth or two but if comparing to a dynamite leaf combo maybe not much. This is just my speculation, not based on solid on-track comparisons, so I may be wrong on the gains possible for rear suspensions.

[Salt Racer]

...You can have a killer car but if the driver can't handle it...likewise a poor tire...

Hey, that sounds like me!!
A set of $84 18" tires didn't work so well either!

Looks like I'll be heading down to San Bernadino in March for B'ville tech inspector meeting, and Speed Ventures will be at Buttonwillow on March 11th. Maybe I need to set the idea of 18x10s aside for a while and get a set of 255/45R18 Yokohama AVS Sport....

Good point on torsional stiffness, but I feel some people may be better off buying a subframe w/ better suspension geometry unless they know how to alter it. It's easier to tie the frame to firewall, add some tubings here and there to improve chassis rigidity.

Great story on the 69 Camaro leading a bunch of GT1 cars! I love it!!

Thanks for chiming in, David. If you can come out to the SoCal track event I'll be attending this year, you're more than welcomed to drive my car. I know it's a totally different platform, but you may be able to tell some differences in behaviors between leaf and 3-link.

[Cdog]

DP, Great post. I've seen the vintage race out at the Tustin Marine base and the first gen. Camaro's were pretty damm fast.

[Salt Racer]

Yes, you're totally right that for fair comparisons, all cars have to be well developed.

The way I look at those testings are a bit different. I think any legitimate suspension manufacturer need to be able to provide baseline setting that are close enough to ideal setting to their customers, via calculations and/or extensive testing. Subtle/small things like sta bar arm length, shock valving, tire pressure, etc, are still up to customers preference, but I have a doubt that minor under/oversteer would result in huge differnce like 0.10G in skid pad performance (for a given tire, of course).

Many of today's best street tires are capable of near 1.0G traction on a well-developed car weighing in 3000~3500 lb range, so if some car put down some miserable performance with those nice tires, personally I'd be skeptical of the engineering behind the products used on the said vehicle (ie, manufacturer was unable to provide baseline settings).

I agree that the testing results won't tell you the whole story, but they at least give me rough ideas

[David Pozzi]

Salt Racer,
Keep me posted on your schedule, I'd like to see your car haulin around some corners, it felt pretty good on the salt at Bonneville!

Ive driven third gen's quite a bit and the lighter rear axle with no weight of leaf springs, felt a little better over bumps than leaf camaros I've driven. The third gen's feel very stable and predictable in the rear, probably very similar to a three link, I'd imagine. I should mention that third gen's have some problems with the front suspension that far overshadow anything that could happen at the rear.

Rear stability is even more important on my Lola T-70 since 65% of the weight of the car is on the rear wheels and the hp to weight is around 2.9 lbs/hp, if the rear isn't super stable, I can feel it right away!

[touring67]

Great post David, I thought it was very informative and pretty neutral, giving others the info they need to make their own informed decision. I am still debating 3 link over great leafs but since I will be gradually stepping up the 'abuse' in all forms of racing to this car maybe I should start with the system that offers a wider range of use and ability, not to mention more adjustable.

[Salt Racer]

Salt Racer,
Keep me posted on your schedule, I'd like to see your car haulin around some corners, it felt pretty good on the salt at Bonneville!

Will do, David! I still had stock coils/shocks in the rear, and stock steering box - it feels much better now.


You're probably right that torque arm feels pretty close to 3-link. Perhaps 3-link may provide a bit more bite out of the corner due to higher AS. I can safely say the 3-link in my car is stable - I'm still alive!

..2.9 lbs/hp...

Nice!! One thing I notice about IRS on old racecars is relatively large scrub radius. You know, it'll be just like torque steer on FWD if you vary the amount of throttle while cornering, though it's probably hard to notice at the limit. Can you make longer arms and use rims with more offset? Probably not legal in vintage racing, huh?

[David Pozzi]

touring67,
Thanks, I was hoping it would come across as pretty neutral since I don't have hands on experience with three link suspensions.

Salt Racer makes a good observation that if a somewhat torsionally "weak" subframe were tied in to a roll cage, it would probably be much stiffer than a stock sub unbraced. I agree with everything he has posted here. I think we both agree we wouldn't design a car from scratch with leaf springs but a highly developed leaf car is not that far behind a car with a three link but you can't tune a leaf setup very easily.

Look at a third or fourth gen Camaro with coil rear suspension, there is more room behind the axle for the exhaust and fuel tank.

[touring67]

I have a 3rd gen Camaro lying in wait in my garage at home. In fact it was my first 'car' and I learned with it. I like the rear setup torque arm and if you have ever removed the torque arm you sure know it works! The stock panhard bar does a nice job of locating the rear and when that is removed it gets pretty loose..not good. As far as your comment on the front suspension goes about third gens I think you are quite right. Although the rear feels quite stable the front doesn't handle hard corners too well even with 245 BFG kdw's. The strut suspension doesn't offer enough camber gain under hard cornering and likes to 'rub' the tires before it holds.

As far as what Salt Racer proposed with the skid pad testing and baseline settings I definately agree. I had been talking to Wayne and was sure I mentioned this before about the skidpad testing of different subframes. I say they can take a frame, build the geometry in and test it. It wouldn't be very accurate but it would be 'rough' as Salt Racer said which is good enough to compare in many cases.

Sorry btw, my name is Kyle.

[David Pozzi]

Kyle, With my IROC I had to brake in a straight line somewhat early and gently, the bumpstops in front are very close to hitting just sitting still. Hitting the bumpstops on hard braking causes one ft wheel to lock, makes you think the brakes are grabby but it's the suspension. If you enter a corner braking hard, the front end wipes out causing understeer. Normally a "good" first or second gen Camaro would get the tail end a little loose in that situation, or it can be made to get a little loose by trail braking it, but a third gen won't respond well at all. You have to enter slow then accelerate from apex out with a (stock) third gen, all due to the front suspension.
There isn't enough neg camber, I ran with as much as I could get out of the stock slots, couldn't mofify anything since we ran SCCA F stock autocross. I finished fifth in F stock one year at the SCCA nationals in Salina KS, with over fifty cars in our class. I got beat by the 1LE Camaros which have no factory air, that takes 80 lbs off the front end in addition they have better brakes and aluminum driveshaft.

If you were to remove a torque arm, I'd think you would be in danger of breaking your drive shaft. Removing a panhard bar would put a tire into the fender.

Back to testing, you could run around a skid pad, but even a flexable subframe could do that pretty well if you played with the settings enough. A better test would be a slalom, but that doesn't test how the car would enter a corner under braking.

Mark Donohue did a test where he drove the car around a four cornered course, it tests acceleration, braking, and cornering combined, but not transient handling like a slalom.

[touring67]

I have never run the car without the panhard or the torque arm but when you remove them you can tell they really make a difference. And as far as hard braking is concerned, yes the front always locks up despite it not being really that 'hard'. And that sounds like some pretty good driving there David! I read about that on your webpage as well. And as far as the stock A/C it is a huge weighty thing that I removed when I swapped engines. It is a monster! And thanks for the responses they are really interesting.

[David Pozzi]

The guy who won my class driving a 1LE was named Neal? Sapp, (forgot the first name) but he won the Mazda challenge where you make timed autocross runs in their cars at events all across the US, they have a US finals at the end of the year and he won it two years in a row!!! He won a new car each year.
Another autocrosser was Jeff Altenburg who is running IMSA events now. Randy Pobst is racing Porsches but started in autocross. Autocross taught me a lot but didn't teach me to concentrate for a half-hour of driving, when I first started track driving I was out of focus after three laps!

[ProdigyCustoms]

I have done one real world test, but without numbers. Only seat of the pants feel. We did a Chris Alston Chassis, a couple years ago. We took a car with all rebuilt suspension, urethane front bushings, good Koni Shocks, no aftermarket arms or any of that. A nice running and driving car. We put the car on the lift 3' in the air, put a engine crane and floor jack and supported the engine / trans in place. Unbolted the subframe and bolted the new subframe in. Took almost all of 2 days. Put the same tires and wheels on it and 48 hours after we drove it in, took it for a ride.
I am not an easy sell on changes. I have a real pet peeve for people that make a change to their car and let the change and claim seduce them into believing it helped. I see it all the time at the track, you run into someone in the staging lanes, I made this and that change, she feels STRONG! Only for them to gain nothing or go slower when the scoreboards are on. So I am a hard sell.
With that said, I will say there was an appreciable difference in ride quality. MAYBE, MAYBE, a bit better handling, but I might have been fooled by the better steering. The biggest advantage by far was the rack and weight savings.
We did not weigh the 2 complete set ups, but the CA set up was noticeably lighter, two guy's picking up one, then picking up the other. They claim 150LBS, it was an easy 100, and 150 is not out of line based on what I felt. This is with willwood brakes versus factory disc.
Funny enough, braking was the area I was least impressed with. It just did not feel any better. The brakes were not the killer 6 piston jobs, they were the 12" willwoods, but none the less, did not feel like an improvement, they surely were not worse, just maybe not better. They were much lighter.

My final report.

Improvements:

Steering - A BIG improvement, feel and terrific weight savings
Ride quality - A nice firm feel, nicer ride for sure
Weight savings - A lot, it did show up later on the time slip
Quality - Very nice quality

Non improvements:

Brakes - Was disappointed, hoped for more, but no worse
Handling - Was disappointed, no hard numbers, but did not feel much better, if any. Could have all been in the steering.

Summary:

I think the Chris Alston unit is great for a staightliners, or a Pro Streeter. Surely the best choice for those cars. For this group, that wants to tear up corners, I do not think there is an appreciable difference in handling, and the weight savings probably won't help as much as in a straight liner, except possibly with front to rear balance which is only so important.

Test car, 1969 Camaro, big block, Automatic, 245 / 60 /15 wheels / tires, urethane bushings all around, Koni's, your typical stocker.

[David Pozzi]

Thanks for the report on the Alston sub. I've seen their Chevy II sub and the Camaro sub and the quality of the parts is very high.
I've been thinking the Alston sub would make a good base for a PT car if there were a fiew improvements done. Like, - go over the geometry and make a fiew changes to optimize handling and insure suspension rigidity, and add some bracing to the crossmember.
Making a big block car handle well is pretty tough for any suspension. You can make them corner flatter and be better balanced, but they just aren't going to change direction very quickly with all that weight up front.

[touring67]

I am not sure how your braking tests where done but I was thinking that it might be quite possible that those brakes weren't seasoned/bedded and that would most definately give you a poor braking feel. You might have broken them in beforehand and maybe they were still poor after that, I don't know, just a thought. The quality does seem to look good on the Alston clip though, however I think I read it as having room for 225 mm tires in stock fenderwells though, maybe not but that is what it alludes to on the website.

[Jagarang]

I can't read all the posts do to a lack of time, but if it hasn't been mentioned yet, here's my problem with "quantifying" change. It's been SOOOOOOooooooo long since I've even had a seat in my car, much less driven it, that my change to a WD sub-frame will be nearly impossible for me to offer even a seat of the pant's impression. On top of that, the car has had such a copious amount of significant modification that it really won't even be the same animal anymore, I don't imagine. At this point really it will be the greatest pleasure to just see the damn thing in one cohesive piece, get in it, crank it, and stomp the go peddle and hear it, feel it, and smell it! I don't think I'll really care much about how MUCH better each individual system/component might be, but OVERALL the car will be world's above what I started with and a complete restification, done the best I could afford to do even if I couldn't do the work myself (which hurts).