Chassis Rigidity and Holy Grails ---

[Christopher Crowe]

During several discussions regarding FB, chassis torsional rigidity numbers have come up, been talked about, questioned, bragged up, etc.

And it's been put forth that extreme ridgitity is definitely something to be sought -- for lots of reasons, predictable chassis tuning being near the top of the list.


Doubtlessly a stiff platform would be more predictable in terms of altering shocks, springs and roll bars, etc. But then guys like Lee Stohr have said that ultimate chassis stiffness ain't no holy grail at all... I believe Lee even said he only pursued high chassis stiffness numbers "when I was younger" -- I suppose meaning that he's advanced away from the pursuit based on things learned.

And Lee's cars go fast.


So. Just how all-important is chassis stiffness in a catagory like Formula B? Would an infinitely rigid CF monocoque win every time against a chassis that's yielding a bit (all else being equal)?

Somehow, that just seems too simple. For instance, imagine a chassis that was hugely stiff for the first degree of torsional twist, then went to hell after that (yielding like hell in the second degree of twist, etc). So the nature of the way a chassis flexes could be important too.

I'm curious about Lee Stohr's (rather lonely) position on this. Anyone have any thoughts in this area?

Thanks

[Stan Clayton]

I'm curious about Lee Stohr's (rather lonely) position on this. Anyone have any thoughts in this area?

This should be your first clue...

[Chris Livengood]

The problem here isn't that Lee completely ignores rigidity, it's that I'm sure he has reached levels that are sufficient enough that increases in rigidity, and perhaps the extreme efforts to improve this aspect given the required methods of constructions (the rules set, tube chassis vs. monocoque), are in low enough amounts that rigidity is no longer a main design focus. I.E. at this juncture, other areas of improvement will provide larger gains. Making comparisons that are outside of the rules set is a meaningless exercise in my opinion. This is because the answer is obvious, of course the monocoque would produce better results, otherwise it wouldn't be the primary tool of the faster formulas (ignoring cost of course).

I'm sure many designers that post on here can further elaborate with practical and theoretical knowledge. My experience lies within the depths of the cars I have driven and the experience I have gained. That said, Nathan's approach on the Radon, the 'semi-monocoque,' is interesting and the information he has provided in many posts is also informative.

[jeff68]

Cockpit opening in a formula car severely limits rigidity.

[2BWise]

Ultimate rigidity doesn't ultimately matter. If your car is a couple hundred lbs/deg stiffer than the next guy that doesn't necessarily equate to an advantage. Chassis stiffness is more of a relative function whereas the car needs to be stiff enough with respect to suspension criteria, drive train, and aero loads. The downside is that making it stiffer usually entails making it heavier, so at some point any stiffness gain because less valuable to the weight gained necessary to attain it.

[nulrich]

High chassis rigidity is a good thing because it allows you to ignore chassis flex when tuning the suspension. It doesn't really make the car any faster, but it does allow you to deterministically find the best setup. Torsional flex of the chassis is just another spring in the system, so even a fairly soft chassis can be set up to go fast (although it does introduce an undamped "spring"). I have had discussions with very successful race engineers that believe a softer chassis is an advantage, and they have achieved excellent results with fairly compliant chassis (I might argue "despite of" not "because of" but who knows?).

True composite monocoques can be made very stiff, but the advantage is primarily that they are lighter than a tube frame chassis for a given stiffness. They also don't need as much bodywork since the monocoque is the outer surface in many areas, saving more weight.

Once your chassis stiffness is an order of magnitude stiffer than your suspension further gains give diminishing returns. If you make your chassis as stiff as a well-designed tube frame (the Citation and Mygale are good examples), then adding more weight to gain more chassis stiffness is probably a bad idea. Maybe Steve Lathrop will share numbers on the Citation frame, which is very well designed.

Actually, the "weak" point in many small formula car frames is the area around the engine bay. The cockpit opening is a constraint, but you can work around it.

Just my opinion, of course!

Nathan

[S Lathrop]

Chris;

I have been doing torsion tests on cars since the late '70s. I know the progress of what I have built. I also have done tests on cars that I have engineered over the years. I have not seen a good treatment of the subject in print.

In short, the stiffer the car in torsion, the better you can control the mas of the car in roll. That increased stiffness can be translated into better mechanical grip. The stiffer the car, then other things become a bigger factor, such as suspension friction. But the end game is a better feeling and handling car.

That is the short answer.

[R. Pare]

Chris:

Basically put, the stiffer chassis will always be better - all other things being equal.

Think of it this (simplified) way - the chassis is an uncontrolled spring connecting and transmitting the reactions of the front suspension to the rear suspension. The stiffer that spring, the faster the rear will react, and the more sensitive the chassis will be to changes.

Obviously, the difference between a 5000#/degree chassis and one of 5200#/degree isn't very much, so for drivers at this level, the change would go unnoticed. But, go from 5000 to 7000, and the change can be easily felt. Go from 5000 to 10000, and it's a game changer.

And no, stiffer doesn't necessarily mean heavier - it depends on where the tubes are placed more than just how stiff each tube is individually.

[Wright D]

[FONT=Verdana]Cockpit openings in a carbon tub or tube chassis present the same problem...A really big hole. A carbon tub is not un-affected by the hole, and great engineering effort has gone into how to mitigate the effect of the cockpit hole on chassis stiffness by every major carbon monocock builder. [/FONT]
[FONT=Verdana]I strive to make my chassis as efficient as possible, meaning highest stiffness possible within a realistic chassis weight. I try to minimize cockpit opening effect by treating the perimeter of the hole as a beam, since the big square hole forms a four bar member. The rest of the chassis can be triangulated well, so high stiffness at low weight can be achieved easily in FB with just a hint of ingenuity. With a little more effort, high serviceably, ease of repair, driver fitment, etc. can all be baked into the design as well. [/FONT]

[Jnovak]

Chassis stiffness is a very complex issue. In my opinion there is an upper functional limit for each type of car that once you are there, there is very limited improvement in the performance of the vehicle. The parameters that affect this "functional upper limit" are many. much depends on the required spring rates the car needs and the roll stiffness required from the bars, what is the required roll couple distribution etc.
Here are a very few thoughts:

1. Weight vs stiffness. This is very important in tube framed cars with low minimum weights.

2. Lateral bending stiffness. This factor is much overlooked and should be considered hand in hand with torsional stiffness.

3. Is your compliance (how much it deflects) linear along the length of the chassis? For instance we once tested an F1 car with a carbon tub. The stiffness of the tub itself was anout 90,000 ft-lbs/deg. The total stiffness of the entire chassis was about 8,000 ft-lbs/deg. They missed something important.

4. VERY important is your constraint method for the test or your FEA model.

This subject is much too complex to discuss in a forum so I will suggest that a small tube framed open wheel car should have a torsional stiffness of approximately 4000 ft-lbs/deg. + 1000 or - 500 ft-lbs/deg. I have measured lots of cars and there have been functional tube framed cars in the range of 2500+ ft-lbs/deg.

I could go on for an hour or two but that's enough.

Thanks ... Jay Novak

[R. Pare]

3. Is your compliance (how much it deflects) linear along the length of the chassis? For instance we once tested an F1 car with a carbon tub. The stiffness of the tub itself was about 90,000 ft-lbs/deg. The total stiffness of the entire chassis was about 8,000 ft-lbs/deg. They missed something important.

That's putting it rather mildly! Even the much maligned March Indy lights car (with it's combined alu/carbon tub) measured at about 16000 axle-to-axle!

[nulrich]

Obviously, the difference between a 5000#/degree chassis and one of 5200#/degree isn't very much, so for drivers at this level, the change would go unnoticed. But, go from 5000 to 7000, and the change can be easily felt. Go from 5000 to 10000, and it's a game changer.

I don't agree. A simple dynamic model of a small formula car will show you that increasing the stiffness from, say, 3,000 to 5,000 will make much more difference than increasing it from 5,000 to 8,000. Every textbook and reference I've read supports that, as does anecdotal evidence I've read about the development of F1 chassis. If you have some experience that suggests otherwise, I'd be interested to hear about it.

The "critical" torsional stiffness depends on the power, weight and downforce of the car. Obviously Formula 1 and Indy cars need much higher torsional stiffness than an FB car. Jay's numbers agree with mine for a small formula car.

And no, stiffer doesn't necessarily mean heavier - it depends on where the tubes are placed more than just how stiff each tube is individually.

For a given designer of a given capability, making the chassis stiffer will make it heavier. That is, if I am capable of designing a car of "x" stiffness that weighs 100 lbs, then I will have to add weight to make the stiffness 1.1x. If I can make it 1.1x at 100 lbs then I didn't do a very good job the first time!

FEA is a great tool for executing the final design, but I like playing with scale balsa wood models to start. I guess that makes me old school.

Nathan

[Jnovak]

BTW, the F1 team stated that their carbon tub, based on their model, was 225,000 ft-lb/deg instead of the 90K it was.

Thanks ... Jay

[R. Pare]

I don't agree. A simple dynamic model of a small formula car will show you that increasing the stiffness from, say, 3,000 to 5,000 will make much more difference than increasing it from 5,000 to 8,000. Every textbook and reference I've read supports that, as does anecdotal evidence I've read about the development of F1 chassis. If you have some experience that suggests otherwise, I'd be interested to hear about it.

I'm not sure where/why you are disagreeing - I quoted first only a .04 change and then a 100% change - with both up in the range of the typical modern FC/FB car. You quoted in both cases a 60% change, with the lower numbers in the range where it is greater percentage of the total package. Obviously, for any given input (lateral and aero loads), the percentage increase in performance will not match the percentage of torsional increase, but be an ever-diminishing return - BUT, there will definitely be a return.

For a given designer of a given capability, making the chassis stiffer will make it heavier. That is, if I am capable of designing a car of "x" stiffness that weighs 100 lbs, then I will have to add weight to make the stiffness 1.1x. If I can make it 1.1x at 100 lbs then I didn't do a very good job the first time!

Which is exactly what I was stating - not all designs are perfect at the start, and can very often be improved greatly without adding weight. It may take totally scrapping the first iteration and starting all over again, but the result is the same - a stiffer chassis at the same weight. Steve's chassis (Citations) have, over the years, all gotten both lighter and much stiffer. Obviously (again), the more optimum a design is, the harder it will be to increase stiffness without adding weight.

Stiffening an existing, already-finished chassis is another story all together.

BTW, the F1 team stated that their carbon tub, based on their model, was 225,000 ft-lb/deg instead of the 90K it was.

What a hoot! I'd say that, based on both their modeling/real world results for the tub and then the final total package, that someone on that team needed to go back to school for a while!

[nulrich]

Okay, I guess we agree! I was mostly responding to this statement:

Go from 5000 to 10000, and it's a game changer.

In my opinion, once you get up around 5000 any additional increase is of marginal benefit, and your time would be better spent on other aspects of the design.

It's pretty hard to mess up the structural analysis of a monocoque shell like an F1 tub, at least by that much. I'm guessing they must have made some sort of ridiculous assumptions about the real world stiffness of carbon/epoxy laminates. Carbon fiber is truly an amazing material, but the final laminate has much less stiffness than you'd think.

Nathan

[S Lathrop]

Jay's numbers are good. The 87 Citation started life at 2500 and evolved to about 3000. The 94 Citation started at 4000 and evolved to above 5000. The 07 Citation is north of 5500 but not much. Interestingly the weight of the frame has not increased from the 94 Citation, less than 90 lbs for the frame and engine bay. These numbers are between the axels of a fully assembled car. The test loads are about 400 foot pounds applied through a front corner, with the load applied to the upright.

Jay's point about the distribution of the flexing is correct. The Stohr that I tested was not all that stiff but it was even down the length of the chassis. My cars have the cockpit as the weakest section followed by the engine bay.

I used a truss element stress model for developing my frames and as it turns out, the numbers I get for the frame and engine bay are almost the same as I get for the complete car. Having the engine bay as the weak section is a problem, I think. If nothing else, a weak engine bay hinders the drivers feeling of the rear of the car.

The FB, I think, requires a higher number than a FF or FC. The FB is seeing higher sustained G loadings than either FF or FC. It also makes significantly more down force just because it is traveling 150+ mph on the same track that an FC will only do in the high 130s.

[rmstringham]

I've attached an SAE paper written on the topic by the Cornell FSAE team. For all the FSAE scoffers, William (Bill) Riley went on to work for Jaguar F1, now works at SpaceX, and is the head of the rules commitee for FSAE.

abstract: the chassis needs to be stiff enough to support your desired roll stiffness distribution

adding to that (and probably echoing whay others have already said),

-everything is a compromise. You need to consider weight, cost, SAFETY etc, all vs stiffness.

-the linearity bit that Mr Novak mentioned. if you get one section the chassis sufficiently stiff but another area is lacking. the front and rear suspension and the chassis can be thought of as springs in series (which add like resistors in parallel) which means one soft part can screw up the whole deal.

-dont forget the little things, like pick up points and load paths.

-poor constraints in FEA can easily artificially stiffen the frame.

is torsional stiffness the only factor in chassis design? no. is it important to understand? yup.

[starkejt]

The contents of the PDF do not live up to the promise made by the file name.

edit: you changed it.

[rmstringham]

The contents of the PDF do not live up to the promise made by the file name.

edit: you changed it.

haha i caught it right after posting. sorry for the false hopes. that was the original file name from my source. Freudian slip?

[Mike Devins]

FEA is a great tool for executing the final design, but I like playing with scale balsa wood models to start. I guess that makes me old school.

Nathan

I have used wood and attached the "weld joints" with hot glue. when you twist the structure you can see the high stress point pretty easy.

[R. Pare]

I'll stick with what I stated originally, but add some explanation:

Within the loads we are seeing in FB, you are correct that doubling from say, 2500 to 5000 will yield a bigger performance increase than the doubling again from 5000 to 10000, BUT, both will dramatically change the feel and tuneability of the car - ie - each will be a "game-changer" in their own right. Going thereafter from 10000 to 20000 will still alter the feel and tuneability, but at a greatly decreased level compared to the first two changes (measurable in driver feel, but not in speed).

If the load were those of an FF, then the increase from 5000 to 10000 won't be anywhere as dramatic as the first doubling, but most definitely will change the feel some measurable amount. The change from 10000 to 20000 would still show some gain, but most undoubtably not enough to warrant the work or expense (if it was even possible ).

[Christopher Crowe]

Exactly how is it done? Would you simply fixture the chassis at the rear then jack up a front upright (front suspension locked and a scale under the jack) until you reached 1 degree of torsional disparity between chassis front and rear, then read the scale?

Should the rear be fixed at the uprights too... or could you just fixture the rear of the chassis in a jig -- say -- at the rear axle centerline? Should all four corners of the car be locked (a tube inserted where spring and shocks would go)... or can you leave the shocks and springs in place and just wait for that 1 degree?

How IS this kind of measurement actually done...

Thanks you guys,

Chris

[S Lathrop]

Chris;

Doing a torsion test is relatively simple.

1. Replace the shocks with solid struts.
2. Support the car at the rear (or front) on bare wheels or the uprights themselves. You will need to be a foot or two above the ground.
3. Support the front of the car on a pivot at the center of the chassis. This can be as simple as a couple inches of heavy angle iron. I have a piece of angle with a flat piece of steel welded to make a triangular box. I place the box so the pivot point is about ground level and the front of the car rests on one side of the box.
4. Construct a beam that attaches to the front upright and gives you a 6 foot lever on the front suspension (6' from the center of the chassis). You will need at least 50 pounds of weight to hang from the beam. I use a bucket filled with scrap metal and sand. Exercise weights would be great.
5. To measure the deflection, clamp beams (1x1 aluminum tubing) at the front, dash, roll bar, and rear bulkheads. Have the front and rear beams in line with the axels. I use 32 inches from the center line of the chassis as my measuring point. Clamp the bars in one place only.
6. Net the deflection at the front bulkhead out of the measurements at the other locations. You have a force (weight x distance) and an angular deflection (net deflection at the various bulkheads). A little math and you have an number. Depending on your chassis and the weight you use, you will see numbers around 0.100 in. net deflection.

I use the torsion number in my calculations for roll stiffness at both ends of my cars. I calculate the chassis stiffness form the CG forward and rear ward. I then calculate the modified roll resistance at the front and rear of the car. This gives you a way to quantify the effect of chassis stiffness on the handling of a car.

[Rick Kean]

I like their serial stiffness model graph regarding the combined frame and suspension member contributions to overall chassis rigidity. I think it adds to Richard and Nathan's posts.

Rick Kean

[peat]

a car is composed by a lot of parts working together as one element. For this reason there isn´t a "Holy grail" about chassis rigidity. I mean to say that there should be a compromise between all the elements (especially between tyre-suspension-chassis-mass). We don´t need to have an ultra-stiff car for been competitive, we should have a package that work well together for been competitive.

Sorry for my poor english, I am trying to improve it.



P.S1: motorsport is a world of compromises where there ins´t almost "holy grails" about nothing
P.S2: I would like to know the torsional stiffness and the weight of all F1000 chassis

[Chris Livengood]

a car is composed by a lot of parts working together as one element. For this reason there isn´t a "Holy grail" about chassis rigidity. I mean to say that there should be a compromise between all the elements (especially between tyre-suspension-chassis-mass). We don´t need to have an ultra-stiff car for been competitive, we should have a package that work well together for been competitive.

Sorry for my poor english, I am trying to improve it.



P.S1: motorsport is a world of compromises where there ins´t almost "holy grails" about nothing
P.S2: I would like to know the torsional stiffness and the weight of all the F1000 chassis

I like this guy. He has a good sense of practicality.

[S Lathrop]

a car is composed by a lot of parts working together as one element. For this reason there isn´t a "Holy grail" about chassis rigidity. I mean to say that there should be a compromise between all the elements (especially between tyre-suspension-chassis-mass). We don´t need to have an ultra-stiff car for been competitive, we should have a package that work well together for been competitive.

You are correct. It is possible to have a very good handling car that is not particularly stiff. But when you get a change in something like tires, some designs have a hard time adapting to changes in the setup variables. The stiffer a car is, the easier it is to adapt to improvements in things like tires.

I did have a situation in the development of my cars where we made a big jump in chassis stiffness and that uncovered a bunch of problems that took some time to identify and fix. Things like suspension friction, motion ratios, shock valving and springs become way more critical that they are exactly right as you increase the stiffness of a chassis.

[peat]

You are correct. It is possible to have a very good handling car that is not particularly stiff. But when you get a change in something like tires, some designs have a hard time adapting to changes in the setup variables. The stiffer a car is, the easier it is to adapt to improvements in things like tires.

I did have a situation in the development of my cars where we made a big jump in chassis stiffness and that uncovered a bunch of problems that took some time to identify and fix. Things like suspension friction, motion ratios, shock valving and springs become way more critical that they are exactly right as you increase the stiffness of a chassis.

I agree with you, the stiffer the better (at least often), but don´t forget the compromise between all the elements.

[peat]

You are correct. It is possible to have a very good handling car that is not particularly stiff. But when you get a change in something like tires, some designs have a hard time adapting to changes in the setup variables. The stiffer a car is, the easier it is to adapt to improvements in things like tires.

I did have a situation in the development of my cars where we made a big jump in chassis stiffness and that uncovered a bunch of problems that took some time to identify and fix. Things like suspension friction, motion ratios, shock valving and springs become way more critical that they are exactly right as you increase the stiffness of a chassis.

This is something different. We can´t talk about a "Holy grail" of race car design, but the process is something like this (at least for me):

-weight distribution
-tyre
-uprights..
-suspension
-chassis
....
In brief, from outside to inside (aero should be somewhere in between, depending on the class). Of course this is just an initial approach, when someone is working goes from one to another without order trying to find a balance.
As you can see, chassis is one of the last thing taking into account (this is just an approach, there isn´t a real order), that´s the reason because you had so many problems, chassis is design to satisfy the previous elements conditions.

This is another thing that I am afraid of, there are a lot of people doing major changes to their cars. I don´t doubt about capabilities of the most of the people arround here, but if someone wants to improve or optimize something, they should be really sure about what they are doing and it means to have a parametric car model (I don´t know if any of you have one ).
A lot of people follow driver feelings, but sometimes there are big differents between what a driver feels and what really happened (use data acquisition to check).
What I mean to say with this big paragraph is that if a designer decided something there should be a big reason for that, he is analizing the car as one complete element (tyre, chassi, suspension...) and not just only as a single element (i.e chassis) because when the race start you race it with the whole car, not just only with the chassis or suspension alone, it mean to say that if you change something in the original design, probably you will have to change something in other areas (one more time all it´s about compromises).

Sorry for such a letter

P.S:anyway, all the people is free for to do whatever they want, this is just my point of view and I don´t pretend to disturb anybody with it.

[jeff68]

I'm between jobs and without access to FEA. It would be enlightening for someone here with an existing FEA model of a frame to fully triangulate the cockpit area, as in ignore driver provisions. The before and after theoretical torsional rigidity numbers would offer some insight IMHO.

[nulrich]

Just recently read an SAE paper about the development of the Swift 014. The numbers they report for torsional rigidity are as follows:

Swift 008 chassis only 13,222 ft-lb/deg, entire car 3,882.
Swift 014 chassis only 19,144 ft-lb/deg, entire car 5,110.

I believe that means that the current Citation FB/FC tube frame chassis is stiffer than a Swift 014 Formula Atlantic.

Nathan

[S Lathrop]

Just recently read an SAE paper about the development of the Swift 014. The numbers they report for torsional rigidity are as follows:

Swift 008 chassis only 13,222 ft-lb/deg, entire car 3,882.
Swift 014 chassis only 19,144 ft-lb/deg, entire car 5,110.

I believe that means that the current Citation FB/FC tube frame chassis is stiffer than a Swift 014 Formula Atlantic.

Nathan

Nathan;

I described my measuring techniques. The numbers are based on the my test procedures and the loads I use. Change any of that and you will get different numbers. Swift was probably using higher loads, more consistent with what an FA would see on the track.

I have tested the 008 Swift and the numbers I got for the first version of the car are not too different from what Swift reported. And yes the 008 was not very impressive, but it was better than my tube frame cars. The first problem we had to overcome was blowing head gaskets because the engine was being over stressed. The first race at Longbeach with the 008 Swift was not fun.

From the roll bar back, my car is way better than a Swift 008 as it first appeared.

I have been an engineer for all the Swifts 008 - 016 and the Ralts 40-41. The Ralts were way easier cars to fit to a driver. I think that a 41 with the right engine package and a stronger transmission might be the car to have in the new pro FA series.

[sbrenaman]

I described my measuring techniques. The numbers are based on the my test procedures and the loads I use. Change any of that and you will get different numbers.

Someone already said this once in the thread, but it bears repeating. Your method of constraining the car can have a profound effect on the torsional stiffness of the car.

A bit of FEA work showed that some fairly popular methods of constraining a car can add 40% torsional stiffness to an FSAE car.

[S Lathrop]

Someone already said this once in the thread, but it bears repeating. Your method of constraining the car can have a profound effect on the torsional stiffness of the car.

A bit of FEA work showed that some fairly popular methods of constraining a car can add 40% torsional stiffness to an FSAE car.

My system does not restrain the car. I test the car against itself. This is how it works on the track.

When I tested my first car, an aluminum monocoque car, I pushed down on the beam and I could hear the tub creek. If the tube had done that every time I loaded it in a corner, it would not have lasted a season. That is when I took care to calculate the load I was placing on the car.

The number I get from the test I use as the "installation stiffness" in the spread sheets when ever that number is important to know.

I have had the opportunity to work with car designs that were very similar but with significantly different chassis stiffness: the Zink Z11 FSV and the Z14 FSV, and the 87 and 94 Citations. The FSV was a 330% increase and the FF/FC was a 160% increase. On the ovals especially, Z14 easily outpaced the Z11 and the Z11 was the SFV championship winning car. The 94 Citation had very few races before the runoffs and both the FF and FC were competitive for the win in both classes. It surprised me how close the setups were when I compensated for the chassis stiffness.

[sbrenaman]

Wasn't implying your method was flawed. Just backing up your statement, and adding that comparison across different fixtures is of little value.

[R. Pare]

Just recently read an SAE paper about the development of the Swift 014. The numbers they report for torsional rigidity are as follows:

Swift 008 chassis only 13,222 ft-lb/deg, entire car 3,882.
Swift 014 chassis only 19,144 ft-lb/deg, entire car 5,110.

I believe that means that the current Citation FB/FC tube frame chassis is stiffer than a Swift 014 Formula Atlantic.

If those numbers are correct, the 014 engine bay is only about 6970, which is pretty horrible!

Seeing these new numbers makes me really wonder about Swift (even more than before) - in a paper they published about the 014 chassis, they claimed 12,500+ for the entire car (which sounded entirely reasonable considering what we knew about the car), and something down around 6000 for the 008 (can you believe that the engine was mounted in rubber bushings? ) - I don't have the paper anymore so my numbers may be off slightly, but there is no doubt about the fact that their older numbers were quite a bit higher. Most likely they changed their test methodology in the meantime.

And yes, a well designed tube frame could indeed be much stiffer than a badly designed carbon tub car - especially if the engine bay is a rag.

[K.Sampson]

http://papers.sae.org/2002-01-3301

The above numbers are correct. This is the paper that the numbers are from. It used to be free to download from Swift Engineering website. I have the pdf, but I am not sure if posting it here would be frowned upon...