Strongest Chassis S1 vs S2

[M030ef00]

Does anyone know whether the S2 chassis modifications to allow infinitessimally easier access made any difference to the torsional rigidity etc?

I think I'd rather be sitting in the chassis than on it for a side impact . . . (S1 fanboy unfortunately)

[Birdthom]

suspect the difference to rigidity (if any) is infinitessimal too. Not an issue IMO.

[F.C.]

Ha-ha, the low sill is the main reason I went for an S2.
I just couldn't get out of an S1 without humiliating myself on hands and knees; I really wanted a Lotus at the time and tried REALLY hard to find a way of getting out easily but just couldn't get the knack.
F.C.

[kambites]

I've never actually noticed any difference between the S1 and S2 it terms of difficulty of getting in and out.

[randy]

S2 is slightly less rigid but it's still a very rigid chassis. Subframe on the later 111R and VX cars is ste though so they are less rigid still.

[Moospeed]

Isn't the chassis for the 2-11 more closely related to the S1 purely for the sake of rigidity?

[kambites]

Moospeed said:

Isn't the chassis for the 2-11 more closely related to the S1 purely for the sake of rigidity?

I read somewhere that it was a hybrid of both, with higher rigidity than either, but it could have been completely wrong.

[Sam_68]

Don't get too hung up on rigidity... the point at which is becomes pretty much academic - in terms of handling -on a road car is a lot lower than most people think.

Remember that in terms of actual deflection, the chassis effectively acts as one of a series of springs. The other springs in that series (the tyres, road springs and bushes) are an order of mangitude softer, so the actual deflection of the chassis is infinitisimally small in comparison. The whole chassis stiffness obsession is (in terms of handling) an obsession that dates back to ladder frame chassis in the 1920's and '30's with stiffness' measurable in the low hundreds of lb.ft/degree, not thousands.

All Elises are plenty stiff enough to do the job.

Edited by Sam_68 on Thursday 2nd April 12:39

[bogie]

M030ef00 said:

Does anyone know whether the S2 chassis modifications to allow infinitessimally easier access made any difference to the torsional rigidity etc?

I think I'd rather be sitting in the chassis than on it for a side impact . . . (S1 fanboy unfortunately)

neglible - and the door beams and other bits n bobs make up for it

Id be more worried about the other vehicle coming over the top in a side impact .........

[randy]

kambites said:

Moospeed said:

Isn't the chassis for the 2-11 more closely related to the S1 purely for the sake of rigidity?

I read somewhere that it was a hybrid of both, with higher rigidity than either, but it could have been completely wrong.

I wouldn't describe it as a hybrid, it's a 111R chassis without the cut out in the sills.

[randy]

Sam_68 said:

Don't get too hung up on rigidity... the point at which is becomes pretty much academic - in terms of handling -on a road car is a lot lower than most people think.

Remember that in terms of actual deflection, the chassis effectively acts as one of a series of springs. The other springs in that series (the tyres, road springs and bushes) are an order of mangitude softer, so the actual deflection of the chassis is infinitisimally small in comparison. The whole chassis stiffness obsession is (in terms of handling) an obsession that dates back to ladder frame chassis in the 1920's and '30's with stiffness' measurable in the low hundreds of lb.ft/degree, not thousands.

All Elises are plenty stiff enough to do the job.

Edited by Sam_68 on Thursday 2nd April 12:39

Yes and no, but more no ;-)

The point is that you want the chassis stiff so that the compliance and movement you have in the suspension can be designed in to happen in desirable ways.

[Sam_68]

randy said:

Yes and no, but more no ;-)

More yes, actually.

Do the sums, and you'll find that the differences in actual deflection between a stiff chassis and a really stiff chassis, on a road car with road tyres, are sufficiently trivial to be meaningless.

People (including a lot of engineers who should know better) continually regurgitate the old textbook dictums without having done the calculations to understand the actual numbers involved.

Edited by Sam_68 on Thursday 2nd April 19:22

[kambites]

Deflection in the chassis acts as an undamped spring. Try driving a car without the dampers and see how fast you can go around corners.

[randy]

Sam_68 said:

randy said:

Yes and no, but more no ;-)

More yes, actually.

Do the sums, and you'll find that the differences in actual deflection between a stiff chassis and a really stiff chassis, on a road car with road tyres, are sufficiently trivial to be meaningless.

People (including a lot of engineers who should know better) continually regurgitate the old textbook dictums without having done the calculations to understand the actual numbers involved.

Edited by Sam_68 on Thursday 2nd April 19:22

On the basis that I can 'feel' the deflection in the rear subframe of an Elise I beg to differ. In the same way you can 'feel' the deflection in many roadsters. Agreed that cutting away some meat out of the VERY stiff chassis sides of any Elise isn't going to make that much difference but there are countless examples of how chassis compliance can cause handling issues. Lotus didn't build a full on compliance rig for nothing...

[shangani]

Sam_68 said:

randy said:

Yes and no, but more no ;-)

More yes, actually.

Do the sums, and you'll find that the differences in actual deflection between a stiff chassis and a really stiff chassis, on a road car with road tyres, are sufficiently trivial to be meaningless.

People (including a lot of engineers who should know better) continually regurgitate the old textbook dictums without having done the calculations to understand the actual numbers involved.

I think you'll find randy has done the figures and in terms of what he puts his race cars through in cornering etc probably does feel difference.

[Sam_68]

kambites said:

Deflection in the chassis acts as an undamped spring.

So does a tyre


Try taking one of your wheels off and dropping it on a concrete surface from, ooh, say 3 feet.

Then do the same with a chassis.

Come back and tell me which one bounces highest.

Honestly, there's so much half-informed bks on this particular subject that it's just not true.

But if you want to continue worrying about the difference in stiffness between an S1 and an S2 for road use, feel free...

[kambites]

Sam_68 said:

kambites said:

Deflection in the chassis acts as an undamped spring.

So does a tyre

And stiffer tyre sidewalls noticeably improve handling.

I would agree entirely that there's bugger all practicable difference between the S1 and S2 though.

Edited by kambites on Friday 3rd April 07:59

[Scuffers]

can I just point out that the OP's question was about "Strongest" not "stiffest" and the two are not that related...

[Sam_68]

The topic title refers to 'strongest'; the initial question, however, refers to torsional rigidity.

But I agree... there's a big difference.

[Sam_68]

kambites said:

And stiffer tyre sidewalls noticeably improve handling.

Not at all. One of the biggest problems with light cars is that the available tyres have sidewalls that are too stiff to give sufficient compliance and feedback.

And there's a very easy way to increase the (undamped) spring stiffness of a tyre... you simply pump it up some more.

Can anyone explain why I'm running my (exceedingly stiff) Westfield at 16 psi all round?

Incedentally: if you want to see how fast a car without dampers can go round corners, take the time to make a trip to Shelsley Walsh when Issigonis' Lightweight Special is running. You might see something that will surprise you...