Hi David,
#1: Yes, if you had an independent rear suspension that consisted of Chapman
struts or upper and lower A-arms. Semi-trailing arm rear suspension and
swing axle rear ends have nastiness that is all their own.
#2 and #3: If lowering the rear of the car restored the A-arm angles to what
the designers originally intended , then you're in business. I once lowered
a Corolla GT-S in the front by first cutting the springs, then putting
machined spacer blocks between the lower end of the struts and the steering
knuckle, to maintain the lower control arm angle close to stock.
In Fred Puhn's book, lowering the car is not an option because Formula cars
have to meet a minimum ride height requirement (either some specified
distance or just "not hitting the pavement"), and the availability of
shorter tires hasn't changed that restriction.
#4: Yes, but two wrongs don't make a right. Raising the rear roll center
causes the car to become more understeery, and stiffening up the rear
suspension will cause it to break traction sooner, which will therefore
induce some oversteer...under certain conditions. I'd have to think hard and
read lots (and maybe do some testing) before deciding that the higher roll
center and the bigger rear sway bar necessarily caused equal and opposite
effects at all times. I would be inclined to think otherwise - better to get
the A-arm angles where they should be, and then maybe play with spring rates
and sway bars to do some fine tuning.
If you're trying to use sway bars to shift the understeer to oversteer
balance around, then you need to take into account that the Tiger is not a
very rigid chassis from a torsional perspective. Going big on the bars just
means you're using the floor pan to tune your suspension.
Is yours a Tiger with a Jag rear end? What if you built some (strong) arched
upper links so that you could set the ride height lower and still clear the
chassis under full compression?
Theo
sosnaenergyconsulting wrote:
> Hi:
> I recently bought a copy of Fred Puhn's book "How to Make your Car
> Handle" and had a question for y'all on the list.
>
> Don't have the book handy, but there's a section where he shows (using
> an early Lotus as an example) how the independent FRONT suspension of a
> car that was designed for large diameter tires (I think he used 26" for
> the example) will change when smaller diameter tires and wheels (I
> believe the example used 22")are used. The lower control arm, which is
> designed to be more or less level when using the larger tires becomes
> angled when using smaller tires. This causes the roll center to rise.
> I'm nutshelling here.
>
> Question #1 is this: Wouldn't the same principle apply to an independent
> REAR suspension?
>
> If the answer to the above question is Yes, then question #2 (ignoring
> the front suspension which WAS designed for the smaller diameter wheels
> and tires being currently used) is: would lowering the car at the rear
> compensate for the higher rear roll center caused by using the smaller
> diameter tires and wheels in the first place?
>
> And lastly, if the answer to the second question is Yes, my final (if
> you believe that I have a bridge to sell you :-) ) question is: would
> lowering the car now cause the lower rear lower control arms to become
> more level?
>
> Okay, on re-reading this, I came up with question #4: If the answer to
> question #2 is "no", or if lowering the car is not an option is it
> possible to compensate for the higher rear roll center in some other
> way, such as a stiffer rear anti-roll bar (possibly upgrading the front
> bar also in order to balance things)?
>
> Thanks in advance for any help you folks can give me.
>
> Regards
>
> David (perpetually confused) Sosna
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