How to ruin the handling of an MX5.by Norman H Gar

[lee]

185/60/14 weighs 7.9 kilo's..205/50/15 weghs 9.7 kilo's...All in the BOOK..

Different tyres have different weights. A Bridgestone 205/50R15 might not weight the same as a Dunlop 205/50R15. Despite the complete incomparability of the two sets of wheels I own, I'll weigh them now to see how different they are.

[Guran]

Put 225 wide tyres on 9 inch rims on Gurans car and he will be slower because they weigh SO much more.. Unsprung weight is SO important.. Those daisy wheels only weigh 5.5 kilos....

Next club trackday at Wakefield Park, I'll see if I can convince Keith or Glenn to let me try my car with their stock 205/45R16 Star Specs.

stock daisies 5.5kg + Star Spec 185/60R14 8.2kg = 13.7kg each
stock 16" x 6.5" 7.0kg + Star Spec 205/50R16 10.0kg = 17.0kg each
(couldn't find weights for 205/45R16 but I estimate about 9.0kg)

So an extra 3kg per corner in unsprung mass and the smaller longitudinal contact patch (less braking grip?), needs to be offset by the (hopefully) improved lateral grip in corners. Interesting experiment.

[Patrick Bramston]

Bryan.. maybe they could run your wheels and tyres for one session as well..It will be interesting to see if you are slower and they are quicker or if the times are similar...

[A.Chen89]

I think people in this topic will find Carroll Smith books interesting.

[Muzdaman]

Put 225 wide tyres on 9 inch rims on Gurans car and he will be slower because they weigh SO much more.. Unsprung weight is SO important.. Those daisy wheels only weigh 5.5 kilos....

Next club trackday at Wakefield Park, I'll see if I can convince Keith or Glenn to let me try my car with their stock 205/45R16 Star Specs.

stock daisies 5.5kg + Star Spec 185/60R14 8.2kg = 13.7kg each
stock 16" x 6.5" 7.0kg + Star Spec 205/50R16 10.0kg = 17.0kg each
(couldn't find weights for 205/45R16 but I estimate about 9.0kg)

So an extra 3kg per corner in unsprung mass and the smaller longitudinal contact patch (less braking grip?), needs to be offset by the (hopefully) improved lateral grip in corners. Interesting experiment.

It would also be good to see a much wider wheel comparison
15x8 6uls 5.7 kg + 205/50R15 Starspecs 9.5kg = 15.2 kgs

If what Emilio states is true the small weight increase would easily be offset by increased grip.

[as_1]

So, how would the car be affected if wheels were to be changed to lower offset, while keeping other factors the same i.e. changing the wheel from 17*7 et55 to 17*7 et35 for an NC, using the same tyres?

[NitroDann]

It would be uunquestionably worse.

Period.

Dann

[Dan]

It would be uunquestionably worse.

Period.

Dann

Does that only apply to a car with the stock suspension?

I'm not saying you're wrong I'm just interested in knowing why since I thought widening the track would be a good thing.

[NitroDann]

It applies with stock geometry, so yeah anything but welding on new pickup and custom arms it will be worse.

Dann

[lightyear]

I did a 1:38.00 at winton on the weekend with the 9" rims and 225's. That's about one million four hundred and tweny five seconds faster than anyone has gone on 7" and 195's.

[rascal]

So, how would the car be affected if wheels were to be changed to lower offset, while keeping other factors the same i.e. changing the wheel from 17*7 et55 to 17*7 et35 for an NC, using the same tyres?

It would be uunquestionably worse.

Dann

Define worse.. and in context of desired outcome.

If you are tracking your car and fit the lower offset rims, then the mid corner grip will be improved NOT made worse..
Widening the track reduces the load transfer onto the outside wheel, improving cornering ability.

If you are talking scrub radius, feel, kickback, then that would get worse.

But depends entirely what your reqs are..

Personally I run wider offset rims on my track car and it helps my times. For me the positives outweigh the negatives..

[as_1]

I always thought wider track will be a good thing as well

So what are the pros and cons?
What else would you need to do to make it all work with the lower offset?

[NitroDann]

I did a 1:38.00 at winton on the weekend with the 9" rims and 225's. That's about one million four hundred and tweny five seconds faster than anyone has gone on 7" and 195's.

ROFL.




Dann

[hb]

185/60/14 weighs 7.9 kilo's..205/50/15 weghs 9.7 kilo's...All in the BOOK..

Different tyres have different weights. A Bridgestone 205/50R15 might not weight the same as a Dunlop 205/50R15. Despite the complete incomparability of the two sets of wheels I own, I'll weigh them now to see how different they are.

185/60/14 weighs 7.9 kilo's..205/50/15 weghs 9.7 kilo's...All in the BOOK..

heres a little comparison. using dunlop star specs for all of them

185/60 r14
weight: 8.16

195/50 r15
weight: 8.16

205/50 r15
weight: 9.98

id love a set of 185s on rp-f1s but the tyre choice is far too limited. 195s are tossable enough for me

[username]

Not gonna bother reading 6 pages of stuff, but these pics might help contribute