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      01-27-2010, 12:33 AM   #1
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Diminishing returns Weight vs Width

I'm curious, maybe some of you folk have some opinion on this..

There's a group buy for light weight track wheels 18"-ers, but they are 9.5 wide at front and 10.5 wide at rear. The reasoning was that wider tires could be fitted, giving better traction for track.

My question is whether the extra unsprung weight of 9.5 rims and 265/18/35 fronts and 10.5 285/18/35 versus 8.5 255/18/35 and 9.5 275/18/35 would cancel/negate the extra traction from the extra 10mm rubber/wheel.
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      01-27-2010, 01:04 PM   #2
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It is very hard, maybe even impossible correctly answer your question. A lot depends on your actuall wheel selection (weight). And even more on your tire. I am using 18x9 front and 18x10 rear with 265 ront and 285 rear. Just ordered a set of Advan RS wheels with the same width.
I am not a race car driver, I doubt that at my level of "expertise" you will see any difference between a minimally heavier setup.
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      01-27-2010, 01:40 PM   #3
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Quote:
Originally Posted by attila View Post
It is very hard, maybe even impossible correctly answer your question. A lot depends on your actuall wheel selection (weight). And even more on your tire. I am using 18x9 front and 18x10 rear with 265 ront and 285 rear. Just ordered a set of Advan RS wheels with the same width.
I am not a race car driver, I doubt that at my level of "expertise" you will see any difference between a minimally heavier setup.

I'm thinking specifically about the ARC-8's that there is group buy talk about. I checked out weights for Michelin PS2 tires

255/35/18 24lbs
265/35/18 26lbs // interpolate to 25
275/35/18 26lbs // interpolate to 26
285/35/18 27lbs

The arc-8 wheels range from 17 to 20 lbs for 8.5-10 so interpolating

8.5 17lbs
9 18lbs
9.5 19lbs
10 20lbs


So for a 8.5/9.5 255/275 setup the weights would be (approx)
24+17=41lbs front
26+19=45lbs rear

vs

9/10 265/285

25+18=43lbs front
27+20=47lbs rear

So basically 2 lbs difference per corner

Seems probably insignificant for most people?

Cost seems (very approximate) about $40/tire to go with the wider sizes. I'm not sure how much price difference there is in the wider rims but that's a one time cost.


Any thoughts?
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      01-27-2010, 05:13 PM   #4
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Yes the slight weight increase for added wheel and tire width is a very big/measurable performance increase. If all other variable stay the same.

A wider wheel supports a tire better, a wider tire provides more lateral grip. We could go into the nitty gritty deals, but for your above question, yes the extra grip will make a significant difference that would be instantly noticeable at a track day, and far exceeds the minor negative effects of a wheel that is 0.2-0.5lbs heavier and a slightly heavier tire.

Is the PS2 a really good performance for your dollar tire? No. There are much better options out there that you should be considering if you're even asking about wheel weight.
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      01-27-2010, 07:30 PM   #5
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Quote:
Originally Posted by paintpro21 View Post
Yes the slight weight increase for added wheel and tire width is a very big/measurable performance increase. If all other variable stay the same.

A wider wheel supports a tire better, a wider tire provides more lateral grip. We could go into the nitty gritty deals, but for your above question, yes the extra grip will make a significant difference that would be instantly noticeable at a track day, and far exceeds the minor negative effects of a wheel that is 0.2-0.5lbs heavier and a slightly heavier tire.

Is the PS2 a really good performance for your dollar tire? No. There are much better options out there that you should be considering if you're even asking about wheel weight.
Thanks for the input.

BTW: I picked the PS2s mainly because they come in a lot of sizes and tire rack has their weights listed, so I could get a relative comparison on the change in wheel weight for different widthss.

I'm still not entirely convinced that 10mm extra rubber per tire is worth the ~2lb increase per corner but I'll be the first to admit I'm no expert.
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      01-27-2010, 08:39 PM   #6
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Quote:
Originally Posted by Paddy View Post
Thanks for the input.

BTW: I picked the PS2s mainly because they come in a lot of sizes and tire rack has their weights listed, so I could get a relative comparison on the change in wheel weight for different widthss.

I'm still not entirely convinced that 10mm extra rubber per tire is worth the ~2lb increase per corner but I'll be the first to admit I'm no expert.
If 2lbs a corner equals a 72lbs chassis load increase. Then what is that as a percentage increase in the vehicles weight vs. the percentage increase in the tires width?


Even easier problem: Find me a fast car that isn't running wider rubber when the rules don't restrict it.
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      01-27-2010, 09:35 PM   #7
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Quote:
Originally Posted by paintpro21 View Post

Even easier problem: Find me a fast car that isn't running wider rubber when the rules don't restrict it.
I'll have to concede that one.
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      01-27-2010, 10:17 PM   #8
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My steering feel is significantly diminished with my 275/30/19 9.5" setup.

So much so that I won't track the car with that setup. I'd much rather go with my stockers and get that lively feel back.
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      01-28-2010, 11:07 AM   #9
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Quote:
Originally Posted by Paddy View Post
I'm thinking specifically about the ARC-8's that there is group buy talk about. I checked out weights for Michelin PS2 tires

255/35/18 24lbs
265/35/18 26lbs // interpolate to 25
275/35/18 26lbs // interpolate to 26
285/35/18 27lbs

The arc-8 wheels range from 17 to 20 lbs for 8.5-10 so interpolating

8.5 17lbs
9 18lbs
9.5 19lbs
10 20lbs


So for a 8.5/9.5 255/275 setup the weights would be (approx)
24+17=41lbs front
26+19=45lbs rear

vs

9/10 265/285

25+18=43lbs front
27+20=47lbs rear

So basically 2 lbs difference per corner

Seems probably insignificant for most people?

Cost seems (very approximate) about $40/tire to go with the wider sizes. I'm not sure how much price difference there is in the wider rims but that's a one time cost.


Any thoughts?
Given your specific combinations of wheels and tires i would go with the wider one for dry track use. The PS-2s however are not ideal track tires. They cannot tolerate the heat load very well.
I would go with the 18x9 and 18x10 wheels. You can fit even 265 front and 285 rear with those.
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      01-28-2010, 02:21 PM   #10
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I've just discovered this is a fascinating subject and something that there is an amazing amount of opinion on (via the web).
The most interesting thing I found is that the general consensus seems to be is that a tires contact patch area remains the same for a given load/psi. So widening the tire increases lateral traction but decreases longitudinal traction, wider but shorter patch. The lateral traction helps in corners, the longitudinal traction helps in acceleration/braking.

Seems counter intuitive to me, you'd think that a wider tire would mean a greater contact area. Apparently tests disprove that and the way to increase contact area for a wider tire is to reduce the PSI.
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