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Tracking / Autocross / HPDE / Drifting What these cars were built for!


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Old 09-15-2015, 02:54 AM   #43
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Originally Posted by strat61caster View Post
Road and Track did it with 215 and 235 Dunlop ZI SS, it's exactly as you predict lateral grip vs. acceleration and straightline speed.

http://www.roadandtrack.com/car-cult...ransformation/

Around a track (I believe some iteration of streets of willow, can't tell) the 215's were faster than the 235's.
keep in mind though, they've also changed the overall diameter, this whole test could've been really good but changing the overall diameter will drastically affect the performance and ultimately the overall lap time, especially with stock power. .they should've used 235/40/17 instead and the results would be a lot different
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Old 09-15-2015, 03:00 AM   #44
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Here is a 285/35-20 Michelin Pilot Super Sport which has a 10.1" tread width (also available in a 10.5" tread width) mounted on a 20x10.5 wheel. This is a perfect tire-to-wheel sizing with a mild stretch, preloading the side wall just enough to improve steering response and performance.
the most important part of the article that I've also experienced many times, with stock or NA power levels 17x9 wheels with 235/40/17 tires is great because it will slightly stretch the tires will give great mechanical grip and responsiveness ..245/40/17 on 17x9 wheels would also work but would be a better match for FI car, since the shorter gear advantage of the NA becomes a disadvantage, )..
anything wider than those sizes will be a bit extreme and I don't think we'll be able to heat them up since we have relatively lighter car

most people forget this , there is a good tire and wheel size for the application so it's not one size fits all
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Old 10-07-2015, 01:38 PM   #45
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Wide in the front and narrow in the back is the way to go...
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Old 10-07-2015, 02:15 PM   #46
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Wide in the front and narrow in the back is the way to go...
Cousin did this on his e21 323i, some moron chewed him out about it 'you NEVER see RWD blah blah blah'

Cheap oversteer if you've got the wheels and tires laying around, not like he's at a time trial...
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Old 10-07-2015, 03:25 PM   #47
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We once tried wider wheels on the front axle of a 125cc kart.
I was constantly pushing, because the front tires would simply not get up to temperature.

(Granted this was an extreme example as the tire pressure (hot) on a kart is less than 12 psi. One would have to extremely wide to allow such low tire pressures on a conventional car.)
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Old 10-07-2015, 04:11 PM   #48
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We once tried wider wheels on the front axle of a 125cc kart.
I was constantly pushing, because the front tires would simply not get up to temperature.

(Granted this was an extreme example as the tire pressure (hot) on a kart is less than 12 psi. One would have to extremely wide to allow such low tire pressures on a conventional car.)
Valid point. If your tires & wheels are too wide it could be tough to get them up to the optimum operating temp on track, depending on how long your stints are, plus the extra drag and weight and whatnot, in which case you'll be slower. And unhappy. And poorer because you'll need to fix that stuff ASAP.

FML because I was that guy.

I once went through a very frustrating time with another car wondering why the 285s on 18x9.5s I was running were turning slower lap times than the 245s + 18x8.5s I had on it previously (R888s). All the signs were there in the tire wear and datalogs but by the time I figured out that wider =/= better it was too late.
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Old 10-07-2015, 07:39 PM   #49
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Wide in the front and narrow in the back is the way to go...
It totally depends on what you are trying to do. There are front wheel drive autocross guys that run this setup and win because it helps their cars turn.

But there are better ways to dial in a setup than gigantic front tires. And I cannot think of a valid reason to have larger front tires in a rear wheel drive car. It is kind of the absolute last thing you should do after suspension and everything else you could possible do is totally and completely maxed out.
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Old 10-08-2015, 02:44 AM   #50
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That was my point. There's no one solution fits all.
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