Wheel width: Is wider always better?

The useful part

From a performance standpoint, what matters more than tire width is optimal wheel width to support the chosen tire size. One of our tire testing mules, the One Lap CRX, can use a staggered wheel fitment: 15x9-inch wheels up front and 15x8-inch wheels in the rear. We also have several sets of each of those wheels, so it's easy to run a variety of front wheel and tire sizes for comparison.

How it works

• Since our front-drive machine achieves most of its grip work with the front wheels, it's easy to quantify the effects of these different setups merely by swapping out the fronts.
• Here's some data collected when testing the Maxxis VR-1 200tw street tire, again at Harris Hill.
• Here's some Harris Hill data comparing Michelin Pilot Sport 4S tires on the OE wheels versus the same tires on the Finspeeds.
• For the track, however, a shorter tire is usually an advantage since it delivers better acceleration in all gears.
• Near the limit of adhesion, a tire is working through a slip angle-the centerline of the tire is pointing a couple of degrees inside of the arc the car is traversing.

What to take from it

The wheels share the same ET36 offset, so track width also remains constant. Mount that 225mm tire on a wider wheel, and suddenly the car has more grip everywhere, circulating a solid half-second quicker. Before hitting the One Lap of America, first a major investment: the right wheels.

Example or evidence

• When we finally gave up on C Street autocross and focused on a direct Sport 5 build for Time Trial competition, we mounted the widest wheels and tires that would fit on the car-245/40R17 tires on 17x9-inch...
• Custom forged wheelmaker Finspeed made us a set that's 1 inch wider front and rear.
• For optimal on-track performance, we have seen faster laps with the wider wheels.
• This also usually equates to about half an inch wider than the measured tread width, but it can vary a bit due to the variety of tread crown profiles and the lack of standards for this dimension.

Details worth keeping

Chris Tropea « » [ GRM + members read this article first. What's the widest tire I can fit under my car? What made our CRX faster: wider tires or wider wheels?

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