What impact does wheel size have on speed

[BmacIL]

20's at the same weight as 18's will have higher rotational inertia, also. This further increases the need for more braking power beyond just curb weight. For performance, go with the smallest diameter wheel you can to fit the brakes and use a tire with stiff sidewalls. Very low-profile tires tend to also be trickier to drive at the limit.

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[NvrFinished]

I wonder how much contact patch area you'd gain, going from let's say 285/35-18's at about 26" tall to 285/35-20's at 28". Assuming the same width wheels.


Norm

I'm glad you brought this up Norm. I'm still in the process of deciding 19" or 20" wheels myself. As an example, the 305/35R19 MPSS tread width is 10.7" at a diameter of 27.4. The factory 275/40R19 diameter is 27.7". The 295/35R20 MPSS has a tread width of 11.6" to 12" depending on which load rating you choose. Diameter is 28.1. That's a tread width increase of up to 1.3" over the 305 size in the 19" diameter.

Of course I'm only talking the rears right now, but it does present a dilemma.

 

[S550Smoke]

Reading this is giving me mixed feelings about the wheels i just ordered. 275/35 nitto 555g2's on a 20x10.5 rim sqare setup....i guess ill find out at sebring aug 13th how they perform

 

[Grintch]

I get what you're saying, Norm, but OP is asking if there is a performance benefit to 20's and a taller tire has a larger contact patch and in order to keep the sidewall stiff you use larger wheels on taller tires.

Now whether anyone in a pony car "needs" more than 18" wheels is another matter. You're probably right about that one. Its one thing to have a performance benefit, its another to need or be able to use it.

You can have 20" wheels and a shorter tire than you can with 19's or 18's. So taller wheel doesn't convert directly to taller tire.

So what is the change in the contact patch from a 295/40-18, a 295/35-19, and a 295/30-20? How about a 315/30-20 or a 255/40-19?
Do the math, say 900lb per rear corner, at 36 psi.
25 square inches for all.

Bigger wheels and tires also don't covert directly to bigger contact patches. Wider tires provide a wider contact patch, which is better for cornering. Taller tires provide a longer contact patch, which is better for acceleration and braking. Bigger/wider tires CAN allow for a lower tire pressure due to the inherently lower loading/stress, which WILL increase the size of the contact patch but is dependent on the tire construction and compound.

Boss 302 race cars use 18" wheels. Most GT3 cars seem to use 18" wheels. Smallest and lightest wheel that will fit over PP brakes is an 18" wheel.

Going to 20's may provide better wheel & tire selection (or worse tire selection for real track tires), but it has no inherent performance advantage and a couple of disadvantages. Now if you want to fit some non-existent 16"+ brake rotors on your Mustang, then 20" diameter wheels might be argued as a performance enhancer.

What I always love about most of these big wheel discussions, is how people hate to admit that their 20's are mostly about fashion. Just admit it, and be happy with how they look. Paint them black and they will all look pretty much the same.

 

[redleg322]

...Taller tires provide a longer contact patch, which is better for acceleration and braking. Bigger/wider tires CAN allow for a lower tire pressure due to the inherently lower loading/stress, which WILL increase the size of the contact patch but is dependent on the tire construction and compound....

That's probably how I should have phrased it. I think we just disagree on how necessary these fancy dubs are. :cheers:

 

[Grintch]

http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

Some actual testing. Not completely apples to apples as they used wider tires with the larger diameter wheels, but still useful.

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