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02-05-2021 #1Registered User
- Join Date
- Apr 2008
- Posts
- 78
Do we want the sidewall straight or stretched on a road race track car?
Hey guys, I never really learned the science between the proper width of a tire on a rim for a all out road racing/track application.
Do you want the rim a little wider so the sidewall is slightly stretched?
Or do we want it where the side wall is straight up and down?
Most tire sizes are usually 35 or 40 aspect ratio, does the sidewall height affect this?
I am putting larger tires on our Rolls Royce race car and want to try and fit a 295/40/18 RS4 for the endurance racing and a 305/680/18 pirelli slick. My thought was try and get a wheel width that can fit both.
Thanks!
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02-05-2021 #2Tire sizes:
So a 295/40/18 translates to 295mm width, 40% of that is sidewall height, and last is diameter of your wheel, so you can calculate the height by multiplying 295 x .40 = .118 mm
If you want inches 118mm / 25.4 = 4.64 “
Or you can use a nice tire/wheel calculator.
Here is one that has all in one shot, great when going +1, +2 in size..
https://www.rimsntires.com/specspro.jsp
I have read some in the discussion of tracking your car you want a slightly stretched tire, so to avoid tire ‘rolling over’ the sidewall.
I would leave to others more experienced to share their knowledge on that.
I would guess a 1/2” to 1” narrower tire, which is 12-25mm
Also depending on tire brand width and sidewall, you may need more pressure in your tires.
The other component is wheel size, an 18x10 wheel is 10” at the mounting surface, but is around 11” from external wheel edge-to-edge.
usually a 245 tire is used on a 8” wide wheel,
a 275 on a 9.5” wheel
a 295 on a 10.5-11” wheel
a 305-315 on a 12”
so now the hard part is fit as wide a wheel/tire combo into your fenders and can still turn.
Usually a ‘square’ tire setup (same width front/back) has best behavior.
HTHDave
84 Monte SS - just a few bolt-ons
02-05-2021 #3Registered User- Join Date
- Apr 2008
- Posts
- 78
That is a really nice tire/wheel calculator.
However, my questions is related to the wheel rim width in comparison to tire width and sidewall height. What is the most optimal rim width compared to tire width? Should the sidewall be stretched (wider wheel) or straight (wheel matched sidewall with perfectly)
02-05-2021 #4I hope the updated post has something more useful, I usually end up timing out, even losing posts if I take too long.
HTHDave
84 Monte SS - just a few bolt-ons
02-05-2021 #5