pres589 wrote:
Something I thought about later; you and I are both talking about running a 245mm wide tire. I know that's tread and the numbers are a little fuzzy from make to make, but every time I look at these tire specs I see something like 7.5" to 9" wide wheels as the recommendation. Unless there's a chance that a guy would take that 245 to 255 in the future, is there a reason to not get an 8" wide tire instead? I can't afford to buy these dumb things twice...
Okay, I'm not 100% sure on what you're asking, but I think the answer might be in the "formulas" for Tire width relative to wheel width.
{commence brain dump!}
Note: any tire sizes below assume that the manufacturer's stated section width is dimensionally accurate. For brands known to run wide or narrow, compensate accordingly.
Most manufacturer's recommend a tire that's 120% of the wheel width. So, for an 8" wide wheel (203.2mm), 120% is 9.6" wide (243.8mm) aka 245.
What I've seen as acceptable range for is anything from 100% to 125%. So, for that 8" wheel, we're talking anything from a 205 to a 255. I've heard of drag racers putting tires that are more like 130% on the rears, but I think that they're being silly to do so. I've seen autocrossers have good results putting the widest tire they can fit on their wheels, but I think this is a very specific instance that's working within a restrictive ruleset, not an optimal setup.
My understanding is that for most performance driving, you really want something more like 110-115%. (for the example 8" wheel, that's a 225-235). Endurance racers apparently prefer something around 95% of the wheel width (according to the Thunderhill tire guys).
Narrower tire sacrafices traction patch size for increased responsiveness. It gives the tire a higher effective spring rate. Wider tire sacrifices responsiveness for more overall grip, and gives the tire an effectively lower spring rate.
So, I'm figuring 245 will be best for my application, because well, I'm used to running 255s on a 9" wheel and don't want to give up that traction patch, but I also don't want to have big fat sloppy sidewalls. Sticking with 120% seems to be a happy medium between responsiveness and grip.
Does that help answer your question?
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