GT350R tire gaffe or good furtune

662

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I took the Carbon wheels to Discount tire to replace the sport cup 2's where they put their best man on the job... I only looked at the rims when I picked them up and did not immediately notice they mounted the 315's on the front and 305's on the rears.

Getting ready to run COTA this Sunday, I finished replacing the brake pads with Pagid's and bleeding and as I installed the fronts I was thinking they looked meaty, then as I started on the rear I instantly noticed the 305's stretched across the rims before even lifting them in place.

At this point I first was disappointed that they were going to have to service the rims to swap, but then I looked closer at the fronts and I liked the way the 315's looked. I ran the wheels through the range of motion and they don't look like they will rub anywhere, and I've been running 325's on some after market rims on the back already so that should be okay so I went to Discount and ordered 325's for the back...

It all looks tight no doubt, meaty and sticky too. Anybody have any bad experiences +sizing the tires that I should be aware of?
 

ANGREY

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315's will "fit" on an 11" front rim and as you tested, if they don't rub or clash, then you COULD run them on the front.

What the tire purists will tell you is that running a track dedicated tire too fat on the rim will stand the sidewalls up vertically and they won't "rollover" properly under lateral load. Apparently, the tire was designed to have a slight rake inward so that when the car turns and loads laterally, the sidewalls "rollover" and the lateral grip is better than if the sidewall started vertically already.

Hope this makes sense. Basically the tire gurus argue that a 305 on the 11" up front will perform better than the 315 on an 11" for turning purposes. For braking and straight line acceleration, the bigger tire/patch is probably more effective, but for maximum turning grip, the sidewalls weren't meant to be squared up.

To what extent this makes a difference, whether there's other factors (like excessive wear at the track one way or the other, how it effects the optimum camber settings, how much heat the tire takes on during repetitive lateral loading, etc) who knows.

Essentially, bigger doesn't necessarily always translate to better when it comes to tire sizing (and turning).
 

AustinSN

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The treadwidth on that tire is 11.5"

Not ideal on an 11" rim but I think it will be ok. Billy Johnson says the general rule of thumb is .5 narrower tread than the wheel, but every tire is different.

I would run them since they are already on. If it's not rubbing you may find you like them.
 

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