17" vs 18"

[fatoni]

Originally Posted by enjoyminutemaid

@Suberman
Are you suggesting that wider tires won't improve grip (with all other factors the same)?

im sure hes not. hes just saying that a wider tire doesnt have a larger contact patch. well it can but contact patch is primarily a function of weight and tire pressure and tire width doesnt change either factor.

[Xanzent]

Originally Posted by jdmblood

will it be a really noticeable decrease in acceleration?

Depends on the size difference. If you go for a similar overall size and some lighter than stock wheels, it won't be bad.

Road & Track put out a brief but excellent article on this. They tried three setups: stock, stock wheels with better tires, and 235x40x18 tires on some ~17lb rims.

The simple tire swap took 2.3 seconds off the lap time and added 0.05g on the skidpad. The 18 inch wheels and tires provided a little bit better grip, but the car couldn't get going as fast on the straights, decreasing lap time by 6 seconds compared to the stock wheels with good tires. They should've gone with 225x40x18, which would've been a little closer to stock radius.

[Suberman]

Originally Posted by jdmblood

will it be a really noticeable decrease in acceleration?

Depends on transmission gearing. The automatic BRZ would likely scoot faster with smaller diameter tires.

I am referring to the shorter contact patch of a wider, lower profile tire reducing grip for acceleration and braking.

The common misconception is that lower profile tires on larger rims improves everything when it doesn't. It depends what you are looking for. The Road & Track article referred to about their BRZ and they found that fitting much better tires to the stock sized rims actually worked best. Note that the tire design alone was good for over 2 seconds a lap, which is huge (the stock tire is hopeless for any sort of competition use, as everyone knows, well except for amateur drifting of course). Some years ago R&Tdid a more comprehensive comparison test which explains this in connection with a 5 series BMW but comparing similar tires. Plus one gave a modest improvement in lap times if I recall correctly.

I think fitting the best 225/45x17 tires you want to afford to a set of lightweight 17x8 rims will probably optimize this low powered car with whacky rear suspension set up. Certainly the stock tires do not lead to quick motoring, wet or dry they are not grippy enough to keep the rear of the car where it oughta be. That's gotta be deliberate drifty stuff for our Japanese friends. Sure goes slow round corners.

[jdmblood]

ok so keeping it 17 inches and going with a wider rim would be more beneficial than going 18? 17s would also be lighter...

[NYCsubaruBRZ]

I want to put a set of 17x8 rims on my brz.

What is the lowest offset i can go with out rubbing on a 245 tire.
What about a 255 tire?

i want to go with an offset that will make my wheels poke out from the fenders as much as possible with out rubbing at stock or 1in lowered ride height.

I plan to drop the car 1in so keep in mind i want it to fit stock and lowered ride height.

i also dont want to have to adjust the camber like crazy or roll the fenders or anything like that.

thanks

[wparsons]

If you want to run 245's or 255's you're better off looking at 9" wheels, but fitting 255's up front without coilovers, poke or camber is going to be hard.

255's will clear the strut/spring seat on a 9" +35 wheel, but you'll have poke and not much room for camber without camber plates.

Why are you looking at such wide tires?

I'm running 225/45/17's all around on 17x8 +45's and they have TONS of grip if you go with a good tire (I have Dunlop Z2's), there's no need for 245's + all around for street driving at all.