40w8

I have 07 RX8 GT 6speed auto that I track sometimes.

I put the 225/40r18 size on to gear down 4%, and shoot me out of corners better.

I also discovered some dealer swapped the stock wheels for 7.5 x18 Enkei GF-1's.

I like the 19# wheels so, I'll even get the 215/40r18 Michelin PSS next time.

I'm a contrarian in that I like to do unconventional mods.

Less is more, and a very light grippy wheel assembly is a great way to cruise or track.

lOOkatme

Just responding in general.


Mazda is pretty smart with their designs. The stock wheel is an 8" width with a 225 wide tire, same with the FD rx7.


The extra grip comes from wider wheels, and you want to fit the tires with a slight stretch, it means the wheel width is wider than the tread width of the tire. this puts the shape of the tire in a position where it holds the contact patch into position. the tire beads are wider than the tread width.


Every 1" of extra wheel width is about 1 second of lap time per minute.


The key if you want speed is getting correct offset wheels and running as wide as possible, then stretch the tire onto the wheel. so an 18x11 +45mm offset with 285/275 width tires. If you go all out and do say an 18x12 +35 with over fenders or what not and run a 295/30/18 would be the best grip.


An added benefit to stretching the tire out some is they don't track grooves in the road, tires that can move (tire beads inside of tread width) like to move around more. also the wider wheel width than tread width has much better feedback and driveability in terms of at the limits, they don't have the "snap oversteer" situation. its more of a controlled slide.


so on an 8" stock wheel I would shop for 225/45/18 size tires as they will provide better feedback and most likely just as much grip as a 245/40/18. a lot depends on the tread width of the tire.


Grip Wheels | URGE designs





Notice how the race car has stretched tires on the wheels.



formula 1 stretch.

9krpmrx8

iTrader: (46)

Here you go with the stretch BS again. The stock 225/45-18 is not stretched on a 8" wheel.

And wheel width does not equal faster lap times, seat time does.

NotAPreppie

Another issue is that competition tires are a poor analog for street tires. Competition tires have very different internal construction from street tires.

Heck, even two sets of street tires are going to respond differently to different widths of wheel. All else equal, a driver might find that one make/model tire gives better lap times mounted to an 8" wheel while another is better on a 9" rim.

That said, it takes a lot of seat time to be able to actually make that determination, so I agree with 9krpmrx8.

ChaosReaper

what? Why would the dealer swap your Wheels?

40w8

I never got that answer in May 2007.

There was a "new" RX8 6 speed auto ( I'd had a 73 RX3 and wanted to feel the smoother auto and not scratch gears even if not as fast) at Mildand Tx Mazda.

Mazda had a $2500 rebate at time, and some dealer put pinstrips, and some other bullshit on a list to add $2500.

Car had 650 miles on it like maybe it was driven from Houston or someone bought and returned. IDK

So, they wouldn't budge on MSRP of $29995, but they didn't charge the bullshit, and i got $2500 out of Mazda.

Car did have a trans problem 2 weeks later where it didn't seem to pull from start. Dealer checked and drained 1 quart out of trans. I think the torque converter would stay filled so looked over filled, since it cratered at 20k miles.

They gave a new trans, car works great, and I like my light wheels so no big deal.

I'm a perfectionist on what I care about, but wheels don't have TPMS, and light doesn't faze me.

My Bilstein B12 kit and Michelin PSS are really incredible in a Honda Civic size tire.

I like the idea of a stickier smaller tire, and it works for me.