What size tire can you mount on the stock 18in rims? What size will keep the same overall diameter similar to keep the speedometer in sync? I have heard of people putting 245/40 on the rears, but only the rears. Thanks

 

There are people with 245/40/18 on all fours without any problems.

http://pw1.netcom.com/~sgalaba/tiresize.htm#ustires will be of use to you.

 

Do you know if 245/80/18 would be an issue if you put springs that lower the car?

 

That I do not know, but would like to. With a mild setup like Racing Beat's I do not think so.

 

I have had 4 MZ-03s installed this Thanksgiving weekend with no problems-on stock rims. I was told by several suppliers and looked at several databases and it seems 245 is as wide as you can go on the 8" wide stock 18 rims. There is a 1cm sidewall height diffrence which amounts to a 1% speed calibration error ((or Speedometer read of 80 is actually 79)).

 

We feet 245/40-18 on our special-stock 8s, but without 25mm spacers. If you're using spacers or rims with less offset you have some problem while fully steering.

 

They should fit on all rims, as the rims are all the same size (8 inches). The only probably is corner clearing, and rubbing, and with a minor increase to 245's that is not a problem.

 

Thanks for the input. 245/40/18 it is, but not for a while. I want to get some money out of the Potenzas. As for the suspension mods, if I go with anything it will Mazda Speed. IMO they know more about what works on the car and you get your monies worth if Mazada installs them. The warranty will carry with your 4 yr, 50K bumper - to - bumper, You can't put a price on that.

Thanks.

 

salituro64,

Be aware that if you go with Mazda Speed, you have to change out the shocks with the springs. Mazda Speed springs will not work (at least well) with the stock shocks. They are specifically made to be used with the MS shocks. A big reason I went with the Racing Beat units (besides the fact that RB makes really top quality stuff) is that they are set to run with the stock shocks, and I really wanted to keep the ride as close to stock as possible.

 

Here's a great link to a calculator to see what various profiles and tire widths do to the stock speedometer calibration:

http://www.miata.net/garage/tirecalc.html

 

anyone try 255/40/18 or 255/35/18 tires on their stock rims yet? Im sure these would fit fine.

 

A number of autocrossers are running 275/35-18's on the stock rims with no rubbing at stock ride height. I'm running 245/40-18 Kumho MX's for the street and IMHO the tire looks "right" on the rim.

 

My OEM's are about kaput. I have a little over 30K on them, in 8 months!
I was planning on going with the Goodyear F1's in 245/40/18.
Has anyone had experience with these?

 

Kwullen:

No expereince but the ratings on TireRack show the F1s far btetter in wet and dry conditions than comparable tires in the size and speed rating.

 

So does the Mazda Speed shocks make the ride much firmer?

 

The F1s do consistently get good test results and reviews. However, so does the Kumho MX. Unfortunately, there isn't a single test on Tirerack that directly compares the two. However, you can find two seperate tests, both performed on IS300s, although the MX was tested on 18 wheels while the F1s were tested on 17 inch wheels.

Now, these tests were performed on different days, so it's impossible to be completely conclusive, but the only obvious advantage the F1 seems to have over the MX is wet braking & lap times. Yes, the F1 posts marginally better number in most categories, but the difference is very small, and inconclusive due to the tests being on different days & conditions.

The biggest difference between the two in my mind is cost. $131 for the Kumhos, and $224 for the F1s. How badly do you want those few extra feet of braking?

 

Wow, I got new tires at 16K. But I had about 5-6 track days on them too.

 

GeorgeH,
Thanks for the informative post, I'll check out the Kumho on TireRack.
Obviously, with 30k plus miles on the OEMs, I do lots of open road driving so noise ratings are quite important to me. The BS 040's have become quite annoying with noise on our Florida asphalt pavement, they've gotten steadily worse with miles. I've had several sets of Khumo tires on other vehicles that did the same, even worse. I replaced my last set on a Prelude at 10k because they were unbearable. The RX8 seems to have about the same level of sound detention as the Prelude, the price you pay for a light car.
At their current tread depth levels the 040s are really fun in our Florida rain with the VSA switched off...............