Why do people do this?

[CurrentlyPissed]

Why do people do xxx/40/18 in the front and xxx/35/18 in the rear? Is there a reason for this exactly? Seen just about every other person doing it, so I did to be safe, I didn't know why though.

[MVDCGTO]

Depends on what the xxx is. I have 235/40 18's in the front and 275/35 18's in the rear. The 40 and 35 are the sidewall heights in terms of the percentage of the tread width, so on the front the sidewalls are 40% of the 235mm tread width. Basically if you have a staggered setup the rears are wider so the sidewall percentage should be lower so the overall height of the tire is roughly the same.

[CurrentlyPissed]

Depends on what the xxx is. I have 235/40 18's in the front and 275/35 18's in the rear. The 40 and 35 are the sidewall heights in terms of the percentage of the tread width, so on the front the sidewalls are 40% of the 235mm tread width. Basically if you have a staggered setup the rears are wider so the sidewall percentage should be lower so the overall height of the tire is roughly the same.

Okay, so then I was correct to do 245/40 and 265/35? 245 would be 98 and 92? 235 would be 85 correct? Think I am understanding..

[Oh4GTO]

Even though the wheel size stays the sam, there is a specific height/width ratio that has to be maintained. The wider you go, the lower the sidewall gets. To a point obviously.

[ElCidAviator]

I did the same go along with the crowd. I'm sure you read my post. I went with 245 to get a little more width upfront.
235/40/18 = 25.4 in dia.
245/40/18 = 25.7in dia.
265/35/18 = 25.3in dia.
275/35/18 = 25.6in dia.

Go with either 235/265 or 245/275

[Doric]

This (http://www.miata.net/garage/tirecalc.html) will help you out tremendously.

[CurrentlyPissed]

I did the same go along with the crowd. I'm sure you read my post. I went with 245 to get a little more width upfront.
235/40/18 = 25.4 in dia.
245/40/18 = 25.7in dia.
265/35/18 = 25.3in dia.
275/35/18 = 25.6in dia.

Go with either 235/265 or 245/275

Order is already shipped, I did 245/265 because TR was out of 275, and I don't want to go straight to 285 because I'm not sure how clearence will be. I'd rather not roll my fenders if I don't need to on a 275. Will this be okay?

[ElCidAviator]

Yeah mine don't look terrible, but you can kinda see the difference in tire height. It depends on how picky you are. The numbers don't lie

[luisvelasco02]

This (http://www.miata.net/garage/tirecalc.html) will help you out tremendously.

thanks for the link, helps a bunch.

[ElCidAviator]

Thats the same site where I got my numbers. I hope this can help future buyers. Currently Pissed, if you already ordered, I wouldn't worry to much. I don't like it but I'm incredibly picky. However, it's not big enough of a deal for me to replace the tires.

[DAFFYDRUNK]

Why do people do xxx/40/18 in the front and xxx/35/18 in the rear? Is there a reason for this exactly? Seen just about every other person doing it, so I did to be safe, I didn't know why though.

The idea is to keep the diameter similar to the factory tires for fitment, and keep the front and back diameter as close as possible to avoid pissing off the TC and ABS. The 245/40-18's diameter is almost dead on compared to a stock 245/45-17. The 265/35-18 will be a little less than 1/2" smaller diameter then your front tire. Should be fine, although I probably would've picked a 265/40-18 in the rear simply to make the 04 speedo more accurate.

Not that the 265/35-18 is bad. I could be wrong, but I thought it was best to keep the diameter difference less than 3% front to back. In that regard, your 265/35-18 is closer to your 245/40-18 than a 265/40-18 would be. Compared to a 265/40-18, the 265/35-18's extra inch of clearance will increase the odds of happy fitment too. Drawback is your speedo will be another 1 mph more optimistic at 60 mph than it already is.

[05TRa4GTO]

This (http://www.miata.net/garage/tirecalc.html) will help you out tremendously.

I played around on that site so much years ago!

[CurrentlyPissed]

Makes alot of sense, and as for the speedo, i'm not too worried about that so it seems I made more of the right choice then.

[LS2-GTO]

+1 to those who went over it already.
245/40/18 front and 275/35/18 (or 265/35) rear is perfect, especially with 8" fronts and 9 or 9.5" rear.
235/40's were a little too slim on an 8" rim. Its a pretty heavy car and always felt like driving on the rims when cornering harder. Every little bit of rubber counts as long as you're not increasing the sidewall.

[Jim346]

I have 245-40-18 front and 275-35-18 rear. Why? Because.

[RPS06GTO]

I have 245-40-18 front and 275-35-18 rear. Why? Because.

Werd.