So I'm looking to get a set of used (but new to me!) rims with tires. The stock tires are 225/55/17 and the new rear set of tires is 275/30/20. The difference is diameter is 0.94% between the rears and the stock rears. The front tires are 0.04% different from the stocks.

I realize 285/30/20 would be optimal, but maybe unnecessary. How sensitive is the AWD system on these cars in regards to the tire diameter differences? Is it an issue that the rears are different from the fronts? Or that they are slightly different from stock? I already have m45 wheels and tires that are 0.12% off from stock, but all 4 wheels have the same tire difference.

I assume the tire diameter differences so small that they probably are a non-issue, but I'm still checking up with you guys to make sure.

 

with your X you have to have the same size rims and tires all around, for it to work properly. as far as your sizing goes thats only up to you how big wide or whatever else you want to go. ride quality, rubbing, specs and so on.

this is a good tool to use as far as speed and size goes.

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

 

Figured that much. But how close in size do they have to be? Is 1% difference in diameter significant?

 

This is not correct. On an X you can have different size tires and rims front and rear as long as the tire diameters are close to each other. For instance there are a bunch of G35Xs running a 225/40/19 and 255/35/19 setup with staggered wheels with no issues.

 

Yea I'm going staggered obviously. But how "close" is close when it comes to the tire diameters between the front and rears?

 

What are the widths (and offsets) of the 20s you plan to run?

 

9 x 20 and 10.5 x 20

 

There are some running a 1.2% difference and they dont have problems. I am running .3 I believe and no problem what so ever. Keep in mind if you have a full size spare you want to keep it close the that because if you get a flat it will help. Trust me on that one.

When I look at tires, I keep it .9 or below. Also try to make the front alittle larger than the rear.

 

offsets

 

My work is done, Ernie, the AWD fitment guru has spoken...rofl!

 

I am not the awd fitment guru. I was trying to beat you in this thread before you got here. LOL

 

+32 fronts, +37 rears.

 

what are you looking for, really stretched, slightly stretch, none what so ever. How low are you going to be?

 

i think it's slightly stretched. Right now I'm on BC coilovers with a little less than a finger gap all the way around. I will be running a little camber to make sure the tires don't smack the fenders.

 

bump. I need info on this soon.