tomscnj

Hi Guys,
New member/SC owner here. I would like to replace current oem tires with 245 45 18's for a little additional sidewall height, ride cushioning, and extra insurance from pothole impact flats and rim damage...DOES ANYONE KNOW OF CLEARANCE ISSUES WITH THIS SET-UP?

I'm also considering this for the added benefit of improved gas mileage thru taller effective gearing, as the change will increase rolling radius by 3.8% :

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

the miata club's tire size calculator is a great tool most of you have seen before,
i inputted the stock size of 245/40/18 vs, 245/45/18

ANYONE ELSE TRY THIS? OTHER SUGGESTIONS?

THANKS!

J954sho

Never go above a 3% differential. For more "cushion" try increasing the width and decreasing the aspect ratio to keep overall diameter.....or avoid potholes like those running 19's.......

grabber2

Thats is like adding almost 1" to the overall height and increase the rotation radius by 3.75%

I have use 235/45/18 on the SC & its fine, 245/45/18 should not cause any rubbing.

You may also try fitting with 255/40/18

thombiz

I went about 1" taller in diameter on my setup and had no clearance issues at all. For mine, I went with 17" wheels and 225/55 tires. The ride and drive is super comfy. Almost a complete opposite from the runflats.

tomscnj

thanks for the responses, just a few nitpicky questions:
j945sho

Why is it the rule to never exceed 3% increase in rolling circumference? i dont care about speedo error, and like I said, it would improve highway mpg and lower cruising rpms

grabber2, the 235/45/18's you ran without clearance issues are still a tiny bit smaller than the 245/45/18's i'm considering, and either are smaller than the 255's you suggested...you must be confident of the clearance, did you put the car on a lift, then lower the wheels onto jackstands with full weight, then run your hand around the tire/fenderwell clearance? even if one were to go to all this trouble, it still wouldnt simulate full suspension compression over bumps. I might dare the 245/45/18's though, based on your experience

altatensio

I am also considering the 245/45/18 vs the OEM 245/40/18 for a smoother ride. Has anybody found any problems by doing this? I would appreciate the pros and cons.

medsc430

I changed out my run flats for non r-f's but also increased sidewall height from 40's to 45's. But I also decreased width from 245 to 235 to minimize speedo difference. My guess (and this is only a guess!) is that you could get away with 245X45 18's as far as diameter is concerned but you would distort your speedo reading (which you mentioned was not a factor for you). The effect on ride quality, going from run flats to regular tires, was considerable. But the cushioning effect of more sidewall has to be fairly major, imho. Huge volumes have been written here concerning the sizable wheel well gap on the SC430 as well as large quantities of cash spent by lowering the car to negate said gap. That may well be proof enough for someone to "take the plunge" and try a set of 245X45(or even 50's for the truly courageous) 18's and report your findings!!