I need new tires- 225/45/R18 91W IS AROUND $200@they have 235\40 r18 95w for only $130 @ will this tire be o.k.thanks

 

what tire?!?!?

 

oh yeah, & to answer your question...
the tire will be slightly wider, & a bit smaller radius.....i think its a -2.2% difference in circumference for 235/40, if i recall correctly, so your speedo will be a bit high. other than that, shouldnt be a problem.

 

Bmp

 

zaglo basically answered your question...the tire is going to be wider but have a shorter sidewall and smaller circumference, causing some speedometer/odometer accuracy issues. It will look a bit different from stock too. Whether that's "ok" is up to you...it'll fit the wheel fine and function properly.

Play with sizes here:
http://www.miata.net/garage/tirecalc.html

 

Do they have a 245/40-18? That would be better.

Wierd that the wider tires are cheaper...

 

I put 245/40/18 on mine. You will have a broader selection of tires in htis size. I chose Michelin Pilot Sport A/S and they are great

 

Did you only put the 245s in the rear or all around?

 

All around.