255/35 / 255/45 on an 18" rim?

 

Both ways will look better, but they will throw your speedometer off. If you go to miata.net tire size calculator you can put in you stock tire size and what tire size you want to try and it will let you know if that tire size will make it seem like your going faster or slower than you really are. for example if the stock tire is 235 45 18 and you put on 255 35 18 when your speedometer shows that your going 60mph your realy going 57mph.

 

^ Yea thanks, I used the tirerack tire calculator but it seems like one will will emit more wheel gap, obviously the 35series. I have some different wheels in stock sizes with a slightly more aggressive offset 38/35 so I'm not sure if these wider tires will stick out too much and look silly. Guess I will give them a shot when it's time to replace by te end of the year.

 

If you go to your local tire shop ask them to see the tires side by side that way you will know, but it they are to wide you will have to get your fendes rolled because they will rub if you hit any bumps even if your car is not lowered and the tires will wear faster because they are not making complete contact with the road, because the xtra width the tires will bowe inweard wearing the inside of the tire.