overall tire diameter?

[gearhead55]

Is there a way to calculate the overall diameter of a wheel/tire setup?

I currently am running a 18 inch rim with a 225/35 tire and i plan on going down to a 17x9 with a 225/45 tire. Which will have a larger overall diameter?

the only variable that i don't know for sure is the width of the 18 inch wheel. I'm guessing probably 8 inch wide, maybe 8.5.

any help would be appreciated. thanks!

[S14DB]

Tire size calculator (http://www.miata.net/garage/tirecalc.html)

[reflexdb]

Go to tirerack.com. Find your tire/size. Look on the "Specs" tab. Overall diameter is listed. For example...

Dunlop Direzza Sport Z1 Star Spec (http://www.tirerack.com/tires/tires.jsp?tireMake=Dunlop&tireModel=Direzza+Sport+Z1+Star+Spec&sidewall=Blackwall&partnum=34WR7Z1SS&tab=Sizes)

Keep in mind, this is the unloaded tire diameter. The loaded tire diameter is dependent on tire pressure, among other things. But, the unloaded tire diameter will give you a pretty good idea for comparison purposes.

[didderson]

Tire Size Calculator - tire & wheel plus sizing (http://1010tires.com/TireSizeCalculator.asp)

I like to use this calculator because you can compare different sizes. It makes it easy for you to calculate mileage differences on non OEM diameter odometer readings (because of the % difference given). I used it to size new tires compared with optimum oem sizing... Yea.

[gearhead55]

awesome, thanks everyone.