Ok! some of you guys run 245 265 even 275 tyres on 17 x 8 bullit rims, mine are not fitted yet, just waiting for rubber, my question is, im running a v6 with 16" pony wheels now, what size profile should i go to so that my speedo is not affected, i was hoping i could get 40's in 265, but then im thinking that 40's might not look right as there would be less sidewall, and that would increase the space between arch and tyre???
Your advice please.

 

245/45/17 for example...

a = 245 = tread width in mm
b = 45 = a percentage of the tread width that is the sidewall height
c = 17 = rim diameter in inches
(a*(b/100))+(c*25.4)

Using your existing tire size multiply the first number times the second as a decimal (245*.45) add that to the last number after multiplying it by 25.4 to convert to mm. Then just find a tire that gives you the same number +/- a few mm's...

that will get you to roughly the same diamater tire, but actually the formula for diameter would be:
2(a*(b/100))+(c*25.4) = diameter = 652.3mm = 25.68"