does the speedo need recalibrating with bigger wheels? help!

[showman]

as above im thinking of fitting 18inch rims instead of the standard caddy jobbies, but with a bigger rolling radius wont the speedo be showing a slower speed than im actualy doing?

[d2a2v2e]

No because you use a lower profile tire so the rolling circumference will stay roughly the same. Something like a 40 profile tyre should do the trick (depending on width of rim). There is various online calculators that you can use to put in your current tyre size then new wheel size

[showman]

cheers bud with 18inch rims and a 40mm profile the difference is only 0.60 which means when the speedo reads 70mph the vans actually doing 70.42mph which is no difference really..... why i didnt think about that