club.liberty.asn.au

Hey guys, I Just ordered 225/45/18 Kumho Ku31 from ebay.. but my spare wheel is a full sized 225/50/17.
I went on a calculator to figure out the differences in size and got this.

circumference
225/50/17 - 2032mm
225/45/18 - 2072.5mm

225/45/18 will have -1.96% speedo error

So a reading at 30mph the 225/45/18 will read at 29.41mph

Is that too much of a difference? Should i buy a 18 space saver or 18 full size and match the new specs to avoid screwing up the the diffs?

Your rolling diameter on your spare is out by 12.9mm, so within legal limits (normally +/- 15mm)

I can't see it being a huge issue as an emergency, definitely would not be driving on it more than you need too.

See if you can get the circumference from the actual tyre company's, usually the actual sizes are different between brands.