Right, just brought some r32 replica wheels for my MK1 octavia.

My car is currently running 16 inch wheels with 205/55R16 tyres on them.

The new wheels have 225/40R18 tyres

What size tyres will i need in order that i wont alter the speedo?

And what size would i need if i wanted to have slightly stretched tyres?

Help would be greatly accepted!

Just double checked and the new wheels have 225/40ZR18 tyres on them. Not sure what difference the Z makes!?

right size tyres already on, Z is just the speed rating, swap with similar if you need new ones.

So the speedo wont be effected at all? Any idea what size i would need if i wanted to half stretched tyres?

Im guessing are the 8j width ?

215/40 may be a diddy stretch

205/40 would be a bit more noticeable

Check tyrestretch.com for pics on both

I think the overall rolling radius is very similar as my old mk2 vrs had 18inch zeniths with 225/40/18s and the spare was a 16inch steel with I think a 205/55/16 so very close I would say.

Edited 29 June, 201412 yr by willy0329

Should be all good with the 225/40/18, I just sorted my new tyres out for new wheels on the way. Currently running 205/50/17 as standard on the spiders and when talking direct with Yokohama the 225/40/18's I've ordered, I had confirmed are a spot on same rolling radius, so should be very similar to your current tyre size of 205/55/16.