Hello all,

wondering if someone can help me out.

I've got a focus Chic special edition, currently on its stock alloy rims with standard 195/60/15 tyres.

However, I've just taken delivery of a set of 17 inch MP3 alloys, won off ebay. They are ok and just require a refurb, which i'm going to get done this weekend.

Now then the tyres fitted to the MP3 alloys are luckilly new, but they are 215/40/17.

will I be OK keeping the 215/40/17 tyres on, or should you strictly have 215/45/17 tyres on. The Focus St170 & MP3 have 215/45/17 tyres fitted as standard, not 215/40/17.

Am I getting my keks in a twist over nothing, will it be OK to stick with the 40 profile tyre, or should I get new tyres with the 45 ratio?

Thanks in advance

Andy

 

This tool is very useful, using your dimensions I came out with -1.7% and -1.8% error for the 45 and 40 profiles respectively. Essentially it makes little difference, both put your speedo out a small amount in the safe direction

http://www.kouki.co.uk/utilities/vis...ize-calculator

 

Thanks very much for putting my mind at rest

Looks like it was Ł195 well spent off of ebay after all!

Off down to a local alloy specialist friday morning that do complete refurbs from Ł30 per wheel. I dont mind spending up to Ł200 for the refurb, considering all the tyres are virtually brand new.

Cheers

Andy

 

Actually, just checked again to make sure lol.

The 40 profile will mean when your speedo reads 30, you are doing 29.5
The 45 profile will mean when your speedo reads 30, you are doing 30.5

So in that sense, 40 seems better just wanted to clear that up.

 

An ace site I use is,
www.kabamus.com/garage/gears.html

With this just put in your tyre size and diff/box ratio and it does the rest, gives you speed in 1000rpm steps.
tabetha

 

Any combo of 205 / 215 & 40 / 45 is fine. Mine had 205/40/17 then 215/45/17 on. The 205/40s where like rubber bands and a bit too hard for my likeing.