My St170 is running 225/45/17's (which isn't stock) on standard alloys.
My question is:
When I need to change the tyres should I stick with 225/45/17's or move to 225/40/17's? whats the difference other than a few % of speedometer inaccuracy?

Cheers

 

This is quite a good tool for estimating speedo error, https://passionford.com/forum/wheels...omparator.html

 

Cheers
So I guess that means ill be sitting 1cm closer to the road which will help, but getting less mpg on motorways (I guess). Maybe better acceleration?

 

I'd say yes to all of them

One thing to consider though, from an aesthetics POV, is that the gap between your tyre and wheel arch would also be 1cm bigger.

 

no to mention you are more likely to kill your wheels if you hit a pot hole!!

and it will be a less comfortable ride.

oh and the tyres will more than likely be more expensive and less choice!

 

Why not use standard tyre size?

 

good question rich?

is 215/45 standard for st170?? cant remember

just tried that tyre size tool and 225/25's are WAY too small, the car must look really silly with them on and your speedo at 60mph will be reading 52.2mph!!!

 

25's? pardon? arhhh I see my typing error
I meant 45's

 

hahahaaa, makes more sense now.

i'd just stick standard size on mate....215/45's

 

but that sounds far to simple to me

 

hahahaa, i know that feeling.

i've got 16's on my focus and standard size for them is 205/50's but i've twigged that 205/55's are a fair bit cheaper and are gonna be better for daily road use so i'm gonna stick them on a set of alloys for road use and keep my oz wheels for track tyres which will prob be 205/45's.

i will never be happy with one tyre size