I have some after market wheels on my Zed and all the tyres have perished so before it goes for its MOT at the end of the month im looking for new tyres.

The wheels are 17" and are staggered, with a 9.5j at the rear and 8j at the front.

The current tyres on the rear are 255/40/17 and a 235/40/17 on the front.

Now ive only been able to find one tyre at 235/40/17 so I want to change so I can get a decent brand, but which way do I go.

I dont want stretched look, I want a nice flat side wall look so thinking of a 245, but would this be too chunky.

The other question is if I go up a size on the front, should I also then go up on the back? Or will it not matter?

Any help would be gratefully received!

Hi Rob,

for the wheel sizes you have, and to keep the rolling circumferences close, fronts should be 45 profile - go for 235/45/17 on the front and 255/40/17 on the rear. You'll find plenty of options with those sizes. That's what I ran when I had the same 17 inch Azevs on my red Zed😉

You might get 265/40/17 on the rear - but brand options may be fewer.

It all follows when you upgrade wheel diameter, you keep the width and drop 5% in profile - I have 18s and my fronts are 235/40/18.

Richard

245 on an 8J will look like a balloon on a 8j….. an 8J is only 204mm wide

The tyres you currently have a 2% smaller in diameter and circumference that the OEM wheel/tyre combo

Personally would be looking at a 225/45r17. Plenty of very nice tyre options and only 0.4% different diameter from OEM size

Might be stating the obvious (to some) but something I didn't realise until I started trying to pick tyres for aftermarket wheels is that the profile figure - e.g. 40 - is 40% of the width.

So for a 255/40/17 tyre - diameter is 255mm, profile / side wall is 102mm (40% of 255), and radius is 17inches.

Learning this made it all make a lot more sense to me. I also have this graphic to refer to. Can't recall where I found it but it's now saved on my desktop!

I also wanted a chunky looking tyre with a solid side wall and after going 245(F) / 265 (R) , have since switched back to 235(F) / 255 (R) as I found the handling was noticeable more boggy and I use the car for fast road and track use. For ref, these tyres are on 18" BBS LMs.

Use this site or similar to get the rolling circumference difference when you change wheel diameter and tyre profiles.

It will tell you how much the speedo will over or under read, and the difference in overall diameter to work out if they will rub anywhere.

https://tiresize.com/tyre-size-calculator/

Cheers all,

I did consider a 225/45/17 but thought that it might be too much chunk on the side wall. But so many more options!

Looking at the calculator, going from a 235/40 to a 225/45 is about 7.5mm more sidewall which isn’t much. Loads more choice too. Think I’ll go for that, thanks for the help