Tyre sizes

[Tony bell]

Hi all
Upgrading from 17 to 18" wheels.
Is there a website that tells you the correct size that keeps the speedo the same and not interfere with the abs
Thanks Tony

 

[Jack Ratt]

The speedo wont be affected if the outside diameter of the tyre is the same. Larger wheels have smaller wall sizes to keep this so.

 

[Keet]

I use this site

https://tiresize.com/comparison/

 

[t-tony]

A word of warning, unless you’ve tried a car on 18’s Tony, you may not like the ride. @Sean d had 18s on his previous car.

Tony.

 

[Sean d]

Unless all your suspension components are on point you may experience tram lining, when I first put 18s on my last z3 it was dreadful and felt dangerous, motorway driving was very unsettling as the tyres would search for the wear from lorries and would suddenly drag you sideways, my current 2.8 has 17s, even though it has had a full suspension rebuild

 

[Rha]

Tony is right, you will notice a difference, when I changed to 18 on my Z3 I already had uprated suspension which magnified it somewhat. If yours still has standard Z3 suspension I don’t think it will bother you so much, your other half will soon let you know if it’s acceptable or not, bit late after they’re fitted though. My wife hated it and wouldn’t come on the longer outings after I fitted the 18s plus the stiffer suspension on the Z3.
My Z4 coupe is like riding in a Lotus Elise and she won’t come in that either. ( most of my fillings have also been replaced, which was an unexpected dental expense....... .)

Most wheel/tyre suppliers will tell you what you can fit although it’s a good idea to see what other Z owners have gone for regarding stance/looks if that’s what your after. As a general rule the lower the sidewall the harsher the ride so going for anything over 18 would probably be OTT unless your going for something that would only be used on very smooth Brit roads.(not any in my area and there probably going to get worse after the next few frosts). Don’t be put off by what I’ve written cos the Z3 can look very nice on a lot of after market wheels and the ride on 18s for some owners can be quite acceptable.


Heres a couple of pics of my old Z3, first one with OEM 17in, others with 18s + uprated lowered 30 mm suspension.

The Z4 came out with 18s and most people accepted the ride quality it being a sports car. Best of luck, keep us all posted on what you decide on.

RHA,ROY.

 

[Tony bell]

What tyre size did you use with your 18"?

 

[Rha]

Hi Tony (bell), the wheel widths were 8.5in front 9.5 in rear with 35 offset, (that's a staggered set up) tyre size for this set up were 225x40x18 front, 245x35x18 rear. This gave me a very slight stretch on the 9.5inch rears but kept the tyre tread just inside the wing with the alloy wheel protruding a few mm outside which was fine for MOT. The very chunky look from the rear was what I was looking for. Looking at the second pic from the L to B run you'll see this (if) a bit exaggerated on the rears. Hope this helps.

RHA,Roy.

 

[Tony bell]

Hi Tony (bell), the wheel widths were 8.5in front 9.5 in rear with 35 offset, (that's a staggered set up) tyre size for this set up were 225x40x18 front, 245x35x18 rear. This gave me a very slight stretch on the 9.5inch rears but kept the tyre tread just inside the wing with the alloy wheel protruding a few mm outside which was fine for MOT. The very chunky look from the rear was what I was looking for. Looking at the second pic from the L to B run you'll see this (if) a bit exaggerated on the rears. Hope this helps.

RHA,Roy.

Have bought style 162 they have 235/40's on I'm going to try them on at the weekend to see if they will fit before doing referb