In an attempt to improve the ride of my 3.0Si with M-sport suspension, I was thinking of going from a 255/35 to a 245/40 rear tire. That's an increase of .7" inches in diameter which I know will make the speedo read about 2mph high at 60mph. There appears to be plenty of clearance as I look at the wheel well. Does anyone think that size increase will be an issue?
Acceptable increase in tire diameter?
- Thread starter lmacmil
- Start date
I see from your other posts that you're not on run flats, but you do want new tyres anyway... New tyres might improve the ride anyway. I don't find ours too bad on 18s, despite our roads being terrible.
But if it was me I'd switch to 17", which is a standard size for the car anyway.
But if it was me I'd switch to 17", which is a standard size for the car anyway.
lmacmil said:
It's what I'll be doing when I finally clean and protect my new alloys and then get new tyres fitted.
Larger tyres front and rear.
The ride is horrific when it comes to bumpy roads and potholes. Need to keep your eye on the road every second. If you don't you get an awful fright from a large bump.
Don't care if it affects the speed by 2mph that's nothing and within usual tolerances.
Handling isn't going to be an issue either should be within tolerances too. Plenty of options to tighten it up if it is looser handling.
LemonConnoisseur
Member
Admittedly not coming from a Z4, but I've fitted different sizes to other RWD cars in the past, and it shouldn't affect the handling a great deal.
Obviously you're going for a taller sidewall, so dependent on the tyre, it should be slightly more compliant. It's a 10mm per side reduction in tread width, not noticeable. You might find it to be ever so slightly more oversteer biased, but again I doubt you will notice the difference unless really pushing it.
BMWs in general come from factory with a staggered setup front to rear to set the car up to be more understeer biased.
Obviously you're going for a taller sidewall, so dependent on the tyre, it should be slightly more compliant. It's a 10mm per side reduction in tread width, not noticeable. You might find it to be ever so slightly more oversteer biased, but again I doubt you will notice the difference unless really pushing it.
BMWs in general come from factory with a staggered setup front to rear to set the car up to be more understeer biased.
I've fitted 255/40/18 to the rear and it does feel much more comfortable ( still not a rolls Royce).
I also went for non XL tyres which will have shifter side walls. Handling the same, although need the tracking doing again.
I will do the same to the front when they wear out.
Note the increased profile is the same as the z4m so shouldn't be a problem
I also went for non XL tyres which will have shifter side walls. Handling the same, although need the tracking doing again.
I will do the same to the front when they wear out.
Note the increased profile is the same as the z4m so shouldn't be a problem
The 17" option is under consideration but that adds considerably to the cost since new wheels are needed. OTOH, my stock wheels are in pretty bad shape from the previous owner's apparent love for rubbing against curbs! Pretty sure the M-sport suspension option is what put it into the 18" staggered setup.roblightbody said:
I have 225/45/18 square on mine - so up a profile from standard. Rears absolutely fine. Fronts rub slightly at full compression just behind the wheel arch and behind the headlight. That’s on ET34 offset wheels. Probably wouldn’t rub at all on standard wheels with no spacers. Makes a bit of a difference ride and steering wise (less twitching) but it’s not huge. Looks cool though
