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I’m looking at a tyre change soon and the rears are going from. 255/30 to 255/35
This has generally been acknowledged as being ok

Q. Does the same ok apply to the fronts ie going from 225/35 to 225/40?

I was looking at the Cont 7’s as a few on here have been singing their praise but the Michelin PS 5 are being offered at very.competative prices.

I apologise for posting what’s been done to death a few times but I’m probably going to be bounced Into a change as i have some characteristic inner edge wear on the rears with an MOT due soon.

Logically it would be best to increase the front to match..you then have the same height sidewall..

Your DSC will like it when you lose control on a slippery road..

It’s the logical thing to do - but as the PS 5 isn’t available in 225/35 my hand has been somewhat forced!
I didn’t want to have PS 4 front and PS5 rear!

Having a 5% wall increase front and rear seems sensible
I only hope the steering feel remains as sharp

Increasing the rear profile shouldn't be a problem. I put 255/45 tyres on my MC instead of the OE 255/40 size and it has made the speedo more accurate.

I didn't change the size or profile of the fronts because I've read that Z4s can get a bit "twitchy" at higher speeds so I thought a few mm higher at the rear might improve that, and maybe improve the ride.

Ive gone 225/40 front and 255/35 Rear without any problems showing up as yet.
I still have to check my speedo calibration - I will use an iPhone app.

The tyres were supplied and fitted by ATS Euro thro their web site but why oh why won't they take off the residue of previous wheel weights while the wheel assy is on the bench?
They have stuck the new balance weights on top of the residue on one of the fronts - it is already pealing off so will require a re balance tomorrow. They do offer a free four wheel alighnment check but I'm reluctant to let them loose on the car to make any adjustments if they cannot stick wheel weight on properly!

I think standard size on the front is 225x40x18 so if you're on 35profile, it's non-standard.
Changing to 40 will be fine.

Std on my car was. 225/35/19 f and 255/30 /19

I’ve gone to 40 an 35 profile without a problem
Other than the clowns not removing the residue if the previous wheel weights and expecting it ro stick!

ronk wrote: ↑Thu Sep 21, 2023 10:31 am Other than the clowns not removing the residue if the previous wheel weights and expecting it ro stick!

You should have taken it to a tyre garage, rather than a circus, Ron.

Pondrew wrote: ↑Thu Sep 21, 2023 4:37 pm You should have taken it to a tyre garage, rather than a circus, Ron.

Circus!!!!

I'm starting to think I've been on a Merry Go Round at full tilt when Im trying to extract common sense out of BMW insured warranty while advising them of the 5% wall profile increase.
Apparently its "none standard" and as such anything that the tyre increase has an effect upon, will not be covered.
My question was, such as what? Their answer, I don't know, ask your dealer! - The answer was from their claims dept!

If their claims department doesn't know, then who does? The dealer service manager and his chief tech didn't know either!
The dealer said it would probably only be a problem if it was an X Drive system.

I'm so pleased that I had the Std / Star Marked / Bridgestone junk fitted to my 335Xd

ronk wrote: ↑Mon Sep 25, 2023 8:56 pm
Circus!!!!

I'm starting to think I've been on a Merry Go Round at full tilt when Im trying to extract common sense out of BMW insured warranty while advising them of the 5% wall profile increase.
Apparently its "none standard" and as such anything that the tyre increase has an effect upon, will not be covered.
My question was, such as what? Their answer, I don't know, ask your dealer! - The answer was from their claims dept!

If their claims department doesn't know, then who does? The dealer service manager and his chief tech didn't know either!
The dealer said it would probably only be a problem if it was an X Drive system.

I'm so pleased that I had the Std / Star Marked / Bridgestone junk fitted to my 335Xd

At your age, Ron, I would have thought you would have known doing the right thing is only going to complicate matters and eventually cost you money.

"What they don't know can't hurt them" would be my go-to attitude for this and many other things in life these days.

Just tell them you've had a change of mind and gone back to the standard 35 and 40 profile! They will probably not bat an eyelid.

The real world reality on this is that in the event of an incident the tyres with good tread would not look out of place on the car..there are so so many variations in tyre sizes within and across models it’s very very unlikely to ever be an issue..

So two points…

If you are concerned you should have stuck to stock sizes like most folks do..

Otherwise as we say in aviation…’better to ask for forgiveness than ask for approval’

Given the vast overall improvement that the tyres have provided I feel that I would make the same choices again.

The car went into the dealership for its mot last week and they did a video health check- no mention of the tyres other than they were new and giving me tread depth!

My low use of the car will probably make any problems someone else’s problems!

It's a matter or risk versus reward!

The risk with a manufacturers warranted car, is that if you have a problem with the transmission, brakes or suspension from a change you have made to the tyres/wheels against what was homologated (star marked excluded as this a recommendation rather than a requirement) then there is a risk that they may not pay out fully or not at all.

Unfortunately the risk is difficult to quantify, with a certain amount of luck involved, it just takes a keen, knowledgeable and astute technician to spot you've gone up a profile......

Neither the service manager nor the chief technician at the dealership could give me a scenario where the tyres would cause a failure.