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Hello all, quick question for you,

I'm going to be sticking some new boots on the car soon, and I'm considering alternative tyre sizes as I've seen them mentioned around here.

Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory.

Thanks in advance!

Mr Wilks is the resident expert and will probably give you the best answer, but I had m tyres sizes on my old Z4 with no issues. ( front and rear 5% up on the aspect ratio) there's tyre calculators on line that let you dabble with sizes and tells you how much it will alter the speedomreading.

No downside whatsoever imo , only positives from upsizing profile & 245 40 i have used many times on 8.5j or 9j with 215 45 front (on 8j )

mjennings23 wrote: ↑Mon Feb 12, 2018 4:55 pm Hello all, quick question for you,

I'm going to be sticking some new boots on the car soon, and I'm considering alternative tyre sizes as I've seen them mentioned around here.

Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory.

Thanks in advance!

I would first check with the satnav what your actual speed is compared to the speedo (just in case you're closer to actual speed than you think)

philbo909 wrote: ↑Mon Feb 12, 2018 8:22 pm

mjennings23 wrote: ↑Mon Feb 12, 2018 4:55 pm Hello all, quick question for you,

I'm going to be sticking some new boots on the car soon, and I'm considering alternative tyre sizes as I've seen them mentioned around here.

Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory.

Thanks in advance!

I would first check with the satnav what your actual speed is compared to the speedo (just in case you're closer to actual speed than you think)

About 3-4% under reading currently, so a 2.5% increase should be ideal?

mjennings23 wrote: ↑Mon Feb 12, 2018 11:00 pm

philbo909 wrote: ↑Mon Feb 12, 2018 8:22 pm

mjennings23 wrote: ↑Mon Feb 12, 2018 4:55 pm Hello all, quick question for you,

I'm going to be sticking some new boots on the car soon, and I'm considering alternative tyre sizes as I've seen them mentioned around here.

Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory.

Thanks in advance!

I would first check with the satnav what your actual speed is compared to the speedo (just in case you're closer to actual speed than you think)

About 3-4% under reading currently, so a 2.5% increase should be ideal?

Whenever ive increased wheel / tyre sizes the speedo does tend to become more accurate . Always worth checking against a sat nav once a new wheelset goes on to know exactly what difference has been made though

mr wilks wrote: ↑Mon Feb 12, 2018 11:03 pm

mjennings23 wrote: ↑Mon Feb 12, 2018 11:00 pm

philbo909 wrote: ↑Mon Feb 12, 2018 8:22 pm
I would first check with the satnav what your actual speed is compared to the speedo (just in case you're closer to actual speed than you think)

About 3-4% under reading currently, so a 2.5% increase should be ideal?

Whenever ive increased wheel / tyre sizes the speedo does tend to become more accurate . Always worth checking against a sat nav once a new wheelset goes on to know exactly what difference has been made though

Appreciated! Think I'll give 245/40 a go on the rear then, but probably stick to factory on the fronts? I can get rubbing on full lock as it is, so I don't really want to go adding more tyre there.

Looking forward to trying this car on UHP tyres, suffice to say I'm not sold on Pirelli tyres on it, especially the 'eco' ones up front! Much more excited at the prospect of Michelin PS4s

mjennings23 wrote: ↑Mon Feb 12, 2018 4:55 pm
Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory

I'm also running a staggered set of MV3s on sport springs, 255/35 on the rear and 225/40 on the front. No rubbing issues at all on the rear but I do get some rubbing on the front when encountering high speed compression bumps.
I would imagine that fitting a taller or wider tyre on the front would definitely result in more frequent and more severe rubbing than I experience at the moment.

patriot66 wrote: ↑Mon Feb 12, 2018 11:27 pm

mjennings23 wrote: ↑Mon Feb 12, 2018 4:55 pm
Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory

I'm also running a staggered set of MV3s on sport springs, 255/35 on the rear and 225/40 on the front. No rubbing issues at all on the rear but I do get some rubbing on the front when encountering high speed compression bumps.
I would imagine that fitting a taller or wider tyre on the front would definitely result in more frequent and more severe rubbing than I experience at the moment.

I can't say I've really noticed it myself on fronts, perhaps the odd time going over a bump at full lock.

Either way, now booked in for 225/40 fronts and 245/40 rears tomorrow, got a good price on Pilot Sport 4s of £450 for all 4 including fitting, quite happy with that!

You have gone for the right setup.

I tried a 235/40/18 but it rubbed, although I was lowered on B12 and spaced out by 10mm.

mjennings23 wrote: ↑Tue Feb 13, 2018 1:04 pm

patriot66 wrote: ↑Mon Feb 12, 2018 11:27 pm

mjennings23 wrote: ↑Mon Feb 12, 2018 4:55 pm
Current wheels are MV3s, so ET34 and 37 respectively, 8" and 8.5" wide.

I've seen that 245/40 is what seems to be a sensible rear swap as 255 is about the maximum you'd ever put on an 8.5" rim (giving both a more sidewall and at a lower cost), but I'm unsure if its worth a change on the fronts, and if the offset will cause rubbing with a taller tyre.

Car is on the sport suspension from factory

I'm also running a staggered set of MV3s on sport springs, 255/35 on the rear and 225/40 on the front. No rubbing issues at all on the rear but I do get some rubbing on the front when encountering high speed compression bumps.
I would imagine that fitting a taller or wider tyre on the front would definitely result in more frequent and more severe rubbing than I experience at the moment.

I can't say I've really noticed it myself on fronts, perhaps the odd time going over a bump at full lock.

Either way, now booked in for 225/40 fronts and 245/40 rears tomorrow, got a good price on Pilot Sport 4s of £450 for all 4 including fitting, quite happy with that!

A bit of a thread resurrection but the rubbing might actually be down to knackered shocks rather than a tyre size issue, especially if your running standard profiles. Hence why some experience it and some dont. Obviously driver and passenger weight plays a bit of a roll as well.
The reason I say this is that 18 months ago i fitting m spec tyres (ps3 front and gdy f1 rear) and 10/20mm spacer front and rear to my M sport suspension equipped 3.0i. Since then Ive always had a bit of an issue with rub on the front over bigger road bumps/road humps etc. At Christmas I swapped out the old shocks and springs for B4s and eibachs. I was expecting this to make the issue worse with the extra 15mm drop but it actually eliviated the problem, which I can only surmise is down to better dampening of the bumps etc. I did toy with the idea of changing to a 10mm spacer on the front but have just spent the last week running around with a set of Bridgestones non runflats in the standard profiles on the car, as well as the 20/10mm f&r spacers and have had no rub whatsoever. Even over road humps that would have caused rub on my original suspension, standard tyre sizes and no spacers. So I think it can only be new better dampening shocks that are making all the difference.

Downsides, well although the m sizes have always looked a bit too big to my eyes and the standard profiles are certainly more asthetically pleasing. I do miss that extra degree of comfort the bigger sidewalls bring. The Bridgestones won't be staying as they are much more noisy despite having a good 6mm of tread left all around and if tyre tests are to be believed are also harder riding than either the ps3 or f1s I had on previously.
For me going forward I think i'm going to try the 245/40 and maybe the 215/45 mentioned above as a halfway house solution between the m spec and standard side wall sizes. Ive got a pair of f1s on the back of my wife's one series in 245/40 and the profile does look much more asthetically pleasing than my 255/40 of exactly the same f1 tyre.