M System (17x8) Tire sizing question...

[MTechnik540i]

Found an especially good deal on some 245/45-17" Potenzas and wondering if they'd fit alright on the 540i?

Factory sizing is 235/45-17, so i'm assuming it might knock the speedo up 1-2 mph at 60-70. Would I have any trouble clearing the strut/fender?

[saj3n]

Just picked up some staggered 18x8 and 18x9 black wheels, trying to find the best tire fitment for looks and funtionality.

[Interceptor]

Found an especially good deal on some 245/45-17" Potenzas and wondering if they'd fit alright on the 540i?

Factory sizing is 235/45-17, so i'm assuming it might knock the speedo up 1-2 mph at 60-70. Would I have any trouble clearing the strut/fender?
Avoid larger tyres - it not only ****s around with your speedo but also with your ABS system. Not to mention that you WILL have rubbing issues with larger tyres if you lowered your car.

[Rigmaster]

Avoid larger tyres - it not only ****s around with your speedo but also with your ABS system. Not to mention that you WILL have rubbing issues with larger tyres if you lowered your car.

Are you speaking from experience with this size of "tyre" or are you just giving a general warning. It seems to me that the jump from 235/45R17 to 245/45R17's should not be a problem- it's only ~10mm nominal difference in width, and very slight difference (0.3" inch) in diameter. Based on the revs per mile given on tirerack.com for these 2 different size tires, it's 820 vs 811, so the 245's will have a speedo reading that is ~1.1% lower than the 235's- hardly a problem if you ask me.


As for it messing with the ABS System- I don't see how this is possible- care to explain??



Bret

[Scott H]

As far as the tire size 245/45-17 goes, many E34 M5 people run that size with no problems. You *may* run a very slight chance of inside rubbing on the front.....easily overcome with a 3-5mm spacer. The only way to find out is to try it. All tires are made a little differently so one 245 width may not be exactly the same as another 245 width in that things like rub bars, shoulder design, etc vary widely.

As far as ABS/ASC/DSC, etc, as long as you are running tires that are close to the same effective overal diameter, you will be fine. It is when you start to comingle tires sizes that are materially different from each other that the wheel rotation counts become different and those technologies begin to act up.

[Interceptor]

Are you speaking from experience with this size of "tyre" or are you just giving a general warning. It seems to me that the jump from 235/45R17 to 245/45R17's should not be a problem- it's only ~10mm nominal difference in width, and very slight difference (0.3" inch) in diameter. Based on the revs per mile given on tirerack.com for these 2 different size tires, it's 820 vs 811, so the 245's will have a speedo reading that is ~1.1% lower than the 235's- hardly a problem if you ask me.
A friend has a lowered E34 M5 3.8 with 245/45R17 tyres in front and you can clearly hear the rubbing on full left/right turn.


As for it messing with the ABS System- I don't see how this is possible- care to explain??
I've experienced funny ABS behaviour in a car with 245/45R17 front and 265/40R17 rear. Maybe it was because different tyre size was used? I do know that there were no problems when all four tyres were 235/45R17.

[jjw]

Well, full lock left and right might be tire rub on the sway bar. Is the bar aftermarket? I have 245/45/17 on my lowered touring and have no rubbing issue. About the ABS issue, don't know, never experience it on my 245/40/18 front and 265/35/18 rear before.

[Interceptor]

Well, full lock left and right might be tire rub on the sway bar. Is the bar aftermarket? I have 245/45/17 on my lowered touring and have no rubbing issue.
He has the M5 Nurburgring sways - he got them with the car and later upgraded the tyres from 235/45R17 to 245/265 combination.

[MTechnik540i]

He has the M5 Nurburgring sways - he got them with the car and later upgraded the tyres from 235/45R17 to 245/265 combination.


Well, the suspension is bone stock, it's supposedly 'Nuburgring pkg' suspension, not sure if that includes the sways or not.

What's the verdict though? Should I chance it, and pick them up?

[DrewZ]

I say get them. If there is any rubbing, it will only be against the front sway bar at full lock. I'm running 245/45/17 Falken Azenis Sports (http://members.aol.com/apzjd/azenis.jpg)on 17x8.5 ET15 BBS RCs. They rub slightly against my Dinan front bar at full lock. The Dinan bar is the same 25mm diameter as the bar on your 540i Sport, but it has different geometry, so you may not experience any rubbing.

As far as speedometer error, the tires may actually make your speedo read more accurately. 245/45/17 is closer to the regular E34 stock tire size of 225/60/15. 245/45/17 is a common Mustang tire size, so there are lots of good an inexpensive options out there in that size. I've tried lots of different tire sizes on my car, but for 17" wheels, I'm sticking with 245/45/17.

Drew Z
6-speed Touring
http://members.aol.com/apzjd/16RKsummersmall.jpg (http://www.bmwe34.net/ASP/DURegistry/RegDetail.asp?id=100)


Well, the suspension is bone stock, it's supposedly 'Nuburgring pkg' suspension, not sure if that includes the sways or not.

What's the verdict though? Should I chance it, and pick them up?

[DueyT]

Especially being non-staggered, I can't see problems with ABS or ASC+T. Rubbing, perhaps at full lock and going over a curb...only 5mm nominal over 235/45-17 many 540 guys run doesn't seem significant. I tbhink your in pretty good shape, M.

Cheers,
Duey

[MTechnik540i]

I say get them. If there is any rubbing, it will only be against the front sway bar at full lock. I'm running 245/45/17 Falken Azenis Sports (http://members.aol.com/apzjd/azenis.jpg)on 17x8.5 ET15 BBS RCs. They rub slightly against my Dinan front bar at full lock. The Dinan bar is the same 25mm diameter as the bar on your 540i Sport, but it has different geometry, so you may not experience any rubbing.

As far as speedometer error, the tires may actually make your speedo read more accurately. 245/45/17 is closer to the regular E34 stock tire size of 225/60/15. 245/45/17 is a common Mustang tire size, so there are lots of good an inexpensive options out there in that size. I've tried lots of different tire sizes on my car, but for 17" wheels, I'm sticking with 245/45/17.

Drew Z
6-speed Touring
http://members.aol.com/apzjd/16RKsummersmall.jpg (http://www.bmwe34.net/ASP/DURegistry/RegDetail.asp?id=100)



Well, that's some peace of mind...may go that route.