Tires and wheels upsize

david.shain · 08-14-2012, 01:33 PM

Hello, I have a 2006 e83 M Sport I'm running stock 18x8 M wheels with all 255/45-18 tires. Now I'm changing to 18x8 front and 18x9 rear wheels, and keeping the 255/45-18 tires on front. I want to run a wider tire on rear but of course keep the tires the same circumference due to AWD. Any suggestions what tire I should run on rear? Thanks

david.shain · 08-19-2012, 06:48 PM

Wow, it's amazing how many responses I had to this thread, NONE! Thanks!

mletchworth · 08-20-2012, 02:57 PM

http://www.miata.net/garage/tirecalc.html

Plugging in your front tire size on the left, and messing around with different values for a 19" rear, I came up with 255/40-19 or 285/35-19.

I have no idea if those 285s would clear the wheel wells though. But at least you won't break a transfer case (hopefully)

R1000K3 · 08-20-2012, 03:14 PM

Quote:

Originally Posted by david.shain

Wow, it's amazing how many responses I had to this thread, NONE! Thanks!

285/40/18 rear will be close to your 255/45/18 front, the difference is only about 0.2 percent. You can test different tyre dimensions here and see how close they are in rolling diameter http://www.e90post.com/forums/forumdisplay.php?f=12

The E83 is very sensitive on equal diameter tyres. Even with a recommended stock set up like 235/50/18 front and 255/45/18 rear the 4wd may be upset and the car will feel jerky under acceleration. This combo gives less than a percent in difference but is noticeably jerky on the transmission. The best is to use the same type dimension in all corners if you want to be sure the car drives perfectly smooth. This limits the dimension to what you have now, which is already a bit too wide front for good steering characteristics.

david.shain · 08-20-2012, 07:23 PM

With all tires the same now I notice jerkiness on full acceleration. The sticker in the door sill of the car says
235/50 R 18 Front and 255/45 R 18 Rear so if I go back to these maybe I will lose that jerkiness.

R1000K3 · 08-21-2012, 12:03 AM

Quote:

Originally Posted by david.shain

With all tires the same now I notice jerkiness on full acceleration. The sticker in the door sill of the car says
235/50 R 18 Front and 255/45 R 18 Rear so if I go back to these maybe I will lose that jerkiness.

I don't think so, I used exactly the combo you are referring to and the car immediately became jerky on acceleration. With a new set of tyres having the same dimension in all corners the jerkiness disappeared completely.

R1000K3 · 08-21-2012, 09:47 AM

Quote:

Originally Posted by david.shain

With all tires the same now I notice jerkiness on full acceleration. The sticker in the door sill of the car says
235/50 R 18 Front and 255/45 R 18 Rear so if I go back to these maybe I will lose that jerkiness.

I missed that the car is jerky also with all tyres the same. Are they evenly worn or not and is the tyre pressure the same in them?

If they are evenly worn and have the same thread dept and the pressure is the same, my first guess would be a faulty servo engine to the 4WD clutch pack.

Andersonpv · 03-18-2013, 11:19 AM

I have a question which pertains to the 19" wheel option.

We have a 2008 X3 with that option and as you know the OEM spec. tires are the Pirelli P Zero Rosso with the front size being; 235/45R19 and the rear being 255/40R19. Both tires spec with (27.2) O.D. Now the interesting part is that the revs. per mile are; 762 for the front and 765 for the rear.

There are only three manufacturers which make the front tire size. I would like to run the Michelin Pilot Sport A/S but it is not made in the front tire size. Recognizing a potential problem with running two different tire diameters I certainly do not plan to change one without the other but before I make a costly mistake, I need to seek counsel from those who know.

I have not read anything pertaining to running a incrementally larger size equal on front and rear. The sizes in review are; 245/45ZR19 and 275/40ZR19. Both tires spec with (27.7) O.D. with a 751 revs. per mile.

Would the difference of (.5) in O.D. and 11-14 revs. per mile make a difference or create an issue either short term or long term, other than a slight difference in the speedometer?

Would greatly appreciate some logical thoughts and experienced responses.

Thank you!

08-14-2012, 01:33 PM	#1
david.shain New Member 1 Rep 11 Posts Drives: 2006 325i Join Date: Dec 2011 Location: Lawton, OK USA iTrader: (0)	Tires and wheels upsize Hello, I have a 2006 e83 M Sport I'm running stock 18x8 M wheels with all 255/45-18 tires. Now I'm changing to 18x8 front and 18x9 rear wheels, and keeping the 255/45-18 tires on front. I want to run a wider tire on rear but of course keep the tires the same circumference due to AWD. Any suggestions what tire I should run on rear? Thanks
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08-19-2012, 06:48 PM	#2
david.shain New Member 1 Rep 11 Posts Drives: 2006 325i Join Date: Dec 2011 Location: Lawton, OK USA iTrader: (0)	Wow, it's amazing how many responses I had to this thread, NONE! Thanks!
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08-20-2012, 02:57 PM	#3
mletchworth New Member 0 Rep 13 Posts Drives: 2007 X3, 2003 325i Join Date: Feb 2012 Location: St. Charles, MO iTrader: (0)	http://www.miata.net/garage/tirecalc.html Plugging in your front tire size on the left, and messing around with different values for a 19" rear, I came up with 255/40-19 or 285/35-19. I have no idea if those 285s would clear the wheel wells though. But at least you won't break a transfer case (hopefully)
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08-20-2012, 07:23 PM	#5
david.shain New Member 1 Rep 11 Posts Drives: 2006 325i Join Date: Dec 2011 Location: Lawton, OK USA iTrader: (0)	With all tires the same now I notice jerkiness on full acceleration. The sticker in the door sill of the car says 235/50 R 18 Front and 255/45 R 18 Rear so if I go back to these maybe I will lose that jerkiness.
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03-18-2013, 11:19 AM	#8
Andersonpv Registered 0 Rep 4 Posts Drives: 2008 X3 Join Date: Mar 2013 Location: Tennessee iTrader: (0)	Change in tire diameter. I have a question which pertains to the 19" wheel option. We have a 2008 X3 with that option and as you know the OEM spec. tires are the Pirelli P Zero Rosso with the front size being; 235/45R19 and the rear being 255/40R19. Both tires spec with (27.2) O.D. Now the interesting part is that the revs. per mile are; 762 for the front and 765 for the rear. There are only three manufacturers which make the front tire size. I would like to run the Michelin Pilot Sport A/S but it is not made in the front tire size. Recognizing a potential problem with running two different tire diameters I certainly do not plan to change one without the other but before I make a costly mistake, I need to seek counsel from those who know. I have not read anything pertaining to running a incrementally larger size equal on front and rear. The sizes in review are; 245/45ZR19 and 275/40ZR19. Both tires spec with (27.7) O.D. with a 751 revs. per mile. Would the difference of (.5) in O.D. and 11-14 revs. per mile make a difference or create an issue either short term or long term, other than a slight difference in the speedometer? Would greatly appreciate some logical thoughts and experienced responses. Thank you!
	Appreciate 0 Quote