At what point is % difference in diameter too great?

BTM · 08-11-2010, 09:06 AM

So I've learned that changing the difference in overall diameter from stock can cause problems, but at what point does this start to get significant? Should I be concerned with a 2%ish difference? Is there a generally accepted "threshold" not to exceed?

MassBimmer · 08-11-2010, 10:22 AM

For xi's, the difference in rolling diameter between front and back should not exceed 1%...I'm not sure about RWD

bimmer_335 · 08-11-2010, 10:26 AM

Are you taling of getting bigger tires on the same wheel? If so, I dont like going bigger tires that raise the center of gravity and can impact handling... if you want to plus size, do it the proper way by getting larger wheels.

BTM · 08-11-2010, 10:33 AM

Quote:

Originally Posted by bimmer_335

Are you taling of getting bigger tires on the same wheel? If so, I dont like going bigger tires that raise the center of gravity and can impact handling... if you want to plus size, do it the proper way by getting larger wheels.

Well I am planning on mounting snow tires on my stock 162s, which will raise my rear profile from 35 to 40, the % difference is <2% in this case. I am also planning on upsizing to 19s, which would change front profile from 40 to 35, and rear from 35 to 30 - again the % difference is <2%. I am concerned about affects on speedometer/odometer - while I don't think a sub 2% difference will have that much of an affect on either, I was curious to know what the threshold was.

neoduffer · 08-11-2010, 10:56 AM

I've heard if you're within 5%, you should be good.

08-11-2010, 09:06 AM	#1
BTM Banned 483 Rep 10,309 Posts Drives: A///MERICAN!!! Join Date: Mar 2010 Location: A///MERICA!!! iTrader: (11) Garage List 2007 BMW Z4 M Coupe [7.20]	At what point is % difference in diameter too great? So I've learned that changing the difference in overall diameter from stock can cause problems, but at what point does this start to get significant? Should I be concerned with a 2%ish difference? Is there a generally accepted "threshold" not to exceed?
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08-11-2010, 10:22 AM	#2
MassBimmer Major General 306 Rep 7,433 Posts Drives: 2023 i4 M50 Join Date: May 2009 Location: MA iTrader: (6) Garage List 2009 BMW [9.24]	For xi's, the difference in rolling diameter between front and back should not exceed 1%...I'm not sure about RWD
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08-11-2010, 10:26 AM	#3
bimmer_335 Major 177 Rep 1,123 Posts Drives: 540 mSport Join Date: Jul 2009 Location: In the middle of nowhere, TX iTrader: (1)	Are you taling of getting bigger tires on the same wheel? If so, I dont like going bigger tires that raise the center of gravity and can impact handling... if you want to plus size, do it the proper way by getting larger wheels.
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08-11-2010, 10:56 AM	#5
neoduffer Fast In, Slow Out 40 Rep 586 Posts Drives: 06 E90 330i Join Date: Jan 2007 Location: SoCal, SGV iTrader: (5) Garage List 2006 330i [0.00]	I've heard if you're within 5%, you should be good. __________________ : Ken
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