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X5 E70 (2007 - 2013)
E70 BMW X5 produced between 2007 and 2013. Discuss the E70 X5 with other BMW owners here.

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  #26  
Old 01-22-2020, 01:06 PM
80t0ylc 80t0ylc is offline
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I think the damage to the drive train would be to the differential on the axle that the off size spare is run on. The axle differential works when turning - it allows different wheel speeds with out binding the drive train when going around corners on high traction surfaces. Using different size tires on an axle would make that differential work continously and cause excessive heat if maintained for an extended time. Re-programming will not eliminate this, unless it can disconnect each axle half individually. I don't think the xdrive has that capability.
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  #27  
Old 01-22-2020, 01:35 PM
Autoputzer Autoputzer is offline
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Quote:
Originally Posted by smassey321 View Post
The space saver spare is the same diameter as the normal tire.

Tire Size Comparison
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
155/90-18 5.5in 14.5in 29.0in 91.1in 696 0.0%
255/50-19 5.0in 14.5in 29.0in 91.2in 695 0.2%
The fog is starting to clear, now. I remember digging up that the E70 and/or F15 X5's spare had the same rolling diameter as the outside tires. That seems necessary for xDrive. But, the G01 X3's doesn't. The outside tires are 245/50-19's (28.65" nominal rolling diameter) and the spare is a 135/80-18 (26.5" nominal rolling diameter).

I wrote a letter to BMWCCA's Roundel magazine's tech' question and answer recurring article, asking if they've overcome the G01's 2+" difference in rolling diameters with software. But, I never got an answer.

We currently have a G05 X5 loaner while the X3 is undergoing a PuMA exorcism. It's a lightly optioned xDrive 40i, but with optional 275/45-20's (29.75" nominal rolling diameter). I doubt the optional spare tire on the G05's have the same nominal rolling diameter). The loaner doesn't have a spare. So, maybe BMW's saved a few dollars per vehicle by using smaller diameter spares and solving the resulting xDrive problem with software.
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  #28  
Old 01-22-2020, 02:04 PM
Autoputzer Autoputzer is offline
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Quote:
Originally Posted by 80t0ylc View Post
I think the damage to the drive train would be to the differential on the axle that the off size spare is run on. The axle differential works when turning - it allows different wheel speeds with out binding the drive train when going around corners on high traction surfaces. Using different size tires on an axle would make that differential work continously and cause excessive heat if maintained for an extended time. Re-programming will not eliminate this, unless it can disconnect each axle half individually. I don't think the xdrive has that capability.
An open differential could be designed to take continuous loading with different diameter tires on the same axle. They'd just have to make the side gears' teeth as strong as the teeth on the ring and pinion gears.
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  #29  
Old 01-22-2020, 03:05 PM
ard ard is offline
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putzer...are you fantasizing about stuff or telling folks what *is*???



smassey has provided the facts. All OE tires, 18", 19" 20" 21" are all the same OD... width and profile changes, not OD. Spare matches that.
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Alignment here: The Definitive Alignment Thread

OE is Original Equipment aka 'BMW Original Parts' aka 'What you buy at the BMW dealer with a BMW label'

OEM is Original Equipment Manufacturer... EITHER the company that made the OE part or.... A part this is identical to the OE part, but is sold by the OEM under their own label


OEM is not what BMW sells


http://www.bimmerzone.com/category/T...ricks_OEM.html

https://www.turnermotorsport.com/t-OEvsOEM
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  #30  
Old 01-22-2020, 03:12 PM
Autoputzer Autoputzer is offline
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Quote:
Originally Posted by ard View Post
putzer...are you fantasizing about stuff or telling folks what *is*???



smassey has provided the facts. All OE tires, 18", 19" 20" 21" are all the same OD... width and profile changes, not OD. Spare matches that.
That's on the E70 and maybe F15 X5's.

The spares on the G01 X3; have a 2" smaller diameter than the outside tires. I'm not sure anybody makes a 29.75" rolling diameter donut spare tires (for the G05 X5's).

When I don't know something for sure, I qualify it with "maybe," or "I suspect" and my speculation is based on logic.

Last edited by Autoputzer; 01-22-2020 at 03:32 PM.
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  #31  
Old 01-22-2020, 03:19 PM
Autoputzer Autoputzer is offline
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Actually, Continental makes a T175/80-19 donut that works out to 30" nominal rolling diameter. Maybe that's what they use on the G05... or maybe not. I do know that Frau Putzer's G01 X3's donut spare has a ~2" smaller rolling diameter than the outside tires, and it's an xDrive.

Last edited by Autoputzer; 01-22-2020 at 03:25 PM.
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