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X1 E84 (2011 - 2015)
First generation BMW X1 availbe as a X1 28i with either sDrive (RWD) or xDrive (AWD) or the US exclusive I6 N55 powered X1 35i xDrive.

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Old 01-24-2019, 01:09 AM
marines122181 marines122181 is offline
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Outstanding run flat experience

This is my 1st set of run flats. They came with the car. Prior to owning these, I've never ridden in anything with them. I wasn't too sure about it and have been back-and-forth regarding the decision to switch to regular tires once these were worn out. I got out of my car and walked around on my way to work last night I noticed this huge blow out. I hit a very large pothole on Sunday. There was oncoming traffic and no shoulder and it became unavoidable. I commute a daily 30 miles each way at 80+mph. This tire hasn't lost one psi of air during my 6 trips. I can only attribute that to the superior construction of the side wall. I've already ordered the replacement and without a doubt will be sticking with these tires. I hardly notice any difference over non RFs and my newly solidified piece of mind is worth the extra cost.

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2006 330xi
2015 X1 xdrive28i
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  #2  
Old 01-24-2019, 08:40 AM
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I sure hope you ordered (at least) TWO tires. Our X-drive systems don't like a different size, as in different wear, on the same axle. And some folks will even tell you that significantly different wear between front and rear axles also can/will kill your transfer box (x-drive clutch). Of course, this has nothing to do with RFT vs. non-RFT tires.
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Old 01-24-2019, 08:47 AM
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Originally Posted by DBU View Post
I sure hope you ordered (at least) TWO tires. Our X-drive systems don't like a different size, as in different wear, on the same axle. And some folks will even tell you that significantly different wear between front and rear axles also can/will kill your transfer box (x-drive clutch). Of course, this has nothing to do with RFT vs. non-RFT tires.
So here’s a question; considering that our DSC cars have open differentials, which tire’s circumference will determine the driveshaft’s rotation rate? Which will be the effective ratio to the transfer case?
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Old 01-24-2019, 11:36 AM
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Originally Posted by Doug Huffman View Post
So here’s a question; considering that our DSC cars have open differentials, which tire’s circumference will determine the driveshaft’s rotation rate? Which will be the effective ratio to the transfer case?
I assume you know the answer, Doug (I sure don't). But I am thinking the wheel that rotates the fastest, i.e. smallest circumference or more RPM (Revolutions Per Mile) will determine the drive shafts rotation rate. Did I win, did I win, did I?
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Old 01-24-2019, 11:50 AM
Autoputzer Autoputzer is online now
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Spoiler Alert!

For open differentials, the drive shaft rotational speed is the final drive ratio times the AVERAGE of the rotation speeds of wheel. With your car in Park and on a lift, if you rotate one of the back wheels and the other one will rotate in the opposite direction at the same speed. The AVERAGE of the two wheel speeds would always be zero, which is also the speed of the driveshaft (since the car is in Park and on a lift).

Actionable Information: The OP doesn't need to order two or four new tires. Tire Rack will shave a new tire down to any specified tread depth for about $35.

The mismatch tire diameter problems with xDrive stressing the transfer case clutches comes when the AVERAGE rotational speed of the front axle wheels are different from the AVERAGE rotation speed of the rear axle wheels.
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Old 01-24-2019, 11:50 AM
Autoputzer Autoputzer is online now
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Spoiler Alert!

For open differentials, the drive shaft rotational speed is the final drive ratio times the AVERAGE of the rotation speeds of wheel. With your car in Park and on a lift, if you rotate one of the back wheels and the other one will rotate in the opposite direction at the same speed. The AVERAGE of the two wheel speeds would always be zero, which is also the speed of the driveshaft (since the car is in Park and on a lift).

Actionable Information: The OP doesn't need to order two or four new tires. Tire Rack will shave a new tire down to any specified tread depth for about $35.

The mismatch tire diameter problems with xDrive stressing the transfer case clutches comes when the AVERAGE rotational speed of the front axle wheels are different from the AVERAGE rotation speed of the rear axle wheels.
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Old 01-24-2019, 02:05 PM
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Originally Posted by Autoputzer View Post
Spoiler Alert!

For open differentials, the drive shaft rotational speed is the final drive ratio times the AVERAGE of the rotation speeds of wheel. With your car in Park and on a lift, if you rotate one of the back wheels and the other one will rotate in the opposite direction at the same speed. The AVERAGE of the two wheel speeds would always be zero, which is also the speed of the driveshaft (since the car is in Park and on a lift).

Actionable Information: The OP doesn't need to order two or four new tires. Tire Rack will shave a new tire down to any specified tread depth for about $35.

The mismatch tire diameter problems with xDrive stressing the transfer case clutches comes when the AVERAGE rotational speed of the front axle wheels are different from the AVERAGE rotation speed of the rear axle wheels.
True that. With one notable exception: If one wheel is spinning (on ice) and the other one is not able to move the car, even though it is on good pavement (car is stationary), then the drive shaft rotation rate would be that of the faster spinning wheel. Of course, our clever Bimmers know to apply the brake to the spinning wheel to equal the resistance on the wheel on pavement and presto, like magic, the car moves.
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Old 01-25-2019, 09:23 AM
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Quote:
Originally Posted by Autoputzer View Post
Spoiler Alert!

The mismatch tire diameter problems with xDrive stressing the transfer case clutches comes when the AVERAGE rotational speed of the front axle wheels are different from the AVERAGE rotation speed of the rear axle wheels.
Ahh! Ah so. So the average of the tire circumferences on each axle ONLY must be the same to avoid excessive wear on the TC.
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Old 01-25-2019, 12:43 PM
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Doug - I believe that is correct. Any difference in the rate of rotation between left and right (on the same axel) is compensated for through the differentials. And the differentials do not have any clutch to wear out.

BTW - I asked the BMW Genius' for the max allowable difference in RPM (Revs Per Mile) between the two axels on an X-drive. They declined to give an answer - instead just saying "go and ask the dealer's service department for tire advice." So, BMW apparently doesn't have a set tolerance backed up by engineering facts - at least not that they want to tell us.
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Old 02-09-2019, 02:17 PM
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sayemthree sayemthree is offline
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Good story…. Although they are good for your 30 minute commute they are useless for a 200 to 300 mile trip away from home and away from home away from urban areas with the BMW dealer that stocks your actual tire size
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