February 21, 2009 at 4:44 pm #58717KENNETH KRUMMSpectator
While living in Washington D.C. in 2001, a BMW rider had a rear wheel bolt failure on his R1100RT, resulting in the wheel coming off at interstate speeds. The conventional wisdom at the time was the bolts weren’t properly tightened to the recommended torque requirements. The bolts eventually worked loose to the point where they broke under stress. However, can bolt failure occur if over-tightened?
While changing the rear tire on my R1150GS, I accidentally over-tightened the rear wheel bolts to 105 Ft lbs vs. 105 Nm. BMW recommends 105 Nm or 77 Ft lbs. My large ½ drive torque wrench clicked on three out of the four bolts. However, the fourth bolt wouldn’t tighten. So I removed the bolt and noticed the metal had weakened and stretched (see photos). So I removed the other three bolts and noticed slight stretching, but nothing to the degree of this bolt. By simply over-tightening the bolts from the recommended 105 Nm to over 140Nm (105 Ft lbs), the bolts stretched to a point where they could have broken in the hub or on the road while operating the bike.
An additional word of caution. The rear wheel bolts are not universal on all BMWs. My R1100RT and K1100LT rear wheels use a 60mm bolt. My K1200RS rear wheel uses a 55mm bolt. My R1150GS uses a 63mm bolt. Mixing the wrong sized bolts could have disastrous consequences.
Even if you have a dealer change your tires, I would recommend checking the rear wheel bolt torque after the bike returns from the dealer. For those of us that change our own tires, paying careful attention to the torque specification is very important.
The Top Bolt is new. The Bottom Bolt was over-torqued.
[IMG]http://i205.photobucket.com/albums/bb12/kenk_bucket/DSCN23611.jpg[/IMG]February 21, 2009 at 4:44 pm #61114ackgsSpectator
Good catch – I would guess you are not the only person who has done this. Also who knows what happens with torque settings at dealers?February 21, 2009 at 4:44 pm #61116ANTON LARGIADERSpectator
Great pic, Ken.
We basically ran this topic (with a picture very much like that one) maybe a year ago in OTL, and previously had another article on wheel bolts, but it’s something that bears repeating on a regular basis. It’s probably been at least a year, so maybe it’s time to hit on it again.
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