Bicycle Mechanics - torque specs aluminum vs. steel -- measuring torque for BB install
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hello, I'm building up my first aluminum bike after working with steel for many years. Just curious whether torque specs for aluminum frames tend to be different and whether I should take extra care in specific areas like BB and seatpost.
Also, curious about how people measure torque when installing BB cups. I've got a Park BBT-9 and I typically apply a Herculean effort when doing BB cups rather than my basic strongman effort for other parts of the bike where I can actually measure torque with my torque wrench.
Are many people actually measuring torque when installing BB cups? If so, which wrench/adaptor are you using?
It depends on the bottom bracket. I use a bottom bracket tool, a socket or a 1/2" to 3/8" reducing extension, and a 1/2" drive Sears beam torque wrench. I don't have any outboard bearing bottom brackets so can't help you there. I torque bottom brackets to specs, the torque used effects chainline some.
In general, no difference in torque specs.
No, individual aluminum threads aren't as strong as steel, but the BB threads (for example) are quite deep so no individual thread is endangered. Elsewhere aren't many places where aluminum is threaded.
I use a torque wrench on most things and torque to about the mid point of the manufacturer recommended torque spec for whatever component I am installing on both my aluminum and steel bikes. I don't have outborad bearing so can't say what torque wrench will work for you.
08-13-09, 03:44 PM
As long as the BB cups are not crossthreaded, there is almost no chance of damaging the threads when using proper torque. The only stripped bottom bracket threads I have ever seen were on an early ultra-crapola cheap-arse dept. store aluminum bike and the damage happened while riding, not during assembly.
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