J
John Thompson wrote:
>> Steel as a material has an infinite fatigue life with the loads
>> applied by whimpy cyclists, but as actually used in bicycle frames,
>> it does not -- at least based on my experience. I have cracked a
>> number of steel frames -- probably due to overheating of the lugs
>> or some other glitch in fabrication. My longest surviving high
>> mileage frame is a 1986 Cannondale T1000. That's old school
>> aluminum. I am not so sure about the new stuff.
> My oldest frames are a couple of steel Atalas from the early 70s
> (1970 and 1972). The older one is built up as my daily commuting
> bike, the other is a fixed gear I ride 100 or so miles a week spring
> through autumn. The older Atala failed at the BB/seat tube joint 20
> some years ago, probably due to a cheap pressed BB shell. The
> failure was a crack that extended all the way around the base of the
> seat tube socket. The seat tube itself was not involved, so I was
> able to sweat the old shell off and braze in a nice investment cast
> shell to replace it. It's been going strong ever since.
Well that still doesn't answer the question about how many miles "old"
the bicycle is. I generally ride 10,000 miles per year according to
my odometer, so a 20 year old frame has some significant miles on it.
The only frame fatigue failures I have experienced were with Cinelli
style (sloping) fork crowns that typically have internal lugs that
cannot be feathered at the transition to the fork blades. They broke
exactly where the fork crown ended in the fork blade. Since then I
have stayed away from such forks that seem to have taken over nearly
all major brands that used brazed fork crowns. Too bad. It was a
stylishly bad mechanical design.
Other than that, I had plenty of crank fatigue failures, about one
every year or more until I modified that interface to a more
reasonable design, of a tapered conical seat instead of the fretting
flat faced pedal axle that augers itself into the crank until failure.
Since modification I have ridden Shimano cranks from that era but with
modification and haven't had a failure since.
Jobst Brandt
>> Steel as a material has an infinite fatigue life with the loads
>> applied by whimpy cyclists, but as actually used in bicycle frames,
>> it does not -- at least based on my experience. I have cracked a
>> number of steel frames -- probably due to overheating of the lugs
>> or some other glitch in fabrication. My longest surviving high
>> mileage frame is a 1986 Cannondale T1000. That's old school
>> aluminum. I am not so sure about the new stuff.
> My oldest frames are a couple of steel Atalas from the early 70s
> (1970 and 1972). The older one is built up as my daily commuting
> bike, the other is a fixed gear I ride 100 or so miles a week spring
> through autumn. The older Atala failed at the BB/seat tube joint 20
> some years ago, probably due to a cheap pressed BB shell. The
> failure was a crack that extended all the way around the base of the
> seat tube socket. The seat tube itself was not involved, so I was
> able to sweat the old shell off and braze in a nice investment cast
> shell to replace it. It's been going strong ever since.
Well that still doesn't answer the question about how many miles "old"
the bicycle is. I generally ride 10,000 miles per year according to
my odometer, so a 20 year old frame has some significant miles on it.
The only frame fatigue failures I have experienced were with Cinelli
style (sloping) fork crowns that typically have internal lugs that
cannot be feathered at the transition to the fork blades. They broke
exactly where the fork crown ended in the fork blade. Since then I
have stayed away from such forks that seem to have taken over nearly
all major brands that used brazed fork crowns. Too bad. It was a
stylishly bad mechanical design.
Other than that, I had plenty of crank fatigue failures, about one
every year or more until I modified that interface to a more
reasonable design, of a tapered conical seat instead of the fretting
flat faced pedal axle that augers itself into the crank until failure.
Since modification I have ridden Shimano cranks from that era but with
modification and haven't had a failure since.
Jobst Brandt
