Quoted message said:I don't think loaded panniers would put as much stress on a frame as a
racer putting out 400 to 600 watts and cornering at 30 mph would, and
they put a whole lot more stress cycles on a frame than any tourer:
Lance is putting in 5 to 6 hours per day on his bike, at a cadence of 90
to 110 rpm. That's a lot of stress cycles in a year of riding. Far
more than almost any tourer would do.
Hmmm.. Conventional wisdom holds that the workhorse tubes (the ones we
are talking now that take all the beating) are the fork blades, down
tube and chainstays. Fork blades, down tube and chainstays are there
to resist twisting forces of many demanding rider. A racer and a
touring cyclist can easily put 5 to 6 hours per day riding. Unlike a
racer, a touring cyclist has to work a lot harder on the hills and
riding against the headwind, but I think the watts output are similar.
Bike touring is a very demanding sport, especially when touring along
many mountain passes. The heavy packs they carry on the sides make the
frame want to flex sideways. This flexing is not that noticeable by
the eye, but can be measurable by the purist in a laboratory setting I
guess. But what's interesting to note is that if the frame flexes
enough, your front wheels feeds this flexing into an ever-increasing
oscillation sensation, which some people calls it the shimming effect
or the fish tailing effect, or I suspect this as the steel riding
effect. That is because, during the surge of bicycle touring in the
early 70s, not a lot is known about the effectiveness of the top tube.
The top tube was considered not important, and hence some bikes don't
even have anything resembling a top tube, or if they do only with thin
walled. Most steel bikes, including my old Miyata touring bike, had
very thinned walled top tube.
I always wondered why my Miyata bike shimmied when I had too much load
on the back and only stopped doing it when I shifted the load more
upfront. Keep in mind that my current aluminium touring bike does not
shimmy at all with far more rear load. And towing a BOB trailer was a
far more sure experience than with my Miyata.
The difference between my old Miyata steel touring bike and my current
aluminium replacement was the fat top tube and downtube. And they are
nice and thick, which makes the ride stiff. But what I didn't realized
later on what when I read an article written by John Schubert about the
Battle of the Top Tubes in one of the adventure cyclists magazine that
I found out the real reason why my aluminium bike performs so much
better touring wise. When it's not loaded, it rides ok. But when it's
loaded, it rides like a Cadillac. Thanks I guess to its inherent stiff
and fatty top tube, the bike handles everything sure and shimmy it did
not with heavy panniers loaded. This is something a racer does not put
his bike through. A racer does not really need a stiffer top tube than
a tourer since he isn't carrying any side loads at all other than
himself. So does a tourer.