J
Jeff Potter (of OutYourBackdoor.com)
Guest
I saw the long chat here last fall about rolling resistance.
I have a few more questions...
How do small wheels relate to bike science, tire behavior and energy
losses? There are increased angle of attack and increased tire squat
(I think). I would think that some losses could be reduced with extra
supple casing and wider tires at comparable or higher pressures. But I
suppose those changes bring on their own losses?
(I guess suppleness reduces energy loss but increases the contact
patch... But it looks like there's still debate as to how this affects
real world losses on "rough" roads---with Jan saying this is important
and Jobst saying it isn't...)
Probably most small wheel science would relate to 20" but Moulton
16-17" have been studied a lot, even if not used often. What happens
as size goes down to the 12" wheels that some micro bikes use? Is good
performance possible?
Small wheels also seem to affect handling---mostly due to change of
contact patch size and less pneumatic trail? A big wheel has a much
longer patch, right? There might be bigger factors, of course... But
frame/fork dimensions should be altered to give stability if small
wheels are used, right?
The small wheel question seems to relate to another tire behavior
question that seemed to get overlooked last fall.
I recall that the German research that was quoted mentioned a couple
things that weren't discussed (buried in here:
http://groups.google.com/group/rec....ling+resistance&rnum=1&hl=en#6bc6e9842c888dd5).
Offhand, it seems that there's a bulge in front of and behind a
contact patch and furthermore there might even be a concavity---I saw
this in a graphic. These effects seem to be due to bias-ply casing
wrinkling as it flattens into the contact patch. There was brief,
indirect discussion of bias vs. radial casing, with the idea that bike
tires are made somewhat on the bias---and so perhaps this results in
the tire wrinkling mentioned? The conclusion of the German research
said that radial bike tires like the handmade Rinki's would roll
better in small sizes (large, too?) because they avoid this wrinkling?
(In part?)
At any rate, it seems that small wheels would end up with more intense
bulging, etc., unless offset by other factors.
Tire science...a swamp!
Thanks, Jeff Potter
I have a few more questions...
How do small wheels relate to bike science, tire behavior and energy
losses? There are increased angle of attack and increased tire squat
(I think). I would think that some losses could be reduced with extra
supple casing and wider tires at comparable or higher pressures. But I
suppose those changes bring on their own losses?
(I guess suppleness reduces energy loss but increases the contact
patch... But it looks like there's still debate as to how this affects
real world losses on "rough" roads---with Jan saying this is important
and Jobst saying it isn't...)
Probably most small wheel science would relate to 20" but Moulton
16-17" have been studied a lot, even if not used often. What happens
as size goes down to the 12" wheels that some micro bikes use? Is good
performance possible?
Small wheels also seem to affect handling---mostly due to change of
contact patch size and less pneumatic trail? A big wheel has a much
longer patch, right? There might be bigger factors, of course... But
frame/fork dimensions should be altered to give stability if small
wheels are used, right?
The small wheel question seems to relate to another tire behavior
question that seemed to get overlooked last fall.
I recall that the German research that was quoted mentioned a couple
things that weren't discussed (buried in here:
http://groups.google.com/group/rec....ling+resistance&rnum=1&hl=en#6bc6e9842c888dd5).
Offhand, it seems that there's a bulge in front of and behind a
contact patch and furthermore there might even be a concavity---I saw
this in a graphic. These effects seem to be due to bias-ply casing
wrinkling as it flattens into the contact patch. There was brief,
indirect discussion of bias vs. radial casing, with the idea that bike
tires are made somewhat on the bias---and so perhaps this results in
the tire wrinkling mentioned? The conclusion of the German research
said that radial bike tires like the handmade Rinki's would roll
better in small sizes (large, too?) because they avoid this wrinkling?
(In part?)
At any rate, it seems that small wheels would end up with more intense
bulging, etc., unless offset by other factors.
Tire science...a swamp!
Thanks, Jeff Potter