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Scamdium strikes again!
http://weightweenies.starbike.com/ph...ic.php?t=19036
Aluminum BB axles are not a good material selection... -- Phil Lee, Squid |
Scamdium strikes again!
In article m,
"Phil Lee, Squid" wrote: http://weightweenies.starbike.com/ph...ic.php?t=19036 Aluminum BB axles are not a good material selection... No. Especially as the left side is more prone to breaking (subject to both torque and bending), and it will break under highest load which is while standing on it. Then you'll get dumped into the road, possibly right in front of a large motor vehicle. The only time I had this happen was in 1984 when I stood up at a stop sign to accelerate from a stop, snapped off the left side of the BB axle, and ended up on my ass in the road. Fortunately it was a low traffic side street. Gouged the heck out of my left ankle, too. |
Scamdium strikes again!
On Tue, 25 Jul 2006 08:50:30 -0500, Tim McNamara
wrote: In article m, "Phil Lee, Squid" wrote: http://weightweenies.starbike.com/ph...ic.php?t=19036 Aluminum BB axles are not a good material selection... No. Especially as the left side is more prone to breaking (subject to both torque and bending), and it will break under highest load which is Forgive the ignorance: does that apply to hollow axle, tapered square, XT b.brackets? If so, which are the ones not made of aluminum? TIA jbr |
Scamdium strikes again!
BigBen wrote:
On Tue, 25 Jul 2006 08:50:30 -0500, Tim McNamara wrote: In article m, "Phil Lee, Squid" wrote: http://weightweenies.starbike.com/ph...ic.php?t=19036 Aluminum BB axles are not a good material selection... No. Especially as the left side is more prone to breaking (subject to both torque and bending), and it will break under highest load which is Forgive the ignorance: does that apply to hollow axle, tapered square, XT b.brackets? If so, which are the ones not made of aluminum? No major manufacturer makes or sells aluminum-axle bottom brackets. Your XT bottom bracket has a steel axle. If you look at the pictures, notice that the break does not traverse the 90-degree inner corner for most of the circumference, where one might expect it to break. Maybe the axle was notched during installation. -- Phil Lee, Squid |
Scamdium strikes again!
Phil Lee, Squid wrote:
http://weightweenies.starbike.com/ph...ic.php?t=19036 Aluminum BB axles are not a good material selection... they're fine if they're dimensionally appropriate for the job. aluminum shimano axles anyone? the problem comes when you use the same size in aluminum as you do in steel given aluminum's much lower strength. presence of scandium in this situation is pretty much irrelevant. |
Scamdium strikes again!
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Scamdium strikes again!
jim beam wrote:
Phil Lee, Squid wrote: http://weightweenies.starbike.com/ph...ic.php?t=19036 Aluminum BB axles are not a good material selection... they're fine if they're dimensionally appropriate for the job. aluminum shimano axles anyone? the problem comes when you use the same size in aluminum as you do in steel given aluminum's much lower strength. presence of scandium in this situation is pretty much irrelevant. It was tongue in cheek, of course. I'm curious to know what proportion of high-mileage Ksyrium SSC SL riders get broken spokes compared to standard-spoke riders. -- Phil Lee, Squid |
Scamdium strikes again!
Phil Lee, Squid wrote:
jim beam wrote: Phil Lee, Squid wrote: http://weightweenies.starbike.com/ph...ic.php?t=19036 Aluminum BB axles are not a good material selection... they're fine if they're dimensionally appropriate for the job. aluminum shimano axles anyone? the problem comes when you use the same size in aluminum as you do in steel given aluminum's much lower strength. presence of scandium in this situation is pretty much irrelevant. It was tongue in cheek, of course. I'm curious to know what proportion of high-mileage Ksyrium SSC SL riders get broken spokes compared to standard-spoke riders. well, those spokes are 3x the size... interestingly, when those wheels first came out, it seemed like i'd see someone shipwrecked with a broken aluminum spoke once or twice a month. the last few years though, i can't say i've seen one. |
Scamdium strikes again!
Chalo wrote:
wrote: It's possible to design an aluminum bottom bracket axle that's safe for even someone of Chalo's size, but it would have to have a larger diameter than most (or all) current designs. Like not 19-22 mm but rather something on the order of 50mm. Whether such a large diameter BB is desireable is a separate question. As a rule of thumb, a tubular structure made from aluminum can be made equally stiff to a steel tube of similar wall thickness if its diameter is increased by a factor of 1.4. Furthermore, if its cross-sectional area is increased to accomodate the difference between the tensile strengths of the aluminum and steel in question, then the aluminum part will almost certainly prove to be as reliable as the steel part. The principle is well illustrated by the aluminum frames that are ubiquitous on bicycles today. For my part, I find cranks with 3/4" (19mm) solid CrMo spindles with fine-pitched splines to be perfectly adequate for my needs. This suggests that an aluminum spindle of approximately 27mm diameter with a 9.5mm wall would be adequate for me, as long as it were made of some very strong aluminum alloy like 7075-T6, 7068-T6, 7055-T77511, or a Scandium-doped alloy. Such a spindle could easily be fitted into an American BB shell along with some reasonably stout bearings. Chalo Colina Thanks for the input, Chalo. Your math makes sense to me. FWIW, I secretly hope that a new BB standard emerges (the American (AKA BMX) spec would work fine) such that we could use 25-30mm aluminum bottom bracket axles with appropriately oversized bearings. One advantage of an Al:Al interface is that both the BB and crank would have similar stiffnesses, reducing the incidence of creaking. People like Peter would hate it, but I suspect we're headed that way; Cannondale, Specialized and Pinarello already offer such BBs. I guess my secret hope is no longer a secret. Jason P.S. Peter, I mean no offense by this; "people like Peter" is meant to mean "those skeptical of change qua change" rather than "people who hate anything new." |
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