Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 (edited) yeah but surly having longer and wider pedals, is going to cause more force than a 3mm spacing...This is exactly true in fact a 3mm more offset at the pedal will increase the shear force at the bearing by a massively more significant amount.I will agree with the fact that it will increase the force but it should not be enough to be the difference between it being fine and failure.A few things need clearing up here.1. is the axle bent2. what spacers are these anyway, mine has no spacers.3. would the cranks have been tight with the spacers.4. would Dave have left the spacers on if his cranks were not tight as a result3. did the axle fail through shear up and down or was it a torsional failure. Edited December 7, 2009 by Matt Vandart Quote Link to comment Share on other sites More sharing options...
Ashley-Wood Posted December 7, 2009 Report Share Posted December 7, 2009 (edited) the pedal causes more force for the axel to try and bend surly? because your standing further away from the centre of the axel.. if you was closer to the centre of the axel there will be less force for it try and bend? i dont understand how the length of pedals wouldnt make a diffrence, but 3mm of spacing would, i have aprox 3mm of spacing on mine because my crank doesnt go that far on.. Edited December 7, 2009 by Ashley-Wood Quote Link to comment Share on other sites More sharing options...
Mark W Posted December 7, 2009 Report Share Posted December 7, 2009 the pedal causes more force for the axel to try and bend surly?It is nothing to do with that. Re-read what Adam said. Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 It is nothing to do with that. Re-read what Adam said.It is everything to do with that. Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted December 7, 2009 Report Share Posted December 7, 2009 It's a trials component.Trials components break.Shit happens.If you've been refused warranty you've been refused warranty. No point dwelling on it/getting lairy on the internet Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 Quote Link to comment Share on other sites More sharing options...
Mark W Posted December 7, 2009 Report Share Posted December 7, 2009 It is everything to do with that.The pedal has nothing to do with where a crank is supposed to be on a spindle, especially relative to where the spindle is designed for the crank arm to fit. Quote Link to comment Share on other sites More sharing options...
Rob Brodie Posted December 7, 2009 Report Share Posted December 7, 2009 LOL this thread is hilarious.Tarty adam knows everything END OF! Quote Link to comment Share on other sites More sharing options...
psycholist Posted December 7, 2009 Report Share Posted December 7, 2009 (edited) The change in bending moment isn't enough to suddenly cause a failure though. However Ali's earlier comment does suggest a very likely way in which the failure could have occurred that does implicate the spacers as the cause of failure. If the failure was down to fatigue (Which is the means by which pretty much all bike parts that don't fail in the first 5 minutes of use will fail), there is a very significant difference in the peak stress in a system where the peak bending moment being applied to the crank lines up with the end point of the crank bolt threads (Which have their own stress raising effect) compared to where the end of the crank does not line up with this point, so there are two separate lower stress peaks along the axle. A couple of photos would confirm this - if the break has a discoloured smooth area (Especially if there are what looks a bit like the growth rings in trees radiating from a point on the outside of the axle (Usual most likely start point as stress is maximum on the outside of a part seeing bending in the absence of other stress risers) as well as a rough looking area for the rest of the break, possibly with some shiny facets, then you have classic fatigue failure for a tough material (Rough dull breaks are ductile failure and usually seen in aluminium/soft metals, BB axles will often have a mix of ductile and brittle fracture surface thanks to the hardness and toughness required for that application, leaving some shiny brittle fracture surfaces). If the crack lines up with the bottom of the crank bolt threads or the point where the crank bolt ended in these threads when the crank was fitted and these points ordinarily would not have been aligned without the spacer, then there's a very good case to say that was the reason. 3mm of increased leverage isn't enough on its own though - unless the person using it snaps BB's relatively regularly anyway in which case it might take a month or two off the BB's life with failure being inevitable anyway. Edited December 7, 2009 by psycholist Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 It is as has been stated by me and a few others that the force acting at the point of shear are to do with the force applied.These forces are applied to the End of the axle whether you space it or not these forces are applied a fixed length away from the bearing.Now by spacing the crank out by 3mm you are not changing the length of the axle so the forces are still being applied at the same distance from the bearing.The spacing out has increased the effective length of the lever created by the crank and pedal lengths which has in turn increased the force being applied at the end of the axle which is still the same length as the original.This increase in force is what people are saying caused the failure but as can bee seen the length of the lever could also be increased by:Longer crank offsetThe cranks not going on as far such as a new set of middleburns Longer pedal axle.On any bike and has not resulted in failure.Also the weight of the rider can vary considerably more than the above length difference which would have a much bigger effect. Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted December 7, 2009 Report Share Posted December 7, 2009 Tarty adam knows everything END OF!Lol, not really, but I can't work out in my head why the spacer would NOT contribute to the axle failure...Matt - looks like the axle has sheared after torsion, I edited my post above a few times to include this:Edit: Had yet another look at the BB, looks like it's broken at the end of the crank bolt, which finishes at almost exactly the same distance from the crank stop as the thickness of the spacer used. There is of course a stress riser from the bolt anyway (solid to hollow section change), but combined with the crank being in the 'wrong place' and not covering over this stress riser... you get the idea. Looks like more of a torsional failure, doubt it would have happened if the crank was up to the stop as designed... Hence Reset not replacing it. Quote Link to comment Share on other sites More sharing options...
Stan Shaw Posted December 7, 2009 Report Share Posted December 7, 2009 Arrghh, I am getting STRESSed, I do hope my RISERbars don't snap Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 The change in bending moment isn't enough to suddenly cause a failure though. However Ali's earlier comment does suggest a very likely way in which the failure could have occurred that does implicate the spacers as the cause of failure. If the failure was down to fatigue (Which is the means by which pretty much all bike parts that don't fail in the first 5 minutes of use will fail), there is a very significant difference in the peak stress in a system where the peak bending moment being applied to the crank lines up with the end point of the crank bolt threads (Which have their own stress raising effect) compared to where the end of the crank does not line up with this point, so there are two separate lower stress peaks along the axle. A couple of photos would confirm this - if the break has a discoloured smooth area (Especially if there are what looks a bit like the growth rings in trees radiating from a point on the outside of the axle (Usual most likely start point as stress is maximum on the outside of a part seeing bending in the absence of other stress risers) as well as a rough looking area for the rest of the break, possibly with some shiny facets, then you have classic fatigue failure for a tough material (Rough dull breaks are ductile failure and usually seen in aluminium/soft metals, BB axles will often have a mix of ductile and brittle fracture surface thanks to the hardness and toughness required for that application, leaving some shiny brittle fracture surfaces). If the crack lines up with the bottom of the crank bolt threads or the point where the crank bolt ended in these threads when the crank was fitted and these points ordinarily would not have been aligned without the spacer, then there's a very good case to say that was the reason. 3mm of increased leverage isn't enough on its own though - unless the person using it snaps BB's relatively regularly anyway in which case it might take a month or two off the BB's life with failure being inevitable anyway.Agreed.Where has the axle snapped I am only assuming it snapped at the bearing if it snapped at the end of the crank arm threads then I agree with the spacer theory. Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted December 7, 2009 Report Share Posted December 7, 2009 ^^ That lame joke was Ali Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 Arrghh, I am getting STRESSed, I do hope my RISERbars don't snap Quote Link to comment Share on other sites More sharing options...
Mark W Posted December 7, 2009 Report Share Posted December 7, 2009 Where has the axle snapped I am only assuming it snapped at the bearing if it snapped at the end of the crank arm threads then I agree with the spacer theory.It didn't snap at the bearing...In news...1. is the axle bent2. what spacers are these anyway, mine has no spacers.3. would the cranks have been tight with the spacers.4. would Dave have left the spacers on if his cranks were not tight as a result3. did the axle fail through shear up and down or was it a torsional failure. Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted December 7, 2009 Report Share Posted December 7, 2009 Where has the axle snapped I am only assuming it snapped at the bearing if it snapped at the end of the crank arm threads then I agree with the spacer theory. Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 (edited) And what is that meant to mean?Reffering to Marks post Edited December 7, 2009 by Matt Vandart Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted December 7, 2009 Report Share Posted December 7, 2009 Oh dear god. Quote Link to comment Share on other sites More sharing options...
Mark W Posted December 7, 2009 Report Share Posted December 7, 2009 1234......3. Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 (edited) Oh I get it now Edited December 7, 2009 by Matt Vandart Quote Link to comment Share on other sites More sharing options...
Mark W Posted December 7, 2009 Report Share Posted December 7, 2009 1. is the axle bent2. what spacers are these anyway, mine has no spacers.3. would the cranks have been tight with the spacers.4. would Dave have left the spacers on if his cranks were not tight as a result3. did the axle fail through shear up and down or was it a torsional failure. Quote Link to comment Share on other sites More sharing options...
Matt Vandart Posted December 7, 2009 Report Share Posted December 7, 2009 (edited) Well looking at the picture I can see how it would have failed torsionally with the spacer it all makes sense I wrongly assumed it had snapped at the bearing.Anyway that was fun.At least I know mine aint gonna fail due to spacerage.Having said that can we see the roundy side if you know what I mean. Edited December 7, 2009 by Matt Vandart Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted December 7, 2009 Report Share Posted December 7, 2009 Anyway that was fun.Internet arguments always are, hehe. Quote Link to comment Share on other sites More sharing options...
Ashley-Wood Posted December 7, 2009 Report Share Posted December 7, 2009 i still think the pedal length could of helped aswell Quote Link to comment Share on other sites More sharing options...
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