StringJunky Posted March 30, 2016 Share Posted March 30, 2016 (edited) This maybe something or not, since my apparatus maybe too imprecisely setup, I was freespinning the front wheel on my new bike and noticed that, no matter which way the wheel started spinning, once it came to nearly rest it always turned a fraction the other way before stopping completely. Where does this slight reversing 'force' come from? It's almost like a recoil. Edited March 30, 2016 by StringJunky Link to comment Share on other sites More sharing options...
EdEarl Posted March 30, 2016 Share Posted March 30, 2016 It is possible your wheel is not perfectly balanced and a heavy spot settles to the bottom. 1 Link to comment Share on other sites More sharing options...
StringJunky Posted March 30, 2016 Author Share Posted March 30, 2016 It is possible your wheel is not perfectly balanced and a heavy spot settles to the bottom. Yes, that's possible. I ought to try spinning it horizontally to negate gravity. 2 Link to comment Share on other sites More sharing options...
Robittybob1 Posted March 30, 2016 Share Posted March 30, 2016 This maybe something or not, since my apparatus maybe too imprecisely setup, I was freespinning the front wheel on my new bike and noticed that, no matter which way the wheel started spinning, once it came to nearly rest it always turned a fraction the other way before stopping completely. Where does this slight reversing 'force' come from? It's almost like a recoil. What sort of distance are you referring to? It could be a type of torque within the bearings. Like if a nut is very tight the tool flexes. The same could be happening if the bearings are reasonably tight. 1 Link to comment Share on other sites More sharing options...
StringJunky Posted March 30, 2016 Author Share Posted March 30, 2016 What sort of distance are you referring to? It could be a type of torque within the bearings. Like if a nut is very tight the tool flexes. The same could be happening if the bearings are reasonably tight. Yes. It seems there's quite a few variables to eliminate that I hadn't thought of. I think I'll give NASA a buzz and see if they'll try it in a freefalling environment , like the IS Station. 2 Link to comment Share on other sites More sharing options...
J.C.MacSwell Posted March 30, 2016 Share Posted March 30, 2016 What sort of distance are you referring to? It could be a type of torque within the bearings. Like if a nut is very tight the tool flexes. The same could be happening if the bearings are reasonably tight. I think it is something like that. When I've seen this phenomenon it always seems to recoil just a fairly small amount, and happens more noticeably with tighter pressure on the bearings. When it is eccentric weight imbalance it is generally a longer reverse rotation depending on where it stops initially. You can check to see if it always heads back toward the same point. 1 Link to comment Share on other sites More sharing options...
Robittybob1 Posted March 30, 2016 Share Posted March 30, 2016 I think it is something like that. When I've seen this phenomenon it always seems to recoil just a fairly small amount, and happens more noticeably with tighter pressure on the bearings. When it is eccentric weight imbalance it is generally a longer reverse rotation depending on where it stops initially. You can check to see if it always heads back toward the same point. weight imbalance would be more of a pendulum effect but dampened pretty quickly. Link to comment Share on other sites More sharing options...
imatfaal Posted March 30, 2016 Share Posted March 30, 2016 I have just done ten trial spins on my front wheel and it does not recoil in any way. This leads me to think one of a few things maybe true: 1. Stringjunky is a dangerous sociopath trying to warp our minds with crazy ideas 2. My old and knackered bearings are not doing the same sort of thing 3. The fact that my bike is suspended absolutely steadily in a workstand removes all other forms of movement which might cloud the experiment and produce false positive results My favourite is number three Merged post follows: [/mp] Am now trying to refute 2 by testing my road bike with uber-posh ceramic bearings rather than my sketchy old commute with pepper-grinder smooth steel cup and cone bearings Merged post follows: Completely different result. Commuter bike stopped dead and had no oscillation whatsoever Road bike oscillated hugely - 22 movements (11 cycles) first trial ending with the valve at just before 3 o'clock and the seam (where the strip of metal which is bent into the a circle to make the rim) is welded at just before 9 o'clock. [mp] 14 oscillations (7 cycles) with final position indistinguishable from trial one Conclusion - it is an oscillation on Stringjunky's bike settling to a equilibrium position; however the state of his bearings are such that it is more than critically damped and only does 1/2 a cycle. I think you may need new bearings - I am certain that I do on my Commuter. 1 Link to comment Share on other sites More sharing options...
Phi for All Posted March 30, 2016 Share Posted March 30, 2016 I think you may need new bearings - I am certain that I do on my Commuter. He said it was a new bike. But then I favor solution #1. I think he stole it from a nun. Who was also a midwife. 1 Link to comment Share on other sites More sharing options...
imatfaal Posted March 30, 2016 Share Posted March 30, 2016 He said it was a new bike. But then I favor solution #1. I think he stole it from a nun. Who was also a midwife. Yes - I missed that. The oscillation are so pronounced on my good bike as to be slightly unbelievable - and the only difference between that and the commuter is the quality of the bearings. It is also disconcerting that the valve - which looks as if it should end up at the bottom ends up half way up one side. New bearings can take a while to fully loosen up - when assembled they should be packed with grease and take a while to get into full rolling mode. The other possibility is that the Quick release bolt is too tight and is bending the axle slightly and causing the bearings to rub I presume the BBC has sold call the midwife to the USA networks? 2 Link to comment Share on other sites More sharing options...
StringJunky Posted March 30, 2016 Author Share Posted March 30, 2016 ... The other possibility is that the Quick release bolt is too tight and is bending the axle slightly and causing the bearings to rub I presume the BBC has sold call the midwife to the USA networks? Ignorantly, I have set my QR very tight; will loosen it pronto. Glad I mention the OP now because I want to keep this new bike as it is. 2 Link to comment Share on other sites More sharing options...
Robittybob1 Posted March 30, 2016 Share Posted March 30, 2016 Ignorantly, I have set my QR very tight; will loosen it pronto. Glad I mention the OP now because I want to keep this new bike as it is. Don't have it too loose either. Link to comment Share on other sites More sharing options...
J.C.MacSwell Posted March 30, 2016 Share Posted March 30, 2016 Yes - I missed that. The oscillation are so pronounced on my good bike as to be slightly unbelievable - and the only difference between that and the commuter is the quality of the bearings. It is also disconcerting that the valve - which looks as if it should end up at the bottom ends up half way up one side. New bearings can take a while to fully loosen up - when assembled they should be packed with grease and take a while to get into full rolling mode. The other possibility is that the Quick release bolt is too tight and is bending the axle slightly and causing the bearings to rub I presume the BBC has sold call the midwife to the USA networks? I would expect a greater difference in the weight imbalance as well. Conclusion - it is an oscillation on Stringjunky's bike settling to a equilibrium position; however the state of his bearings are such that it is more than critically damped and only does 1/2 a cycle. I think you may need new bearings - I am certain that I do on my Commuter. The reason I suspect it is not this in SJs case is that I think StringJunky would recognize it fairly readily. I don't believe he would have started the thread if it was essentially just a gravitational/pendulum affect, and if sufficiently dampened to only do 1/2 a cycle it should be sufficiently dampened to not happen at all during some of the trials...unless he was remarkably consistent with each trial, and at that in each direction. The affect that I believe is happening in the OPs case (assuming it is the affect I am familiar with) is that the slowing wheel loads the bearings and puts a torque on the system, including forks or what have you, which can put a bit of bending moment and add a bit of energy to the system...this also increases as it comes to a stop as the friction transitions from dynamic to static, and then of course leads to a recoil affect after coming to a stop. Link to comment Share on other sites More sharing options...
imatfaal Posted March 30, 2016 Share Posted March 30, 2016 Don't have it too loose either. Remember your weight is on the axle so it is kinda held in place - but it should not be too tight nor too loose; too loose is probably worse. You should not fight to close the QR lever - but nor should you be able to turn the axle on its axis by turning the QR lever. If String has disc brakes it would be better to be a little on the tight side (disc brakes apply force/torque on only one side of the fork and therefore there is a torque around the axis of the steerer tube) - rim brakes (which would make sense as he posted a picture of some nasty Clarks brake pads last week ) produce no torque in that axis as the retarding torque/force is applied on both sides of the wheel equally. You can test by holding brakes on and pushing the bike forward and pull backwards against the front wheel braking - there should be no movement whatsoever of the axle in any direction. Shimano recommend that there should be some axial play in the wheel on the axle before attachment to forks - but that the action of the QR clamping down should bend the axle enough to take up the play. But crucially you should not get an increase in the friction on the wheel when you clamp it in; ie it should spin as freely when in your hand as when clamped into the forks - this is why you need the play beforehand. String - if you are gonna be doing any maintenance (and forgive me if you already know all this) check out Park Tools website for their huge array of tips and advice / Sheldon Browns Website / andor By Zinn and the Art of Bicycle Maintenance 1 Link to comment Share on other sites More sharing options...
StringJunky Posted March 31, 2016 Author Share Posted March 31, 2016 Moral: If you want simple, don't talk to scientists, or its enthusiasts. Don't have it too loose either. It's got to be Goldilocks tight... not too much, not too little. Remember your weight is on the axle so it is kinda held in place - but it should not be too tight nor too loose; too loose is probably worse. You should not fight to close the QR lever - but nor should you be able to turn the axle on its axis by turning the QR lever. If String has disc brakes it would be better to be a little on the tight side (disc brakes apply force/torque on only one side of the fork and therefore there is a torque around the axis of the steerer tube) - rim brakes (which would make sense as he posted a picture of some nasty Clarks brake pads last week ) produce no torque in that axis as the retarding torque/force is applied on both sides of the wheel equally. You can test by holding brakes on and pushing the bike forward and pull backwards against the front wheel braking - there should be no movement whatsoever of the axle in any direction. Shimano recommend that there should be some axial play in the wheel on the axle before attachment to forks - but that the action of the QR clamping down should bend the axle enough to take up the play. But crucially you should not get an increase in the friction on the wheel when you clamp it in; ie it should spin as freely when in your hand as when clamped into the forks - this is why you need the play beforehand. String - if you are gonna be doing any maintenance (and forgive me if you already know all this) check out Park Tools website for their huge array of tips and advice / Sheldon Browns Website / andor By Zinn and the Art of Bicycle Maintenance Thanks for all the replies guys, I'm glad I asked, what was, really, just an off-the -cuff question. Imatfaal, so as not to mess up the science section - that's been answered - I think I'm going to start a new thread on bikes in The Lounge. Link to comment Share on other sites More sharing options...
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