Hmmmmm?    photo: @fat cyclist

Hmmmmm? photo: @fat cyclist

When the Wheels Come Off

by / / 53 posts

This is perhaps painfully obvious to everyone but me and if so, sorry I’ve yet again wasted  your time. The other day, after falling off another floating board in the ocean I had to admit my balance might suck. And my coordination too or I might have been good enough at baseball to actually like it and play it. Nope, ball sports are right out. What I want to celebrate is the fact that our bikes have two magic gyroscopes spinning underneath us. You want to sit up at 40 kph, casually reach behind and tuck your gilet under your jersey? Be my guest but you can only do that because of the gyroscopes, not your awesome balance. If good balance was required to ride bicycles every prat and his brother wouldn’t be chatting on their iphone while zipping down the lane.

Descending at great speed is so damn much fun because the bike is rock solid when hauling such mighty ass, until it isn’t and that is is pilot error, not the fault of your dualing gyroscopes. To quote one of Maine’s greatest exports, Yvon Chouinard, “speed is safety”. He was talking about mountaineering and the need quickly get across exposed couloirs to avoid potential rockfall or avalanche but it’s also true for cycling, to a point. OK, he could have said speed is stability if he was more of a cyclist.

Does this mean we shouldn’t own deep section carbone wheels, with their lighter rotating mass providing less momentum? No, folly my friends, the deep section wheels are spinning faster because you are going faster due to the aero-awesomeness of those wheels. A year into my tubular tire/50 mm Cancellara carbone wheels and I’m more chuffed than ever about them. Unless it’s raining heavily and I’m descending then, not as chuffed. But I digress, that is another lecture.

So far so good. What the hell is absent minded professor talking about? All this spin angle momentum and torque should have us riding in circles not going in straight lines. That is your weekend homework. Test on Monday. Buon weekend.

 

// Musings from the V-Bunker

  1. I read the article, and the first few comments, aaaannnnndddddd I still have no idea what you’re on about !

    Ohh is that the time,

  2. I’m still too scared to go no hands. Unless the brake cables come out on top of the hoods and the gear levers are on the downtube.

    I’m going to hang out with Julius over the weekend!

    Why is it so?!

  3. @sthilzy

    I’m still too scared to go no hands. Unless the brake cables come out on top of the hoods and the gear levers are on the downtube.

    I’m going to hang out with Julius over the weekend!

    Why is it so?!

    Damn that takes me back.

    And now I have an unaccountable urge to buy some Cadbury’s chocloate.

  4. @cognition

    Is that a serious question?

    Okay, since I’m a high school physics teacher for my day job, I’ll take a stab at this.

    Classical mechanics can be divided into three broad families: motion in a straight line, motion along a curve (which is really just motion in a straight line plus directed acceleration), and rotation. Most people who study physics spend way more time on motion in a straight line; it’s easier to see and visualize. One of the sub-categories of straight line motion is momentum. It’s the idea that something moving in a straight line has a strong tendency to keep moving at the same speed, and in the same direction, unless something else comes in and messes with it.

    Thankfully, all of the ideas in straight-line motion have their analogues in rotational motion. The analogue to momentum is angular momentum. A thing that is rotating has a strong tendency to keep rotating at the same rate of spin, and in the same direction, unless something else messes with it. The trick here is that the direction of rotation is not just the top of the wheel going “forwards” — think about the direction that the axle is pointing. That’s what we think about when physicists talk about the direction of rotation. And that direction has a strong tendency to keep pointing in the same direction, in three dimensions, creating the “gryoscopic effect”…

    …and letting all of us think that we’re more graceful than we really are.

  5. @hudson

    It would be a lot better if I could show you stuff in real life, or at least diagrams drawn on a board.

    But if you want to check it out, take a front wheel. Hold one side of the quick release, then use your other hand to set the wheel spinning (faster is better, same as in The Rules). After the wheel is spinning, take your second hand and hold on to the other side of the quick release. Now try to change the direction of the axle. You’ll feel — strongly — the resistance of the wheel to changing direction. That’s the gyroscopic effect.

    @Cam is correct, too, though, about that study. I didn’t want to get into it because I didn’t want to geek out fully. But what the heck! The author in the study builds a bike that can basically hold a second front wheel (off of the ground), sets the second wheel spinning the opposite direction, and observes that the bike is still rideable. His postulate is that the trail of the bike is what keeps it stable. I haven’t done the experiment, but it looks solid. I’d love to set up some kind of arrangement where I could get two wheels linked together similarly to his pair of front wheels, set them spinning in opposite directions, and see whether they’re easier or harder to torque off-direction. My analytical sense is that it should be easy, but my intuition wonders whether it wouldn’t be twice as resistant. Something to rig up for next year’s class, perhaps…

  6. @cognition

    Well, and mind you it come from someone wildly incompetent, since the axle is hard to move in both directions, a second wheel pointing the same direction but in reverse would also be hard to move in the same both directions.

    A second wheel off the ground but perpendicular to the one on the ground would be a mess tough.

    Am i making sense?

  7. @LeBelge

    I think so. Imagine a doubly-long quick release that would let you put two wheels right next to each other. My question — and I think yours, too — is whether two wheels spinning in opposite directions would be more stable, or whether the two vectors in opposite directions would cancel each other out.

    I genuinely don’t know. My analytical intellectual sense says that they would cancel each other out. My intuitive sense thinks that maybe it would be twice as stable.

  8. @cognition

    All I can say is that the WWII Patrol Boats (UK MTBs, US PTs) had contra rotating props otherwise they would have about a 15 deg list due to engine torque at full power.

    I believe the later UK ones did not for cost savings and were a bit of a ‘mare.

  9. @Teocalli

    Ooh, cool. Always nice to hear about real-world examples.

    Now I’m going to have to rig something up so I can check it out for myself and demonstrate it to my students…

  10. @Teocalli

    @cognition

    All I can say is that the WWII Patrol Boats (UK MTBs, US PTs) had contra rotating props otherwise they would have about a 15 deg list due to engine torque at full power.

    I believe the later UK ones did not for cost savings and were a bit of a ‘mare.

    This is presumably why the American track team have developed a new track bike with Felt that has a left hand side drivetrain to counteract the natural skewiffiness of righthandside drivetrains and anti-clockwise banking? Or is it simply because they like switching things to the wrong side to confuse is Brits?

  11. The Chinook helicopter is a terrific example of how counter rotation can be used to cancel out torque steer.

    It only prevents the fuselage from spinning, and allows the chopper to use power for forward momentum. Blade pitch is is to steer.

    Counter rotating wheels on the same axle should react the same as each other

  12. @Cam

    On the insignificance of the gyroscopic effect when riding a bicycle.

    Mother Fucker! Truth, you are a cruel mistress! Thanks Cam. I guess.

  13. Damn, I hate when that happens. FFS. Well. If I was Dutch I’d continue to argue my point and ignore Cam’s article.

  14. >>>The reason why the M cancels is because the moment of inertia has an M in it…None of this is intuitive…<<<

    Physics is Phun. Cheers all

  15. @Cam

    On the insignificance of the gyroscopic effect when riding a bicycle.

    >>> The faster we ride, the smaller the steering adjustment needs to be, simply because the bike moves much further in a given time. When riding very slowly the steering adjustments required are very large. <<<

    And this I suspect is why I am far more likely to wreck on a mtn bike when going slow vs going fast yes?? maybe??

  16. This also explains why riding on rollers is significantly more difficult (in regards to balance) than riding on the road. You have the same gyroscopic forces but no forward motion and therefore no trail.

  17. @Randy C

    > The faster we ride, the smaller the steering adjustment needs to be, simply because the bike moves much further in a given time. When riding very slowly the steering adjustments required are very large. <<<

    And this I suspect is why I am far more likely to wreck on a mtn bike when going slow vs going fast yes?? maybe??

    @ Randy C Nope, the reason for wrecking while going slow on a mtb is because any impact to your front wheel (roots, rocks, etc.) will make it stop more easy if you´re slow, whilst your body will try to keep the momentum at going over the handlebar. On the other hand, if you´re faster it´ll be bumpier óver those roots&rocks but you´ll be able to clear the obstacles and keep on rollin´…

  18. To self-balance, a bicycle needs to have a tendency to steer into the lean by itself. There are three factors that make standard modern bikes do this:

    • The aforementioned gyroscopic effect.
    • The aforementioned trail.
    • The fact that the steering system’s center of mass is in front of the steering axis, so that when the bike is leaning it tends to fall lower than the steering axis and thus turn the wheel into the lean. This is somewhat similar to how trail works, but it is an independent factor.

    Any one of these factors can be enough to make a bike self-balance, as long as there are no other factors opposing it. Luckily, modern bikes have all three working in unison (barring some wacky front end setups).

  19. Some more about the formal discovery of that third factor: http://www.cornell.edu/video/andy-ruina-explains-how-bicycles-balance-themselves

  20. Ghostie your #1 and see how good the gyroscopic effect is!

  21. you can only do that because of the gyroscopes, not your awesome balance

    Huh?

  22. Then there is this…..

  23. @sthilzy

    you can only do that because of the gyroscopes, not your awesome balance

    Huh?

    OK already, I admit I am totally wrong here. That robot is fab. Chapeau to that engineer.

  24. @Teocalli

    I remember an article many years ago about experimental bikes with either no trail or negative trail and the bikes are basically unrideable. Too bad I didn’t remember that before I wrote this dog’s ass article in the first place.

  25. @Gianni

    I have often thought that Rule #5 and #9 also apply to writing articles!

    I have also considered carefully the scientific evidence, theories and proofs in all of this thread vs your original postulation and come to the considered opinion that based on scientific fact, you balance is indeed, crap.

  26. @Gianni

    Ah, but as Frank would say — gyroscopes make for a better story, and thus have an element of truth in them.

  27. @cognition

    @Gianni

    Ah, but as Frank would say — gyroscopes make for a better story, and thus have an element of truth in them.

    Heheh… Indeed… And Tim Krabbé just might second that notion. Something along the lines of: “Gyroscopes are cool: they represent the essence of all that is mysterious and beautiful about bicycles. Those physics data are inaccurate…” or words to that effect

  28. @Gianni

    @sthilzy

    you can only do that because of the gyroscopes, not your awesome balance

    Huh?

    OK already, I admit I am totally wrong here. That robot is fab. Chapeau to that engineer.

    Agreed; amazing stuff. And for some reason, while being absolutely awe-inspiring, the cycling robot strikes me as hilarious, too – in a very good way. That little wave at the end of every successful ride is priceless.

  29. The professor is Dutch, so he must be right.

  30. No fair. It’s already Monday morning and I’m just finding out about this test. Will a note from my mother get me out of it?

  31. @Ron

    No fair. It’s already Monday morning and I’m just finding out about this test. Will a note from my mother get me out of it?

    I suspect it comes down to the length of the axle at the point of suspension. Net abstract conclusion is that the fact that we mount the axle at both ends cancels it out as it goes the other way when you reverse it. Alternatively it proves that the forks should attach at the centre of the hub – which would be interesting in a number of ways (mostly resulting to risk to life and limb). Then again Cannondale have the Lefty which should go round in circles.

  32. interesting topic: but how does this physics explain speed wobbles?

    I’ve experienced and seen some shockers – even in the recent Amgen Tour of California one of the riders in the break had a pretty obvious case. I’ve read and listened to a variety of explanations but none seems to consistently explain the phenomenon using science.

    Anyone?

  33. @PT

    interesting topic: but how does this physics explain speed wobbles?

    I’ve experienced and seen some shockers – even in the recent Amgen Tour of California one of the riders in the break had a pretty obvious case. I’ve read and listened to a variety of explanations but none seems to consistently explain the phenomenon using science.

    Anyone?

    I suspect longitudinal flex and spring starts to come into it. Many moons ago I used to ride good old solid British motorbikes. Built like the proverbial brick shithouse. A mate was into new fangled Japanese stuff. So one day we swapped bikes. Basically after getting used to something that felt near half the weight of mine I decided to see what it could do. Went into a bend fairly quickly (but not excessive) notched a gear down on the exit and opened it up. SHIIIIIIIITTTTTTT ! I felt the frame flex then was hit by a ginormous speed wobble. Scared the proverbial out of me. Went back to my mate and asked him if he’d ever had issues in fast bends – he never had. So I concluded he had never really pushed the thing.

  34. @PT

    @PT

    interesting topic: but how does this physics explain speed wobbles?

    I’ve experienced and seen some shockers – even in the recent Amgen Tour of California one of the riders in the break had a pretty obvious case. I’ve read and listened to a variety of explanations but none seems to consistently explain the phenomenon using science.

    Anyone?

    I was riding down a hill in the rain, a little under-dressed, and got a persistent speed wobble. I thought it was a problem with the bike, but after a while I figured out that it was caused by my own shivering. Sorry, not a useful answer.

  35. @Teocalli

    I tried a backwards bike that was brought in to the LBS by a prof from our local university. You very quickly realize there is no chance. I wasted maybe 20 sec’s giving it a try. This cat stuck to it for 8 mo’s! Then couldn’t ride a regular bike !!!??? Yowza.

  36. @geoffrey

    Speed wobbles can be caused by frame construction/alignment/forks/centre-of-gravity/rider weight/rider build/muscle tension/lack of tension/ability/headset problems/wheel construction/tyres/loose quick releases/wind/road surface or any combination of those factors, and probably others I’ve forgotten.

    That’s why speed wobbles are still on the whole a bit of a mystery; almost every case is individual.

  37. I fucking love physics.

  38. @Oli

    @geoffrey

    Speed wobbles can be caused by frame construction/alignment/forks/centre-of-gravity/rider weight/rider build/muscle tension/lack of tension/ability/headset problems/wheel construction/tyres/loose quick releases/wind/road surface or any combination of those factors, and probably others I’ve forgotten.

    That’s why speed wobbles are still on the whole a bit of a mystery; almost every case is individual.

    When I was riding the Bear 100 gravel ride this weekend in Laona (northern WI), my speed wobble was caused by going about 40kms down a rather sandy, gravelly descent. I was adhering to the rule about descending at speeds considered ludicrous (something one of my companions remarked upon). Mind you, at one point I did think I was heading for big trouble, but saved the day at the last minute! Serious squeeky bum time. As well as this one turned out, a couple of winters ago I had a speed wobble. Fortunately there was a nice soft snow bank to tumble into.

    Physics? Sat it twice in HS and failed both times. Nuff said.

  39. @wiscot

    @Oli

    @geoffrey

    Speed wobbles can be caused by frame construction/alignment/forks/centre-of-gravity/rider weight/rider build/muscle tension/lack of tension/ability/headset problems/wheel construction/tyres/loose quick releases/wind/road surface or any combination of those factors, and probably others I’ve forgotten.

    That’s why speed wobbles are still on the whole a bit of a mystery; almost every case is individual.

    When I was riding the Bear 100 gravel ride this weekend in Laona (northern WI), my speed wobble was caused by going about 40kms down a rather sandy, gravelly descent. I was adhering to the rule about descending at speeds considered ludicrous (something one of my companions remarked upon). Mind you, at one point I did think I was heading for big trouble, but saved the day at the last minute! Serious squeeky bum time. As well as this one turned out, a couple of winters ago I had a speed wobble. Fortunately there was a nice soft snow bank to tumble into.

    Physics? Sat it twice in HS and failed both times. Nuff said.

    I’ve been thinking more and more about how physicists, like mountain climbers, are mostly genetically gifted folks. Sure, you still gotta put in some work, but a rouleur will never be a goat and a creative, artistic person will never breeze through Calc III.

    I worked my way up through Calculus II, Chemistry II, Physics II…but eventually hard work just couldn’t crack the next level. Meanwhile, I know a person from high school who is an astrophysicist and never even tried, just came naturally. Everyone in her family and extended family also has a very strong, technical mind.

  40. @Ron

    but a rouleur will never be a goat and a creative, artistic person will never breeze through Calc III.

    That’s why I work in an art museum!

  41. @wiscot

    … and a creative, artistic person will never breeze through Calc III.

    I did from what I remember, but it is all long forgotten. I ended up satisfied with being creative.

  42. @tmgrasso

    I fucking love physics.

    Physics is too predictable.

  43. Here’s another article just out on the subject.

  44. @universo

    @wiscot

    … and a creative, artistic person will never breeze through Calc III.

    I did from what I remember, but it is all long forgotten. I ended up satisfied with being creative.

    Likewise here – Calc III was a breeze. It lead to disaster in differential equations – which require a more cookbook approach to the solution.

  45. @Ron

    Sure, you still gotta put in some work, but a rouleur will never be a goat and a creative, artistic person will never breeze through Calc III

    Simply not true, Ron. Well, maybe the rouler/goat thing is. Many gifted with math and science abilities are also accomplished artists. Brian May and Brian Cox are two contemporary examples that come to mind, but there are many many more, and not all named Brian. Mathematics, for example, is a highly creative pursuit. I don’t mean learning procedures and rules and applying them to slightly different problem sets. I mean generating mathematics. The same can be said for engineering. A lot of these folks simply never turn their attention to artistic endeavours.

    The folks I’ve had worked with in mathematics that are the best, are often not as fast with the procedural stuff as I expected them to be. They are good, of course, but not stella. Walk into any large music store in a city, and you’ll find teenagers would will run rings around Mark knopfler or Jeff Beck with their technical ability, but they will never generate music that will move millions of the next generation. Same deal.

  46. Some interesting discussion here on math, sciences, engineering vs creative artistic kinda characteristics. I’ve always wondered about Italians and specifically what is it with the Italians and machines? A person has to admit that Italians have a long history of blending artistic craftsmanship and engineering together to form some beautiful machinery. Bikes and cars and motorcycles yes but also everything from shotguns and heavy steel making equipment. Such a classic element of style in their engineering and design. Very cool.

  47. @Randy C

    Some interesting discussion here on math, sciences, engineering vs creative artistic kinda characteristics. I’ve always wondered about Italians and specifically what is it with the Italians and machines? A person has to admit that Italians have a long history of blending artistic craftsmanship and engineering together to form some beautiful machinery. Bikes and cars and motorcycles yes but also everything from shotguns and heavy steel making equipment. Such a classic element of style in their engineering and design. Very cool.

    I’ve often thought that about the Italian approach to things, especially when spending time there. I don’t know why it is, but it is clear that function and form are weighted more equally there than in many other places. I’ve noticed the same about the Japan, thought it might not seem as obvious to westerners.

    You say “math, sciences, engineering vs creative artistic”, and I know what you mean by it, but I don’t see it like that. A quick check of the Meriam-Webster online definition of creative yields: “having or showing an ability to make new things or think of new ideas: using the ability to make or think of new things : involving the process by which new ideas, stories, etc., are created: done in an unusual and often dishonest way”. Conjuring in the mind some new algorithm, new engineering approach, novel use of a statistical method, and the like, then bringing it into existence, is a creative act. Nowadays, people tend to think of ‘creative’ as synonymous with ‘artistic’, and this not only dilutes the meaning of ‘creative’, but by some trick of the mind leads us to make category errors that have consequences. But, it seems I’m in the minority on this. Rant over…

    Interesting thread. I’ve been reading bout the bike and balance thing for a couple of hours. The guy from that youtube video with the backwards bike – I wonder if he can ride it without hands on the bars? I think I initiate turns by leaning then letting the bars compensate with rotation, not the other way around. This is the only way to navigate turns when riding ‘look Mum, no hands!’. After riding a balance bike for a year or so, my son recently started learning how to ride a bike. I put training wheels on. At first, he found it difficult to turn, as he would lean and nothing would happen. On his balance bike, he seems to like to get up some good speed, lift his feet and put them on the chainstays, then lean and turn. The riding robot can keep balance and make turns, but does so by rotating the bars, so it is not really riding the way we do in full. Getting a robot to initiate turns by leaning seems a much more difficult challenge.

  48. @stooge

    After riding a balance bike for a year or so, my son recently started learning how to ride a bike. I put training wheels on. At first, he found it difficult to turn, as he would lean and nothing would happen. On his balance bike, he seems to like to get up some good speed, lift his feet and put them on the chainstays, then lean and turn.

    My daughter also had a balance bike for about a year, when she was around 3, but we never used stabilisers on her first pedal bike. We went to our local park, found a downslope, and after no more than 15 minutes of falling she was pedalling and riding.

  49. @davidlhill

    @stooge

    After riding a balance bike for a year or so, my son recently started learning how to ride a bike. I put training wheels on. At first, he found it difficult to turn, as he would lean and nothing would happen. On his balance bike, he seems to like to get up some good speed, lift his feet and put them on the chainstays, then lean and turn.

    My daughter also had a balance bike for about a year, when she was around 3, but we never used stabilisers on her first pedal bike. We went to our local park, found a downslope, and after no more than 15 minutes of falling she was pedalling and riding.

    I began with no stabalisers, but put them off after he struggled. He struggled with the weight at first. It’s more than double the weight of his balance bike. He got the hang of the weight pretty fast, but then it was turning the pedals thing. It looks to me like he just doesn’t have the strength in the legs. He likes to train at it for about 20 minutes, then asks for his balance bike, then asks to go to the BMX track. Seems keen so I’ll let him find his way a bit. He’s just turned 3 and I’ve got him on a 14” Specialized Hotrock, which might be a tad big. It’s a lot of fun helping him out, and brings back some pretty special memories which I would otherwise have forgotten. Looking forward seeing him have that Eureka moment.

  50. When a rotating wheel (gyro) is rotated off axis (ie. leaning in a corner) a torque is produced on the wheel in the opposite plane (ie. turning left or right). i don’t believe these torques to be high enough with a road bike wheel though to keep you up. you feel the ‘stiffening’ of steering at high speed due to this though.

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