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Old 2018-02-25, 10:11 PM   #61
OneTrackMind
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Larger diameter wheels have a lower rolling resistance.

The height of any bump is smaller in proportion to the larger wheel so the larger wheel rolls over them more easily.
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Old 2018-02-26, 03:02 AM   #62
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Originally Posted by tholub View Post
The 36" is marginally less affected by road bumps because its tire profile is taller, and you may be riding faster. The forward momentum is important, but the rotational momentum doesn't really have an effect on bumpiness. Forward momentum is mostly a function of velocity, so at the same forward speed, there's probably not much difference between the 36er and 29er.

The gyroscopic effect is not substantial in unicycle or bicycle wheels.
http://www2.eng.cam.ac.uk/~hemh1/gyrobike.htm
I agree that the larger diameter wheel of the 36er will allow it to roll over larger bumps then a smaller wheel just because of the size with no consideration for weight. However the greater flywheel effect of the larger heavier wheel is also part of the picture and would allow the larger tire to roll over obstacles larger then just the increase due to tire size alone.

The gyroscopic effect on bicycles has been show to be not the only effect that makes a bicycle self-stable but it seems to be part of it. Unicycles are a different story. Just as any disk shaped object can be rolled along and maintain stability at some minimum speed I believe the very same gyroscopic effect aids in keeping larger wheeled unicycles stable.

If anyone doubts the effect they can very do simple experiment. I tired this with my 26 and 36" unicycles and the effect was amazing with the 36er. Although it is clear that the gyroscopic effect has no effect in maintaining stability in the forward and back direction, it is clear that it aids in the sideways or left/right direction.

Here is the experiment:
Hold the unicycle off the ground in front of you with one hand on the seat post. Place the second hand on the fork above the cranks. In this position (without the wheel spinning) you can easily tip the unicycle to the left or right as if you were starting to fall to the side. Now using the hand on the fork, spin the wheel up to maybe a cadence of 100 (about 10.7 mph on a 36er) and put the hand back on the fork (don’t get your fingers in the spokes!). Now you have one hand on the seat post, one on the fork above the cranks and the wheel is spinning. Try to tip the unicycle to the left or right as if you were starting to fall sideways. On the 36er the effect is immediate and quite forceful. When it is tipped to the right the uni turns to the right and vise versa. This is the self stabilizing effect caused by the spinning wheel/gyroscopic effect. On the 26er the effect is almost non-existent. The smaller wheel wobbles quite a bit and there is little clear gyroscopic effect as on the 36er. With the larger heavier wheel the effect is quite strong.

Try it, but don’t get your fingers in spokes.

Jim
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Old 2018-02-26, 06:01 AM   #63
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Quote:
Originally Posted by JimT View Post
I agree that the larger diameter wheel of the 36er will allow it to roll over larger bumps then a smaller wheel just because of the size with no consideration for weight. However the greater flywheel effect of the larger heavier wheel is also part of the picture and would allow the larger tire to roll over obstacles larger then just the increase due to tire size alone.

The gyroscopic effect on bicycles has been show to be not the only effect that makes a bicycle self-stable but it seems to be part of it. Unicycles are a different story. Just as any disk shaped object can be rolled along and maintain stability at some minimum speed I believe the very same gyroscopic effect aids in keeping larger wheeled unicycles stable.

If anyone doubts the effect they can very do simple experiment. I tired this with my 26 and 36" unicycles and the effect was amazing with the 36er. Although it is clear that the gyroscopic effect has no effect in maintaining stability in the forward and back direction, it is clear that it aids in the sideways or left/right direction.

Here is the experiment:
Hold the unicycle off the ground in front of you with one hand on the seat post. Place the second hand on the fork above the cranks. In this position (without the wheel spinning) you can easily tip the unicycle to the left or right as if you were starting to fall to the side. Now using the hand on the fork, spin the wheel up to maybe a cadence of 100 (about 10.7 mph on a 36er) and put the hand back on the fork (don’t get your fingers in the spokes!). Now you have one hand on the seat post, one on the fork above the cranks and the wheel is spinning. Try to tip the unicycle to the left or right as if you were starting to fall sideways. On the 36er the effect is immediate and quite forceful. When it is tipped to the right the uni turns to the right and vise versa. This is the self stabilizing effect caused by the spinning wheel/gyroscopic effect. On the 26er the effect is almost non-existent. The smaller wheel wobbles quite a bit and there is little clear gyroscopic effect as on the 36er. With the larger heavier wheel the effect is quite strong.

Try it, but don’t get your fingers in spokes.

Jim
The link you're referring to addresses your example directly.

Quote:
Anyone who has held a bike wheel in their hands and has felt the huge gyroscopic effect will swear that the forces are huge - so large that they simply must be important when riding a bike. But consider this: when holding the axle of the bike wheel in my fingers I notice that the force is big but it can't possibly be more than a few kg at best - ie a few percent of my body weight - because my fingers are not all that strong. So when I ride a bike the gyro effect at the ends of the forks is only a few kg - nothing compared with the 100 kg or so that the combined weight of the bike and rider exert. This is effectively saying the same thing that was deduced by calculation above, ie that gyro effects are there but small compared with other things.
So yes, there are gyroscopic forces, and those forces are larger on a 36er. But they're not substantial compared to the other forces affecting the unicycle.
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Old 2018-02-26, 05:29 PM   #64
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Originally Posted by tholub View Post
.... So yes, there are gyroscopic forces, and those forces are larger on a 36er. But they're not substantial compared to the other forces affecting the unicycle.
Thanks for the comment.

In the summary of the report I linked they acknowledged that the gyroscopic effect is a contributing factor in the self stability of a bicycle. I believe that when you remove some factors on a bicycle like caster and trail of the front wheel and when you consider the greatly increased moment of inertia of the larger unicycle wheel, the gyroscopic effect has a much larger effect on the unicycle then a bicycle.

Just looking at the spreadsheet in this thread and comparing the moment of inertia of a 20 or 24” uni to the moment if inertia of a 36” it is clear that the effect of the larger wheel is much more then just the increased diameter. The moment of inertia increases by a factor or five to ten times by going from the smaller to larger wheel. For example the spreadsheet shows the 24” Vee Tire MK3 118mm with a moment of inertia of 7.41 kg/m^2 and the 36” Night rider at 59.5 kg/m^2. That is an eight times increase in the gyroscopic effect. That is huge and this calculated effect agrees with my hands on experiment comparing a 26 and 36” unicycle.

Also in the linked report they were comparing the gyroscopic effect with a 100 kg or so combined weight of the bike and rider. If you do my experiment on a larger unicycle it is clear that the gyroscopic effect on the unicycle is not acting on the total weight of the rider and unicycle. The gyroscopic effect on the unicycle is only slightly changing the direction of travel (steering right or left) to stabilize the unicycle. The unicycle only needs a relatively small force to slightly change the direction of travel and stabilize the uni in the sideways direction. When you start to tip to one side or the other at cruising speed it only takes a very small change in direction to bring the unicycle back directly under your center of gravity. At slower speeds you loose the gyroscopic effect and a rider has to resort to twisting or flailing their arms to steer and maintain stability in the sideways direction.

Jim
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Old 2018-02-26, 05:57 PM   #65
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Quote:
Originally Posted by JimT View Post
Thanks for the comment.

In the summary of the report I linked they acknowledged that the gyroscopic effect is a contributing factor in the self stability of a bicycle. I believe that when you remove some factors on a bicycle like caster and trail of the front wheel and when you consider the greatly increased moment of inertia of the larger unicycle wheel, the gyroscopic effect has a much larger effect on the unicycle then a bicycle.

Just looking at the spreadsheet in this thread and comparing the moment of inertia of a 20 or 24” uni to the moment if inertia of a 36” it is clear that the effect of the larger wheel is much more then just the increased diameter. The moment of inertia increases by a factor or five to ten times by going from the smaller to larger wheel. For example the spreadsheet shows the 24” Vee Tire MK3 118mm with a moment of inertia of 7.41 kg/m^2 and the 36” Night rider at 59.5 kg/m^2. That is an eight times increase in the gyroscopic effect. That is huge and this calculated effect agrees with my hands on experiment comparing a 26 and 36” unicycle.

Also in the linked report they were comparing the gyroscopic effect with a 100 kg or so combined weight of the bike and rider. If you do my experiment on a larger unicycle it is clear that the gyroscopic effect on the unicycle is not acting on the total weight of the rider and unicycle. The gyroscopic effect on the unicycle is only slightly changing the direction of travel (steering right or left) to stabilize the unicycle. The unicycle only needs a relatively small force to slightly change the direction of travel and stabilize the uni in the sideways direction. When you start to tip to one side or the other at cruising speed it only takes a very small change in direction to bring the unicycle back directly under your center of gravity. At slower speeds you loose the gyroscopic effect and a rider has to resort to twisting or flailing their arms to steer and maintain stability in the sideways direction.

Jim
It is not the gyroscopic effect which provides stability at higher speeds, on bicycles or unicycles. (Riding a bike slowly is just as hard as riding a unicycle slowly).

If you were to construct a counter-rotational apparatus for a 36er to cancel the gyroscopic effect, as various bikers have done to demonstrate this point, I'm sure the thing would still be rideable, and feel pretty much like a normal 36er.
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Old 2018-03-06, 05:38 AM   #66
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Quote:
Originally Posted by tholub View Post
It's not the inertial weight which makes rolling up curbs easier, it's the tire height.
Isn't it both? In answer to the earlier question, if I'm using the correct terminology, I think inertia is a big part of what makes a 36" uni so much more stable to ride.

My big wheel riding experience goes back to 1981, where I got to try 40" Tom Miller wheels, and later a (heavy) wooden wagon wheel. And finally in 1982, my own 45" Tom Miller big wheel. These were all heavy wheels, so they had that inertia (again if I'm using the right term) that kept them tending to roll unless you gave them some definite input.

But that effect wasn't fully realized, as those unicycles all had hard, solid tires. Low friction, which is great, but nobody wants to ride a ton of miles on a tire pumped up to 300 psi. I didn't really "get" the best quality of the Coker until I rode one in the 10k race at Nationals in 2001. The thing just wanted to keep going, and going straight! The air tires are much more resistant to sharp turning, which also makes them a little resistant to the "wobble" effect. And they're so much more comfortable! Needless to say, once I got my own, the old 45" wheel was only used for shows and showing off; not to get somewhere.

Quote:
Originally Posted by JimT View Post
Just as any disk shaped object can be rolled along and maintain stability at some minimum speed I believe the very same gyroscopic effect aids in keeping larger wheeled unicycles stable.
This is true, but is "messed up" (insert proper physics term) by the "wobble" (that is the proper physics term) effect, caused by the cranks and pedals. Granted this is greatly reduced on a larger, heavier wheel, but that wobble definitely subtracts a portion of any gyroscopic force that's being generated. I think.
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Old 2018-03-06, 06:42 AM   #67
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Isn't it both? In answer to the earlier question, if I'm using the correct terminology, I think inertia is a big part of what makes a 36" uni so much more stable to ride.

My big wheel riding experience goes back to 1981, where I got to try 40" Tom Miller wheels, and later a (heavy) wooden wagon wheel. And finally in 1982, my own 45" Tom Miller big wheel. These were all heavy wheels, so they had that inertia (again if I'm using the right term) that kept them tending to roll unless you gave them some definite input.

But that effect wasn't fully realized, as those unicycles all had hard, solid tires. Low friction, which is great, but nobody wants to ride a ton of miles on a tire pumped up to 300 psi. I didn't really "get" the best quality of the Coker until I rode one in the 10k race at Nationals in 2001. The thing just wanted to keep going, and going straight! The air tires are much more resistant to sharp turning, which also makes them a little resistant to the "wobble" effect. And they're so much more comfortable! Needless to say, once I got my own, the old 45" wheel was only used for shows and showing off; not to get somewhere.
If inertia, particularly rotational inertia, is what is providing the stability, the 45" should be much more stable than the 36". I've ridden your 45"; it's not nearly as stable as a lighter 36". (In fact it feels quite surprisingly twitchy).
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Old 2018-03-06, 09:03 AM   #68
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The rotational inertia of wheel works both for and against, trading stability for response. A highly responsive wheel has its own advantages and pleasures especially to an experienced rider.

My collection's most recent addition is a 26 x 2.15 Maxxis DTH on a 42 mm Dominator rim with a light weight tube. It is a joy to ride because it is so manoeuvrable and controllable on suburban foot paths while still retaining the rollover ability of a 26.

It would be entirely possible for a wheel to exhibit too much precession and over compensate the steering induced by a lean. Perhaps that is the case with the 45"?
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Old 2018-03-06, 02:34 PM   #69
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If the gyroscopic effect was significant, unicycles would be a lot easier to ride. On a unicycle instead of the geometry providing the self steering effect it all has to come from the rider. Sure an impossible wheel will stay upright if you roll it on its own, but when being ridden the aim is to keep the rider above the contact patch of they tyre (you balance a unicycle by moving the contact patch of they tyre in the direction of the CoG of the rider) not keep the wheel in balance and the even on a 36 the gyroscopic effect has a very minor input to that.
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Old 2018-03-07, 02:30 AM   #70
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If the gyroscopic effect was significant, unicycles would be a lot easier to ride. On a unicycle instead of the geometry providing the self steering effect it all has to come from the rider. Sure an impossible wheel will stay upright if you roll it on its own...
More to the point: Think about the difference between an impossible wheel (which really is a little like a gyroscope) and an ultimate wheel (which is imbalanced, though not as much as a real unicycle). It's possible to roll an ultimate wheel and have it stay upright but it's way harder, and it tends to want to wobble, not stay straight.
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Old 2018-03-07, 03:12 AM   #71
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If inertia, particularly rotational inertia, is what is providing the stability, the 45" should be much more stable than the 36". I've ridden your 45"; it's not nearly as stable as a lighter 36". (In fact it feels quite surprisingly twitchy).
It is hard to be sure that the 45 has more rotational inertia unless you have calculated the inertia of both the 36 and the 45. Despite the 45 being bigger the 36 looks like it has a much heavier rim and tyre than the 45. Then it is muddied by the fact that the 45 has what appears to be a 1.5cm wide tyre which surely must handle very differently to a wide 36er tyre even with inertia differences. I would think a 1.5cm wide tyre would always be twitchy compared to a 5cm wide tyre even with inertia.

If you had the same width tyre and knew the rotational inertia or the 45 inch was higher then this example would provide better evidence that the gyroscopic effect is minimal in the wheel.
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