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Old 2012-01-14, 05:22 AM   #16
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Originally Posted by Danitz View Post
With the same crank length, the 26" unicycle should accelerate faster. However, because of an extra heavy 3" wide tire on the 26" wheel, it was heavier than the 29". So, that offset the difference in wheel diameter and crank "gearing".
Then there's the "other" elephant. a 29" street-riding unicycle, with normal-sized or narrow wheel, is going to be great for riding down the street. A 26" with a 3" wide tire is going to be great for riding on the trails. Each will be lousy at doing the other. In other words, if you want to ride on dirt, you have to choose: Quick response in a light wheel with a harsh ride and limited lifespan, vs. slower response in a tire that can take the pounding, grip the dirt and mud, be much more comfortable to ride, and will last through much abuse. Acceleration isn't really a factor.
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My big assumption here is that more acceleration would provide more control over the unicycle.
A little. Not enough to matter for someone who's learning to ride.

Here's an example of when acceleration actually matters, the 100 meter final (men) at Unicon 12, at the Olympic stadium in Tokyo
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Old 2012-01-14, 07:41 PM   #17
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For a very rough comparison between two unicycles you could take

[total weight (you and unicycle) + rotating weight] / gain ratio from chart = unitless number relating to acceleration potential of you on your unicycle.

Or if you are looking for just the potential for acceleration of the wheel without rider etc.

Rotating weight / gain ratio = potential wheel acceleration. (this number might be better for figuring out how much control you should theoretically have.

If you know the weights of the components you could figure rotating weight as roughly tire + rim + tube + .5*spokes + petals/gain ratio + cranks/(2*gain ratio)


EDIT: of course this will have very little bearing on how easy a unicycle is to ride in real life.
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Old 2018-02-15, 08:36 PM   #18
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I thought this forum was for nerds, I am amazed at how dismissive everyone is of someone trying to calculate wheel characteristics of unicycles. No wonder the OP has only posted 25 times since 2012 when this was the reception to his first post.

ANYHOW for unicycle team sports (hockey) I have been eager to be able to compare wheel abilities for a while. I came to a similar conclusion to the OP that using inertia and total gear ratio was the way to go.

I believe the handling of a wheel in hockey is different to many other disciplines in that it is a game of fast acceleration/deceleration and turning meaning the ability to accelerate may be as or more important than top speed.
What I did

1. Determined the total gear ratio from crank radius and inflated tyre radius. Used this as a proxy of potential for speed.
2.Determined *rough* moment inertia of wheels using rim and tyre of setup and radius from the centre.
3. Determined Torque based on a estimate of 80N (Crank length in meters * Newtons of force)
4. Determined angular acceleration of the wheel setup. (Angular acceleration = torque/moment of inertia. Used the angular acceleration as the wheel ability to accelerate.
5. Plotted this on a scatter graph to compare different wheel builds speed/acceleration potential.[/LIST]
The resulting graph shows that lighter rim/tyre combos make a big difference in acceleration ability, particularly that the stock nimbus 2 rim with Pimp Gusset tyre, a build that >70% in my country use and think is the best option is actually worse than a well built 24. It also shows the trade off in crank length for acceleration/top speed.


Assumptions:
  • I ignored spokes and hubs in this calculation as hubs are so small in radius and similar weights that for this rough attempt I don't think it matters. Spokes I have worked out previously and are tiny compared to rim/tyre. Worked out rim and tyre inertia based on radius of tyre (exception in the case of the 36") meaning the total inertia would be slightly lower for these setups as the rim has a smaller radius. I would add both hub and spokes in if I was going to take it super serious. This is a proof of concept not a final attempt at the best data that can be gained.
  • The Total gear ratio as a proxy for speed assumes that smaller cranks are able to be spun faster than longer cranks. If the smaller cranks are spun at the same cadence as the larger wheel then the larger would obviously have the higher speed. In this case someone on a 24" with 165mm cranks could go faster than someone on a 20" with 89mm cranks. Until I get some hard data that smaller cranks can be spun faster due to smaller circumference of the feet this is just an assumption.
  • Acceleration ability is important to hockey but may not be nearly as important for a rider in the marathon. As you can see on the list the nimbus nightrider has much higher TGR (and suprise suprise goes faster) and a much lower acceleration ability. A rider in a marathon is probably more keen on having high inertia to keep the wheel rolling than having it slow down so easily. For different disciplines you would look for different variables as desirable.
  • This is an assessment only of EQUIPMENT not the RIDER. I realise that an individual rider/their abilities/what crank length they are used to makes a difference to top speed. However I believe a given rider will always be able to accelerate a wheel faster when it has a lower inertia. Also performance characteristics make a difference, that is why track cycling is a game of numbers.

Calculations
https://docs.google.com/spreadsheets...it?usp=sharing
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Last edited by Pinoclean; 2018-02-15 at 08:39 PM.
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Old 2018-02-16, 12:04 AM   #19
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The resulting graph shows that lighter rim/tyre combos make a big difference in acceleration ability, particularly that the stock nimbus 2 rim with Pimp Gusset tyre, a build that >70% in my country use and think is the best option is actually worse than a well built 24. It also shows the trade off in crank length for acceleration/top speed.
What you completely forgot, is to factor in the weight of the rider. Even though it is a constant, I think it's important to scale it, to put it in proportion. What we can see is how much more momentum one setup has compared to another, but I would like to see how much of a difference that makes overall, my guess would be that a 75 kg rider weight compared to 70 kg rider weight is going to be more of a difference than the best momentum of inertia you calculated compared to the worst moment of inertia.

I might add that calculation tomorrow.
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Old 2018-02-16, 02:31 AM   #20
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Originally Posted by finnspin View Post
What you completely forgot, is to factor in the weight of the rider. Even though it is a constant, I think it's important to scale it, to put it in proportion. What we can see is how much more momentum one setup has compared to another, but I would like to see how much of a difference that makes overall, my guess would be that a 75 kg rider weight compared to 70 kg rider weight is going to be more of a difference than the best momentum of inertia you calculated compared to the worst moment of inertia.

I might add that calculation tomorrow.
This is a comparison of equipment irrespective of rider weight. If we are taking into account rider weight we may as well say if rider A can produce 80N and rider B can produce 200N rider B will accelerate faster whatever he is riding. Or if rider A can ride at 130RPM and rider B can ride at 200RPM then rider B will have a higher top speed no matter what his RPM. There is no real need to factor in rider weight for these calculations as this is about how two pieces of equipment will behave.

Taking into account frame weight is fair enough, however I think it is probably minor compared to the rotational inertia. Keen to see that info though, I assumed frame weight would be relatively minor compared to rotational weight in acceleration as usually the difficulty in acceleration is not moving your body forward but ensuring your feet can get your wheel moving fast enough, so ignored it.

If we take into account body composition I think most disciplines would benefit from a rider being as lean as possible with the highest strength to weight ratio as possible.
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Old 2018-02-16, 02:39 AM   #21
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Originally Posted by finnspin View Post
What you completely forgot, is to factor in the weight of the rider. Even though it is a constant, I think it's important to scale it, to put it in proportion. What we can see is how much more momentum one setup has compared to another, but I would like to see how much of a difference that makes overall, my guess would be that a 75 kg rider weight compared to 70 kg rider weight is going to be more of a difference than the best momentum of inertia you calculated compared to the worst moment of inertia.

I might add that calculation tomorrow.
Also I have both the high inertia and low inertia wheels in 20 and 24, for the same rider the difference between them in control and acceleration makes a huge difference. I was amazed how much when I first built them.

So if you are a rider comparing wheelbuilds I think it is more useful than comparing yourself to another rider on another wheel.
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Old 2018-02-16, 06:11 AM   #22
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Quote:
Originally Posted by Pinoclean View Post
The resulting graph shows that lighter rim/tyre combos make a big difference in acceleration ability, particularly that the stock nimbus 2 rim with Pimp Gusset tyre, a build that >70% in my country use and think is the best option is actually worse than a well built 24. It also shows the trade off in crank length for acceleration/top speed.
Have you done anything to test your model? Because I'm willing start with the assumption that the best riders have settled upon the best setup for their discipline by iterative processes, so if your model disagrees with their intuition, your model may be the thing that's wrong.

Certainly it's true that weight, particularly rotating weight, is a factor in acceleration. But rolling distance between power positions is also a huge factor in unicycle sports. I'd ride a 20" for uni basketball except I'd have to give up 2 inches, which is important in basketball but not in hockey.
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Old 2018-02-16, 06:52 AM   #23
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Pinoclean,
This is an interesting exercise, the whole process takes out some of the human unscientific impressions.

I did look some at the Nimbus Nightrider and Nightrider Light calculations. It looks like the tire size is too small (cells D16 and D17). It has also been reported that the Nightrider Light is larger diameter then the normal Nightrider. The larger lighter tire would tend to reduce the effect of the lighter tire compared to the normal weight tire. I also see that there is no formula in cells I16 and I17. If you copy the formula in cell I15 down to cells I16 and I17 it changes the result significantly in the Angular Acceleration and Inertia x Gear Ratio fields.


Quote:
Originally Posted by finnspin View Post
What you completely forgot, is to factor in the weight of the rider. Even though it is a constant, I think it's important to scale it, to put it in proportion. What we can see is how much more momentum one setup has compared to another, but I would like to see how much of a difference that makes overall, my guess would be that a 75 kg rider weight compared to 70 kg rider weight is going to be more of a difference than the best momentum of inertia you calculated compared to the worst moment of inertia.....
I tend to agree with finnspin. The rider is the largest part of the picture and to leave the rider out greatly over calculates the difference between different options.

Jim
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Old 2018-02-16, 08:49 AM   #24
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Originally Posted by tholub View Post
Have you done anything to test your model? Because I'm willing start with the assumption that the best riders have settled upon the best setup for their discipline by iterative processes, so if your model disagrees with their intuition, your model may be the thing that's wrong.

Certainly it's true that weight, particularly rotating weight, is a factor in acceleration. But rolling distance between power positions is also a huge factor in unicycle sports. I'd ride a 20" for uni basketball except I'd have to give up 2 inches, which is important in basketball but not in hockey.
Done anything to test my model as in have 10 riders complete 10 runs per wheel and time them all? No, light gates would be needed for accurate acceleration over short distances. However since I am in exercise science I desperately want to.

I compete in the A comp at UNICON and there are around 40 of us in the world who do so, so arguably I could be considered up with the best? However as I know most of the guys I compete against I also know that the majority of riders have not built their own wheels and therefore have not arrived at the ideal setup through trial and error.

They ride whatever wheel build their unicycle came with and whatever tyre is generally accepted to have good grip. Very few people actually tinker with their setups at all. I have 5 of the wheels on the list and have built one other for someone else. So I have actually ridden a large range of them with the main exceptions being the 114mm crank builds. You can definitely feel the difference in acceleration (and control) on the light wheels. It is quite drastic.

The team who got 4th in the German hockey league ride the tyres they do because it matches their team colour of green. Majority of the other riders ride white tyres so they don't have issues with hall hire and marking tyres.






Quote:
Originally Posted by JimT View Post
Pinoclean,
This is an interesting exercise, the whole process takes out some of the human unscientific impressions.

I did look some at the Nimbus Nightrider and Nightrider Light calculations. It looks like the tire size is too small (cells D16 and D17). It has also been reported that the Nightrider Light is larger diameter then the normal Nightrider. The larger lighter tire would tend to reduce the effect of the lighter tire compared to the normal weight tire. I also see that there is no formula in cells I16 and I17. If you copy the formula in cell I15 down to cells I16 and I17 it changes the result significantly in the Angular Acceleration and Inertia x Gear Ratio fields.

I tend to agree with finnspin. The rider is the largest part of the picture and to leave the rider out greatly over calculates the difference between different options.

Jim
Good find JimT I put the 36ers in as an afterthought calculating the radius of the tyre and rim seperately for it. That was why it had a different calculation in the inertia, but you were right that it was incorrect. Apologies about that. I've corrected it by just using the one diameter and dragging the formula down. It is massively higher and that's how it feels to ride, you cant quickly accelerate or decelerate it at all. I haven't measured the diameter of the old nightrider I just used identical values. Also many are reporting lower weights in the new nightrider.

Rider weight makes a difference between riders, but the same rider will still feel the difference between equipment. Technically trials riders could lose 1/2kg of fat instead of taking 1/2 a kg off their unicycle but it still makes a difference in feel to them, my guess because it allows them to tuck the unicycle up quicker.

If anyone builds a light rim/tyre 24" and a regular nimbus 2 24" they will feel the difference the inertia makes to being able to accelerate, decelerate and control the wheel.
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Old 2018-02-16, 04:58 PM   #25
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A unicycle is not a physics problem
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Old 2018-02-16, 06:44 PM   #26
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Originally Posted by Pinoclean View Post
Done anything to test my model as in have 10 riders complete 10 runs per wheel and time them all? No, light gates would be needed for accurate acceleration over short distances. However since I am in exercise science I desperately want to.

I compete in the A comp at UNICON and there are around 40 of us in the world who do so, so arguably I could be considered up with the best? However as I know most of the guys I compete against I also know that the majority of riders have not built their own wheels and therefore have not arrived at the ideal setup through trial and error.

They ride whatever wheel build their unicycle came with and whatever tyre is generally accepted to have good grip.
Unicycle hockey has been a competitive sport for over 30 years. It is true that not every rider spends time trying different setups, but hundreds of riders have played hockey on many different types of unicycles. The conventional wisdom that 20" is better than 24" is based on long experience. Any suggestion that 24" might be better should be treated with skepticism; the null hypothesis is that the conventional wisdom is correct.

It's like bike hardware. Every now and then someone comes up with the idea that recumbents, or elliptical chainrings, or solid tires are better for biking. All of these ideas were tried and discarded 100 years ago in favor of what we now know as the bicycle. It's not that recumbents have no advantages over diamond-frame bicycles; it's that their disadvantages outweigh the advantages in most situations.

Quote:
If anyone builds a light rim/tyre 24" and a regular nimbus 2 24" they will feel the difference the inertia makes to being able to accelerate, decelerate and control the wheel.
Yes, of course. That doesn't mean it will be better than a 20" for unicycle hockey.
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Old 2018-02-16, 08:35 PM   #27
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Originally Posted by tholub View Post
Unicycle hockey has been a competitive sport for over 30 years. It is true that not every rider spends time trying different setups, but hundreds of riders have played hockey on many different types of unicycles. The conventional wisdom that 20" is better than 24" is based on long experience. Any suggestion that 24" might be better should be treated with skepticism; the null hypothesis is that the conventional wisdom is correct.

It's like bike hardware. Every now and then someone comes up with the idea that recumbents, or elliptical chainrings, or solid tires are better for biking. All of these ideas were tried and discarded 100 years ago in favor of what we now know as the bicycle. It's not that recumbents have no advantages over diamond-frame bicycles; it's that their disadvantages outweigh the advantages in most situations.



Yes, of course. That doesn't mean it will be better than a 20" for unicycle hockey.


But my maths doesn't say that a 24 is better than a 20, it purely says a good 24 setup is better than a bad 20 serup. If you look at it the top 3 Unicycles om the graph are all well built 20's

It enables someone to Compare the setup they are riding to an alternate setup (in the same wheel size even).

Using a racing bmx rim vs a nimbus 2 rim is like 305 vs 505 grams and a racing bmx tyre vs the one most use 375 vs 740grams. These things make a difference.

And what technology was available has changed drastically over 30 years. Yes a 20inch is decided on as being better than as 24 because it is (and which my maths agrees with).

Is a heavy crap setup of a 20 better than a racing bmx setup of a 24? Can current riders make their unicycle ride better by a simple change of tyre? That is what hasn't been mucked around with enough.

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Old 2018-02-16, 09:24 PM   #28
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Is a heavy crap setup of a 20 better than a racing bmx setup of a 24? Can current riders make their unicycle ride better by a simple change of tyre? That is what hasn't been mucked around with enough.
I'm pretty sure that the best unicycle hockey player in the world will still be the best unicycle hockey player in the world on a heavy crap setup of a 20. And that I will still suck at unicycle hockey on a racing bmx setup of a 24, or whatever other unicycle you put under me. And I'll be better than you at basketball no matter which unicycles we're using.

The difference between riders is so much greater than the difference between unicycles that the unicycle setup is in the noise.
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Old 2018-02-16, 10:14 PM   #29
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I'm pretty sure that the best unicycle hockey player in the world will still be the best unicycle hockey player in the world on a heavy crap setup of a 20. And that I will still suck at unicycle hockey on a racing bmx setup of a 24, or whatever other unicycle you put under me. And I'll be better than you at basketball no matter which unicycles we're using.

The difference between riders is so much greater than the difference between unicycles that the unicycle setup is in the noise.
I think you are failing to grasp this concept. This is saying that the best unicycle hockey player in the world will likely be better than his current self on a better unicycle, and gives you way to compare the two UNICYCLES for handling. Most riders want to perform as good as possible each time. Handicapping yourself with a wheel that through huge inertia cannot accelerate as fast for a given torque probably is not conducive to that rider being the best player they can be.

This is why track cycling spend millions of dollars to find the best setup and equipment for their riders. You can't necessarily make your rider better than someone else through equipment alone but you sure as shit don't want your rider on a bike with the aerodynamics of a schoolbus.


Nowhere does this say that equipment will make you a better player than someone who is currently better than you or vice versa. It doesn't say that the worst unicycle hockey player in the world on a good unicycle will be better than the best unicycle hockey player on the worst unicycle, that would be idiotic.

If you get two players who are almost identical in riding ability and skills then could it make a difference? Who knows. But as long as a rider knows he is riding the best setup possible then he doesn't need to worry bout that fact.
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Old 2018-02-17, 12:58 AM   #30
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I think you are failing to grasp this concept. This is saying that the best unicycle hockey player in the world will likely be better than his current self on a better unicycle, and gives you way to compare the two UNICYCLES for handling. Most riders want to perform as good as possible each time. Handicapping yourself with a wheel that through huge inertia cannot accelerate as fast for a given torque probably is not conducive to that rider being the best player they can be.

This is why track cycling spend millions of dollars to find the best setup and equipment for their riders. You can't necessarily make your rider better than someone else through equipment alone but you sure as shit don't want your rider on a bike with the aerodynamics of a schoolbus.
I see the point of your calculation, and indeed, it might be useful to some, and something interesting to play around with. It's helpfull in comparing two setups, especially when two wheelsizes and crank setups are involved. The reason why track cycling spends millions of dollars on testing equipment, however, is that it helps them make many million dollars. That is the world we live in.

What interested me, is tangent to what you were doing, so i took your spreadsheet, modified it, fixed some stuff that is important for my calculations, but not yours (to convert from mm to m, you need to devide by 1000). What I calculated was the force needed to accelerate a 70 kg rider at 5 m/s^2 on different setups, and the force needed to do the same with a 75 kg rider. When leaving out crank setups (using a fixed gain ratio of 1, which would be equivalent as having cranks as long as your tire radius), the difference in force between the two rider weights is huge compared to the difference between different wheelsetups. I used a gain ratio of 1, since I was only interested in the comparison of tire weights, the change different cranks can do is fairly obvious. (I did also calculate the same for including crank length, which might be useful for something, I don't know what though)

Link to my spreadsheet: https://docs.google.com/spreadsheets...it?usp=sharing

Maybe I shouldn't be sharing this now, since I am super tired, and didn't really make it clean and presentable, but I am as sure that there aren't any mistakes in my calculations as someone that hasn't slept a lot in the last days can be at 2 am.

Why did those calculations interest me? Because for me, it's important to see how much of a difference something makes overall. So now I know, the influence of roating mass on your (straight line!) acceleration and deceleration capabilities on 20" and 24" unis is only small.
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