MUST WATCH: E-Thirteen Finally Answers the Age-Old Question

[Capricorn]

Porqui: just keep in the mind the difference between the linear and angular vectors; velocity/momentum etc. You are not wrong, but are missing a part of the puzzle.

Edited August 28, 2014 by Capricorn

[Captain Fastbastard Mayhem]

It accelerates till it reaches the top of the wheel where it will be doing 2x the speed you are doing on the bike

then it starts to decelerate. Imagine a small dot on the outer circumference of your tyre and follow its path as you ride

 

Yep. It stays in motion. Otherwise there's no forward momentum on the bike. As long as you're moving forward, the wheel has momentum at all points along its circumference. And at each place in the spokes.

 

AH! There you go. Place the dot on the spokes. At any point in time during the wheel's rotation, does the dot stop? No. Same rule applies to the tire. It's just that the tire contacts a SINGLE portion of ground, as it is rolling. It doesn't stop then roll stop then roll... It just rolls.

 

So yes, it does just touch one portion of the ground at any point in time. But that doesn't mean that the wheel is at rest. It just means that that is the contact point. The wheel continues to move through it's circumference, and then pulls away from the ground. At no point has the wheel stopped.

[Captain Fastbastard Mayhem]

Porqui: just keep in the mind the difference between the linear and angular vectors; velocity/momentum etc. You are not wrong, but are missing a part of the puzzle.

 

Thanks Cap. I knew I was leaving something out of the explanation. Linearly, the wheel, at the contact point, has no momentum. But it has not stopped rotating or slowed down...

[straatvark]

It appear that my 29er wheels should start to turn backwards when it notice a dead stop ahead

[droo]

 

Maybe if a rider wears two of these (on for each wheel) he will be in balance, experience less OTB's and go faster.....the only question is that if you wear two......won't the one cancel the effect of the other?

 

Put them round the hubs before you lace the wheel up and you'll have clean shiny hubs forever too. So much win.

[rudi-h]

stupid experiment. It's hard to believe that whoever went through the trouble of making that rig even thought it is remotely useful, scientific or representative.

 

The major thing (other than weight) that makes a bike faster or slower is rolling resistance which is a function of wheel diameter, tyre pressure and tread pattern. Bearing and seal design in the hubs can also play a role as well as the rubber compound of the tyre, but bearings, seals and rubber compounds are generally not that much different between manufacturers. With road bikes the rim depth and spoke geometry also comes into play when you spend a lot of your time riding at speeds above the 35km/hr mark.

 

Changes in rotational kinetic energy and angular momentum is way way way smaller on the importance scale, unless you ride around your dining room table where you never actually get the opportunity to get up to speed and need to start/stop all the time.

[Captain Fastbastard Mayhem]

stupid experiment. It's hard to believe that whoever went through the trouble of making that rig even thought it is remotely useful, scientific or representative.

 

The major thing (other than weight) that makes a bike faster or slower is rolling resistance which is a function of wheel diameter, tyre pressure and tread pattern. Bearing and seal design in the hubs can also play a role as well as the rubber compound of the tyre, but bearings, seals and rubber compounds are generally not that much different between manufacturers. With road bikes the rim depth and spoke geometry also comes into play when you spend a lot of your time riding at speeds above the 35km/hr mark.

 

Changes in rotational kinetic energy and angular momentum is way way way smaller on the importance scale, unless you ride around your dining room table where you never actually get the opportunity to get up to speed and need to start/stop all the time.

 

It's all of those, actually. A wheel with a heavy rim and light hub will accelerate slower than a wheel of the same overall weight, with a lighter rim and heavier hub. Fact. That's all they were trying to demonstrate.

[MTBeer]

No. the part in contact with the ground retains angular momentum & velocity. It has to. Otherwise you'd have infinite sessions of acceleration to 30kph (assumed speed) and then in the same instant, instant deceleration. You'd be at rest, effectively. That's the ONLY time at which a wheel doesn't have momentum - when you're stopped.

my sarcasm font wasn't working....

[Captain Fastbastard Mayhem]

sorry Porks. I was a tad overexuberant in my efforts to convince you of your misunderstanding. Bashing it in vs coaxing, I think...

[Captain Fastbastard Mayhem]

my sarcasm font wasn't working....

 

Comic sans, man!

[rock]

disclaimer: haven't read everything

 

I though it was common knowledge that, for example, lighter tyres and rims are a better upgrade than lighter hubs? as the parts on the outside of the wheel have more affect in terms of rotational (is that a word?)weight?

[Daniel J Méssem]

I would like the input of an engineer here.

In this experiment the wheels spin around an almost centre point so really spinning

The thing about a wheel that is in contact with the ground is that the tyre is stationary when on the ground but moving at 2X the cycle speed when at the top of the wheel - rolling. It has 0 momentum at the bottom and then momentum increases to a max in 1/2 a circumference. In experiment momentum is almost constant.

How would the forces differ.

 

 

 

many things to take into consideration, I will do a proper calculation sometime, or find one online to review.

Here a a few considerations

 

- 26er wheel needs to spin faster for the same ground speed as a 29er - so if the wheels are the same weight, and the weight is distributed similarly in both, there may be no difference in acceleration

- 29er still has more mass, so will take more force from the rider to get it going (assuming the same tires and rims)

- 29er rims need to be a little beefier to give the same strength as an equivalent 26er

 

Imagine 2 26ers, one with light tires one with heavy tires, this is close to what is happening

 

What would be interesting in the calculations if the actual effect this has on the system as a whole, tires/rims are pretty light compared to rider and bike

[MarcBurger]

TLDR

 

26er: Accelerates faster (good) + Slows down faster (bad*)

29er: Accelerates slower (bad) + slows down slower (good**)

 

*Bad when slower is bad. Not so bad when slow is good (braking before cliffs etc)

**Good for keeping up momentum to overcome small obstacle resistance (force vectors and inertia stuff), bad for cliffs.

 

 

 

[edit]Have to add: 26er good for wallet (no science needed)

Edited August 28, 2014 by MarcBurger

[MTBeer]

Comic sans, man!

yes, forgot about that

[Jigghead]

I would like to see what the effect would have been if the bolts were attached in the same positions and the wheels were proportionately differently sized or even no bolts with proportionately different sized and weighted wheels.

[Erroli8a8]

that experiment shows nothing between 26" and 29". what it shows is that weight further away from the center accelerates slower that's all.

 

if they wanted to show the difference between the two, the weights need to be in the same place, give or take a millimeter for the difference in weight, and the cones need to be of different sizes eg: 2.6" and 2.9". only then can you say that the smaller or larger cone is faster.