Climbing wheels??????and physics questions...

[anerobic]

i'm sick of ads proclaiming that wheels are for climbing. how did this come about?
there's nothing special about climbing as far as a wheel goes. yes wieght matters a little as it does over all of the bicycle, but i don't see seat posts described as "climbing seatposts" because they weigh 50 grams less. i'd be very surprised if a 175 lb rider plus a 20 lb cycle could feel the climbing difference in a wheelset that was 100 grams lighter (88530 gms vs 88630 grams)
by the way, can any physicists out there tell me how much contribution 100 grams makes, say, in the rim of a wheel when you are trying to sprint for the finish and you weigh 195 lbs with the rest of your bicycle? or how much energy goes into non aero spokes vs aero spokes in a sprint?

 

[Blimp]

Originally posted by anerobic
i'm sick of ads proclaiming that wheels are for climbing. how did this come about?
there's nothing special about climbing as far as a wheel goes. yes wieght matters a little as it does over all of the bicycle, but i don't see seat posts described as "climbing seatposts" because they weigh 50 grams less. i'd be very surprised if a 175 lb rider plus a 20 lb cycle could feel the climbing difference in a wheelset that was 100 grams lighter (88530 gms vs 88630 grams)
by the way, can any physicists out there tell me how much contribution 100 grams makes, say, in the rim of a wheel when you are trying to sprint for the finish and you weigh 195 lbs with the rest of your bicycle? or how much energy goes into non aero spokes vs aero spokes in a sprint?

my physics are a bit rusty, but it has something to do with the rotating mass of the rim.

I do know that my lightweight wheels make a big difference in comparison to the clunkers that came standard with my bike.

 

[el Ingles]

To be honest I think we´re all getting conned on this wheel thing ; strong , light , cheap -- choose two , that was an advert headline from Tom Ritchey and it´s still true . According to the theory anything that moves should be light to avoid giroscopic effects , but as most modern wheels put mass at the rim to save hub / spoke weight I can´t see any real advantage over good 32 spoke 3 cross wheels , and they are a lot cheaper and most mechanics can maintain them without problems .
ps if you buy those Shimano wheels do get a set of those rim washers that the spokes go through , as when the spoke breaks it tends to snap there and the bit that´s left is a b*gger to remove without damaging said washer

By the way I´ve got a climbing rear wheel --- it´s 32 spoke ·cross with a 13 --28 cassette and a sticky tyre ( for the decents ) , normally I ride 13 --23 with the hardest , most puncture resistant tyre I can find , the cars will keep leaving their windshieds lying about on the roads here.

 

[pillchild]

To answer anaerobic's question about energy use and climbing. You use 52 neutons per kg per metre. So if your wheels are 1kg lighter than the fella next to you and you and you climb one metre (vertical) you will have used 52 neutons less than him.
On the other hand if you have a full drink bottle or a fat gut the advantage dissapears.
Climbing wheels are great for the up but if you need to come down the other side you still want the aero some wheels combine both. I guess people are willing to pay for any advantage, at the end of the day the best riders could still win on a milkmans bike. Who knows whats best? If you like it use it, but at 195 lbs i reckon you bend a climbing wheel first time on the road.

 

[Budarz]

I happen to have read this albeit a bit after it was posted. I also happen to be a physicist/cyclist. The answer to how much wheel weight matters if the weight is all at the rim, it is exactly a factor of 2. In other words, if you save 100g on a rim/tire combo, it's as good as taking 200g off the non-rotating part of the bike. In the end, the effect is quite small either way. One more workout, or an elbow tucked in to aviod the wind would've made more difference at the finish line

 

[pudster]

Some thing else to think about is where the weight of the wheel is. Wheels that have very few spokes and they are aero shaped have all there weight at the rim because the rim has to stay stiff with so few spokes. A 32 or 28 spoke wheel has less weight at the rim and more towards the center. Weight that is as close to the center of a rotating mass fells light er than a wheel with more mass at the outside of the rotating mass feel heavier. I think that is right??? I think that rim weight has more to do with things than wheel weight

 

[larry barr]

All I know is that I sure was faster after I switched to Campy nuetrons from my Mavic open pros, which are built with Record Hubs. The weight difference was measurable as was the acceleration difference. Maybe it is psychological, but I will take whatever edge I can find.

 

[r0161]

all i really careabout is if the whole bike is light enough. 25lbs or less and im good

 

[pineapple]

My guess is that climbing wheels put more emphasis on pure weight rather than gyro effects, since with climbing:

1. The wheels turn more slowly so the gyro effect is diminished.

2. Climbing is against gravity so the effect of pure weight is increased.

Therefore maybe climbing wheels really are suited to climbing rather than flats? That's my guess anyway.

 

[mjw_byrne]

Has anyone considered the stiffness issue? When you climb, the rear wheel experiences high stresses. If they make the wheel flex in any way (say, by stretching the spokes or causing minor amounts of buckling in the rim or hub), the rider's energy is going into deforming the rear wheel. Yes, the deformation is not permanent (i.e. it is elastic, not plastic deformation (you hope!)) but some energy is still lost because as most people know, any deformation (elastic or plastic) of a material heats it up. This applies to frames too, a less flexible frame wastes less of the rider's energy.

Having said all this, I have no idea exactly how much of an effect this has. It could be immeasurably tiny, or it could make enough of a difference that some wheels genuinely are better for climing than other ones of equal mass.

 

[skareb]

I've read somewhere that rotating weight are 3 X greater than dead weight, hence 100 grams on your wheels equals 300 grams on your frame. Of coz power transfer are important too if your spokes are so tiny and it flex then it eats up your energy hence why aero spokes are on most pro rims, they have better power transfer and aerodynamics.

I can confirm about the weight easily when I switch from my Alex rims (weight 550g) to mavic 317 (weight 395g) I can climb the hills I normally train much much easier.

About the aero spokes I've never tried em, perhaps ppl who owns one of those SSC rims can give us a better idea.

 

[TrainingWheels]

Originally posted by pudster
Some thing else to think about is where the weight of the wheel is. Wheels that have very few spokes and they are aero shaped have all there weight at the rim because the rim has to stay stiff with so few spokes. A 32 or 28 spoke wheel has less weight at the rim and more towards the center. Weight that is as close to the center of a rotating mass fells light er than a wheel with more mass at the outside of the rotating mass feel heavier. I think that is right??? I think that rim weight has more to do with things than wheel weight

That's correct. The further away from the centre point of the wheel your weight is the more the weight is felt. The weight multiplied by it's distance from the centre gives you the "Weight Arm". Same reason why holding a metre plank of wood level holding it by the end is harder than by holding it in the middle

 

[vlad]

If your tires weigh 100 grams each, and my tires weigh 1100 grams each would I enjoy a benefical flywheel effect?

granted I would exert more energy getting started, but once inmotion would it take more effort for me to maintain a given speed?

would not my heavier tires tend to remain in motion, once they are in motion??

 

[pineapple]

In theory your heavier tyres have greater inertia (and therfore momentum), both forward and rotational, therefore once going, it would take a greater force to slow them down.

However, heavier tyres usually mean fatter tyres, which means much greater drag on the road surface.

Also the heavier they are, the greater the force they exert on the road. Because in a very basic model F=uR (i.e. fricton F is proportional to weight R), this means that the very fact that they weigh more results in a greater friction. This probably eliminates any advantage of increased inertia.

 

[mjw_byrne]

I've got serious problems with the idea that rotating weight is somehow "more" than non-rotating weight. Can anyone point me at a document/URL with a physical justification for this?

 

[Budarz]

FOr a justification, open any physics text. Look up rotational kinematics or rotational dynamics or rotational kinetic energy. It should be under one of those.
Ultimately rotating weight is only "more" when trying to accelerate or slow down the bike such as sprints to the finish. At constant speed it makes no difference.
A very brief expanation is that to speed up your bike's non-rotating parts all of your energy goes into moving them faster in a linear fashion. For the rotating parts, they not only need to move faster linearly, but energy is required to rotate them faster as well.
Hope this helps.
As a test, take an ice cube and "race" it with a ball that will roll (not slide) down an incline. The icecube will win because gravity does work only to produce linear motion on the icecube. Gravity on the ball is split between linear and rotational contributions... same concept as the bike wheel.

 

[mjw_byrne]

Originally posted by Budarz
FOr a justification, open any physics text. Look up rotational kinematics or rotational dynamics or rotational kinetic energy. It should be under one of those.
Ultimately rotating weight is only "more" when trying to accelerate or slow down the bike such as sprints to the finish. At constant speed it makes no difference.
A very brief expanation is that to speed up your bike's non-rotating parts all of your energy goes into moving them faster in a linear fashion. For the rotating parts, they not only need to move faster linearly, but energy is required to rotate them faster as well.
Hope this helps.
As a test, take an ice cube and "race" it with a ball that will roll (not slide) down an incline. The icecube will win because gravity does work only to produce linear motion on the icecube. Gravity on the ball is split between linear and rotational contributions... same concept as the bike wheel.

Sure, when accelerating, this holds perfectly. But some of the posts in this thread seem to imply that lifting a rotating body somehow takes more effort than lifting a non-rotating body of the same mass, which seems really odd to me.

 

[Budarz]

If they claim that, they're incorrect. No difference unless accelerating. As a trackie I never really think of hills relating to bike weight. Reducing weight for us has only to do with improving one's jump. For hill climbs at constant speed, dead weight or rotating weight is the same.
T

 

[rayner]

Originally posted by vlad
If your tires weigh 100 grams each, and my tires weigh 1100 grams each would I enjoy a benefical flywheel effect?

granted I would exert more energy getting started, but once inmotion would it take more effort for me to maintain a given speed?

would not my heavier tires tend to remain in motion, once they are in motion??

You would exert more energy getting started, but you would also exert more energy throughout your ride. This is because to maintain a constant speed you are constantly (without realising) having to accelerate the wheel due to external factors such as air and rolling resistance. In effect you are accelerating from rest, but on a smaller scale, every time you turn the pedals.

I'm not sure on this one but your tires should stay in motion (on the dead flat) for exactly the same amount of time as the lighter tires. This is because there is an equal weight on both the top and bottom of the wheel so the wheel is accelerating equally as much coming down as it is decellerating going up. For a downhill the heavy tire will obviously go faster and vice versa.

If you like going up hills get a light tire wheel combination and if you like going down 'em get a heay combination.

 

[wrench23]

Step 1. Draw a free body diagram of the bike. You always have acceleration on level ground and hills even without velocity increase (Force = mass*acceleration). On level ground to maintain a constant velocity you must overcome the force of rolling resistance/ frictional forces and any force due to wind resistance. The forces working against you and your bike (and therefore acceleration associated with them) increase on a hill due to gravity. On level ground gravity is normal to you and your bike, going up a hill it has both a normal component (gravity*sin(angle of the hill)) and a component working against you at the angle of the hill (gravity*cos(angle of the hill)). So in order to keep a constant velocity going up a hill you have to equal the acceleration of the frictional forces/rolling resistance, wind resistance AND the new component of gravity that is working against you.

You know the basic answer you would find in an introductory physics book.

This all boils down to rotating mass (wheel weight) actually does matter more on hills than it does on the flats because you are actually having to put more force ( and since your mass stays the same, this means more acceleration) to stay at a constant velocity on a hill.

Hope this helps someone.

I've got serious problems with the idea that rotating weight is somehow "more" than non-rotating weight. Can anyone point me at a document/URL with a physical justification for this?