why clincher more pricey???

[Prince]

 

I think the answer to this is either 42

 

?

 

?

I agree' date=' seeing that the ultimate question has not been posed yet it could be C.[/quote']

 

 

 

 

 

"You are not going to like the answer" - Deep Thought

[Johan Bornman]

 

It is always an interesting discussion when it comes to wheels.  The fact is lighter wheels feel a bit faster and the cool sound that deep section wheels make is probably also part of that sensation.  However' date=' I find it really difficult to justify paying 10x more for a set of wheels simply for an actual improvement (as demonstrated) of nothing and a marginal improvement in the wheel "feeling" faster.

[/quote']

 

I agree with you. Acoustic feedback contributes a lot to the sensations we perceive. I once found a nice set of semi-OK Vredenstein Fortezza (?) tyres in a dumpster outside a bike shop and fitted them. They sounded incredibly fast and I loved their thin, fast whine.

 

However, if you look at the figures, their RR was about 1 gram at 40kph less than what I had on before and therefore I didn't really feel any difference.

 

This shrink-factor has of course a role to play in the mind games of top-class athletics but me....I just cruise around the block.

 

 

[Jules]

JB, I'm no expert, but your calculation assumes the nipples are travelling at 30kph. Surely they are going much faster than that?

[Jules]

To add to this:

 

 

 

A nipple at the centre of the wheel is going slower than a nipple at the perimeter of the wheel at the same bike speed. This is because a nipple at the centre of the wheel has a far shorter distance to travel.

 

 

 

Therefore your calculation would have to work out the difference in speed between a nipple at the centre and a nipple at the perimeter at 30kph.

[Johan Bornman]

To add to this:

A nipple at the centre of the wheel is going slower than a nipple at the perimeter of the wheel at the same bike speed. This is because a nipple at the centre of the wheel has a far shorter distance to travel.

Therefore your calculation would have to work out the difference in speed between a nipple at the centre and a nipple at the perimeter at 30kph.

 

It's all factored in. Unless this is one of those Mud Dee trick questions??

[Wyatt Earp]

I vote we leave Mud Dee out of this, Jules makes a valid point, how do we clarify ?

 

Caadman

 

Picture a 42 C, can you feel it

 

[Jules]

JB, not a trick question. The only difference I see in your two calculations is 400g for the wheels.

 

 

 

The speed is 30kph in both calculations, as far as I can tell.

[Nancy Drew]

I think the answer to this is either 42

 

 

I agree' date=' seeing that the ultimate question has not been posed yet it could be C.[/quote']


"You are not going to like the answer" - Deep Thought

 

cool!! a Douglas Adams thread.... about nipples, the answer to life, the universe and everything

[Kiwi]

http://www.analyticcycling.com

 

http://www.analyticcycling.com/AnalyticCyclingLogo.gif	http://www.analyticcycling.com/WheelsConcept_Heading.gif

---

How much does a wheel's weight, rotating inertia, and drag affect performance? Topics on this page: Magnitudes of the Forces and Measurements Wheel Aerodynamics Table of Coefficients of Wheel Drag Wheel Rotational Inertia Table of Wheel Inertia and Mass Equations of Motion Forces on Rider Wheels are a small portion of the forces on a bike and rider. The differences between wheels are small. Ordinarily power can be measured to what is normally a small tolerance, say plus or minus 3%, maybe plus or minus 1% under ideal conditions. As the table below shows, a typical difference between wheels may be 1% or less. Clearly, another approach, other than direct power measurement, is needed. The table below gives typical values for the forces on two riders. The Standard Rider is on 32 hole standard wheels and the Test Rider is on Specialized tri-spokes. Forces are in grams of force since such forces are often quoted that way.    Standard Rider  Test Rider    Force (gmf) % Force (gmf) %  Speed (m/s)  10.76    10.76   Total Force on Rider  2337  100  2287  100 Wind Resistance  1811  77.5  1811  79.2 Rolling Resistance  304  13.0  304  13.3 Gravity Force  0  0  0  0 Drag on Front Wheel  127  5.4  98  4.3 Drag on Rear Wheel  95  4.1  74  3.2 Wheel Aerodynamics A paper by D. I. Greenwell, et. al., entitled "Aerodynamic Characteristics of Low-Drag Bicycle Wheels", Aeronautical J., Vol. 99, No. 983, Mar. 1995, pp.109-120, has a good discussion of the aerodynamics of bicycle wheels. Conclusions by Greenwell et al: The total drag of the wheels is in the range of 10% to 15% of the total drag on a bike. Drag improvements between wheels can reduce this by 25%, or 2% to 3% of the total drag. Axial drag forces are difficult to measure precisely. Most single valued measurements should be suspect. Deep section aero wheels are better than a conventional 36 spoke wheel and are all about the same within the limits of measurement. Disk wheels are better yet. (Don't run a disk in front if there is any chance of wind.) The rotational drag on a wheel does not change as speed changes or with different wheels. The drag on the rear wheel is reduced by 25% due to the seat tube. The forgoing applies to zero yaw angle. Read the paper if you want to know the results for non-zero yaw angles.   http://www.analyticcycling.com/WheelsConcept_WheelFor1Blue.gif     Coefficients of Drag Reported for Various Wheels (1)      Wheel  Cxo Conventional 36-spoke 0.0491 Campagnolo Shamal 16-spoke 0.0377 HED CX 24-spoke 0.0379 Specialized tri-spoke 0.0379 FIR tri-spoke 0.0382 HED disk (lenticular) 0.0361 ZIPP 950 disk (flat sided) 0.0364   Please note that for the coefficients given in the above table, the conventional wheel is significantly different from the deep-section wheels, and deep-section wheels are significantly different from the disk wheels. However, there is no significant difference between the deep-section wheels or between the disk wheels. Wheel Rotational Inertia It's easy to calculate a wheel's rotational inertia using a kitchen scale, a stopwatch, and a tape measure. The general approach is to measure the time period for a wheel swinging at the end of a pendulum. See Figure 1. From the time period of a swing, one can calculate the rotational inertia of the wheel about the point of rotation of the pendulum. The rotational inertia about the point of rotation of the pendulum can be transformed into the rotational inertia about the center of gravity of the wheel. http://www.analyticcycling.com/WheelsConcept_WheelFor2Blue.gif     http://www.analyticcycling.com/Figure1.gif   Most of the error of the method comes from measuring the period. Timing 100 swings and dividing by 100 gives a good estimate. This minimizes the error of starting and stopping the stopwatch by hand. A pendulum has the property that its period is constant as it slows down. Take care that the wheel swings in the same plane at all times. The method will be invalid if it does not. Go to Calculation of Inertia to calculate rotational inertial for your own wheels. Data on some wheels is shown in the following table. Wheels were complete, meaning they had tires, tubes, rim strips, rims, spokes, hub, skewers, free wheels, just like they would be ridden. As individual components, rims lend themselves to calculation of rotational inertias; tires and tubes don't. There is a large variation between advertised weights and actual weights as manufactured. More real-world, meaningful results come, in my opinion, from measuring wheels in an "as ridden" state. Hence the values here are for fully rideable wheels, just like the ones handed to you from your support vehicle. Rotational Inertia and Mass for Various Wheels  Wheel  Details  Ic (kg m^2) Mass (gm) Wire Spoke Rear, Std Rim, 700, track, 36 spokes, w/o tire, w/ axle, nuts  0.0528 1177 Wire Spoke Front, Std Rim, 700, 32 spokes, w/ tire, tube, rim strip, axle, skewer 0.0885 1264 Wire Spoke Rear, Std Rim, 700, 32 spokes, w/12-21 cassette, tire, tube, rim strip, axle, skewer  0.0967 1804 Specialized tri-spoke Front, 700, w/ tire, tube, axle, skewer 0.0904 1346 Specialized tri-spoke Rear, 700, w/ 12-21 cassette, tire, tube, axle, skewer  0.1032 1771 Specialized tri-spoke Front, 650, w/ tire, tube, axle, skewer  0.0683 1207 Mavic Front, Std Rim, 650, 28 Bladed Spokes, w/ tire, tube, rim strip, axle, skewer 0.0632 1179 MTB Front, 32 Spokes, w/ tire, tube, rim strip, axle, skewer 0.1504 1847 Equations of Motion Wheel weight and wheel rotational inertia matter when a rider and bike are accelerating. Drag matters whenever a rider and bike are moving. It is not enough to estimate rider and bike performance under constant conditions. Differential equations are used to describe motion under transient conditions. Such equations let us evaluate the combined effect of wheel weight, rotational inertia, and drag. The following differential equation, with an appropriate starting point and initial speed, describes the position, speed, and acceleration of a rider over time. Using this equation, a comparison can be made between a "Standard Rider" and a "Test Rider" to see the effect of various alternatives. This is the equations that is evaluated in each of the case studies presented here. http://www.analyticcycling.com/WheelsConcept_DiffEqMotionBlue.gif

 

 

 

 

[Wyatt Earp]

Nancy

 

You are such a hunny

 

[Nancy Drew]

Nancy

You are such a hunny

 

[Johan Bornman]

JB' date=' not a trick question. The only difference I see in your two calculations is 400g for the wheels.

The speed is 30kph in both calculations, as far as I can tell. [/quote']

 

OK then, I'll explain. 

 

The point of my approach is to show that the largest portion of the mass that gets accellerated is the linear portion. We and our bikes weigh much more than a few nipples. Therefore the biggest effort goes into accellerating us. The fact that the few lightweight nipples also has to spin is negligible.

 

 

There are more than one way to approach the problem.

 

I could have said for a given rider with a given power output, riding first one bike, then another, we measure his accelleration or final speed or even final distance after a given effort. We would then have compared that with a similar example using another wheel.

 

I said, forget about power input, accelleration etc (I don't like the date since the sampling rate is only 5 seconds) and lets see how much energy is stored (i.e. was need to get it to a certain speed) in two different wheels fitted to two similar bikes.

 

I therefore calculated the stored energy in a wheel rotating at 30kph (the speed is arbritary but reasonably relevant to our case) vs the stored energy in a similar wheel/s 400 grams lighter going at the same speed.

 

I then added this to the stored energy in the rider and bike and calculated the percentage variance.

 

The speed of the nipples, relative to the road or bicycle is therefore irrelevant and will be the same for both light and heavy wheels. It is only the inertia in the nipples that matters.

 

Does that help?

 

 

[Johan Bornman]

cut cut cut cut cut cut cutalottastuff.....

 

 

And?

[Jules]

Edit: inertia is the wrong word.

 

 

 

JB, we agree that a nipple at the perimeter of a wheel travels faster than one at the centre.

 

 

 

Do we therefore agree that it will require slightly more force to accelerate a wheel that has its nipples at the perimeter?

 

 

 

Just forget weight for a moment. Assume the wheels weight the same. Jules2008-11-28 07:43:05

[Kiwi]

He we go, I cut the relevant bit out for you:

 

Wheel Rotational Inertia

It's easy to calculate a wheel's rotational inertia using a kitchen scale, a stopwatch, and a tape measure.

The general approach is to measure the time period for a wheel swinging at the end of a pendulum. See Figure 1. From the time period of a swing, one can calculate the rotational inertia of the wheel about the point of rotation of the pendulum. The rotational inertia about the point of rotation of the pendulum can be transformed into the rotational inertia about the center of gravity of the wheel.

http://www.analyticcycling.com/WheelsConcept_WheelFor2Blue.gif

 

 

http://www.analyticcycling.com/Figure1.gif

 

Most of the error of the method comes from measuring the period. Timing 100 swings and dividing by 100 gives a good estimate. This minimizes the error of starting and stopping the stopwatch by hand. A pendulum has the property that its period is constant as it slows down. Take care that the wheel swings in the same plane at all times. The method will be invalid if it does not. Go to Calculation of Inertia to calculate rotational inertial for your own wheels.

Data on some wheels is shown in the following table. Wheels were complete, meaning they had tires, tubes, rim strips, rims, spokes, hub, skewers, free wheels, just like they would be ridden. As individual components, rims lend themselves to calculation of rotational inertias; tires and tubes don't. There is a large variation between advertised weights and actual weights as manufactured. More real-world, meaningful results come, in my opinion, from measuring wheels in an "as ridden" state. Hence the values here are for fully rideable wheels, just like the ones handed to you from your support vehicle.

Rotational Inertia and Mass for Various Wheels  Wheel  Details  Ic (kg m^2) Mass (gm) Wire Spoke Rear, Std Rim, 700, track, 36 spokes, w/o tire, w/ axle, nuts  0.0528 1177 Wire Spoke Front, Std Rim, 700, 32 spokes, w/ tire, tube, rim strip, axle, skewer 0.0885 1264 Wire Spoke Rear, Std Rim, 700, 32 spokes, w/12-21 cassette, tire, tube, rim strip, axle, skewer  0.0967 1804 Specialized tri-spoke Front, 700, w/ tire, tube, axle, skewer 0.0904 1346 Specialized tri-spoke Rear, 700, w/ 12-21 cassette, tire, tube, axle, skewer  0.1032 1771 Specialized tri-spoke Front, 650, w/ tire, tube, axle, skewer  0.0683 1207 Mavic Front, Std Rim, 650, 28 Bladed Spokes, w/ tire, tube, rim strip, axle, skewer 0.0632 1179 MTB Front, 32 Spokes, w/ tire, tube, rim strip, axle, skewer 0.1504 1847

Equations of Motion

Wheel weight and wheel rotational inertia matter when a rider and bike are accelerating. Drag matters whenever a rider and bike are moving. It is not enough to estimate rider and bike performance under constant conditions. Differential equations are used to describe motion under transient conditions. Such equations let us evaluate the combined effect of wheel weight, rotational inertia, and drag.

The following differential equation, with an appropriate starting point and initial speed, describes the position, speed, and acceleration of a rider over time. Using this equation, a comparison can be made between a "Standard Rider" and a "Test Rider" to see the effect of various alternatives. This is the equations that is evaluated in each of the case studies presented here.

http://www.analyticcycling.com/WheelsConcept_DiffEqMotionBlue.gif

The best answer is to ride the two types of wheels of the same profile (full carbon clincher and alloy/carbon clincher) back to back so that you have just the rim weight to compare as that was what the original question was.

 

I have the full carbon clincher and can get the same with alloy rim to compare (I also have the same wheel with the tubbie version of the rim if someone wants to compare that) then you just need a bike with a power meter and go and do a race and see for your self.

 

I am sure when teams like CSC, Rabobank and Astana are looking at equipment that is what they do and also why they dont ride heavy wheels.

Kiwi2008-11-28 07:47:39

[Johan Bornman]

Edit: inertia is the wrong word.

JB' date=' we agree that a nipple at the perimeter of a wheel travels faster than one at the centre.

Do we therefore agree that it will require slightly more force to accelerate a wheel that has its nipples at the perimeter?

Just forget weight for a moment. Assume the wheels weight the same. [/quote']

 

Yes, we agree on the first instance.

Yes we agree on the second instance.

 

Yes I have calculated the difference and it is in the formula.

 

Here it is: "The wheel?s rotational energy is also 1/2M*V^2"

And the end result is the difference in force to accellerate the two wheels. It is exactly what this is all about.

 

 

 

 

 

 

.