Cranck length decision

[Johan Bornman]

Yes a longer crank will increase the torque and hence the power to the rear wheel but by very little

 

Not true, Torque and Power are not related and quite easily confused.

[Johan Bornman]

It can be felt if you move from one extreme to the other, but your overall output, be it torque or power varies very little with a difference in crank length.

 

Also, don't forget, as men get taller their torsos get longer. As females get taller their legs get longer. Therefore dont assume a tall person has proportionally longer femurs to us shorties.

 

Stick with the crank you have unless it is some silly lengh such as 160mm or the hour records 190mm.

 

 

[1kTT]

 

Not true' date=' Torque and Power are not related and quite easily confused.

[/quote']

 

I'm confused, could you pls explain ?

 

[The Guy in Pink]

Where the hell did you get a 180mm from?? I WANT!!

 

If It's Campy you want you gotta go for Record.  totalcycling.com.

 

[Racing Hart]

Not true' date=' Torque and Power are not related and quite easily confused.

[/quote']

I'm confused, could you pls explain ?

 

If torque increases power doesn't necassarily increases! because

power = torque * radial velocity(cadence)

so torque can increase but your cadence would decrease and this could have a slight negative/slight positive effect but in most cases about the same/insignifcant differance.

Racing Hart2008-04-18 10:23:36

[Johan Bornman]

Torque is a measure of a static force and expressed as Newtonmeters. Note, not Newtons per meter but NM. 1 NM = 1 newton of force applied to a lever 1 meter long. It is static and has no time dimension.

 

Power is a measure of how much work can be done per second.

 

It is a bit like comparing a strongman to an 800m athlete. The 800m runner can generate huge amounts of power and maintain it over time, whereas Tarzan can lift a huge weight but only once and instantaneously.

 

I need to work on my explanation, but try to understand in the meantime.

 

 

[zerocool]

INTERESTING

 

 

Interesting to see that most of the riders won the Tour with

175mm ( The tour is won in the mountains or a TT)

 

 

 

Most of the sprinters rode shorter crank?s ( 172.5mm)

 

 

 

Chris Boardman rode 170mm (he is a specialist on the track

where they normally ride 165mm)

 

So there must be benefit in longer cranks for TT?s and

climbing and sprinting the shorter option would be better.

 

 

 

[THE BODY CENTRE]

Yes a longer crank will increase the torque and hence the power to the rear wheel but by very little

 

Not true' date=' Torque and Power are not related and quite easily confused.

[/quote']

 

 

Johan - i understand why you say that torque and power can be confused, but  can you expand on why you say they are not related? I understood power to essentially be the product of the RPM and the torque?

[Racing Hart]

related is the wrong word..the right one is proportional eg boyle's law : pressure is proportional to temperature.

People sometimes think that if torque increase power also increase but this is not the case. Eeven though torque does effect power it depends of radial velocity if power would increase and vica versa..

 

Rather make it simple. Think of a person cycling on a flat keeping the same power. the person then shifts up to a lighter gear and his cadence increases, but he keeps his power the same. This is because the torque has decreased and cadence increased..

Remember power = torque * cadence

 

Okay so to make it a bit more complicated..this person shifts down and cadence decreases, but power stays again the same..because torque has now increased and cadence decreased..

 

The same with crank lenghts..

Longer cranks = lower cadence at the same power = higher torque = more climbing benifit.

shorter cranks = higher cadence at the same power = lower torque = less strain on muscles.

Racing Hart2008-04-18 12:55:46

[1kTT]

 

 

Johan - i understand why you say that torque and power can be confused' date=' but  can you expand on why you say they are not related? I understood power to essentially be the product of the RPM and the torque?

[/quote']

 

that was what I was trying to ask as well

 

[1kTT]

 

 

Rather make it simple. Think of a person cycling on a flat keeping the same power. the person then shifts up to a lighter gear and his cadence increases' date=' but he keeps his power the same. This is because the torque has decreased and cadence increased..

Remember power = torque * cadence

 

[/quote']

 

got it, thats what I had always understood, I thought JohnB was saying something different.

 

[Johan Bornman]

Ronel and 1kTT, look at Racing Heart's explanation. I can't put it better than that other than to add this: You can exert torque (or force for that matter) on something without generating even one watt.

 In order to produce power you need to move a mass whereas to produce torque or force you simply have to push against something. A wall doesn't move when you push against it and therefore you don't generate any power when you do so.

When you do a trackstand, you exert torque on the crank but generate no power.

 

 

[THE BODY CENTRE]

When you do a trackstand' date=' you exert torque on the crank but generate no power.

 

 

[/quote']

 

Correct, but will you be able to generate power without torque (in the above example)?

 

[JasonW]

When you do a trackstand' date=' you exert torque on the crank but generate no power.

 

 

[/quote']

 

Correct, but will you be able to generate power without torque (in the above example)?

 

 

Assuming that you are applying force to the cranks during the trackstand then there must surely be power musn't there? Its just that the force exerted is being offset be gravitational forces, resistance, the brakes, or a combination of these.

 

Will need to try this with a power meter!

[Canaris]

Okay, I think that many explainations are about the mechanics of a formula and only about a single variable.  ie crank length.

 

As the "Engine" is the human who is infinitely variable, it is simplistic to say 175 mm cranks are x or y and 172 mm is a or b.  THe best is to study the human mechanicts of pedaling, and see what the impact on the subject is.(one very specific cyclist-  results may vary)

 

THe human leg is a collection of levers of varying lengths.  THese levels are activated by diferent muscles.  THe important thing is each muscle has a particular "power cycle", where at specific lengths they are able to pull stronger (normally before they are at the extremes of there electicity).  Also with levers, and joints when a joint is bent beyond about 90% it takes the muscle more to work.

 

THerefore, when chosing a crank it is important to study (across various crank lengths) which length bends the joints and stretches the muscles too much or too little, and then find the correct "Window"

 

This obviously assumes that cranks can be too short or too long.

[Johan Bornman]

When you do a trackstand' date=' you exert torque on the crank but generate no power.

 

 

[/quote']

 

Correct, but will you be able to generate power without torque (in the above example)?

 

 

Just for this explanation, consider torque just a force that goes "round the bend" and lets just simplify it to linear force for a moment.  Your question would then be can you generate power without applying a force to a body?

 

No.

 

Why?

 

Power is measured in Watt and one Watt is the lifting of one Newton of weight to a height of 1 meter over a period of one second.

 

Clearly you have to exert a force on this weight to get it to lift. Therefore, if you don't exert a force, it won't lift and you cannot generate power.  Now translate the linear force back to radial force (torque) and you have the same answer.

 

For there to be power (Eskom, pay attention) there has to be work generated over time. If you take away any of the time, distance or weight dimensions you don't have power.

 

 

Johan Bornman2008-04-23 00:00:10