cadence

sirdjango

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

rolf_f

Anywhere from 0.1 km/hr if you have a tiny chainring and a cassette ring as big as your rear wheel to 1000 km/hr if you have a huge chainring and only one tooth on your smallest cassette ring.

(it depends on the gear you are in)

PS - why don't you just work it out for yourself - cycle at a constant speed and count how many 360 degree pedal strokes you make in a minute. Increase the speed til you are in the 90-100 cadence range and check your speed.

Herbsman

sirdjango wrote:

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

That question is impossible to answer. IIt depends entirely on what gear you're riding in.

It's easy to estimate your approximate cadence. 90rpm is 1.5 pedal revolutions per second or three every two seconds.

optimisticbiker

Assuming a 700 x 23 wheel and 170mm cranks the maximum speed for a 50 chainwheel and 11tooth sprocket is 51.5kph

Do your own calcs at http://www.sheldonbrown.com/gears/

rolf_f

OptimisticBiker wrote:

Assuming a 700 x 23 wheel and 170mm cranks the maximum speed for a 50 chainwheel and 11tooth sprocket is 51.5kph

What does crank length have to do with it?! 1 revolution moves the bike x inches irrespective of what the length of the crank is.

MountainMonster

How long is a piece of string?

thescouselander

You can get cadence calculator apps on most smart phones (Andriod, Iphone etc) - you just need to know your gear ratio, wheel size and the speed you were going.

I was thinking about developing a simple app so you could stick the phone in your pocket and use the accelerometers to sense cadence from the leg movement.

optimisticbiker

Rolf F wrote:

OptimisticBiker wrote:

Assuming a 700 x 23 wheel and 170mm cranks the maximum speed for a 50 chainwheel and 11tooth sprocket is 51.5kph

What does crank length have to do with it?! 1 revolution moves the bike x inches irrespective of what the length of the crank is.

ummm, it doesn't for this calculation... I was copying it from the Sheldon output and for some reason he includes it... I suspect there were other intended calculations such as power/torque etc which would use the crank length

jim453

sirdjango wrote:

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

25.5 km/h

FSR_XC

http://sheldonbrown.com/gears/index.html

This will give you the answer . . .

FSR_XC

Rolf F wrote:

OptimisticBiker wrote:

Assuming a 700 x 23 wheel and 170mm cranks the maximum speed for a 50 chainwheel and 11tooth sprocket is 51.5kph

What does crank length have to do with it?! 1 revolution moves the bike x inches irrespective of what the length of the crank is.

The longer the crank the further a revolution is - by increasing the diameter of a circle, you increase the circumference, hence a revolution will take you further.

rolf_f

FSR_XC wrote:

The longer the crank the further a revolution is - by increasing the diameter of a circle, you increase the circumference, hence a revolution will take you further.

What about magnet position - does putting the magnet closer to the hub increase my cadence?

PS - we have already done the Sheldon Brown bit in the thread but you might want to experiment with the calculator a bit - try some different crank lengths to see what the difference is

oldwelshman

FSR_XC wrote:

Rolf F wrote:

OptimisticBiker wrote:

Assuming a 700 x 23 wheel and 170mm cranks the maximum speed for a 50 chainwheel and 11tooth sprocket is 51.5kph

What does crank length have to do with it?! 1 revolution moves the bike x inches irrespective of what the length of the crank is.

The longer the crank the further a revolution is - by increasing the diameter of a circle, you increase the circumference, hence a revolution will take you further.

You could put a 1meter crank on and turn it once and while the circumference your foot travels is further the bike will still move same distance as with 160mm craks because the gear ratio is still the same i.e. chainset/rear sprocket.
Maybe we need new style gears where the crank length is changed instead of sprockets and chainrings

optimisticbiker

oldwelshman wrote:

FSR_XC wrote:

Rolf F wrote:

OptimisticBiker wrote:

Assuming a 700 x 23 wheel and 170mm cranks the maximum speed for a 50 chainwheel and 11tooth sprocket is 51.5kph

What does crank length have to do with it?! 1 revolution moves the bike x inches irrespective of what the length of the crank is.

The longer the crank the further a revolution is - by increasing the diameter of a circle, you increase the circumference, hence a revolution will take you further.

You could put a 1meter crank on and turn it once and while the circumference your foot travels is further the bike will still move same distance as with 160mm craks because the gear ratio is still the same i.e. chainset/rear sprocket.
Maybe we need new style gears where the crank length is changed instead of sprockets and chainrings

No you couldn't.....









.... cos the crank would hit the ground and then you'd be lying there on your side looking stupid :roll:

sirdjango

jim453 wrote:

sirdjango wrote:

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

25.5 km/h

tq jim... all i need is just estimation...

rolf_f

sirdjango wrote:

jim453 wrote:

sirdjango wrote:

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

25.5 km/h

tq jim... all i need is just estimation...

Even though it is meaningless? Why do you want to know?

boblo

Jim453 may just have been taking the Mick.... It's probably more like 25.4999999999999999999 km/h :-)

MountainMonster

sirdjango wrote:

jim453 wrote:

sirdjango wrote:

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

25.5 km/h

tq jim... all i need is just estimation...

What gear are you in? That means alot more than cadence. You could have a cadence of 90 going up a mountain in tiny gear, and be going 13kmh. Or you could be in the biggest gear, and be going 40.

MountainMonster

sirdjango wrote:

jim453 wrote:

sirdjango wrote:

i don have a cadence function on my bike computer and don't planning to buy one in the near future. just want to know in what speed (km/h) is for a cadence between 90-100 rpm?

25.5 km/h

tq jim... all i need is just estimation...

What gear are you in? That means alot more than cadence. You could have a cadence of 90 going up a mountain in tiny gear, and be going 13kmh. Or you could be in the biggest gear, and be going 40.

Herbsman

FSR_XC wrote:

The longer the crank the further a revolution is - by increasing the diameter of a circle, you increase the circumference, hence a revolution will take you further.

You misunderstand the basic principles of physics.

P_Tucker

FSR_XC wrote:

The longer the crank the further a revolution is - by increasing the diameter of a circle, you increase the circumference, hence a revolution will take you further.

Brilliant. I remember having a discussion with someone who thought that car, which for the sake of argument could do 120mph flat out, would be able to do 240mph if only tyres were fitted with twice the circumference. Bless.

StageWinner

According to my gear calculator app - the length of the crank changes the 'gear ratio' but has no bearing whatsoever on speed, etc.

Anyone explain what that means in the real world?

MichaelW

Cadence is totally separate from travelling speed and even from your power.
Cadence is the revs/minute of your pedalling.
Work for one rev is the pedalling force x pedalling circumference (crank length x2pi ) in joules
Power is the work / second in watts.

The connection between how fast your feet spin, how how much power you produce and how fast you travel are the sprockets and chains of your transmission.

Assuming that your power output is constant (you cant just magic more power, you can train or take drugs to add a small amount extra but basically, it is fixed):
Assuming your pedalling force is constant (your muscle don't get stronger on demand)
Assuming your crank length is constant.

You can chose a cadence. You then adjust your gears to maintain cadence at your power output and pedalling force over any gradient or terrain or wind.
Travelling speed is the OUTPUT, the dependant variable. It is not an independent input into your cycling equation.

Crank length is part of the gearing in that the longer your crank, the more work you do per rev (at constant pedalling force). If you do more work, you would expect to go further BUT your constant power demands a slower cadence.
Longer crank= slower cadence*
Shortercrank=faster cadence
(adjusting your gears to match for your force/power requirements)

There is no free power and no mechanical/gearing way to go any faster.

In cycling, you use cadence to balance the amount of work done by your heart/lungs and by your legs. If your legs hurt, gear down and spin up. If your lungs hurt, gear up and spin down. If they both hurt, you've got it right.

...............................
* crank length (long/short, med) is best considered relative to your leg length. Whats long for me may be short for you.

Herbsman

StageWinner wrote:

According to my gear calculator app - the length of the crank changes the 'gear ratio' but has no bearing whatsoever on speed, etc.

Anyone explain what that means in the real world?

cranks are levers. levers can be either 'force magnifiers' or 'distance magnifiers'. the longer the distance from the end of the lever to the pivot, the less force is required to move the load at the other end. a shorter lever will require more force to move the load, but the distance that the loadmoves by is higher in proportion to the length of the lever (although the distance moved by the bike remains the same, it's the ratio of crank length to distance moved that changes)

anyway so.... what i meant to say is:
longer crank = more leverage = less effort required to turn the crank per revolution

rolf_f

StageWinner wrote:

According to my gear calculator app - the length of the crank changes the 'gear ratio' but has no bearing whatsoever on speed, etc.

Anyone explain what that means in the real world?

Lets see your gear calculator app. Have you checked to see if changing the crank length makes a difference? Basically, unless your chain is wrapped round your crank, changing the crank length won't change the gear ratio; that is just the difference between the size of the gear at the front that the chain is sat on and that at the back. Neither crank length nor wheel size affect that though the latter does affect how far you travel per pedal revolution and the former how easy it is to make that revolution.