Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.carleton
02-24-09, 01:14 AM
(This is a double post, but I figure both sub-forums would benefit)
You ever wanted to know your cadence and only have a computer that tracks speed? Fixed/track bikes are unique in that the cadence is directly related to the speed.
I'll let that sink in for a minute...
I used the Factor Label Method to figure this out. The bottom line is you need to know:
- Chainwheel Tooth count
- Rear Cog Tooth Count
- Speed (current or average)
- A magic number (that corresponds to variable tire sizes)
I won't bore you with the proof of the formula. Just make an excel spreadsheet with 4 fields plus a calculated one.
Field 1: Chainwheel Tooth Count
Field 2: Rear Cog Tooth Count
Field 3: Speed (in MPH)
Field 4: Magic Number Constant (use list below)
Field 5: Calculated as follows
(1,056 * RearCog * Speed) / (ChainWheel * MagicNumber * 3.14159)
That is your cadence!
For example:
Chainwheel: 48
Cog: 16
Speed from computer: 20 MPH
Magic Number: 26.28 (700c wheels with 23c tires)
Cadence = 85RPM
So how can you use this?
Cadence Training:
If you want to follow a cadence training program that says, 60RPM for 2 minutes then 90RPM for 30 seconds that would mean pedal up to 14MPH for 2 minutes then ratchet up to 21MPH for 30 seconds.
Average:
If you have a computer with an "auto" mode that only records average speed when the bike is moving then you can log your average cadence over your ride. Average speed of 15MPH = Average cadence of 64RPM.
Why did I do this?
Bike computers are pretty cheap ($15) even the wireless ones ($25). Wired cadence computers aren't that expensive (around $50), but wireless cadence computers start at $100+. So, using the following you can know your current and average cadence if you have a basic computer that records current and average speeds for about $25. That and I'm bored.
I got these magic numbers from Sheldon Brown's site:
29.13 = 700 X 56 / 56-622 / 29 inch
28.94 = 700 X 50 / 50-622 / 29 inch
27.86 = 700 X 44 / 44-622 / 29 inch
27.32 = 700 X 38 / 38-622
27.17 = 700 X 35 / 35-622
27 = 700 X 32 / 32-622
26.76 = 700 X 28 / 28-622
26.38 = 700 X 25 / 25-622
26.28 = 700 X 23 / 23-622
26.14 = 700 X 20 / 20-622
26.53 = Tubular / Wide
26.38 = Tubular / Narrow
28.15 = 28 X 1 1/2 / 40-635
27.18 = 27 X 1 3/8 / 35-630
27.08 = 27 X 1 1/4 / 32-630
27 = 27 X 1 1/8 / 28-630
26.88 = 27 X 1 / 25-630
You ever wanted to know your cadence and only have a computer that tracks speed? Fixed/track bikes are unique in that the cadence is directly related to the speed.
I'll let that sink in for a minute...
I used the Factor Label Method to figure this out. The bottom line is you need to know:
- Chainwheel Tooth count
- Rear Cog Tooth Count
- Speed (current or average)
- A magic number (that corresponds to variable tire sizes)
I won't bore you with the proof of the formula. Just make an excel spreadsheet with 4 fields plus a calculated one.
Field 1: Chainwheel Tooth Count
Field 2: Rear Cog Tooth Count
Field 3: Speed (in MPH)
Field 4: Magic Number Constant (use list below)
Field 5: Calculated as follows
(1,056 * RearCog * Speed) / (ChainWheel * MagicNumber * 3.14159)
That is your cadence!
For example:
Chainwheel: 48
Cog: 16
Speed from computer: 20 MPH
Magic Number: 26.28 (700c wheels with 23c tires)
Cadence = 85RPM
So how can you use this?
Cadence Training:
If you want to follow a cadence training program that says, 60RPM for 2 minutes then 90RPM for 30 seconds that would mean pedal up to 14MPH for 2 minutes then ratchet up to 21MPH for 30 seconds.
Average:
If you have a computer with an "auto" mode that only records average speed when the bike is moving then you can log your average cadence over your ride. Average speed of 15MPH = Average cadence of 64RPM.
Why did I do this?
Bike computers are pretty cheap ($15) even the wireless ones ($25). Wired cadence computers aren't that expensive (around $50), but wireless cadence computers start at $100+. So, using the following you can know your current and average cadence if you have a basic computer that records current and average speeds for about $25. That and I'm bored.
I got these magic numbers from Sheldon Brown's site:
29.13 = 700 X 56 / 56-622 / 29 inch
28.94 = 700 X 50 / 50-622 / 29 inch
27.86 = 700 X 44 / 44-622 / 29 inch
27.32 = 700 X 38 / 38-622
27.17 = 700 X 35 / 35-622
27 = 700 X 32 / 32-622
26.76 = 700 X 28 / 28-622
26.38 = 700 X 25 / 25-622
26.28 = 700 X 23 / 23-622
26.14 = 700 X 20 / 20-622
26.53 = Tubular / Wide
26.38 = Tubular / Narrow
28.15 = 28 X 1 1/2 / 40-635
27.18 = 27 X 1 3/8 / 35-630
27.08 = 27 X 1 1/4 / 32-630
27 = 27 X 1 1/8 / 28-630
26.88 = 27 X 1 / 25-630