Instructables
Cadence is the speed at which the pedals turn, measured in Revolutions Per Minute.
Inexperienced riders tend to pedal too slow which will put stress on their knees.

I always wanted to know how fast I was pedaling but I didn't
want to spend a lot of money to do it. Most experienced riders
have a Cadence of 70 to 90 RPM's. When I started using the meter
I found 60-80 to be my norm, but since then I moved up into the
70-90 range without realizing it.

Here is my solution for less then $12 and super easy to do.
 
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Step 1: $10 Cycle Computer

Picture of $10 Cycle Computer
I bought this at Walmart, but many other
stores carry them. They are very accurate
and simple to use. They also turn on
automatically when the magnet passes
the sensor.

It will also record your maximum and
average Cadence plus the number of
times the crank turned. It will also
keep track of the time you are actually
pedaling. When compared with the time
on the speedometer it will tell you
how much coasting you did.

The only drawback is the meter only
reads to 99.9, but you can set it to read
1/2 and remember to double the reading.


Step 3: One Dollar Magnets

Picture of One Dollar Magnets
RADIO SHACK MAGNETS.jpg
I picked these up at a Dollar store.
You can use about anything, just
check that they are fairly strong.

Phil B found 1/2 inch ceramic magnets
at Radio Shack for $1.99
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m.p1 year ago
How to calculate de cadence in te crank arm with 1 magnet. The arm messures is 160cm
Not all chain ring bolts are steel, some are aluminum. Thus magnets will not stick to them. Realistically this whole thing cost you $22 after purchasing 2 computers. You might be better off (a little less complicated too) just buying a $45 cadence computer like this one: http://www.rei.com/product/751831

No sense reinventing the wheel!
Also this will allow you more handlebar space for lights etc. Especially since the above computer can be stem mounted as well.

Also using the hose on your bike, especially in the area of your bottom bracket/crank is not advisable. This could force water into the bearings and cause rust / corrosion.
If your magnet has a hole in the middle, you can run a zip-tie through it, through the chain-ring, around one of the spider arms or around one of the arms of the chainring if it is a pinned crank.
Sailor Bob (author)  thatcherthatch6 years ago
I agree with you the Cat Eye Strada is a nice computer, but I didn't want to spend anymore then I had to. I pulled another computer off of one of my other bikes to see if it would work and I liked it so much I think I'll keep it the way it is. I like the big readout you get, plus it shows your average Cadence which the Strada wont do. I did put a dab of rubber cement on the magnets to help keep them there. No problem they just peel off if needed. I find myself watching the cadence meter more the the speedometer though, it has really helped on the climbs. I don't think a lot of people want to spend $45 for a computer for their $100-200 bike but they probably already have a speedometer. This was just a cool project for #12.
JJJordan6 years ago
Dude, that's awesome, totally geek! I really appreciate it, but it is not as cheap as it looks like (you can get cheap cadence capable cycle computer for less than $40 herehere). But if you already have computer, than this might be your cadence meter... So it doesn't really worth it (except the tickle that you got your bike geeked by yourself) and is not reliable reliable - I think zip ties are one of the greatest human inventions.
Oh, and something else - if you want to have a heart rate monitor too, than your handle bar will look more like the Maltese Falcon dashboard'Maltese Falcon' dashboard

But I really like your "not in a box" style thinking.

P.S. I am not an expert, but I've heard that 90rpms is recommended speed for normal ride, about 100rpms is for sprints and uphills and 80rpms is when you want your legs to rest (at downhill or flat).
It depends a lot on the bike and purpose. On casual touring rides I usually pedal around 50-80 for most of the flats, and around 90-100 for hill climbs (sitting). On my old road racing bike, I used to pedal around 90-120, but would drop to around 40-50 for standing climbs. I am not a strong climber.
Using a pedal cadence meter will help you determine your optimal cadence for different situations, and the visible readout will tend to motivate you. It can also help you compile some basic data to see if you need shorter or longer crankarms or a different chain-ring selection.
hintss5 years ago
I have a bell branded cycle computer. the only thing is that it looks different, but the harness, sensor, and magnet that came with it look the ones that came with yours. It also has 2 buttons, and programs in exactly the same way, showing 2124 as default with 4 highlighted, and you also push the right button and push left to go to next digit. Everything else is also the same. Do you think one brand copied off another?
They are likely made by the same company in China and rebranded.
kgtateddy6 years ago
i dont get why you use 5 magnets instead of just one..... like on the wheel can someone explain me??
For each revolution of the device measured (wheel or crank arm), the magnet triggers the computer that 1 revolution has been made, and it calculates speed from how many times per minute the magnet triggers it and multiplies by a formula.
each gear operates differently it can change the way it calculates the speed
See my comment below. I used one magnet stuck in the crank arm recess at the end of the left pedal. I programmed the cyclometer for a wheel size of 1667. It worked great. I ignored the decimal point for a direct reading of my cadence. I think the author used multiple magnets so the two display numbers would both be large, not the smaller decimal place number. He said the sun may glint off of the screen and make the smaller number hard to read. I did not have enough wire to reach the handlebar and mounted the display unit on my top tube near the headset. My body shields the display unit from the sun. It worked for me that way. I was concerned that magnets stuck to the caps of the chainring bolts could come off if I hit a big bump on the road. The recess at the end of the crank arm seemed like good insurance.
gdl12285 years ago
i have a question will it work on a go cart??? if so, what should i enter as a wheel size??
It can work on a go-kart, but you will need to mount the magnet on the wheel or driven cog. If you want to calculate ground speed, enter the number of MM of your wheel circumference (mark ground and tire with chalk and have someone push the cart with you on it, and mark 2 revolutions out, then divide by 2, for accuracy).
If you want RPM, mount the magnet on the driven wheel or gear and enter 2682 and select MPH. Ignore the decimal point.
Jodex gdl12284 years ago
It depends on your wheel's size.
Put 2682 into it for "MPH" It will read out your RPM (of the crank, with magnet on crank) as 5.5 MPH for 55 rpm. http://www.youtube.com/watch?v=qrL476g662I
karakris4 years ago
Hey, I've just purchased a cycle computer for less than $8.00 that shows wheel cadence, and the same bunch of other things. Just glued the magnet on the crank, and voila! No need for additional magnets.

I'm new to Instructables, so I don't know whether it's okay to post links. Just PM me and I'll tell you.
postg the link anyway...
I built with only one magnet attached to the crank arm. Set it using MPH and it can read in increments of 2 rpm by making use of the decimal. 7.0 = 70 20.0 = 200 etc. these computers only read in fifths of a mile per hour, hence it increments at 2rpms. but yes this idea works well, with the added benefit of tracking average cadence and max cadence.
and for the persnickety riders, 1magnet means less weight than 4 or 5 magnets :D
In order to do it this way, what wheel size do you have to set the comp. to? Also, what do you mean it increments at 2 rpms? You mean it won't count lower than 2rpm? (If so, who cares.) Or, do you mean, you have to divide your number in two? Sorry for being so dense, I (literally) have sort of a mental block when it comes to simple math.
Phil B6 years ago
I made one of these for a 2nd bike I have in the city where our children live. The magnet was stuck onto the inner end of the left pedal spindle. There was no recess for it to sit in. Somewhere I hit a bump and lost my magnet. Now I am moving the sensor a little closer to the bottom bracket and fixing the magnet more pernamently to the crank with electrical tape. It will also sit in a recess in the pedal casting.
Sailor Bob (author)  Phil B6 years ago
I stopped in at the local Family Dollar store to pick up another set of magnets to use on my comfort/trail bike. I have been riding rails/trails more lately because it's cooler and there is more shade. I glued the magnets to my road bike chain ring just to be safe and will do the same on the 2nd bike. I may just move the computer over to the other bike instead of buying another one. I have been using the Cadence meter for a month now and like you have noticed an improvement on my speed and time. I knocked off 15-20 min from my 22 mile trail ride without even noticing it. I looked back at my data and couldn't believe it.
I got 1/2" round ceramic magnets at Radio Shack. They are $2 for five (stock #64-1883). They save breaking apart the plastic or ceramic from a refrigerator magnet. I have also noticed that tired is tired. If I am fatigued, it becomes harder to hold a higher cadence, even in a lower gear. In the comment above I should have said the magnet will sit in a recess in the crank casting, not the pedal casting.
Sailor Bob (author)  Phil B6 years ago
Phil B6 years ago
This cadence meter has changed my riding for the better. If I ride hard, I can often do my normal 14.4 mile route in 60 to 65 minutes. Tonight I should have been a little tired, but I rode while trying to keep my cadence at 85 to 95 rpm. Sometimes it dipped to the high 70's. I found myself shifting earlier and more often than usual. But, my overall speed was higher and I did my usual course in 56 minutes and 47 seconds, which is my best time ever. And, I am probably do not feel as tired as normally.
Geordiepom6 years ago
Perfect timing for me. I just bought a similar unit and the magnet flew off the spokes 1st time out. Now I've seen this idea I can get either another meter and do what you've done or just fix the existing one with a fridge magnet. Thanks!
LightSpeed16 years ago
Ingenious adaptation of available cheap technology! Thank you for the suggestion. Locally, that bike computer from Walmart (I already have two) sells for under $9 each and is 10x more accurate than many models ten times the price since you can set it to mm circumference (others only do cm). I recommend it. Another alternative is to know what gear you are in and calculate the gear inches of the gear to determine the speed you have to maintain in that gear to be doing your optimal cadence. For instance, my third gear is 83 GI. At 90 rpm cadence, I am going 22.2 mph. If I am going slower, I am under 90 cadence. All I need is to memorize (or make a handy chart taped to my top tube) that number for each gear to have a guide. For 70 rpm, it is 17.3 mph. So to be in my range in third gear, I need to be going between 17 and 22 mph while pedaling. This way one speedometer is all you need. But you have to do the calculation and remember the ranges. Your method is easier to remember. Thanks for your instructable!
Phil B6 years ago
I did this and it works very well. I used one magnet and set the wheel size for 1667. The magnet rests very nicely in a little recess at the end of my left crank and sticks to the end of the pedal. I made a heavy wire attachment to hold the pickup coil in place. This attachment uses the water bottle screws on the seat tube.

I went for a ride this morning and memorized my speed, gear, and cadence reading. Then I fed it through the following formula and it shows the cadence meter to be quite accurate. Cadence = 336 x mph/gear in inches. 336 is a constant.
Sailor Bob (author)  Phil B6 years ago
Good Job

After I got mine setup I printed out a Cadence
gear ratio chart from here. You can cut it
out and tape it to your bike.
http://www.sheldonbrown.com/gears/
rseymour6 years ago
Cool, relatively easy hack. Thanks... added to my list of things to try.
jmshnsy6 years ago
Thanks for a really good idea. I notice that your computer has 3 digits to display the speed; so if you used 1 magnet and programmed the wheel circumference to 1667mm(?) the computer would display 1/10 of cadence... 126rpm would read 12.6 km/h this both simplifies the setup and allows all normal pedal speeds to be displayed.
Sailor Bob (author)  jmshnsy6 years ago
Your theory is good ,but in reality its hard to read the tenth's. Any sunlight or reflections make it almost imposable sometimes. When I first set it up I had 2 magnets and used 4166 as the circumference and had to double the reading. I stayed between 30 and 40 (60-80 RPM). Now I am running 70-90 RPM 60 just feels too slow now, but when I get up around 99 I find myself starting to bounce. I know some of the complaints on the some of the Cadence computers is the readout is too small for the Cadence. The Cat Eye Astrale would let you switch the Cadence to the larger display. If I start having a Cadence over 100 RPM's I'll just set it up to double the reading. Don't be fooled by the price of this computer, it's very accurate and durable if you set it up right.
Congratulations for being on Lifehacker!
Sailor Bob (author)  Yerboogieman6 years ago
Thanks
Nkevin906 years ago
awesome!
richelton6 years ago
Very cool idea. I have this exact gizmo (got it at the same store you mentioned) but never thought of using TWO of them. Thanks!
Julesomega6 years ago
Good move to use black ties - the white ones disintegrate under sunlight. Black pigment stops UV penetration, giving a life expectation of decades. Same with rubber, hence black tyres
kington996 years ago
Might be necessary to check how high the wheel circumference on your bike computer will go before buying it, my and other's experience from riding 36" wheels is that some computers won't let you set them above about 3000mm.
36" wheels? Really? Largest I've seen is 29" - and that's not that common...
yes, 36" wheels are very common for distance unicycling.
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