Steepness, gears, cadence, power and such

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The recent post A bit about gearing got me thinking.

Given a certain steepness, a desired cadence and the ability to rock a given amount of power, what should your low gear be?

Method
I did a little basic math and plugged it into this Excel calculator. It’s not as rad as I want it to be, but it’ll do for now.

If you’re a nerd, you must download this. Numbers are FUN!

Assumptions
– Road bike with 34t small ring.

– Bike and rider weigh 200 pounds.

– Grade is 10 percent.

– Pedaling cadence is 60 rpm. Not as spinny as the “ideal” 80 rpm, but still pretty good on an extended remix death march.

– No headwind.

– Looking for fun and feeling groovy.

Results
34t x 28t gear – Rider must sustain 284 watts.

34t x 36t gear – Rider must sustain 215 watts.

What this means
An easier gear requires less power to turn up a steep hill. Duh.

The 34×28 is good for an averagely gifted but decently fit rider. As a matter of fact, my Tricross and I weigh 200 pounds, I run a 34×28, I climb lots of 10 percent grades and I can currently sustain about 280 watts. It’s funny how the math works out.

Last winter before I did my 12-week indoor trainer death interval program, I could only sustain about 220 watts. That 34×36 would have been nice, but I’m glad I trained hard and got stronger.

The moral of this hasty tale: Choosing your low gear has nothing to do with cool factor. How much do you weigh? How steep are your hills? How fast do you want to spin? How much power can you make? Are you looking for fun? Are you feeling groovy?

Download this chick-impressing Excel calculator and run some numbers for yourself.

Braaap!

— Lee

Know more. Have more fun!

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4 replies
  1. ChrisQ says:

    Hey Lee,

    Is there any tangible difference, two gears of equal ratios, say a 36t ring x 18t cog and a 32t ring x 16t cog? Mathematically they give the same ratio of 2:1, but are there other less obvious forces at play here?

    The reason I ask is because I’ve always chosen to ride a bigger ring x bigger cog combination over a smaller ring smaller cog. It’s always felt more responsive when accelerating. I ride with 1 chainring now and I use a 34 because I’ve always thought the slightly bigger ring had a bit more pull in flowing singletrack situations. I don’t really understand torque, so maybe it could be torque. Maybe it could be just the increased number of teeth being used = stiffer? Am I crazy?

    Also, if you get the time, I would appreciate some sort of infographic on things that impress chicks. Maybe just a basic scatter plot comparing Excel spredsheets, scars and bike tricks. Back in the day I used to ride a lot of trials and I am pretty sure that chicks aren’t impressed by bike tricks.

  3. aussie chris says:

    Of course I don’t remember whom, but a paper was done on the efficiency of drivetrains and the biggest loss was the wrap around the derailler jockey wheels – so perhaps if you can run the same ratio use the one that takes up the most chain.

    I did see a photo of a TdF rider’s lower jockey wheel and it was HUGE as suggested in the paper – perhaps to increase the efficiency?

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