Hi guys. I’m confused. I ride a PowerTap for races and I’m noticing an odd trend in the data. My torque numbers seem to be rising without a material change in cadence or power, which I had thought were all connected. In other words, I thought that if I applied higher average (or pedaling) torque at a higher (average or pedaling) cadence, I would naturally see higher average or pedaling power numbers. But looking at the data below, I’m not seeing that at all.
I listed below my three latest 70.3 races, which were all done on exactly the same bike setup, same helmet and same rider at the same weight.
At Vineman last year I had the following data: 198 Ave. Power, 210 Pedaling Power; 7.27 Ave. Torque, 7.29 Pedaling Torque; 76 Ave. Cadence, 81 Pedaling Cadence.
Oceanside this year I had the following data: 196 Ave. Power, 208 Pedaling Power; 7.95 Ave. Torque, 7.96 Pedaling Torque; 81 Ave Cadence, 86 Pedaling Cadence.
Wildflower this year I had the following date: 202 Ave. Power, 212 Pedaling Power; 9.52 Ave. Torque, 9.52 Pedaling Torque; 79 Ave. Cadence, 83 Pedaling Cadence.
Average cadence and/or average torque may not include zeros while average power does. If you coast more but pedal faster or harder then torque or cadence can go up/down while power goes down.
That if you are using PowerAgent, the torque data are meaningless from a physiological perspective, as that is the torque applied to the hub, not the torque applied to the crank. The relationship between the two depends on what gear you are using, so the only way to know the torque at the crank is calculate it based on power and cadence (or hub torque, cadence, speed, and wheel diameter).
Andrew, thanks for the insight. I’m a big fan of your Training and Racing with Power book. It’s pretty dog eared right now.
I am using PowerAgent to see the measurements. I hadn’t considered the difference between crank torque and hub torque.
So given that it’s hub torque that I’m seeing, is that measurement irrelevant, or is there something to be learned from the fact that it seems to be the only measurement that has dramatically “improved” (or at least changed) since last year?
And FWIW, I seem to be quite a bit faster on the bike this year relative to prior years on the same courses with the same set up – despite no parallel change in power or cadence. Could hub torque be “seeing” a more efficient pedaling motion (i.e. spin scan score)?
If you knew your gearing it may be relevant. You would have to look at your speed and cadence to determine what gear you were in and back calculate a crank torque. You could do it if you wanted to put in the time.
The point of being more efficient is to be able to put out more power with the same energy. You are putting out the same power so it doesn’t look to me that you are improving, you are just possibly pacing better and/or the conditions are more favorable. That is why people look at power numbers because it takes out all the other factors - wind, tires, tire pressure, etc to determine if you are pnysiologically improving (assuming position is the same which could make this not true because a more aero position may be faster with less power).
Hub torque, per se, tells you nothing about your performance as an “engine”. It is useful only to 1) verify that the zero offset of your PowerTap has been set correctly, and 2) understand why your cassette is digging into the body of your ultra-lightweight aluminum cassette carrier.*
If you are going faster this year despite no change in power output, then the physical forces resisting your forward motion must be lower. For example, perhaps you have changed your position to be more aerodynamic, have lost weight, or maybe just the weather has been better. In any case, a lower resistance to forward motion combined with no change in cadence will mean that the torque applied to the hub will also be lower - but you don’t need to know your hub torque to reach the prior conclusion, i.e., your speed and power alone already tell the story.
To understand what is going on with you (versus your equipment), you’d have to calculate the crank torque based on your power and cadence (or alternatively, average effective pedal force based on your power, cadence, and crank length). Please see pages XXX-XXX of the 1st edition of our book or pages 126-142 of the 2nd edition for more info.
*I’d say “…understand why it is so hard to remove your freewheel”, but most people here probably don’t know what a freewheel is.
*I’d say “…understand why it is so hard to remove your freewheel”, but most people here probably don’t know what a freewheel is.
You should have seen the looks on the faces of the mechanics at the bike shop I took an old wheel into because I couldn’t get the freewheel off. You’d have thought I’d brought in an astrolabe or something… :-/
I am just starting to develop the ‘rutting’ of the cassette on the hub casing. Have you noticed it being an issue with getting accurate power numbers or is it completely irrelevant?
Don’t really want to switch it out if I can help it but not at the expense of bad power data.
I am just starting to develop the ‘rutting’ of the cassette on the hub casing. Have you noticed it being an issue with getting accurate power numbers or is it completely irrelevant?
Don’t really want to switch it out if I can help it but not at the expense of bad power data.
IMO, it’s pretty much irrelevant as pertains to power readings. It just makes it hard to get the cassette off later
