I am taking a highly analytic approach to Full Frontal Gear Selection. While perhaps too revealing of my inner nerd, I thought I’d share.
I’m getting ready for my first Full Frontal tomorrow. As recommended, I did some open rides and experimented with level mode. What I really wanted was a chart that showed me power at various gearing combinations and cadence to help me sort out what gears (and cadence) I need to be in to be around my expected power (and how much I need to change cadence to go up or down in smallish increments). Because power numbers go wild when you’re changing cadence or shifting (and the flywheel isn’t a steady state), knowing the steady state numbers ahead of time seems like it will be helpful.
Because I couldn’t find any useful data, I did some experiments and collected my own.
(Perhaps the minions could publish something like this for the most popular trainers.)
My goal was to estimate a formula formula that expresses power as function of rear-wheel/cassette RPM at different trainer levels at steady state (i.e. the flywheel is at steady speed). Armed with the formula, anyone could put in their own gearing ratios to sort out the best gears for their power targets. Based on my abilities, I estimated the formula for Level 1 on the KICKR using data from riding 30 seconds in each gear at steady cadence and then measuring average power and cadence once the numbers calmed down. Assuming that power increases with the square of rear-wheel RPM (which fit my data best and I think is theoretically how the power curves work on the KICKR–but I’m not certain), here’s what I got for my KICKR in Level 1. Observing that Rear-Wheel RPM = Gear Ratio * Cadence,
Level 1 Steady State Watts = 0.0039 * (Gear Ratio * Cadence)^2 + 13
where Gear Ratio is simply the ratio of teeth on the chainwheel to teeth on the cog for the gear you’re in (e.g. if you’re in the 36 tooth chainwheel and 17 tooth cog, the gear ratio is 2.118). For the statistically inclined, the R^2 using that formula was 98%. Since I couldn’t hold a steady cadence in the really big gear ratios, I couldn’t expose my estimate to those. It would have been better if I could have.
Using that formula, I calculated a table for a couple different cadences that I hope to use to help me select gearing and cadence ranges for the various efforts in Full Frontal. Since small changes in cadence can cause pretty big changes in power (relative to my targets), I expect to change cadence to adjust for my ability as I go. But for that to work, I need to be in the right gear. Here are a couple tables showing power in different gear ratios for a 90 and 95 RPM cadence respectively.
Has anyone else done something like this? Could the minions help make it better?