Here is a simplified version of a reasonable power limit, considering both the weight of the rider, and the duration of the effort:
- average your weight with 75 kg. For example, if you’re 75 kg, this stays the same. If you’re 65 kg this becomes 70 kg. This accounts for the fact that efforts on the flats require more W/kg if you’re lighter, and races include both flats and climbing.
- Then apply the power limit: 2.4 W/kg, 3.2 W/kg, 4.0 W/kg.
- This is your critical power limit. For any effort in a race, add 2 minutes to the duration, then determine the average power for that duration. This comes from the critical power formula: APmax = AWC/T + CP, using a typical value that AWC/CP = 1.5 minutes. I round up to 2 minutes to give riders the benefit of the doubt.
So examples:
- if I weigh 55 kg, the average of that and 75 kg is 65 kg, so my limit for category B would be 260W.
- Consider a 8 minute effort. I add 2 minutes and this becomes 10 minutes. Averaging 260W for 10 minutes is the same work as averaging 325W for 8 minutes (power times time is the same). So if I exceed 325W for 8 minutes, I should be an A.
- Consider a 20 minute effort. I add 2 minutes and this becomes 22 minutes. Averaging 260W for 22 minutes is the same as averaging 276W for 20 minutes, so 276W is my limit for 20 minutes.
- Consider a 60 minute effort. Averaging 260W for 62 minutes is the same as averaging 269W for 60 minutes, so that’s my limit for 60 minutes.
- back to a 75 kg rider… the critical power limit for B would be 300 W (the average of 75 and 75 is 75, then I multiply by 4). This becomes 310 W for 60 minutes, 330 W for 20 minutes, or 360 W for 5 minutes.
These numbers could be tweaked, of course, since this simplification would generally increase the power limits for riders in the 50-75 kg range versus what they are now.