This week I’m going to explain all about power-to-weight ratio. For example, if 2 riders have a similar functional threshold power then the lighter rider will have the better P/W and will generally be faster.
To calculate power/weight ratio you need 2 figures: Functional Threshold Power (which I explained last week), and bodyweight in kg’s.
For the sake of this article and some simple maths, lets say your FTP from your test result was 300 watts. If your bodyweight is 75kg, then the power-to-weight ratio is 300/75 = 4 watts per kg.
Lets go back to our rider who weighs 75kg. Remember he has an FTP of 300 watts and a P/W of 4watts/kg. If our rider loses 3kg to get down to 72kg and his FTP remains at 300, his new P/W is 300/72 = 4.16. This means our athlete gained .16 watts per kg of bodyweight. (4.16 vs 4.00). Multiply this figure by the bodyweight, (0.16 x 72) gives a figure of 11.5watts. Our rider effectively gained 11.5 watts just by losing weight.
Looked at another way, if he had remained at 75kg then he would have had to gain 11.5 watts to go faster. Thats almost a 4% gain in watts (at 300 watts, 3 watts = 1% so 12 watts would equal 4%). This would take the average athlete approximately 6-8 weeks to achieve, and it would certainly be a lot harder work than having a disciplined knife and fork.
But, what if our athlete had been able to gain a few watts in FTP at the same time as losing weight? His training goes well and he gains 10 watts in power. Now his FTP is 310 and his new bodyweight is 72kg 310/72 = 4.30 watts/kg. So he is now .30 watt/kg better off than before which in real terms is a gain of 21.6 watts. My estimation is that 20 watts is equivalent to approximately 0.5mph, which over 180k is a gain of 9 minutes, or over 40k a gain of around 2 minutes. Either way training hard and losing a bit of weight is a double win and one that is within the grasp of most cyclists.
High Performance Coach