All very true. Also, since we measure W/kg with body mass alone, given equal W/kg the heavier rider will also be a bit faster on the climb. The equipment that a heavier rider carries may be slightly heavier than for the lighter rider, but not in proportion to mass.
I was interested in the impact of weight alone. In the GCN video the same rider needed 50 W more for the same performance. So that was counter intuitive, but could be explained by increased drag from the vest and the rolling terrain.
My own experience is that when my weight goes up 6 kg I tend to be a bit slower on flat roads. Then as I come back down in weight I also get faster. But this is likely because an increase in weight correlates with less time on the bike and a decrease in weight coincides with me starting again to put in consistent training.
Weight does matter for accelerating though, and when races aren’t won on climbs they’re won on accelerations. Either at the finish or at all the decisive points prior to the finish where splits occur. Paris Roubaix winners are relatively big for cyclists, but they’re still in the 70-80kg range which isn’t really that big. So there is clearly a point even on flatter races where weight becomes a penalty and W/kg matters, otherwise you’d expect to see some 90kg guys with slightly lower W/kg but bigger absolute FTP doing well.
Guess another explanation is that there are too few flat or cobbled races suited to riders >80kg for teams to be able to justify giving contracts to those bigger guys. I.e. The 80kg classics specialist who still has good enough W/kg to get over the mountains at a Grand Tour and be a rouleur is more valuable than a 90kg guy who can only do flattish races.
Useless datapoint: Today I rode my usual (flat) commute with a small but heavy backpack. I did not feel slower, but Garmin gave me both a -11 performance condition rating and an automated +5 FTP boost. I can only assume this means that adding weight makes one both better and worse at cycling simultaneously.
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Momentum on flat/rolling terrain can be an asset for heavier riders and if underestimated a liability for lighter riders.
Let’s be real, the first type of rider is extremely rare and the second type of rider is a dime a dozen.
In the real world, two riders of such different size are typically going to have at least a 1.0 watt/kilo difference in PWR.
The rolling resistance will actually be quite a bit higher for both riders, but especially the heavier one.
The bigger rider will probably have a significantly higher CdA.
In a TT, the bigger rider will be faster.
If you add technical corners requiring accelerations, it will basically be a wash.
Super helpful explanation 
Its just an easy to understand example, works well for its purpose. 
If your current W/kg is greater than 2.5 that would be a good trade, otherwise, it is not a good trade. Your complaints are about having a lower W/kg and not specifically about being heavier.
Yes, it is typically easier for a lighter rider to maintain a higher W/kg, but given the same W/kg, the heavier rider will be at least marginally faster than the lighter rider in all of the scenarios you listed.
You are wrong on this. I’m sorry. The physics is all described in the thread above. No need to repeat.
I’m 80kg and 4W/kg. And it takes a lighter rider with a noticeably higher W/kg to beat me, especially if the roads are rough/gravel.
Best of luck on shedding those kg’s! If you have unnecessary mass, it will be very helpful to get rid of it and you will be faster!
I don’t recall seeing an example using a physics model.
- 20mph / 32kph on flat terrain (0% grade)
- no wind
- bike weight 18lbs
Comparing power requirements with rider weight from 165lbs/75kg up to 210lbs/95kg
| 165lbs / 75kg | 190lbs / 86kg | 200 / 91kg | 210 / 95kg | |
|---|---|---|---|---|
| Wind resistance | 141 watts | 141 watts | 141 watts | 142 watts |
| Rolling resistance | 36 watts | 41 watts | 43 watts | 45 watts |
| Drivetrain losses | 4 watts | 4 watts | 4 watts | 4 watts |
| Total Watts | 181 watts | 186 watts | 188 watts | 191 watts |
Only 9 watt difference over 20kg. Now if you can lower CdA by going to a lower weight, then it would be a bigger difference.
If you want to play around, here is the model at 165lbs / 75kg:
Somehow it feels like the wind resistance should make a bigger difference.
See for example here for modeling CdA: Training and Racing With a Power Meter Journal: Estimation of CdA from anthropometric data
Using just the first model in the link above, for a 1.8 m rider if the weight goes from 70 kg to 90 kg there is a 10% increase in frontal area, meaning also almost a 10% increase in power at high speeds, just from drag alone.
So is your assertion that if a 80kg rider is maintaining 160W (2 W/kg) to stay in the draft of a group, a 60kg rider will only have to maintain 80-90W?
yes, that Gribble model is a bit low. I do a lot of endurance riding on flat routes, here is one
Gribble at 18.7mph with air density and estimated total weight of that day:
- 161 watts at 18.7mph
Actual with a 3-4mph north wind that myWindSock estimates a 1.9% impact (majority of route was west/east):
- 184 watts at 18.7mph
That was with a GP5000 tubed tire (butyl) on Roval Rapide CLX wheels. So a pretty low rolling resistance and mid-aero wheelset on a Tarmac SL7. Aero helmet. Temp of 64F / 18C.
I’ve got wide shoulders and a big chest, not very aero. Built more like a truck than a Ferrari.
This is a very specific apples to oranges case of a larger rider drafting a smaller rider vs a smaller rider drafting a larger rider. Larger riders are also allowed to draft larger riders.
I think your last paragraph is leading you to a discovery here. The lighter rider, with an even higher W/kg than you (he climbs faster) gets dropped if he rotates through on the flats. Consider: if the larger riders had the same W/kg as him, they would climb at least as fast and drop him even quicker on the flats.
Just to play devil’s advocate; on hot days and/or long climbs, would the larger rider equal w/kg rider be at a disadvantage with regards to overheating? They’re doing more absolute work but not losing as much heat (proportionally) to the environment as the smaller rider.
I’ve thought about this too. I suppose this is theoretically possible, since cooling is more of a function of surface area where mass is a function volume. I’m certainly unqualified to comment on such a physiological question. Practically, and based on my experience I would think that this effect would be significantly less than the physics impacts except for very specific situations.
Maybe a super long tailwind climb at the end of a long day in very high heat and humidity.
I’m sorry, but this is starting to get very confusing. Can you please explain how the lighter rider (with equivalent w/kg) is getting dropped from your paceline despite your assertion that lighter riders (with equivalent w/kg) have the advantage?
If he gets such a better draft and has advantages that you don’t, he should be pulling through fresher and easier than you rather than being the one that “gets dropped if he doesn’t skip his pulls.”
Cheers. Crush it this off season!