A larger framed rider could have a higher drag coefficient—wider shoulders, bigger body. I’m 6’4”, fairly flexible and I push a ton of wind.
Really good TTers tend to be larger and have a higher threshold, but take a smaller guy Remco Evenpoel, who has a lower threshold than say Rohan Dennis. This is an excellent example of a small, but very slippery time trialist.
A lighter rider will almost always have an advantage on a climb. I’ll use myself, an 84kg rider as an example vs a 64kg rider. At 4.5w/kg I would need to put out 378w. That’s world tour level power. But a 64kg only needs to put out 288w to be at the same w/kg as me. 288w is low Sweet Spot for me. That’s a 100w difference, which is huge.
You are correct. A heavier rider will have a greater drag coefficient, but usually not in proportion to weight. (2D vs 3D).
On climbs, we always talk about Watts per kg, but it’s really about Watts per kg+bike. Given the same W/kg, a rider who is 30% heavier will have 30% greater power, but not a 30% heavier bike.
This is correct and always seems to be ignored. Weight of equipment, rolling resistance (and aero on a climb under about 9%) are important factors.
I’ll never had as high a W/kg as my team mates because I’m 87kg. But I am at 4.7w/kg when on form. At that point my 60kg team mates need more like 5.0W/kg to go faster than me in an individual timed effort up a climb.
If we are riding up together/racing up then they’ll need more again to drop me as I can use their (tiny) draft but that’s a separate discussion.
Related, I’ll be riding in the Dolomites with a friend of mine that’s 20kg heavier than me… however, once the bike weights are taken into consideration, we’ll basically be exactly the same power to weight ratio.
Should be fascinating. Will also suck quite a lot because I’m down 70w on my old power (shattered hip and then COVID).
I was bored at work, so I made some Charts with the help of http://bikecalculator.com/
So we have two riders, both ride at 4.5 W/kg, both have bike+equipment of 9 Kg
Blue guy weighs 60 Kg (rides at 270 W), Red guy is 80 Kg (rides at 360 W):
You can see that the heavier guy is consistently faster, that’s because his W/kg is actually higher, taking the equipment into account. it’s 4.04 W/kg vs. 3.91 and also because aerodynamics still matte and therefore higher raw power is more advantageous.
This, you can see really well in the following chart (Speeds normalized to 60 kg-guy):
The difference is bigger at lower gradients (and higher speeds), because of the raw power advantage. And at higher gradients (lower speeds) the difference levels off at about 3.9 % faster for the 80 Kg-guy. This is because of the mentioned higher relative W/kg (taking equipment weight into account)
Do they account for rolling resistance and drivetrain losses too? Or is that a wash?
E.g. riding at 360W, the heavier rider might lose 7W to drivetrain losses and say 40W to rolling resistance. Do those scale linearly with weight at the same (similar) speed or is there a further benefit for the heavier rider?
the calculator does account for rolling resistance. I think it uses an estimate Crr, based on what settings you put for tires. Same for CdA I think. It also says, it uses a generic 5% drive train loss.
Thanks, it looks like rolling resistance and drivetrain losses are even between the two riders (when expressed in W/kg) so they don’t change the outcome/speed.
RR scales linearly with weight and velocity.
Drivetrain loss is assumed as a percentage of total input power.
Partially disagree. Unless we’re talking TT, the disadvantage of having lower raw watts can be largely offset by drafting. The selective parts of races where they’re won or lost invariably involve a climb and/or a big acceleration. That’s where W/kg makes the difference. Not necessarily FTP/kg - that’s one for the mountains for sure - but W/kg for whatever duration the selection or series of selections lasts for. Extra weight doesn’t just cost you extra energy going uphill, it costs you extra energy every time you have to accelerate out of a corner, to close a gap, etc. If that extra weight is useful mass that gives you extra watts over relevant durations and/or greater repeatability of those watts, then all well and good. But even for a cyclist who only does flat races, W/kg is still relevant.
I’m primarily a triathlete so you would think that I only care about raw Watts. (on the bike, yes. 5kg one way or the other will have little impact on my performance.) But I do really care about weight for the run portion as that has a huge effect.
So that being said I use FTP/kg as an overall judge of my own bike fitness if for no other reason than it helps me keep an extra eye on the kg portion of the equation while trying to continually bump up the Watts.
I like watts/kg, mostly because I’m 50kg and it makes me feel much better about myself than my raw watts
As others have said though, I think it’s pretty discipline-specific. I do feel that it has some value as a performance metric- but also that it should be taken in a similar way to FTP and used to assess your own progress in the context of your specific goals, rather than compared to other people’s or held up as an absolute measure of fitness/success. Weirdly It seems like most people I know are pretty good at keeping their FTP results in perspective, but when it comes to watts/kg they start feeling like they need to achieve some arbitrary level or beat themselves up because they don’t put out pro numbers.
Rolling resistance is definitely scales linearly with velocity. Regarding weight, correct me if I’m wrong, but wouldn’t rolling resistance only scale linearly with weight if the heavier rider doesn’t appropriately add tire pressure? Riders usually pay attention to tire pressure according to weight, and thus deformations are the same. I thought this was a large part of the reason why bigger riders are faster on rougher surfaces, as rolling resistance is roughly constant across different sized riders moving at the same speed.
As a larger rider at ~93-94kg race weight, I’ve sort of stopped caring about W/Kg and just target events that suit my profile. At peak, I’m at about 4.4w/kg (410w ftp), and race mostly flat crits/road races and time trials. I’ve yet to feel like my weight has held me back. I’d be dropped like a rock in a climby race though. I say just do you and ride/race the types of events that you’re good at.
Good grief, I’m 98kg and just barely at 300 watts for my FTP. On our local group ride, my only hope is getting to the front of the group and peak while I’m still attached to the back of the group. Screaming downhill would be nice if it wasn’t neutralized
I think you might be right and I got confused! I had just had a quick look at the rolling resistance formula in here: Understanding Rolling Resistance | TrainingPeaks
And took the linear with weight and velocity from it but actually pressure will impact the Crr value.
Long way round, but I think the heavier 4.5W/kg rider does have an extra edge due to RR. 60kg rider might have say 20W of RR which is 0.33W/kg, whereas the 80kg rider might have 24W of RR which would be 0.30W/kg.
Ultimately, an 80kg rider with the same W/kg as a 60kg rider will be faster over all gradients (assuming skills are equal). Therefore W/kg is not a great comparison of two riders at different weights.
