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Been thinking about this recently and genuinely interested to hear peoples experiences.
If you compared two riders, one at 50kg with an ftp of 200 and the other at 80kg with an ftp of 320. Assuming both have the same level of fitness across all zones and both have the same W/kg etc. Who would have the advantage in different conditions?
As a light rider I really struggle in a strong head wind while larger riders don't seem to be as affected. And notice a significant difference in speed and acceleration when on a lighter bike.
Assuming those figures, the heavier rider would win, on the road at least. Because aerodynamics would play a bigger part and they don't increase linearly with weight (at a guess it's probably about the 1.5 root of weight as the frontal area (m2) is one dimension less than volume/weight (m3)).
In reality, an FTP of 320 and weighing 80kg would be far more exceptional than an FTP of 200 and weighing 50kg (although that's pretty good/unrealistic too). FTP is as much dependant on cardiovascular fitness as it is your legs. And cardio fitness doesn't weigh much.
So in the real world the comparison is the 50kg ride has an FTP of 200 but no sprint beyond that. The 80kg rider has an FTP of somewhere in between, say ~270, so is getting dropped up hills, but has bigger leg muscles that can produce better anaerobic efforts and demolish the little guy over the line as long as it's not at the top of a hill.
On the flat, rolling resistance and the like is pretty much the same (a heavier rider may squash tyres slightly and increase contact patch but that's marginal) and as speed increases in particular, most of the effort goes into overcoming air resistance which is proportional to the frontal area. And while a larger rider has a larger frontal area, it's not proportional to weight because we are three dimensional, not two. It's also proportional to V^2, which is why as speed goes up the effect of drafting gets higher and higher.
So a heavier but more powerful rider should go better on the flat.
On hills - the work done to lift the extra weight becomes more significant while as V decreases the work against air resistance becomes less significant....especially if you climb like a biffer at 4mph!!
Thats pretty much what I was thinking.
Surely though if two riders have the same watts per kg, they will be the same speed uphill regardless of weight?
Just had a play with number on that calculator.
Kept the W/kg the same for a 50kg rider and 100kg rider on different gradients and head winds and couldn't find a scenario where the lighter rider wins.
Assuming the same CdA, the more powerful rider wins every time.
For the larger rider, bike weight also is a lower %age of total weight.
me too..... and I agree.
I'm now questioning received wisdom!
I suspect in the real world power is not scalable to size, although heavier riders have more power your endurance power (FTP as a proxy) depends not just on muscle bulk but cardiovascular fitness and all the pros will have largely speaking similar CV systems. So while there may be high 50's / low 60's of kg up to high 80's in the pro peleton (say a 150% weights ratio) the FTP's will be a lower differential between low weight and high weight riders. So to change the W/kg in your favour, it's harder to increase the power/FTP than it is to decrease the weight.
http://theclimbingcyclist.com/gradients-and-cycling-how-much-harder-are-steeper-climbs/
Moving away from the road, as a heavy rider, currently light for me @ 92kg. FTP around 305, I get utterly trounced in a short enduro event. I have to keep accelerating my mass from a low speed, where the course has lots of sections to slow you down.
On bigger courses that aren't limited by elevation, I'm in my element as I can keep my momentum and do much better.
I'm too heavy
On the flat its negligible up hill very very noticeable
I used to ride with a couple of fairly big guys, in the 100 kg to 120 kg range and a few inches taller than me. I'm 75 to 80 kg. I could easily outclimb them, they just carry so much weight that they would have to be massively powerful to overcome it, but then their lungs wouldn't be able to supply enough oxygen. On the flat, they were pretty quick for 5 or 10 minutes, they had a lot of power and I've never been a sprinter. After that, they would just run out of breath and I could cruise off into the distance.
A couple of years ago, I was probably the fittest I've ever been and took a guy from work out mountain biking. He does triathlons, but had never ridden off road. He's pretty small, maybe 5'6" and 60 kg. Looking at the Strava times for the climb (17:10 for me, 17:30 for him), we were neck and neck on the steep sections, but then I cruised away when it flattened out, so basically the same thing of being bigger helps on the flat. Given that he was riding a borrowed bike and had never ridden that trail before, I think he'd clean me out on the steep climbs if he had decent XC bike and a chance to practice a bit.
There's more to performance than just ftp as well. The ability to recover from repeated efforts over threshold for example, could be markedly different for two riders with the same ftp. Ditto their ability to ride at a percentage of that figure for extended periods.
As a real world example, a few years back I started riding with a neighbour who was an iron man triathlete. On the road, where his ftp was undoubtedly way higher than mine, I could barely hold his wheel, but on trails in the Peak, I found he would explode after only two or three hard anaerobic efforts because he was basically conditioned to ride for hours at below threshold. It was interesting.
So I know that goes beyond the scope of the original question, which I guess assumes other aspects of the two riders' fitness profiles are also comparable, but in the real world it rarely works like that.
Watts/kg is where it matters if you’re racing in most cases. I used to road race at below 60kg and even on a moderately hilly course the field of 60 would be whittled down to 10 by the final lap. I was doing a race in the Surrey Hills that fractured into small groups - there was one long hill of about 3km, a flat section and then a descent back to the start of the hill. Three guys were chasing me in 4th - they would catch me each time at the bottom of the hill and I’d drop them again. On the final lap, when they caught me again on the descent one of them did comment of the pointlessness of chasing me down. CX was the same, I could ride up the steep banks and long drags that would slow down heavier riders. The only time where the big guys had any benefit was on crits or flat circuits where it would inevitably end in a sprint.
Never any numbers measured, so this is purely anecdotal. Did a bit of riding with a fit runner friend who was starting biathlons. He’s tall, lanky and 20kg lighter than me. I could easily ride away on flats and rolling terrain but as soon as it went sustained uphill he just disappeared. Sure I could produce more outright power than him but his superior CV system made all the difference.
More anecdotal 'science' - we have an ex rugby player in our riding group who weighs c.240 lbs yet is a complete animal uphill. The two skinny Tri guys can pull away on a long climb but on shorter climbs he is right there with them. He must generate an astonishing wattage which wouldn't surprise me from the amount he eats!
I don't know how realistic zwift is but in the STW race series I (<70KG, ~230W FTP) seemed to do much better on the courses with long climbs. On short roller type slopes I couldn't do the short bursts of massive power to keep my speed up over them, but once we got a long 5% climb I'd grind my way up it quicker than the group around me. Even whenI'd been killing myself to keep up with that same group on the flat. On flatter courses it seemed like the bigger riders did better.
Zwift seems to be more about W/kg. I use to use Bkool which was more about power. I couldn't keep up with many others on there on flat or climbs.
You can see the marked difference in the pro peloton. If you are heavy you are in the groupetto on the mountain stages on the flat stages you can be competitive. Heavy is 80kgs up.
When I used to race on the road I targeted races that suited my strengths. I am lightish and good at climbs but have no sprint. I can sit on the wheel of the big powerful guys on the flat. They provide a good draft. On the climbs I need to drop them and get into a break. I have no chance if the big sprinters are in my group at the finish.
Big guys can get over short power climbs but on a decent length and gradient climb they struggle. The cut off is a remarkably short duration climb probably around 3 minutes.
So the moral is play to your strengths.
Interesting stuff about sprinting.
I'm 60kg and like repeated short hills, but also love short sprints, especially uphill.
Long flat sections with a slight head wind just kill me. Last weekend was about 18mph winds on a long road that averaged about -3%. I couldn't roll any of it. If I stopped pedalling at 16mph I just stopped as if I had flat tyres.
Zwift seems to be more about W/kg.
IIRC swift has quite a high penalty for weight in terms of wind resistance. The big guys should be able to break away, but it's not as marked as in the real world.