messing around with bikecalculator.com. I tried 2 riders (60kg and 95kg) riding same weight bike up slopes of 3%, 7%, and 10%, at the same speed (roughly 20kmh for 3%, 12 kmh for 7%, and 9kmh for 10%. There didn't deem to be much variation in how much more power the heavier rider would need ( between 1.43 times as much and 1.52 times as much)
I was a bit surprised - I'd expected the amount of extra power required to increase more dramatically?
I realise wind resistance not tken into account
anyone know the science?
thanks
So all things being equal, the rider that weighs ~50% more, needs ~50% more power to get up the hill. Who’d have thought it. 😉
Work = mass x distance
You wanna try being the bigger one !
Needing 300w where the lightweights need 175w !
Yep twice the mass needs twice the work
Which is why saving 200g on a pair of wheels won't have much impact on your Strava times....
Yep twice the mass needs twice the work
Which is why saving 200g on a pair of wheels won’t have much impact on your Strava times….
That’s only considering one element.... nicer wheels might be more aero so and the polar moment of inertia so when you’re acellarating nd decelerating the lighted wheel will be better. You have to consider the whole system.
Not with a 35kg weight difference you don’t...
No idea why people keep assuming we're all obsessed with Strava times. Every time Strava is mentioned almost all the posts are telling the world that they don't give a shit.
Light wheels feel nicer, that's why we buy them. Not to shave seconds off anything.
Anyway. Even if you were chasing Strava times, light wheels help more than that calculation suggests. Because every time you accelerate you have to spin them up, so even on flat single-track if it's twisty like an XC race circuit you are spinning them up and slowing them down all the time. This takes energy from your legs and dumps it into the brakes.
Work = mass x distance
Work = force x distance. Which in this case (being weight times vertical ascent, and weight being mass times gravitational acceleration) is proportional to mass, but not mass.
There didn’t deem to be much variation in how much more power the heavier rider would need ( between 1.43 times as much and 1.52 times as much)
If all that's being modelled is the gain in potential energy (ie work done against the hill) then, assuming a 10kg bicycle, I'd expect the power ratio to be a constant 1.5 (105kg vs 70kg, with the same altitude gain over the same time period). So I assume something else is being accounted for…?
It takes a lot more energy to accelerate 70 kg of rider than 3 kg of wheels and tyres.
so twice the mass needs twice the work
- on the flat?
- @ 1% gradient?
- @ 3% gradient?
- @ 10% gradient?
- @ 15% gradient?
- @ 20% etc etc???
Yes. All of those, assuming the same constant speed.
You wanna try being the bigger one !
Needing 300w where the lightweights need 175w !
Try being a lightweight when everyone is coasting along on the flat and you're doing your FTP just to avoid falling off the back. There must be a happy medium somewhere... *Munches Pringles*
I apoligise for mentioning Strava. It was meant to be a metaphor for time to cover a fixed distance, which is the subject of the thread isn't it
But
nicer wheels might be more aero
Hmm I thought we were debating riding up steep hills. But you are of course correct aero wheels will be faster
polar moment of inertia so when you’re acellarating nd decelerating the lighted wheel will be better
It is true that if you save 200g on the rims that is like saving 400g off the frame when accelerating. For me that would increase my accerelation by about 0.5% or less. But in reality it's often the hub which is lighter. Of couse if you are on the rivet trying to hold a wheel out of a corner that might be all you need not get dropped. But I'm generaly not riding like that
You have to consider the whole system
Excatly. But people seem to loose sight of the fact that most of the system is the rider perhaps 80%-90% for the road
Try being a lightweight when everyone is coasting along on the flat and you’re doing your FTP just to avoid falling off the back.
Except your air resistance and rolling resistance will, if anything, be less than the clydesdales, so you'll be doing less work to keep the same speed. And if you're at the back you're getting a tow from them as well. Stop moaning 😉
Except your air resistance and rolling resistance will, if anything, be less than the clydesdales, so you’ll be doing less work to keep the same speed
But the evidence from the pros sugest that the little guys are fastest up the hills and the bigger guys are faster on the flat....
I started the winter bemoaning my coach telling me to increase my carbs through the build phase, to maximise muscular growth and endurance and recovery during training . I was convinced - and was right - that I'd put on weight . He argued I'd lose it again once I moved back to volume - which is about now as I'm reversed periodized.
So, I put on 2.5kg or about 2% of system weight, but power at pace went up 4% over the winter The recent Scott Marathon compared with 2018 shows I rode 11% improvement but that doesn't account for other rider variables .
Before the next Marathon on 26 May I will be dropping that weight naturally through volume .
So in conclusion, I got stronger enough to overcome a weight gain, and will now drop weight naturally and train to maintain my gains and ride 2% lighter than last weekend at the next marathon.
In the classic £ per gram of bike bits equation that amount to spending £2500 of weight saving .
Interesting thoughts!
But the evidence from the pros sugest that the little guys are fastest up the hills and the bigger guys are faster on the flat….
Yeah, because the bigger guys have more meat and once you're in a proper racing position there's not such a huge difference in aero position. (Rolling/drivetrain resistance differences will be tiny.)
So for a pair of professionally fit athletes operating at a similar percentage level of max output, the big guys will put out more power and hence be faster on the flat where weight isn't an issue.
But the smaller riders still need to output a bit less absolute power to keep the same speed. It's just that, once you're racing, that's not really relevant.
So for a pair of professionally fit athletes operating at a similar percentage level of max output, the big guys will put out more power and hence be faster on the flat where weight isn’t an issue.
This is isn’t always true, muscular endurance / profile comes into play. I rode with a big guy on a fat bike in the aforementioned Marathon. He was much more powerful on climbs and I’m a crap climber but I reeled him in and eventually passed and extend minutes on him in the flat sections.
Its not always about “power” it’s also how you can / are physiologically able to use it. The op’s science doesn’t take that into account.
Yeah, everything's necessarily a bit simplistic/generalised here, and physics isn't the same as biomechanics.
...and back to the OP’s question, yes it all figures and painfully evident at HoNC at the weekend where my mate (I’m guessing 9.5 stone) skipped up the climbs like a mountain goat compared to many of the riders including myself (14 stone).
NB I have not been sub 10-stone since I was about 12yrs old.
...I have two super light HT MTBs, I just need to lay off the biscuits in order to benefit from an improved power:weight ratio.
Work = mass x distance
Science teachers despair
Isn't the key number power to weight? My mate is 15 kilos heavier then me and has to put out about 35 watts extra on a 6% gradient to get the same time.
Even if you were chasing Strava times, light wheels help more than that calculation suggests. Because every time you accelerate you have to spin them up, so even on flat single-track if it’s twisty like an XC race circuit you are spinning them up and slowing them down all the time. This takes energy from your legs and dumps it into the brakes.
Only if you lose the momentum by braking.
And otherwise a test a while ago found that for road bikes there was **** all difference between rotating and static weight.
