Wind and Hills
- Thread starter neslon
- Start date
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MacB
Lover of things that come in 3's
- Location
- Farnborough, Hampshire
having experienced wind and hills now I'd say the hills take a bit more out of me, that's probably due to my mass though. If I lose the weight I plan then I'd have thought wind would become the tougher test. It's quite hard to assess accurately as I'm also getting fitter, stronger and more bike fit as I go along as well. But my view:-
hills - I started out wanting to lose 32kg's, having now lost 13kg, the hills have become easier. This can't just be my fitness levels, not hauling an extra 13kg must have an impact.
wind - my weight loss isn't going to have the same level of improvement in reducing my wind resistance profile. I think the fitness improvements will be of more benefit here. Fully slimmed down I think my battle will be wind more than hills, but that's really gut feeling and not a scientific analysis.
I'm sure Jim can put me right if I've erred in my calcs
hills - I started out wanting to lose 32kg's, having now lost 13kg, the hills have become easier. This can't just be my fitness levels, not hauling an extra 13kg must have an impact.
wind - my weight loss isn't going to have the same level of improvement in reducing my wind resistance profile. I think the fitness improvements will be of more benefit here. Fully slimmed down I think my battle will be wind more than hills, but that's really gut feeling and not a scientific analysis.
I'm sure Jim can put me right if I've erred in my calcs
Will1985
Über Member
- Location
- South Norfolk
PT is 3 months old - basic recalibration is done using the headunit. +/- 2.5% accuracy is claimed by CycleOps. FWIW it shared values +/- 2% when put on a CompuTrainer last month.
Compare it to the powercalc table of course. We're not talking exact science to be published in a respected journal here are we!!
Compare it to the powercalc table of course. We're not talking exact science to be published in a respected journal here are we!!
As you reduce your weight, your Inertia reduces.
With the same Xsection area and 'generic cyclist's' shape, the wind will want to pick you up and blow you backwards more.
It will become more difficult to ride against a howling gale.
It will, however, be easier to climb hills because you are lifting less mass against gravity.
With the same Xsection area and 'generic cyclist's' shape, the wind will want to pick you up and blow you backwards more.
It will become more difficult to ride against a howling gale.
It will, however, be easier to climb hills because you are lifting less mass against gravity.
Will1985 said:
I did a hill rolldown test with an £8 cycle computer.
I researched my tyre Crr.
I weighed my whole vehicle.
On a known gradient, I freewheeled down and recorded the max speed.
From this, I could pop the numbers into the Velocity/Power equation.
All the rest is physics.
I get +/- 2% of PowerCalc, so must be at worst 4% away from Computrainer.
Not bad for an £8 outlay on a 'cheapo' cycle computer.
Oh PS. The hub will have a strain gauge, which by it's nature, will drift in time and use.
I should know, I worked on Motorcar engine test dynamometers.
PowerTap is a s**t load of money for something I wouldn't take as accurate, even repeatable in different climatic conditions.
jimboalee said:350 Watts will get a 10st 7lb rider on a 15 lb roadrace bike along at 26ish mph.
10/10.
That's the thing though, I'm not doing it on a racebike, I put in the values 75kg, 0.55 area, 1.0 Cd, Cr =0.040, 90% transmission, 18.6mph and 15km/h winds and it comes out with 905 Watts. Cr might definitely be a bit on the high side but it's sure not 0.010. I sometimes do it at a much higher speed and that's why it came back as 1000. It comes out at somewhere 700-1000 pretty much whatever on the last stretch. The normal ride can come out above 200Watts for the whole lot (taking an average speed) and assuming no hills (it's about 7 miles slightly uphill) which is surprising as isn't a beginner supposed to be able to do something daft like 15mph?
MacB
Lover of things that come in 3's
- Location
- Farnborough, Hampshire
jimboalee said:
thanks Jim, as I suspected then, one bit gets harder as the other gets easier
marinyork said:
I ran your numbers, 802 Watts.
What bike was it??
What tyres are you riding on, and at what pressure. I have some listings.
0.04 sounds very high.
0.55 area is an average man standing up. A cyclist and his bike might be more like 0.425 m^2.
Your gear meshing won't lose 10%. 97% efficiency for a well lubed system.
Your 18.6 mph is 30 kmh?
jimboalee said:
Marin city bike. 700x35 marathon plus tyres. Usually at about 40-50psi. It does sound high but 0.010 it is not. The rolling resistance is so poor compared to my race bike and it seems the same as a mates mountain bike with knoblies although it should be a fair bit lower it never seems to be.
jimboalee said:
It is probably somewhere in between the two. I have flat bars and am very high up, I don't wear lycra and I wear a coat that I think you described about one you'd worn elsewhere rather well as a "sail". As the chain skips a lot I stand up a lot of the time thesedays. I worked out the Cd ages ago and it was a lot higher than 0.4. That is why I inputted higher numbers.
jimboalee said:
Perhaps not. That said the chain has stretched, skips a lot and you can't get the power down. It's certainly a very long way from a well lubed system. I'd have thought it'd be 93-95%.
With wind. The home straight normally has a headwind on it. That's about the slowest I do it thesedays unless it is a bad day. I've sometimes got it well into the 20mphs. I'm just interested as to the power requirements for a short sprint of a mile or so as that's the only flat place round here to put the power down. The whole ride has a much lower value of around 200 Watts. I'm interested in the flat bit really to see whether I'm feebly cruising along as 20mph + or that's about the most I can expect out of the bike.
I'm just interested in the power numbers, not to show off (cyclogs and other posters here make it clear I'm one of the slowest riders on the forum despite being a lot younger than many others) but because I got a race bike recently. Took it out in a howling gale, up some steep hills and it didn't feel like I'd been exercised at all. Done the same on a more trivial ride on the old bike and it's a completely different matter. When you compare the power requirements they are vast.
I've got a Crr figure of 0.0047 for the Schwalbe Marathon Plus at 80 psi.
Use this number and the Wattage drops to around 550.
That's more reasonable for a jacket wearing upright sitting rider on a 'City' style bike.
Good going if you can produce this for more than 20 minutes
Use this number and the Wattage drops to around 550.
That's more reasonable for a jacket wearing upright sitting rider on a 'City' style bike.
Good going if you can produce this for more than 20 minutes
Will1985
Über Member
- Location
- South Norfolk
Still very unlikely. Cancellara averaged 629W for the 2008 ToC prologue which took him just under 4 minutes and he was spent at the end. A mere mortal couldn't sustain even 500W for more than 20-30 seconds.
Will1985 said:
You're probably correct.
If I tear-arse down the A45 from Coventry under the Meriden turn overbridge on my SWorks, I can get to about 35 mphish. Then the road levels out all the way over Stonebridge Island and on to the M42 junction.
My speed drops to high 20s ( 28 mph = 500 W ) and I can keep this for about 2 minutes.
Not enough to breakaway from the pack with 20 km to the finish
