Speed, Power and Lycra

[Tiberius]

Mark Cavendish won the Tour de France stage yesterday with a time of 4.5 hours (give or take 3 seconds).

The stage was 187 km. That works out as an average speed of 26 mph. Many of our bikes struggle to achieve that as peak speed.

So, according my basic model of bicycle physics, either Mark is pumping out about 500 Watts continuously, or he and his bike have very low aerodynamic drag.

I think I might have to get some skinny tyres and some lycra.

Discuss.

Nick

 

[AndyOfTheSouth]

Hi Nick

Interesting post. Could you say something about the basic model?

Thanks

Andrew

 

[rog_london]

Mark Cavendish won the Tour de France stage yesterday with a time of 4.5 hours (give or take 3 seconds).

The stage was 187 km. That works out as an average speed of 26 mph. Many of our bikes struggle to achieve that as peak speed.

So, according my basic model of bicycle physics, either Mark is pumping out about 500 Watts continuously, or he and his bike have very low aerodynamic drag.

I think I might have to get some skinny tyres and some lycra.

Discuss.

Nick

Keep taking the tablets (rotten joke, I know)

There aren't many of the lycra brigade I encounter who can get anywhere near that. Since I started riding the Wisper I've been overtaken and left behind by precisely one rider - a non-lycra on a mountain bike. The lycras I see jump in front at roundabouts and sometimes in traffic because I don't like to ride so aggressively and **** off motorists, but on any open bit - no chance.

How many of the standard of Mark Cavendish do you know? You'd probably only encounter them if you got mixed up in a club run, I guess. These guys spend more time in the saddle every week than the rest of us spend working, and even if they're not truly 'professional' riders, that requires some serious dedication.

Rog.

 

[Tiberius]

Hi Nick

Interesting post. Could you say something about the basic model?

Thanks

Andrew

Hi Andrew,

Its just a question of calculating the overall drag from 3 factors.
Rolling resistance, which can be very low on a well set up bike.
Hill gradient, which I've taken as zero in this case, so it doesn't matter.
Aerodynamic drag, which dominates as soon as you have any significant speed.

I have set up my own spreadsheet, and it uses the standard formula for aerodynamic drag based on air density and frontal area. The results come out in line with the published results.

There are (or used to be) various on line calculators that will do it, such as Kreuzotter.
That doesn't seem to be there any more; maybe someone can post a link, or you can do a google search.

Nick

 

[Tiberius]

Keep taking the tablets (rotten joke, I know)

I'm already a big user of lithium salts

 

[styx]

Mark Cavendish won the Tour de France stage yesterday with a time of 4.5 hours (give or take 3 seconds).

The stage was 187 km. That works out as an average speed of 26 mph. Many of our bikes struggle to achieve that as peak speed.

So, according my basic model of bicycle physics, either Mark is pumping out about 500 Watts continuously, or he and his bike have very low aerodynamic drag.

I think I might have to get some skinny tyres and some lycra.

Discuss.

Nick

I think you have to take into account the enormous effort a sprinters team put into protecting him. He will spend the entire stage on the back wheel of his team mates and rarely "put his nose into the wind" so he is effectively slipstreaming which has an enormous effect on his aerodynamic drag .They then lead him out at the last possible moment for the sprint and he is then expected to deliver and boy does Cavendish deliver .

 

[AndyOfTheSouth]

Thanks, Nick. So the resolution to the problem lies in the coefficient of friction which is applied. As Styx has pointed out, it is necessary to take into account the effect of team mates, and as you have hinted, at the way that Cavendish minimises his own drag and that of his bike.

Andy

 

[Tiberius]

Hi Styx,

Yes, I appreciate the team effect, so Mark Cavendish himself is not having to do the equivalent of 26 mph for the entire 117 miles. But it is still impressive.

At any one point in the race, though, someone is doing this speed. The main peleton is only seconds behind at the end of the race so is moving along at the almost the same average speed, and there is always someone at the front who isn't getting the benefit of slipstreaming.

My point is that these guys are producing very impressive performances, so either they are generating more power than we think possible, or they have got the aerodynamic drag down below what was once generally assumed.

Nick

 

[SEATALTEA]

I got toasted by a roadie in lycra towing a single wheeled trailer with half a dozen house bricks in it a couple of weeks ago. I asked what he was doing, 'training for a triathlon' came the reply.

I couldn't keep up.

 

[flecc]

Impressive indeed, and I agree with Styx about the protection advantage. The late great Miguel Indurain is still held in awe over a one hour continuous Tour de France climb at a calculated rate of 450 Watts, so 500 Watts for a whole stage is a little unlikely. Probably nearer to 400 Watts, but still an astonishing achievement. Lets hope he goes on to beat his last year's four stage wins.
.

 

[Barnowl]

A fit rider, light bike, skinny tyres, lycra, supportive team and not having to use the brakes. Most of us fail to qualify on all counts - well at least I do . I'm a "12.8 MPH" er, and quite enjoy the odd freewheel and no way am I getting into lycra.

 

[musicbooks]

Mark Cavendish won the Tour de France stage yesterday with a time of 4.5 hours (give or take 3 seconds).

The stage was 187 km. That works out as an average speed of 26 mph. Many of our bikes struggle to achieve that as peak speed.

So, according my basic model of bicycle physics, either Mark is pumping out about 500 Watts continuously, or he and his bike have very low aerodynamic drag.

I think I might have to get some skinny tyres and some lycra.

Discuss.

Nick

The shape I'm in, I'd be better off wearing the tyres. It's going to take a little more than thinly stretched nylon to make me aerodynamic
bw
musicbooks

 

[flecc]

The shape I'm in, I'd be better off wearing the tyres. It's going to take a little more than thinly stretched nylon to make me aerodynamic
bw
musicbooks

Maybe that's not so certain.

Modern bulk cargo ships have discarded the sharply pointed "streamlined" bow at the waterline in favour of a belly-like bulbous domed projection which makes them faster and more efficient through the water.

And then there's the tuna, a portly fish if ever there was one, but one of the fastest fish in our seas, catching other fish with ease until it ends up in tin cans.
.

 

[rog_london]

Maybe that's not so certain.

Modern bulk cargo ships have discarded the sharply pointed "streamlined" bow at the waterline in favour of a belly-like bulbous domed projection which makes them faster and more efficient through the water.

And then there's the tuna, a portly fish if ever there was one, but one of the fastest fish in our seas, catching other fish with ease until it ends up in tin cans.
.

How delightfully rude! Subtle, but rude!

Rog.

 

[musicbooks]

How delightfully rude! Subtle, but rude!

Rog.

I prefer to think of my shape more akin to a deep fried mars bar.
.. or since I started e-biking, deep fried milky bar.
bw
musicbooks