The penalty of extra weight & cold conditions

siamon

There is a way of working out how much extra flab costs you in terms of performance for runners. It works out to about 2 seconds per lb. I thought this was a load of codswallop until I piled on the wobbly stuff like a baby whale over Xmas and the extra 10lbs I managed to stack on costs me 25 seconds per mile .

Does anybody know if there is a similar formula for cycling?

Secondly, what about winter? How much does the cold thick air cost you in terms of average speed on one of your regular rides? I'm hoping it's about <2mph.

Alex_Simmons/RST

siamon wrote:

Does anybody know if there is a similar formula for cycling?

No, because the balance of resistance forces in cycling are considerably different to running and it's a cubic equation.

siamon wrote:

Secondly, what about winter? How much does the cold thick air cost you in terms of average speed on one of your regular rides? I'm hoping it's about <2mph.

At same barometric pressure and altitude, difference between 0C and 20C will be ~ 0.5mph on flat windless terrain at 200 watts. However in cold weather you are typically riding with more clothing and the impact on aerodynamics could be quite substantial, maybe 1-1.5mph less speed.

Add the extra mud around the middle and well there you go.

LeicesterLad

I notice quite a substantial 2mph dip when the weather gets close to freezing, I do find it harder to breathe, but as said above the added weight of the winter jacket, flapping about providing extra drag doesn't help, i also find my commute slower in the cold because its a short commute, and my legs never really get the chance to warm up sufficiently if its really cold...

siamon

Thanks Alex, I'm surprised there is no way of singling out the effect of weight, ceteris paribus but I appreciate knowing the effect is much less than I imagined.

Leicester - glad it's not just me!

Alex_Simmons/RST

siamon wrote:

Thanks Alex, I'm surprised there is no way of singling out the effect of weight, ceteris paribus but I appreciate knowing the effect is much less than I imagined.

Oh you can single it out, just not with a simple formula.

The reason for that is the speed-power relationship in steady state cycling is much more a function of aerodynamics (cubic) and gradient (linear), making the overall equation a cubic one. Then throw in accelerations and descents and it's not quite as simple. All you need is a road with variable gradient and you can see why it's not simple.

In running the speeds are much lower and aero has a much reduced impact, meaning body mass has a proportionally higher influence on speed.

So if cycling on the flat, then the impact of mass change (ceteris paribus) on speed is minor (a bit less speed due to slightly increased rolling resistance and slightly worse aerodynamics cause you are fatter), but if you are on a steep uphill then the impact is almost inversely linear with the increase in mass. The equation is here:
http://i220.photobucket.com/albums/dd22 ... ling-3.png

However that's just the physical. Extra flab usually means there is also a physiological impact (lower fitness/power).

daxplusplus

I was wondering about the cold vs average speed question over the last couple of weeks. Up until recently I had been cycling in very cold conditions with pretty minimal protection from the wind .. I was invariably very cold at the end of a ride. Maybe not extremeties but reckon my torso had had a good chilling. My average speed on my long commute was noticably lower (middle teens) than at warmer times of the year (upper teens) however top speed on descents was not effected (just under 50mph).

I have since bought a windproof jacket (very good fit so probably as good if not better aero than my fleece jerseys I had been wearing) and my torso is noticably warmer/not chilled after a long ride in cold conditions. Although I haven't tested my top speed just yet my average speed appears to have improved. Now it's perhaps a little early to compare but it appears that by keeping my torso warmer my average speed is better .. I was just wondering if all of this is b*llocks with way to many variables to prove anything either way or whether people had noticed an efficiency vs core temperature corelation themselves?

I will give the top speed on descent a go and try out and see what happens .. if that has improved then perhaps it's was just the better aero of the jacket all along (like I said, it is a very good fit ).

Just wondering.

jago43

Not sure about the technical side of things, i'm always an easy 2 mph slower on the coldest of days, and 1 - 1/2mph slower through the winter, i just find the winter months demoralizing because it all seems hard work. not sure extra weight is a big a penalty in winter as i find i have to grind up most inclines this time of year. as thro the warmer months i seem to have the energy to get out the saddle and attack the hills.

siamon

Alex, thanks for taking the time to resolve that. I normally take the JFT approach but this was really beginning to niggle.

Dax, where are the 50mph descents Gloucester way? From what Alex said and the link, if top speed is unaffected then your aero profile can't have changed much, if the jacket is a proper corset job and you can still get in the right position top end might increase a bit!!

daxplusplus

The descent is the A435 Cirencester Road into Cheltenham. 10% for a mile or so. No bends and, most important, no slip roads or junctions on any part of the hill - so you can max out without worrying about cars pulling out.

Herbsman

siamon wrote:

There is a way of working out how much extra flab costs you in terms of performance for runners. It works out to about 2 seconds per lb.

Two seconds per lb per what?

siamon

Sorry it's +2 seconds per extra lb per mile.

simon_e

Cold air is denser and not pleasant to breathe in too deeply. High pressure, as we have now, also makes the air denser, so the combination makes it feel 'thicker'. You wear more (flappy) layers and are likely to be in a less aero position than a warm day wearing lycra. Psychologically, the dark mornings don't help. I rarely feel like riding hard on a winter commute. All these things are going to affect your speed.

In terms of being overweight, I'd suggest that, besides the benefit of fat loss from muscles and organs, the sensation of feeling lighter and healthier is of greater benefit than the drop in weight itself.

An article on the effect of weight when climbing:
http://cyclinginfo.co.uk/blog/3945/cycl ... s-on-bike/

A commuting doc found the lighter bike didn't make his daily journey significantly quicker:
http://www.bikeradar.com/commuting/news ... tor-28693/
I've been commuting on lumpy country roads and found my Giant SCR on 25mm tyres (9.9kg) feels lighter and better than my old Kona rigid MTB with 26x1.5" slicks (13kg) but the time differences aren't as large as I had expected.

mclarent

Simon E wrote:

In terms of being overweight, I'd suggest that, besides the benefit of fat loss from muscles and organs, the sensation of feeling lighter and healthier is of greater benefit than the drop in weight itself.

Sorry, despite your linked articles, that's codswallop. Simple maths tells a different story. Say you push 200 watts at 100kg to achieve a certain time, that's a power to weight ratio of 2. Then you drop 10kg, you're now pushing 200/90 = 2.2 watts/kilo, purely from losing weight, i.e. a 10% increase in performance for no additional power output. And this ignores the fact that in dropping that 10 kilos you will have (probably) been training, therefore increased your maximum power, such that 200 watts is a lower percentage of your maximum power, i.e. easier to attain and maintain.

Tom Dean

mclarent wrote:

Simon E wrote:

In terms of being overweight, I'd suggest that, besides the benefit of fat loss from muscles and organs, the sensation of feeling lighter and healthier is of greater benefit than the drop in weight itself.

Sorry, despite your linked articles, that's codswallop. Simple maths tells a different story. Say you push 200 watts at 100kg to achieve a certain time, that's a power to weight ratio of 2. Then you drop 10kg, you're now pushing 200/90 = 2.2 watts/kilo, purely from losing weight, i.e. a 10% increase in performance for no additional power output. And this ignores the fact that in dropping that 10 kilos you will have (probably) been training, therefore increased your maximum power, such that 200 watts is a lower percentage of your maximum power, i.e. easier to attain and maintain.

Power/Weight does not = performance.

The maths is not so simple, see Alex's post.

mclarent

rearrange that formula in terms of tf and decrease m, tf will decrease. simples.

Alex_Simmons/RST

Tom Dean wrote:

Power/Weight does not = performance.

The maths is not so simple, see Alex's post.

W/kg is not as a good predictor of speed on flat terrain as power to aerodynamic drag (W/m^2), but W/kg is still an excellent overall indicator of performance (better than most).

It isn't however as good a predictor of performance as performance itself.

simon_e

Tom Dean wrote:

The maths is not so simple, see Alex's post.

Thank you.

I was suggesting a less mathematical angle on improvement in riding speed uphill. As mclarent rubbished my suggestion (which is all it was) without providing any proof why then I take it he may be just another 'internet expert'.

I propose that one should not underestimate the power of the brain in this context.

Alex_Simmons/RST

Simon E wrote:

I was suggesting a less mathematical angle on improvement in riding speed uphill.

Speed uphill is much better as an indicator of performance (or change in performance) as the influence of many variables on the power - speed relationship are greatly reduced, the dominant factors being power output and weight of bike & equipment + rider. See this item:

http://www.bikeradar.com/fitness/articl ... ting-19175

Wind conditions can still be a factor though on hillclimbs, as shown in this item:
http://alex-cycle.blogspot.com.au/2011/ ... rtals.html

mclarent

Simon E wrote:

Tom Dean wrote:

The maths is not so simple, see Alex's post.

Thank you.

I was suggesting a less mathematical angle on improvement in riding speed uphill. As mclarent rubbished my suggestion (which is all it was) without providing any proof why then I take it he may be just another 'internet expert'.

I propose that one should not underestimate the power of the brain in this context.

Glad you posted that, give me an excuse to post this.

Never underestimate the power of science.

mclarent

Alex_Simmons/RST wrote:

<snip>

Damn, you beat me to it! Fair do's though, it is your blog!

Alex_Simmons/RST

Alex_Simmons/RST wrote:

Speed uphill is much better as an indicator of performance (or change in performance) as the influence of many variables on the power - speed relationship are greatly reduced, the dominant factors being power output and weight of bike & equipment + rider.

and just to further illustrate my point, the following chart gives some idea of the change in energy demand of the various resistance forces at different positive gradients:



Hmm, pic isn't sizing well, so here's a link to view:
http://i220.photobucket.com/albums/dd22 ... orce-2.jpg

As the road gets steeper, so gravity dominates the equation, and that part of the power-speed equation is linear. 10% faster on a steep climb = 10% higher power to weight (nearly).

mclarent

Alex_Simmons/RST wrote:

Alex_Simmons/RST wrote:

Speed uphill is much better as an indicator of performance (or change in performance) as the influence of many variables on the power - speed relationship are greatly reduced, the dominant factors being power output and weight of bike & equipment + rider.

and just to further illustrate my point, the following chart gives some idea of the change in energy demand of the various resistance forces at different positive gradients:
<snip>

Hmm, pic isn't sizing well, so here's a link to view:
http://i220.photobucket.com/albums/dd22 ... orce-2.jpg

As the road gets steeper, so gravity dominates the equation, and that part of the power-speed equation is linear. 10% faster on a steep climb = 10% higher power to weight (nearly).

Alex - given that that graph is calculated based on a bike+rider of 75kg, is it fair to say that gravity would play an even bigger proportional effect for heavier riders?

simon_e

mclarent wrote:

Simon E wrote:

I propose that one should not underestimate the power of the brain in this context.

Glad you posted that, give me an excuse to post this.

Never underestimate the power of science.

I never would (and I have read Alex's article more than once). But I would venture that it is foolish to dismiss the idea that human beings are no more than robots, the analysis of which is restricted to gradients, watts and kilos.

mclarent

Simon E wrote:

I never would (and I have read Alex's article more than once). But I would venture that it is foolish to dismiss the idea that human beings are no more than robots, the analysis of which is restricted to gradients, watts and kilos.

True, which is why there are Sports Psychologists. But even they follow the scientific method.

blackhands

I suspect that top pro climbers on Alpe D'Huez, who are going at about 14mph, will also start to become affected by increased drag. In fact, I was at a lecture where Phil White reckoned the aerodynamic properties of his frames also gave an advantage on mountain climbs.

Of course most of this is irrelevant in this country as climbs are short.

Alex_Simmons/RST

mclarent wrote:

Alex - given that that graph is calculated based on a bike+rider of 75kg, is it fair to say that gravity would play an even bigger proportional effect for heavier riders?

Most likely - all that would happen is the numbers on the gradient axis would be shifted to the left a bit.

It's the general trend from the dominance of air resistance on flatter terrain to gravity on ascents that I was showing - the chart will have the same overall shape for everyone, but the precise breakdown at various gradients will be different for each individual (depending on their aero and mass properties).

Of course on descents, there is a return of energy from gravity which assists heavier riders more.

kettrinboy

Alex_Simmons/RST wrote:

Of course on descents, there is a return of energy from gravity which assists heavier riders more.

Probably why Thor Hushovd was about the fastest at 69 mph in the TDF last year and he is one of the heaviest and powerful riders in the field.