Cycling UK Forum

Just for a bit of fun having clocked up 2000 miles since January (I wish it was more but that's another story....) I thought I would play with some numbers...

Calories, energy
2000 miles at an average of 14mph = 142 hours of cycling
142 hours using 400 calories per hour = 56800 calories
Knowing there are about 95 calories in a banana....
56800 calories divided by 95 = 588 bananas needed
(that means a banana will fuel me more 3.4 miles)

Costs
The bike cost, in round numbers, about £1000.
I estimate that half the miles were purely for leisure. The other 1000 miles were in commuting and where I left my car at home. Using the HMRC mileage rate of 45p per mile, means I have saved £450 in petrol and running costs. At this rate the bike will have paid for itself after 5000 miles.
The cost of de-stressing, good worthwhile exercise, quite reflections, seeing so much more in the countryside than driving my car = priceless!

Sorry to shoot you down.

At 14 mph, burning 400ish ( 100 kCals/hr TRACTIVE and 300 kCals/hour heat expulsion ), over half of this will be from fatty acids in the blood and liver.

One banana ( mostly CHO ) is good for 15 miles flat riding ( a 15 mile loop ). You will eat plenty of other foods during the day to replenish the fatty acids you took out of your liver.

1000 mile commuting since January could have been done on nowt to eat, thus saving you the price of 67 bananas.

Ayesha wrote:Sorry to shoot you down.

At 14 mph, burning 400ish ( 100 kCals/hr TRACTIVE and 300 kCals/hour heat expulsion ), over half of this will be from fatty acids in the blood and liver.

One banana ( mostly CHO ) is good for 15 miles flat riding ( a 15 mile loop ). You will eat plenty of other foods during the day to replenish the fatty acids you took out of your liver.

1000 mile commuting since January could have been done on nowt to eat, thus saving you the price of 67 bananas.

I think that at average 14mph you're using more than 400 kcal per h.

Gearoidmuar wrote:

Ayesha wrote:Sorry to shoot you down.

At 14 mph, burning 400ish ( 100 kCals/hr TRACTIVE and 300 kCals/hour heat expulsion ), over half of this will be from fatty acids in the blood and liver.

One banana ( mostly CHO ) is good for 15 miles flat riding ( a 15 mile loop ). You will eat plenty of other foods during the day to replenish the fatty acids you took out of your liver.

1000 mile commuting since January could have been done on nowt to eat, thus saving you the price of 67 bananas.

I think that at average 14mph you're using more than 400 kcal per h.

Please show your workings.

PS Dougie and I are svelte race whippets with hardly any width. We also wear tight fitting race vests and lyca tights.
It should be 375 kCals/hr but we have mudguards fitted.

Looking at my records, I seem to be using about 875cals per hour.

Mind you, my normal riding gives me 100ft of climbing for every mile. If you only consume 400cals per hour, you must live somewhere flat or continually ride down hills.

Web calculators ( except Machinehead ) are VERY wooly at kCals.

The 'rough and ready' calculator is kCals/MILE for a circular route. What you expend uphill, you regain downhill ( almost ), and if the wind is in the same direction throughout the ride, that 'more-or-less' cancels out. Hills are a nuisance because the speed of climbing attracts more windchill ( per time ) from a sidewards direction than on the decent.
To get an idea of your 'flat road' power requirement and thus your 'flat road' kCals/mile, do a hill rolldown test ( equalibrium velocity ).

All talk about ROLLING power requirements pale into insignificance when Windchill and thermal maintenance come into the equation.
For long distance riders, wrap up warm. For weight loss riders, wear a string vest and swimming trunks in a snowy blizzard. The kCals expended keeping you skin from freezing greatly overshadows the kCals involved in moving the bike forward

Ayesha wrote:What you expend uphill, you regain downhill ( almost ), and if the wind is in the same direction throughout the ride, that 'more-or-less' cancels out.

I was commenting on the cals per hour, not the distance.

As climbing hills uses more cals than going down them, and climbing hills takes longer than going down them, the hilliness of a circular ride certainly does not cancel out. Far from it.

Mick F wrote:

Ayesha wrote:What you expend uphill, you regain downhill ( almost ), and if the wind is in the same direction throughout the ride, that 'more-or-less' cancels out.

I was commenting on the cals per hour, not the distance.

As climbing hills uses more cals than going down them, and climbing hills takes longer than going down them, the hilliness of a circular ride certainly does not cancel out. Far from it.

The ONLY sensible measure of energy consumption for road vehicles is units per DISTANCE. Hence 'mpg', 'l/100km' and 'g/km' in the motor industry.

When calculating the energy requirements for a circular ride, I firstly calc the theoretical 'flat road' consumption in kJ per km. It usually comes to around 120 kJ / km for me. I then add on the appropriate kJ for the uphill bits and subtract kJ for the downhill bits. Climbing and descending can be got from BikeRouteToaster. Speed does not enter the equation therefore time is irrelavent.

Then convert to kCals/km and round to the nearest 50. 50 kCals either way is 'splitting hairs'. If you're worried about 50 kCals, have two extra spoons of sugar in your tea,

But remember, over half of the total is me getting rid of unwanted fat, so I don't have any sugar in my tea.

This was thrashed out in the mid nineties for the Audax UK handbook. They used to suggest 8 kCal/min until I told them exactly what I have just said. They then stopped publishing kCals numbers per time because its not representative.

Mick F wrote:

Ayesha wrote:What you expend uphill, you regain downhill ( almost ), and if the wind is in the same direction throughout the ride, that 'more-or-less' cancels out.

I was commenting on the cals per hour, not the distance.

As climbing hills uses more cals than going down them, and climbing hills takes longer than going down them, the hilliness of a circular ride certainly does not cancel out. Far from it.

I'd agree. My flat speed is around 20mph; my 14.5 commute to work, which has more downhill than uphill (starting altitude c. 400', finishing altitude c. 200', lots of ups and downs in between) takes at least 56min.

Consider a ride that's a simple climb over a 10% hill (same both sides). Now, I don't know about you, but I ascend a sustained 10% at about 6mph if I'm really trying. So suppose it's half a mile up and half a mile down. Were it flat, that mile would take me 3 min. But at 6mph it'll take me 5 min. just to get to the top. I can only get the up and down to cancel out if I exceed light speed on the way down and travel backwards 2min. in time. By my calculations, 20mph flat and 6mph on a 10% are both 275 watts on a road bike, so that implies my figures are about right here.

Lesser slopes have a less pronounced effect, but it's always there. You can never get back on the down what you lose on the up.

Same is true, incidently, with cars. The industry may well quote MPG but I know I get less in hilly Derbyshire than I would out in flat East Anglia. The ups and downs fail to cancel in exactly the same way.

Is that 275 Watts at the flywheel, rear hub or at the tyre/road interface?

Physics is physics, It takes Joules to move air and Joules to lift mass against gravity.

Moving air, the equation is a square law. Double the speed, quadruple the required energy.

Raising mass, unless its done very quickly and has aerodynamics involved, ( so low for a cyclist, it can be ignored ) it can be taken as a 'constant'.

1 J = 1 Newton per metre.

If you insist on bombing along at 20 mph on the flat, no wonder your 10% climbing suffers.

Incidentally what is that bike which requires 275 W at 20 mph? The one with a parachute behind it ?
Even with 7.5% taken off for tranny losses, its still high.

Wait a minute. My Raleigh 20 with panniers needs 280 W at 20 mph. My appologies.

Ayesha wrote:Is that 275 Watts at the flywheel, rear hub or at the tyre/road interface?

Physics is physics, It takes Joules to move air and Joules to lift mass against gravity.

Moving air, the equation is a square law. Double the speed, quadruple the required energy.

Raising mass, unless its done very quickly and has aerodynamics involved, ( so low for a cyclist, it can be ignored ) it can be taken as a 'constant'.

1 J = 1 Newton per metre.

If you insist on bombing along at 20 mph on the flat, no wonder your 10% climbing suffers.

Incidentally what is that bike which requires 275 W at 20 mph? The one with a parachute behind it ?
Even with 7.5% taken off for tranny losses, its still high.

I was using an online calculator; really not that bothered; the maths work out the same way. You don't get back on the downs what you lose on the ups. Take the example I gave; the moment you hit a gradient that reduces your climbing speed to half your flat speed, you cannot possibly gain back the lost time. Consequently at a constant power, the total time is longer, therefore more energy is required. Physics is indeed physics, but I'm not sure you're using the right physics for the job, since your answer contradicts what's easily observable.

Use the spreadsheet on the CTC website. Its near being correct.

Concerning that 1 mile conical hill.
If it were flat, it would take 50 kCals to complete.
Climbing, 1/2 mile at 10% would be 1/20th mile elevation gain. That's 80 metres. If your entire mass is 400 N, its 160000 J or 160 kJ or 40 kCals.
You won't be pedaling down the second half of the hill, so half the 50 kCals can be removed from the total.

The total for climbing and then descending will be 65 kCals !

In reality though, if the hill looks tough and a ' round the hill' route is chosen, the 'flat' distance is 1mile x pi/2 = 1.6 miles ( half the circumference of the conical hill.)
Going 'round the hill' on the flat now requires 78 kCals.

Let that be a lesson to the 'Hill dodgers'...


PS. If you do download PowerCalc.xls off the CTC website, you will notice the column entitled "Work" is in units kJ/km.

MPG is a stupid method of calculating fuel consumption. It takes no account whatsoever of driving style or terrain. I suppose it's the best method we have, but it doesn't mean it's a good system.

This is the same with cycling. Riding a bike takes TIME not miles. Miles can be easy or difficult, fast or slow, boring or entertaining or any other variable. Hilly terrain takes longer to ride than flatlands for the same distance.

TIME is the thing that matters. How long will it take to cycle to work? How long have I got until tea time when I can ride home again? What time will I get home?

Cals per hour is a better figure and more worthwhile than cals per mile. I'm not an athlete, far from it and I tend to put the same effort into each and every pedal stroke - using gears to vary speed as much as I can. I come to a hill and change down so the power in my legs remains the same, this then makes me slower, making the distance per time smaller. Therefore it's time that matters, not distance.

The mpg number on a new car's sticker is gained from a specific laboratory emissions test. The test is strictly controlled so every manufacturer performs the same test. Then mpgs can be directly compared.

I perform a test on my indoor trainer. I ride a distance of ten miles as fast as I can and compare it with last week. If its less minutes and seconds, I'm happy.

dougie wrote:Just for a bit of fun having clocked up 2000 miles since January (I wish it was more but that's another story....) I thought I would play with some numbers...

I bet you wish you had not started this bit now.

dougie wrote:The cost of de-stressing, good worthwhile exercise, quite reflections, seeing so much more in the countryside than driving my car = priceless!

I do not believe you could be challenged on this by any sane person.