Is my maths correct?? Climbing and w/kg

[mr4fox]

Help me out here weightweenies

I'm trying to get a tangible feeling for how much time and/or power a lighter bike actually saves on a climb.

Ok so let's say I'm climbing a hill at 400w.
Me+helmet/shoes/clothes weighs 74kg.

Bike in scenario 1 weighs 6kg
Bike in scenario 2 weighs 5kg

So in scenario 1 I'll be climbing at
5w/kg=400/(80)

So to work out the power needed to climb at the same speed in scenario 2...is it as simple as

400/80=x/81

x=400*81/80

=405w?

Furthermore

If 1kg of upgrades or drop in body mass is worth 5w at 5w/kg

And 5w is 1.25% of 400

Then, on a 10min climb (600sec) I would reach the top 600*0.985= 591sec
= 9second faster?


Is this how to work it out?


Does gradient change the equation? Or is it simply w/kg that determines climbing speed at any given gradient?





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[elSid]

http://www.analyticcycling.com/

[destinationwarmth]

Not really 9 seconds faster... it may vary depending on the gradient, the speed, etc.

It depends what's the Watts used to overcome gravity (slope), aerodynamics, and rolling resistance

Try http://www.bikecalculator.com to try out different numbers for free

[RimClencher]

Something none of these calculator sites seems to mention is the assumption you are riding at constant velocity. Almost no one is able to maintain an absolute constant velocity riding uphill. Even the pros tend to yo-yo along depending on where they are in the pedal stroke. Each small deceleration requires a small acceleration, which takes more energy than riding at constant velocity. These decelerations get more pronounced the steeper the gradient, so the steeper the gradient the less accurate these online calculators, and your calculations, will turn out to be.

[Marin]

Something none of these calculator sites seems to mention is the assumption you are riding at constant velocity. Almost no one is able to maintain an absolute constant velocity riding uphill. Even the pros tend to yo-yo along depending on where they are in the pedal stroke. Each small deceleration requires a small acceleration, which takes more energy than riding at constant velocity. These decelerations get more pronounced the steeper the gradient, so the steeper the gradient the less accurate these online calculators, and your calculations, will turn out to be.

If you follow your own train of thought, the decelerations and accelerations will cancel out. Where should the energy go?

[sungod]

^^^this

conservation of momentum is a wonderful thing

[mr4fox]

Not really 9 seconds faster... it may vary depending on the gradient, the speed, etc.

It depends what's the Watts used to overcome gravity (slope), aerodynamics, and rolling resistance

Try http://www.bikecalculator.com to try out different numbers for free

So how does the gradient effect the out come
in this scenario scenario assuming the same rider/position/equipment/tyres/drag coefficient/gradient etc. the only difference is 1kg.


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[Marin]

If you're going slow enough that rolling and air resistance are very low compared to the lifting work (i.e. a steep gradient), the weight savings will matter the most, and 1% saved weight will make you almost 1% faster.

[Marin]

I like this calculator: http://kreuzotter.de/english/espeed.htm

[sungod]

If you're going slow enough that rolling and air resistance are very low compared to the lifting work (i.e. a steep gradient), the weight savings will matter the most, and 1% saved weight will make you almost 1% faster.

yeah, this is the best way to look at it

[jekyll man]

Dan (DJ OConnell) did all this years ago.
Somewhere on here is his working out and explanation. Can't be arsed to search for it.
Basically it makes FA difference.

[shinzomaeda]

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[Marin]

The classic - I was too lazy to post this chart before

Consider that rolling resistance also is proportional to weight, and at a gradient of only 8 in 100, 93% of the power you are spending is linearly scaling with every kilo you are lifting.

If you are doing less than 300W and are thus going slower, the air resistance is even less and weight matters even more.

[shinzomaeda]

The classic - I was too lazy to post this chart before

Yes, sorry, I was being very lazy. Is chart relevant or helpful?

[darnellrm]

If you follow your own train of thought, the decelerations and accelerations will cancel out. Where should the energy go?[/quote]

Not at all... The heavier bike will decelerate quicker and accelerate slower each cycle.