# lighter weight and climbing performance



## kneejerk

Anyone have a formula for loosing grams off the bike/rider compared to climbing hills and time? I thought I saw one floating around somewhere. What is a meaningful weight savings? I know that the rotating parts are likely the most important to be critical of mass. What about the other parts and rider?


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## spade2you

Simply put, it's less effort to haul less weight up a hill. Usually, the rider can shed more weight than a bike could. 

Nowadays, it's not too difficult to get your bike to be 15lbs or less.


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## ukbloke

For hills that are of a reasonably consistent and steep enough grade, the energy required to climb it is linear with total mass. For the last couple of years, I've used the obvious formula to estimate power on hill climbs using potential energy gain (total mass times g times height gain) divided by time plus a constant to estimate the power required to over-come resistance. I started off with a constant of 50W, but I reduced it to 40W when I had the chance to calibrate with a power-meter. Given a suitable climb the data from this equation and a PowerTap are very close.

Another way to look at it, is that (given the same power output from the rider) a weight reduction will decrease your time by the percentage that you decreased the total mass. If you and your bike weigh 200 pounds and you drop 2 pounds of weight (from you or from the bicycle), then your time will drop by 1%. If it is a 20 minute climb you will have saved 12 seconds.

In my experience, for climbing performance it makes no difference whether the weight comes off the rider, the bike or the wheels. I have had much more success getting performance gains by improving the condition of the rider than anything else!


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## Hank Stamper

The big problem with any formula will be the assumptions it will need to make which aren't really safe assumptions.

To calculate a how weight off the bike helps climbing you'd need to assume no loss in stiffness. Some super light wheels won't help if they're really flexy.

To calculate the benefits of weight of the rider you would have to assume no loss of muscle or gain in fitness. In other words to say something like an X pound reduction in body weight = X mph benefit would not be something you could realistically apply accross the board. If some lard ass loses 10 pounds through working out that will obviously have a different impact as compared to someone in tip top shape losing 10 pounds by starvation.


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## kbiker3111

http://www.analyticcycling.com/

Play around here. The nice thing is, assumptions or not, you can make comparisons that apply to the real world. (ie, if I get that carbon stem, how much faster will I climb)

Rotating weight is only important in accelerations. Assuming you're climbing at a constant speed, or close to it, rotating weight will have the same effect on climbing as static weight.


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## samh

*losing weight*



Hank Stamper said:


> To calculate the benefits of weight of the rider you would have to assume no loss of muscle or gain in fitness. In other words to say something like an X pound reduction in body weight = X mph benefit would not be something you could realistically apply accross the board. If some lard ass loses 10 pounds through working out that will obviously have a different impact as compared to someone in tip top shape losing 10 pounds by starvation.


 Really unintelligent comment.


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## Camilo

samh said:


> Really unintelligent comment.


how so?


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## Jay Strongbow

samh said:


> Really unintelligent comment.


Why? It made sense to me. Saying something is unintelligent without explaining why on the other hand....


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## steve_e_f

I stink at math, but here are some figures that I was trying to break down to see if weight impacted things at all. I've climbed the same hill many times since January and recorded it every time /w my Garmin + Power Meter.
The hill is 5.42 miles long. 1500 foot gain.

Each of these times has higher wattage and a faster time, so how do I adjust the times to reflect if they were all done at the same wattage?

The 4th ascent I did with wheels/tires that are roughly 450gr lighter than the first three times. Did the lighter weight help (significantly) or was it just the higher power? My weight has been pretty constant between then and now, but would a pound of weight increase offset a pound lost in wheels?

I'm not even sure if anything can be read into these numbers. Maybe there are too many unknown factors to draw comparisons between each workout.

What I'd like to do is re-compute these times @ 300w each and see if the adjusted times are similar or notably different.

Time 1: 29 minutes. 287w average
Time 2: 26.4 minutes. 300w average
Time 3: 26.28 minutes. 305w average
Time 4: 25.35 minutes. 330w average


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## ukbloke

steve_e_f said:


> I stink at math, but here are some figures that I was trying to break down to see if weight impacted things at all. I've climbed the same hill many times since January and recorded it every time /w my Garmin + Power Meter.
> The hill is 5.42 miles long. 1500 foot gain.


If your hill climb is consistently up (e.g. grade of >= 5% and no intermediate flats or descents), and speeds are consistently low (e.g. ~10mph), I have had great success with the obvious potential energy calculation plus a constant offset. For example:

power = (mass x g x height) / time + constant

where power is in Watts, mass is in Kg (total for bike + rider), g is 9.81, height is elevation gain in metres and time is in seconds. The constant is a power in Watts that empirically accounts for rolling resistance and aero effects. I have found that a value of 40W works well for me to give good correlation between this calculation and a power-tap.

So what could you do with this? Given that you know mass, g, height, time and a guess constant of say 40W for each of your rides, you can calculate the estimated power. You can then compare this with the power that you measured. You could see if there is any significant delta between them and whether this correlates with perceived improvements in your bike weight or rolling weight. Or you could figure out how to normalize your timing measurements to constant power - this should be a reasonably accurate conversion. You can pretty much just multiply the actual time by actual_watts / 300W since it is almost a linear relationship for "well-behaved hills" (ie. ignore the constant).

My experience - I went from a crappy cheap Al bike to a very nice carbon bike and dropped a few pounds and upgraded the wheels. Overall effect on hill climbing performance due to the weight drop was projected at about 20-30 seconds in a 20 minute benchmark climb. In practice I could not measure the benefit as it is less than my week-to-week performance variation. I have improved my PR from 19:45 on the old bike to 19:15 on the new bike, but this is just as likely to be due to other factors than the weight alone.


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## steve_e_f

hmm... the hill has one downhill section which lasts for about :45. I guess that would mess the calculation up?


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## ukbloke

steve_e_f said:


> hmm... the hill has one downhill section which lasts for about :45. I guess that would mess the calculation up?


Yes. To deal with this I would try to factor that part out of the ride. Let's say the ride has parts A, B and C where A is the first up, B is the down and C is the second up. You would calculate the elevation gain of A + C and ignore the elevation drop of B. Then figure out the time spent in B (top of crest to bottom of dip) and subtract this from the total time. This isn't quite right because you carry some speed from B into C but I think you can ignore that. Alternatively, just do the calculation for A or for C alone.


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## tedgrant

one cant ignore elevation drop. heavier objects will decend faster than light objects, up to terminal velocity 

I found out the fun way when I dropped my buddy who is 40 lbs heavier than me going up a big hill, only to watch him fly by on the downhill as he yelled out "Gravity, mother****er!" as he went by....


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