Power improvements vs Speed improvements

[fergie]

Have a new bike that is a lot lighter than my previous rig. Going up a regular climb I achieved a 1.49% improvement in power but a 4.62% increase in speed.

Is such a difference to be expected and does this mean that Lance is wrong and it is about the bike?

Hamish Ferguson
Cycling Coach

 

[Woofer]

It's just a book *title* not a scientific theory.

We can simply plug numbers into www.analyticcycling.com to find out how much faster we can climb a hill with lighter equipment.

Or you can read Kraig Willett's analysis of the difference between just wheels for racing on different courses.

 

[fergie]

It's just a book *title* not a scientific theory.

We can simply plug numbers into www.analyticcycling.com to find out how much faster we can climb a hill with lighter equipment.

Or you can read Kraig Willett's analysis of the difference between just wheels for racing on different courses.

It was just a *joke*.

The question was should I expect just a difference in improvments to be totally accounted for by a lighter bike.

Hamish Ferguson
Cycling Coach

 

[Eldrack]

You probably get a psychological boost from the nice, shiny bike that has "Go faster" written all over it. The lower weight probably helps too though .

Second thought: If you have two bikes, both the same weight and output the same power on both of them but one is stiffer then the stiffer one will go faster as more power is "transferred" into making you go faster.

 

[velobob]

I assume that your new bike has lighter wheels? I think lower rotational mass could be part of the reason for the disproportionate boost in speed over power.

 

[RapDaddyo]

I think it's unlikely that you gained such a large increase in speed due to the bike weight alone, but it's entirely possible that you gained the increase due to a more efficient use of power on the climb. No climb is constant grade and it makes a huge difference where you increase power a bit and where you float a bit. This can easily account for the difference. I'm guessing the bike weight accounted for no more than 2% of the difference.

 

[Squint]

Yeah, 'cuz of all the nano-accelerations between pedal strokes...

I assume that your new bike has lighter wheels? I think lower rotational mass could be part of the reason for the disproportionate boost in speed over power.

 

[Woofer]

It was just a *joke*.

The question was should I expect just a difference in improvments to be totally accounted for by a lighter bike.

Hamish Ferguson
Cycling Coach

Given that you did not list the elevation gain or length of the climb, those things may be possible with those parameters.

It really is as simple as plugging in numbers at www.analyticcycling.com. The physics involved at bicycle speeds are well understood.

A popular climb near me has inspired R Chung to make a web page dedicated solely to calculating power from rider input parameters:
http://anonymous.coward.free.fr/wattage/olh.html
It's within 3 % accurate for me just by inputting the correct rider weight, equipment weight, and time, which is within the precision range of the PowerTap that I am using.

 

[RapDaddyo]

It really is as simple as plugging in numbers at www.analyticcycling.com. The physics involved at bicycle speeds are well understood.

But, only if the climb is constant grade and the rider uses constant power. As soon as you depart from either of these two assumptions (which are almost never both true), you introduce variance by virtue of where the rider used more power and where he used less power. I think these differences can easily add up to a 5% difference in elapsed time, holding everything else constant (e.g., rider + bike weight, wind, tires, rider position and NP).

 

[Woofer]

But, only if the climb is constant grade and the rider uses constant power. As soon as you depart from either of these two assumptions (which are almost never both true), you introduce variance by virtue of where the rider used more power and where he used less power. I think these differences can easily add up to a 5% difference in elapsed time, holding everything else constant (e.g., rider + bike weight, wind, tires, rider position and NP).

Yes that's possible but that is also *ballpark* within the precision range of SRM and PowerTap.

This particular climb is not constant (optimum pacing is probably non constant power) and multiple riders report this particular estimate to be accurate within a couple of percent or dead on.

If Fergie wishes to play a little bit with the numbers he will get a very good estimate of how much influence on performance there is in saving equipment weight.

 

[whoawhoa]

Have a new bike that is a lot lighter than my previous rig. Going up a regular climb I achieved a 1.49% improvement in power but a 4.62% increase in speed.

Is such a difference to be expected and does this mean that Lance is wrong and it is about the bike?

Hamish Ferguson
Cycling Coach

What was the % gain in power to weight, including the bike savings?

 

[kmavm]

This particular climb is not constant (optimum pacing is probably non constant power) and multiple riders report this particular estimate to be accurate within a couple of percent or dead on.

I'll back up Steven on this. Inputting my weight and times from some of my ascents of this climb is within a watt or two of my actual average powers. While Old La Honda isn't constant grade, the up and down pitches are awfully short; e.g., my NP is almost always exactly my AP for a well-paced effort, even though my effort is swinging wildly from 200W to 350W throughout, because all the little surges are less than 30 seconds long.

 

[RapDaddyo]

I'll back up Steven on this. Inputting my weight and times from some of my ascents of this climb is within a watt or two of my actual average powers. While Old La Honda isn't constant grade, the up and down pitches are awfully short; e.g., my NP is almost always exactly my AP for a well-paced effort, even though my effort is swinging wildly from 200W to 350W throughout, because all the little surges are less than 30 seconds long.

I'm not sure what Old La Honda has to do with the OP's question. He's wondering if the difference in bike weight accounts for his speed increase, which is greater than his power increase on his climb. My point was that his power profile may have been different (more efficient) on the most recent effort, accounting for a significant percentage of the speed increase. It has nothing to do with Old La Honda.

 

[Woofer]

One can use any of the online estimators that use the basic physics of bicycle propulsion to get an estimate of the gain in time performance by reducing equipment weight for a climb.

 

[velobob]

Yeah, 'cuz of all the nano-accelerations between pedal strokes...

You're right - none of the pros use light weight wheels on climbing stages even though their bikes are already at the UCI weight limit.