How much does weight influence performance?

[sias]

I must bow to Johan Bornman's superior knowledge of all things cycling! I thought Asker Jeukendrup would know what he was talking about, but apparently he is a twit according to Johan.

Not every one is a budding Einstein with several PhD's in astrophysics and rocket science.

With knowledge I do have, I seem to be doing OK on the bike, so I'm probably not that stupid...

[Man with no name]

Assumptions: Anything under 1% is enough to effectively discard in the practical world.

 

Unless of course' date=' the performance differential between the two situations you are comparing is of the order of a single percentage point.  Then an absolute value of 1% change becomes huge in relative terms

[/quote']

 

What would the percentage differential be in a bunch sprint - both time and distance wise? Surely that's less that 1%!

 

Statistically 1% is (more or less) 2 standard deviations, which is not enough ito confidence intervals when you deal with situations like this, so I don't think a "real world" argument applies here.

Man with no name2007-08-30 07:39:48

[Johan Bornman]

I must bow to Johan Bornman's superior knowledge of all things cycling! I thought Asker Jeukendrup would know what he was talking about' date=' but apparently he is a twit according to Johan.

Not every one is a budding Einstein with several PhD's in astrophysics and rocket science.

With knowledge I do have, I seem to be doing OK on the bike, so I'm probably not that stupid...

[/quote']

Sias, I'm saddened by your sarcasm and bitterness. You posted something on a public forum which wasn't correct and someone corrected you. Live with it, but learn. You're the second person on this forum who responed by wallowing in mock self-pity. Elementary physics isn't rocket science and you don't need a Phd in astophysics, whatever that is, to understand some of the basic concepts. I think anyone here can, with a little bit of effort, understand the physics of cycling. It requires common algebra, not even integration and an enquiring mind. Don't blindly repeat what you read in bike magazines.

BTW, who is Asker Jeukendrup?

[Johan Bornman]

[quote name=Man with no name

 

What would the percentage differential be in a bunch sprint - both time and distance wise? Surely that's less that 1%!

 

Statistically 1% is (more or less) 2 standard deviations' date=' which is not enough ito confidence intervals when you deal with situations like this, so I don't think a "real world" argument applies here.

[/quote]

 

The 1% that was bandied about here was the increase in energy required for accellerating a bicycle and rider with two wheels 400g heavier (at the rim) than a bicycle and rider with lighter wheels but with the saved 400g  in his belly to a given speed over a given time. Point was, it was very, very little extra energy. Since this energy only comes to play when accellerating (which contrary to popular believe bicycles don't do much of) and climbing, the conclusion is that a weight saving on the wheel holds nowhere near the benefits bandied about in bicycle magazines and repeated on chat groups.

 

As for the mistaken belief that I know will pop up next, that a 1% saving (in the example above) equates to a 1% increase in speed or, a 1% faster time, that's not true either. But lets debate that one seperately when it crops up.

 

 

[xak1]

Its a pity the topic degenerated into this.  I introduced it in order to generate some views on science compared to real life.  As in all of science, you get the formulas, but then you get real life.  With regard to this issue, there are so many variables, and any combination of any of them can result in a different outcome.  It is therefore quite simplistic to try and isolate one.  I also think that the bike industry has a lot of "urban" legends, which unfortunately very few LBS employees try to understand.  One of these is the "loosing weight on the wheels" issue.  The answer is probably a bit more complex.  Weight at the center of a wheel has exactly the same effect as weight on the bike or person.  Weight on the outside of the wheel (tyre, rim, etc.) does have a rotational effect.  Remember the experiment holding two weights to your chest on a turning chair.  The moment you extend your arms, you go slower, when you bring them in, you go faster again.  I am, however, not sure how big effect it really has on performance.  My view is that weight lost on a wheel provides such a small benefit over weight lost in other places, that one can ignore it.  Furthermore, as I originally indicated, there are so many variables, that in practice, we can not get to accurate calculated numbers.  We can, however, say that weight has the biggest effect on an uphill, and little or no effect on flats and downhills.  If I look at it practically, I think you will probably not loose more than 1-2 minutes on a 13km climb with 600m ascent, for every 1 kg heavier.

Another area that LBS employees are very bad informed about, is full suspension design and the effect of this on pedalling efficiency.  People tend to focus on the shock, but suspension is all about how the pivots work.  This is maybe a whole new "scientific" topic.

[TitusTi]

Cycling is all about working against the forces that are working against you, not so. Hence to remain at a constant speed on an incline you would have to remain in eternal acceleration. This would be a little less so on a flat but still present.

[shadowchaser-d]

I have never been a great climber and probably never will.....but i don't think that the bike weight has any effect on my ability to climb a hill faster.  My training bike weighs in at 8.6kg and my racing bike at 7kg and there is a particular hill that i ride and i can see very little difference the lighter bike made.  I have increased my power/weight ration 4watt/kg and i still can't climb, i would have to go with that muscle fibre theory then as i can't see the benefits of spending 20k on wheels to make you a better rider.......although i is nice to have cool wheels.

[TitusTi]

Spot On Xak1, the actual shock is less important than the actual design.

[Sean Badenhorst]

I don't know how to make one of these url links 'live' so just cut and paste this and have a look at the document called Col de la Tipping Point. It's sets about explaining that lightness isn't everything and that aerodynamics plays a bigger role than most may think. It's very interesting, but make sure you've got about 10 minutes to read it properly.

 

http://www.cervelo.com/content.aspx?m=Engineering&i=WhitePapers#4

[bruce]

Cycling is all about working against the forces that are working against you' date=' not so. Hence to remain at a constant speed on an incline you would have to remain in eternal acceleration. This would be a little less so on a flat but still present.[/quote']

 

Nope, afraid not.  Acceleration is defined as the rate of change of speed.  So if speed is constant, there is zero acceleration.  So the forces pushing the bike, and the forces opposing the bike balance each other when speed is constant.  The greater the speed, the greater the forces opposing you, and the harder you have to work to maintain constant speed.

[fandacious]

Technically Titus is correct, but so is bruce..

It all depends on relativity. Even if your speed is constant on an incline, you're accellerating because gravity has an accelleration of 9.8m/s2. So if you've moving up at any speed, you're accellerating, albeit not relative to the surface you're travelling on

[Johan Bornman]

Technically Titus is correct' date=' but so is bruce..

It all depends on relativity. Even if your speed is constant on an incline, you're accellerating because gravity has an accelleration of 9.8m/s2. So if you've moving up at any speed, you're accellerating, albeit not relative to the surface you're travelling on

[/quote']

 

[javadude]

You guys are all getting too technical. Do whatever you "think" will make you  go faster, and more than likely you probably will.

[Harryn]

its been a facinating debate. bottom line: I'll stay off the chocolate cake

[Willehond]

 

Sias' date=' I can't blame you for repeating the stuff you read in bike magazines and hear from other people who heard it from someone who read it in a bike magazine. In the PR business, they know that if someone hears something three times from three different sources, it is considered as the gospel truth, and they design PR (publicity) campaigns around that.

 

But back to physics. The notion that weight saved on a wheel is somehow more valuable than weight saved on the bike or body, is pure nonsense. The effect is so miniscule, in the order of less than one half a percent for an 85kg rider and bike losing say 400grams on the wheel, that it is completely negligible. Weight is weight, save it and you gain. Weight (saved) on a wheel is jsut weight saved.

 

[/quote']

 

Johann, I loved your discussions on Rotor blades and dispelling their scientific mumbo jumbo, but sometimes your arrogance is slightly misplaced and over the top.  Accusing Sias of being duped by "stuff you read in bike magazines" is a bit rough, not to mention condescending...

 

If you want a credible source of the rotational weight theory, look at research done by Ed Burke (I hope you know who he is.)

He did studies on so called rotational element (wheels and pedal-and-shoe systems) indicate that saving 250g on each shoe (easily done) would save 1.3 percent of rotational power at constant speed on a flat road, plus 0.4 percent extra on climbs!  This translates to 1.5 to 1.7% extra power required by a cyclist.  Not bad for "weight is weight" hey?

Burke suggests that a pound added to the wheel rim is equal to two pounds on the bike frame.  I know what you think about that, but his reasoning on energy required to provide the kinetic energy for rotational and linear motion makes sense to me, so before you fob it off as "stuff you read in magazines", make sure that credible sources have not actually done studies first.

 

Remember that wind resistance slows you down, for which you have to compensate by accelerating the wheels forward and around, in my mind it makes sense that rotational elements will require extra force to accelerate.  Stating that rotational systems take ZERO force to accelerate against resistance does not cut it in my physics book.  I would have flunked applied mathematics if I claimed that...

Willehond2007-08-30 14:27:18

[epoh]

Iban Mayo and Mauricio Soler is in the leading group up 10km from the summit of the Col du Calibier. Soler realises he has still got a piece of newspaper tugged in from the previous descent. So he pulls it out and starts reading it. Coincidentally Le Equippe published this thread in the paper (How random is that?). Soler starts reading it and realises it  is the biggest load of sh!T he has ever read. He throws it away, he gets up and attacks haard!

 

Mayo tries to follow and Soler is like STFU!!$ and attacks again. Mayo is dropped and lots of stuff is running through his mind... "Omg im on EPO, my bike is 2KG below the UCI limit , my wheel is 200grams.. gees my freakin Powertap training program..heelp! How is Soler doing it!?! He is not riding for a pro tour team! He can't afford a powertap!! his bike is heavier than mine.. i weigh lighter than him.. OMG!!

 

Soler takes the victory without knowing a watt from a heart beat!!