Weight! Does it really matter?

[darkstar]

Only when I'm down to my target weight will I deserve a lighter bike

Completely agree, i don't understand why people get the lightest bike they can possibly afford when they have extra kgs of pointless body fat! My own strength to weight ratio is not perfect so what difference does a marginally lighter frame make? if anything a heavier one will get me fitter
Only racers or top athletes should worry about the weight of the bike when it is this marginal imo, unless a slight improvement of time is really that important to the average rider.

 

[dodgy]

I've lost a few pounds this year, but I already had a light(ish) bike. I like having a light bike and I don't feel the need to justify it. I'm going to buy a new winter bike soon and it will be well over specced for the job, but that's what I want. I love bikes and cycling.

 

[just4fun]

not just weight the components also come into it too. im in the situation of needing to loose it more from my body than my bike, that way when i get on my lead weight MTB it wont be so slow

 

[arallsopp]

I'm not getting into the science of it, but can offer this observation based upon daily 30 mile cross town commutes. The BigOrangeBeastie and Furai travel at an identical average speed. The Furai climbs a little faster, but descends a little slower. The BigOrangeBeastie has an 8kg weight penalty over the Furai, but is NO slower overall. This is based upon averaging the time over +6months of riding both.

I will concede that BoB takes more energy to ride, and that I tend to arrive more knackered when riding it than the Furai. That's why I take the Furai on anything over 150 miles...

Up to that distance, they're the same.

 

[HJ]

Did you realise that once you've got going, heavier bikes are better when cycling against the wind. Momentum and all that.

From experience that just ain't so...

 

[jimboalee]

From experience that just ain't so...

I had to think about that as well.

In theory, maybe so, but in practice....???

The classic analogy is the ping-pong ball and the steel ball bearing of the same size.
Same size, same shape but the steel ball is many times heavier.
Place them side by side and wave a hair dryer at them. See the ping-pong ball blow away in the wind while the steel ball rolls away slowly.

If you roll the balls along the floor and someone opens the door and lets a gust of wind in, the ping-pong ball will stop and roll off in the opposite direction while the steel ball carries on with little decelleration.

The same principle applies to two rolling bicycles of same cross section area and shape.

So why does it feel more difficult on a heavier bike?

 

[tyred]

I would imagine the momentum thing would apply if you were maintaining a constant speed on a flat, straight road with nothing to impede your progress but if you are speeding up and slowing down for tight corners, hills or poor surface or whatever, the heavier bike needs more energy to accelerate it again (and more braking effort to slow it down).

 

[lit]

That's why it's better to regulate your speed/pedalling.

 

[jimboalee]

I would imagine the momentum thing would apply if you were maintaining a constant speed on a flat, straight road with nothing to impede your progress but if you are speeding up and slowing down for tight corners, hills or poor surface or whatever, the heavier bike needs more energy to accelerate it again (and more braking effort to slow it down).

Climbing a hill and accellerating are essentially the same thing.

The analogy for this is the old 'golf ball in a dustbin lid trick'.

Place an upturned dusbin lid on the passenger seat of a car ( or on your handlebars ). Put a golf ball in it.
As you accellerate, the golf ball rolls to the rear. How far up the curve of the dustbin lid depends on the rate of accelleration.

Now drive ( or ride ) up a hill. The golf ball will roll to the rear. How far up the curve of the dustbin lid depends on the gradient of the hill.

 

[jimboalee]

The pukka device is a 'pendulum inclinometer/accelorometer'.

 

[jimboalee]

Once you've measured your accelleration, you can go to our friend Sir Isaac and see Force = mass x accelleration.


"Shut up Jimbo, you're talking 'mumbo jumbo' again.

 

[jimboalee]

On a hill, the acceleration part is g ( 9.81 m/s^2 ) multiplied by the Sin of the inclination degrees of the hill, in addition to any 'roadspeed' acceleration happening.

 

[swee'pea99]

The fitter you are, the less time difference it makes, so a TDF rider would lose maybe 50sec for carrying an extra 5kg
It doesn't make any difference whether the weight comes off your waist, out of your panniers or off the bike.

Six pages in, if there's been a definitive answer to this, from page one, I've not noticed it. It's always seemed to me like the nub of the matter.

Yes, it's better to lose a few pounds by cutting down on the pies. Yes, a lighter bike will, other things being equal, be an easier, faster ride than a heavier bike. But is it the weight of the bike that matters or the weight of 'the total package' as someone described it? Does losing 1Kg off the waistline and 1Kg off the bike have exactly the same effect?

Tim Krabbe's 'The Rider':

"Jacques Anquetil, five times winner of the Tour de France, used to take his water bottle out of its holder before every climb and stick it in the back pocket of his jersey. Ab Geldermans, his Dutch Lieutenant, watched him do that for years, until finally he couldn't stand it any more and asked him why. And Anquetil explained.
A rider, said Anquetil, is made up of two parts, a person and a bike. The bike, of course, is the instrument the person uses to go faster, but its weight also slows him down. That really counts when the going gets tough, and in climbing the thing to do is make sure that the bike is as light as possible. A good way to do that is: take the bidon out of its holder."

So, was Anquetil wise, or bonkers?

 

[MajorMantra]

If your climbing style involves chucking the bike all over the place whilst keeping your body reasonably still, then I suppose there could be some logic in what Anquetil said. I'm sceptical about it making much difference though and I would have thought the inconvenience of having a bottle in your pocket outweighed any possible advantages. Anquetil may have been a great rider but that doesn't make him a great physicist.

Matthew

 

[Woz!]

Makes some sense to me - the bike will be moving far more than the rider when the rider's really going for it. If you're out of the saddle and pumping the bike will be moving side to side with every stroke, but a good rider will tend to stay vertical with just forward motion.
If you've got any extra weight on the bike then the side to side motion will be sapping a lot of energy as you have to decelerate and accellerate that weight every time the bike sways, irrespective of the forward motion of the bike.

Personally though, my bike's a tourer and I load WAY too much junk in my panniers because I never know when you might need that yo-yo/camera/monocular (honestly*!) on my 26 mile round trip commute


*I've yet to need the yo-yo or the monocular. But you never know.