Rotating weight does it make any difference and why?

Excellent point

Good point re weight – it's not the be all and end all by any means, but light is good (assuming all other factors are good enough)

aracer – Member
On the contrary, it's impossible to feel a 0.06% difference – we're into placebo effect here.

How on earth can you prove that?

cynic-al. It's very difficult. especially as high levels of acceleration (when small percentage changes can make a real difference) may be relatively sparse.

Let's assume for a second that a ride can accelerate constantly at 0.5 g (4.905 m/s/s). He will ride for 100 m, he finishes in 6.386 seconds.

He switches to a bike which gives a 0.06 % increase in acceleration

He finishes in 6.3836 seconds

Less than 3 milliseconds difference in 100 m of constant acceleration.

I ain't saying you can't notice, but you'd have a very finely tuned sense of judgement if you could.

Kinetic energy of a non rotating moving object = 1/2 x mass x velocity squared.

Total kinetic energy of a rotating hoop (ie a wheel) roughly = mass x velocity squared.

So the total kinetic energy of the rotating wheels of a moving bicycle roughly equates weight for weight for twice as much kinetic energy as the non rotating parts of the bicycle. Hence the reason for the saying that 50g off the wheels is worth 100g of the frame. When you accelerate, you are adding kinetic energy.

That's the maths, as too how much effect it has is arguable – see all above threads…. 😉

That's my point chops.

IMO/E you develop a feel for your bike and can detect minor changes. I'm not saying you could detect 100gm of both wheels, but no-one should say you couldn't without some proof!

If anyone wants to do real numbers I'd be most interested in seeing the difference between a 2kg Alu wheelset vs 1.5kg carbon wheelset.

I presume if I said gravity made things fall down you'd want me to prove it?

Assuming about 100kg for rider plus bike, then swapping out 2kg wheels for 1.5kg wheels would see about 0.5% reduction in potential energy input for hill climbs plus 0.5% reduction in kinetic energy input for acceleration.
For those that argue that 0.5% is naff all, it's worth remembering that it's not a linear scale – ie if I put a 100kg weight on the back of my bike I'd take more than twice as long to get up some of the hills round here! Also,0.5% is half a mile over a 100 mile course.
(not saying you;ll get that much gain because of other factors – but just demonstrating that 0.5% gain is not to be sniffed at)

All the calculations are based on saving time…do those % savings directly translate into energy saved? Ie not increasing acceleration but decreasing effort required for the same acceleration.

stuart – all my calcs are based on reduction of energy input 😀

stuart – all my calcs are based on reduction of energy input

Aye, i saw that after i posted…haha, takes me too long to type!

0.6% = woopiedooo!! – I'll have me some of that! I had some weight weenie wheels on my full suss, ended up with one rim dinged and the other tacoed – needless to say my latest wheels have erred on the side of robustness 🙂 I'm now of the opinion – if it weighs less than 30lb, OK, but sub 25lb prob isn't necessary. will you be able to feel that improvement of 0.6% – I think you're kidding yourself if you think you can.

I can't imagine it makes any difference at all.

I mean, when you watch MotoGP they can pick a wheel/tyre etc up easily in one hand, whereas on a road bike the wheel is heavy enough, without the tyre/disc etc. But thats' just fashion of course. 😉

I can certainly tell the difference; we once went to Afan after a day uplifting in Cwmcarn – heavy wheels, thick tubes, 3-ply tyres and 203 discs – jesus was it difficult, and unenjoyable.

aracer – Member
I presume if I said gravity made things fall down you'd want me to prove it?

🙄