touring wheels upgrade

[531colin]

It’s the same fallacy….its easy to feel the difference in 1kg tyre weight when you are accelerating just the wheel by spinning it with your fingers, but as soon as you have to accelerate rider, luggage and bike, just in order to accelerate the wheel then the difference of 1kg won’t be noticed, wether it’s on your tyre or your head.

[mattheus]

You can say that tyre/rim weight is unimportant ...

... as long as you can also - honestly - say that you don't care AT ALL about weight on the bike/luggage.

Everyone will have some sensitivity lower limit!

[roubaixtuesday]

There's no fallacy just maths.

Weight at the rim of a tyre takes twice the effort to accelerate than mass on a frame.

The reason is that you need to spin the wheel as well as moving it forwards, and simply because of the physics, it takes exactly double the effort.

The wheel diameter doesn't make any difference.

It's easier to show with energy than force and torque.

Physics of a spinning ring:

Moment of inertia I = Mr2
M= mass of tyre
r = radius of the tyre

https://unacademy.com/content/upsc/stud ... -cylinder/

Energy to spin an object E = 0.5* I*(omega)2
Omega = angular velocity

https://unacademy.com/content/jee/study ... ic-energy/

So E = 0.5 * M * r2 * (omega)2



But the tyre is rolling on the ground, so
V = r* omega
V = forward velocity
So omega = V/r, and substitute into the energy equation

E = 0.5 * M * V2

Which is exactly the same as you need to accelerate the mass if it doesn't rotate, and you need to do both to the wheel, hence double the effort.

Of course, even if your tyres are 500g each more than they would be with super lightweight tyres, that's still only a kg, ~a large water bottle, and it only applies whilst accelerating, not when going uphill at steady pace.

[Chris Jeggo]

In English please?

Is the following true?

Apart from the weight they add to the overall weight of the bike, heavier wheels and tyres make very little difference to pulling away or rolling.

Someone has written on the touring tyre thread "So pulling away at a junction, 1kg on a tyre feels like 2kg on the frame". Is that untrue,?

roubaixtuesday has beaten me to it, and he's dead right. He has bitten the bullet and produced the equations I declined to do previously. The rotational kinetic energy of rim+tyre equals the translational kinetic energy. So yes, 1kg on a tyre feels like 2kg on the frame when accelerating.

[531colin]

I can accelerate the wheel by brushing it with my hand.
I need to use both legs to accelerate rider plus bike.
While I am accelerating rider plus bike, the difference between a regular tyre ( accelerate the wheel with a brush of your hand) and a light tyre ( accelerate the wheel with a light brush of your hand) is insignificant.

Unless you would like to produce real numbers demonstrating that accelerating a bicycle wheel takes a significant proportion of what it takes to accelerate rider plus bike plus any luggage.

[Chris Jeggo]

I can accelerate the wheel by brushing it with my hand.
I need to use both legs to accelerate rider plus bike.
While I am accelerating rider plus bike, the difference between a regular tyre ( accelerate the wheel with a brush of your hand) and a light tyre ( accelerate the wheel with a light brush of your hand) is insignificant.

Unless you would like to produce real numbers demonstrating that accelerating a bicycle wheel takes a significant proportion of what it takes to accelerate rider plus bike plus any luggage.

True. The inertia of rims+tyres is insignificant compared with inertia of rider+cycle+luggage.

[rareposter]

You don't really need maths to prove anything though. Put some 2.5kg wheels on a bike, go and ride up a hill.
Replace the wheels (keeping the same tyres/pressures etc) with a pair weighing 1.5kg , go and ride up the same hill at the same power.

The lighter wheels will feel better (which is a bit subjective) and will be measurably faster (which is purely objective).

There's a reason that performance wheels are lighter and it's not all marketing or snake oil!

OK, for touring I'd probably prioritise reliability and standard parts over purely lightweight but it'd still be a consideration even once a bike is loaded with touring gear.

[Chris Jeggo]

You don't really need maths to prove anything though. Put some 2.5kg wheels on a bike, go and ride up a hill.
Replace the wheels (keeping the same tyres/pressures etc) with a pair weighing 1.5kg , go and ride up the same hill at the same power.

The lighter wheels will feel better (which is a bit subjective) and will be measurably faster (which is purely objective).

There's a reason that performance wheels are lighter and it's not all marketing or snake oil!

OK, for touring I'd probably prioritise reliability and standard parts over purely lightweight but it'd still be a consideration even once a bike is loaded with touring gear.

Equally true. The inertia of rims+tyres is significant compared with inertia of rider+cycle when a second or so really matters.

[roubaixtuesday]

You don't really need maths to prove anything though. Put some 2.5kg wheels on a bike, go and ride up a hill.
Replace the wheels (keeping the same tyres/pressures etc) with a pair weighing 1.5kg , go and ride up the same hill at the same power.

The lighter wheels will feel better (which is a bit subjective) and will be measurably faster (which is purely objective).

There's a reason that performance wheels are lighter and it's not all marketing or snake oil!

OK, for touring I'd probably prioritise reliability and standard parts over purely lightweight but it'd still be a consideration even once a bike is loaded with touring gear.

As per above, it makes no extra difference where the mass is when cycling up a hill, that only matters when accelerating.

Of course the mass itself does make a difference on hills

[531colin]

Numbers? I'm just a simple biologist with rapidly declining facilities, trying to make sense of the world.

Simple numbers for a simple man....

Say bike + rider + bag = 100 Kg

Say excess wheel & tyre weight at the rim = 1/2 Kg per wheel

Is it then the case that as accelerating the wheel rim "counts double" the excess for 2 wheels is equivalent to accelerating an extra 1 Kg?

....in other words an extra 1/2 Kilo per wheel is 1% when but only when accelerating.

[roubaixtuesday]

Numbers? I'm just a simple biologist with rapidly declining facilities, trying to make sense of the world.

Simple numbers for a simple man....

Say bike + rider + bag = 100 Kg

Say excess wheel & tyre weight at the rim = 1/2 Kg per wheel

Is it then the case that as accelerating the wheel rim "counts double" the excess for 2 wheels is equivalent to accelerating an extra 1 Kg?

....in other words an extra 1/2 Kilo per wheel is 1% when but only when accelerating.

Exactly correct.

[Edit: just to be precise, it's 1% more than it would be if the mass were on the frame, 2% more than if the mass were not added anywhere]

[531colin]

Thank you for the confirmation; I won't be drilling holes in my rims any time soon.

[simonhill]

You don't really need maths to prove anything though. Put some 2.5kg wheels on a bike, go and ride up a hill.
Replace the wheels (keeping the same tyres/pressures etc) with a pair weighing 1.5kg , go and ride up the same hill at the same power.

The lighter wheels will feel better (which is a bit subjective) and will be measurably faster (which is purely objective).

Excuse the shouty but...For me this is where the lighter v heavier wheel debate goes astray.

Yes, taking 1kg off the bike WHEREVER will be 'better', but that doesn't prove if the lighter wheels are actually better or if it's just because the overall bike is lighter.

To do the comparison if lighter wheels are better you need to ADD the equivalent weight to the bike somewhere. Then you can see if the wheels are better. Otherwise all you are doing is feeling the weight loss of the wheels.

Nonetheless, given the scientific/mathematical proof I am happy that lighter wheels accelerate 'more easily*'. This is not to be underestimated as an ongoing advantage as almost all riding is slightly up and down speed wise.

There is also the pre stated advantage of reducing overall bike weight. Win, win.

Excuse me labouring the point, but felt that this post was unfinished. I'm happy now.

Phew!

*attempt to seek a meaningful non scientific term.

[Thehairs1970]

Surely on a bike, like any vehicle, you are either accelerating or decelerating most of the time and rarely at a constant velocity? So wheel weight will affect you all the time.

However, I think this is quite an irrelevant fact as toughness/reliability are more significant for tourers.

[roubaixtuesday]

Surely on a bike, like any vehicle, you are either accelerating or decelerating most of the time and rarely at a constant velocity? So wheel weight will affect you all the time.

However, I think this is quite an irrelevant fact as toughness/reliability are more significant for tourers.

If you're accelerating and decelerating a bit all the time it will cancel out. The only real difference is when accelerating hard.

I agree it's all but irrelevant for touring, but it is good to get the facts straight IMO