Reducing front wheel weight

[Profpointy]

F1 cars, at high speeds weigh more than my Honda Civic. If you could stick an F1 car on a scale while it is traveling at top speed, you'd expect to see closer to around 2200kg (vs it's static mass of 790kg ish)

Pedantically speaking the apparent weight becomes 2200kgf ie the weight of a 2200kg mass. "static" mass is poor terminology here - it's just "the" mass which is of course unchanged (for non relativisitic speeds - but let's not go there)

That out of the way, more importantly, the point you make, though true is irrelevant to acceleration which is proportional to the mass, as is hillclimbing. The downforce from aerodynamics only changes the grip available when cornering / accelerating / braking

 

[Justinslow]

So would anybody like to summarise the benefits or disadvantages of "reducing front wheel weight" as opposed to reducing that weight from anywhere else on the bike, as in the thread title?

 

[derrick]

So would anybody like to summarise the benefits or disadvantages of "reducing front wheel weight" as opposed to reducing that weight from anywhere else on the bike, as in the thread title?

 

[Justinslow]

It is good one isn't it??

 

[Profpointy]

So would anybody like to summarise the benefits or disadvantages of "reducing front wheel weight" as opposed to reducing that weight from anywhere else on the bike, as in the thread title?

I'll give it a go.

Cycling along steadily on flat: weight doesn't matter regardless of where it is.

Cycling uphill: weight is weight so no difference between wheel and bike but lighter is better.

Accelerating (eg from rest) t - roughly twice as bad if weight is on the wheel compared to bike; . less so if weight concentrated in the hub rather than rim

As a great Scottish engineer said "ye cannae break the laws of physics"

And another new, albeit minor, difference - where you have suspension, even if just fork flex, it is better ride and roadholding wise if the weight is on the bike rather than the wheel. Suspension engineers refer to the ratio between sprung and unsprung weight. I personally doubt this would matter on a road bike since most of the "suspension" is the tyres

 

[samsbike]

So I agree with the above. My only qualification is that cycling is not only about the numbers, but how it makes us feel. Not only the aesthetics but how it handles etc (otherwise we would all be on a honda nc700, as fine as it is or dutch bikes or whatever you like). Lighter wheels, and other go faster bits like ultegra groupsets add to that experience (as does being lighter and faster), so subjectively they make a difference (as I tried to articulate earlier - it made a huge difference to me, but I was probably no faster but it felt nicer).

So, get whatever makes you happy, ride more and gain out of the experience, otherwise what is the point?

 

[T.M.H.N.E.T]

I reduced my front wheel weight, my rear wheel weight, my seatpost weight, my saddle bag weight(by trimming down it's contents) my wallet weight and my weight (by losing upwards of 8stone)

My wheels have mirrored decals and make lovely patterns on the road. I have no clue regarding the science and physics of wheels, I'm away for a ride all the same

 

[fatblokish]

I'll give it a go.

Cycling along steadily on flat: weight doesn't matter regardless of where it is.

Cycling uphill: weight is weight so no difference between wheel and bike but lighter is better.

Accelerating (eg from rest) t - roughly twice as bad if weight is on the wheel compared to bike; . less so if weight concentrated in the hub rather than rim

As a great Scottish engineer said "ye cannae break the laws of physics"

And another new, albeit minor, difference - where you have suspension, even if just fork flex, it is better ride and roadholding wise if the weight is on the bike rather than the wheel. Suspension engineers refer to the ratio between sprung and unsprung weight. I personally doubt this would matter on a road bike since most of the "suspension" is the tyres

I think that the first line could be adjusted to suit pedants like me to "cycling at constant velocity on flat..." since velocity is a vector quantity and possesses both magnitude and direction. Of course, constant velocity is very difficult to achieve on a two wheeled bike since many small corrections in steering are needed to keep the bike upright and heading in the right direction and such corrections bring about a change in velocity. With each of these changes in velocity there has to be a corresponding loss of kinetic energy resulting from the change in momentum of the front wheel and so a front wheel of smaller mass results in a smaller loss of momentum.
So a "lighter" front wheel would be "faster".

 

[Profpointy]

I think that the first line could be adjusted to suit pedants like me to "cycling at constant velocity on flat..." since velocity is a vector quantity and possesses both magnitude and direction. Of course, constant velocity is very difficult to achieve on a two wheeled bike since many small corrections in steering are needed to keep the bike upright and heading in the right direction and such corrections bring about a change in velocity. With each of these changes in velocity there has to be a corresponding loss of kinetic energy resulting from the change in momentum of the front wheel and so a front wheel of smaller mass results in a smaller loss of momentum.
So a "lighter" front wheel would be "faster".

Whilst I approve of the pedantry, your conclusion doesn't sound right. I don't think the kinetic energy changes after these changes of direction - just like the kinetic energy of a spinning wheel doesn't change despite each component of the rim continuously changing velocity as it goes round in a circle. No work is done by the (centripetal) force which keeps the rim going round in a circle - work is force x distance and the spokes ar fixed length. The wobbling about changes in direction you mention are akin to this.

I dare say we're losing the non-pedants here !

 

[derrick]

At the end of the day. Just fit it and stop causing arguments.

 

[Fab Foodie]

I'm hoping @Yellow Saddle returns to the debate. I understand his frustration with us but with patience I think his knowledge gently explained and respectfully debated is valuable.

From my own POV, as a scientist (but not physics or engineering) I get much of what he says. Just have some difficulty squaring it with my own 'experience'.

So let's try and break the problem into smaller pieces and see where we agree or disagree.

For example, turn a bicycle upside down and crank the rear wheel. A heavier wheel WILL take more effort to spin up than a lighter one. F=MA and all that.

It also makes 'sense' to me that for a given weight of wheel having the same mass distributed around the rim as opposed to at the hub makes the wheel also harder to spin BUT doesn't that contradict the simple F=MA equation? Or is my 'sense' plain wrong.
Inertia plays a part here I'm certain! Flywheels and all that.

The Brompton Question:
Again it's widely written that Brommies accelerate so quickly (and my experience says that's true) because their little wheels 'spin up so quickly'. Brommies are not light bikes and neither are their wheels.
So again, I'm conflicted. If our upturned bicycle has a small diameter 1.5 kg wheel or a large diameter wheel of the same weight, which will spin up quickest. F=MA states that they'll be the same.

The thing with riding a bicycle however is that we don't spin wheels in free space. We spin them in contact with the road and in my case with 100kg connected to them.
So to take @Yellow Saddle point regardless of the wheel weight, diameter and mass distribution, as long as the total package weight (wheel plus bike plus rider) remains the same ( add the weight loss in the wheel to the bike) then the amount of force required to move or accelerate it remains the same.
Thus with Yellow Saddles analysis the only benefit to a wheel that is 0.5 kg lighter is that you have removed half a kg or 0.5% of the total weight from the system to be accelerated. Like removing a full water bottle.
I can understand that too.

BUT: It just doesn't seem to chime with people's experience and reportage .... But myth busting is line that and perception not scientific. Alternatively the model might be too simple?

So I'm stuck in my mind why 2 world record attempts built special heavy wheels when a heavier bike would have done .... And why Brommies are the fastest accelerating bikes on the planet :-)

 

[EltonFrog]

I know nothing about bikes, wheels or the science thereof. My wife bought me some blinged up wheels for my birthday a couple of years ago, I didn't ask for them, I didn't hint, she did the research and spent nearly half what the bike cost on these wheels, a lovely gift. When I fitted them and went out for the first ride I couldn't tell the slightest bit of difference between them and the original set. BUT they look sooooo pretty. I love em. It's emotional.

 

[derrick]

Does @Yellow Saddle actually ride a bike? And if so what type of bike. Serious question.

 

[Fab Foodie]

Does @Yellow Saddle actually ride a bike? And if so what type of bike. Serious question.

Well that really helps the debate.

 

[derrick]

Well that really helps the debate.

It would help me understand @Yellow Saddles way of thinking. I know a coupe of guys who talk bikes all the time but they ride 10 miles a week on a £200 mtb.