Wheel upgrades

[Johan Bornman]

What I am trying to say might more easily be felt like this:

 

Take a heavy wheel. hold the skewers in your hand and spin the wheel... In a straight line it feels stable...now try turn it.

 

repeat with a light wheel' date=' and observe the difference.

[/quote']

 

You are now describing the gyroscopic force exerted on a spinning disk changing direction around its axis.

 

Perhaps you want to elaborate on how that exerts a lateral force on a bicycle wheel in a turn?

[GoLefty!!]

Pro teams ride deep section wheels because it provides a bigger surface area for their wheel sponsor to advertise the brand of wheel.

In bunch riding there is no aerodynamic advantage to deep section wheels.

[niterider]

 

 

Pro teams ride deep section wheels because it provides a bigger surface area for their wheel sponsor to advertise the brand of wheel.

In bunch riding there is no aerodynamic advantage to deep section wheels.

 

Really?! So there is no measurable performance benefit to deep section wheels? The reduced power required to drive a more aerodynamic wheel is not maybe part of the reason?

 

Maybe in your bunch-riding you never spend any time at the FRONT of the bunch where the benefit would most definitely be felt.

 

What are all those time-trialists and triathlete's thinking?

niterider2008-09-14 22:54:03

[Bike Mob]

http://www.blackstonetek.com/proudly_sa.htm

 

These guys are the only Carbon Wheel manufaturer for motorcycles in the world. And they are South African.

 

JB Please read their finding regarding lighter wheels.

 

You are now describing the gyroscopic force exerted on a spinning disk changing direction around its axis - It's a relevant force is it not? We are actually riding these bicycles after all.

 

Perhaps you want to elaborate on how that exerts a lateral force on a bicycle wheel in a turn? - It doesn't exert a force - you do when you steer it.

[MarkD]

 

You are now describing the gyroscopic force exerted on a spinning disk changing direction around its axis - It's a relevant force is it not? We are actually riding these bicycles after all.

 

Perhaps you want to elaborate on how that exerts a lateral force on a bicycle wheel in a turn? - It doesn't exert a force - you do when you steer it.

 

Without proclaiming to be an expert on the forces at play with a rotating wheel, my only comment would be that if the wheel is rotating fast and you are trying to steer more than a fraction of a degree, I think that you should then be more worried about a couple of other forces which will suddenly become relevant:

 

1 - Gravitational force which will accelerate your body towards the ground, followed soon thereafter by...

2 - Frictional force between your body and the ground.  Note - this force will be affected by the roughness of the tar

3 - if you are really unfortunate there may be an additional impact resulting in extreme deceleration.

 

Of course, none of these forces depend in the slightest on which wheels you are using.....

 

The "gyroscopic" force I would think is largely responsible for the fact that the bicycle tends to stay upright when travelling in a straight line (note that it is generally easier to ride "hands-free" at faster speeds), but any significant "steering" at high speed is a recipe for disaster. 

 

 

 

 

MarkD2008-09-15 00:39:38

[Bike Mob]

 

 

The "gyroscopic" force I would think is largely responsible for the fact that the bicycle tends to stay upright when travelling in a straight line (note that it is generally easier to ride "hands-free" at faster speeds)' date=' but any significant "steering" at high speed is a recipe for disaster. 

 

 

 

[/quote']

 

It is not going to significant, but without knowing it you actually do make steering inputs to turn even at speed. On a bike it is a counter steering action, i.e you turn the bars left, you go right...

 

try this...

 

Ride at 15-20kmph with you hands lightly on the bars...then push forwards quickly and lightly, just a tap with your right hand (turning the bars to the left) observe which way the bike goes.

Tarmac-GSTR2008-09-15 03:54:42

[Johan Bornman]

Pro teams ride deep section wheels because it provides a bigger surface area for their wheel sponsor to advertise the brand of wheel.

In bunch riding there is no aerodynamic advantage to deep section wheels.

 

This particular advantage of deep sections has never occurred to me but makes perfect sense. I like it.

 

I concur with your statements of no advantage in bunch riding.  I find it very difficult to sell that concept to my customers.

 

 

I maintain my sanity in this regard only thanks to one particular pro that puts his business my way. It's a box section rim for him each time.

 

 

 

 

[Johan Bornman]

 

 

Yes there are...however they are overcome by cornering force during a turn...thus nullifying them.

 

You have a skewed view of the forces acting on a bicycle/motorcycle wheel in a corner.

 

When turning or riding straight ahead, the bicycle wheel experiences ZERO  lateral force. All forces are purely radial. The centrifugal force generated by the turn is purely overcome by you leaning into the corner. The relevant vector of your weight in the lean equals the centrifugal force of the circle's radius which can be calculated by F=MV^2 /R

 

You'll notice from this formula that the larger the radius of the turn, the smaller the centrifugal force and hence the less you have to turn.

 

We know wheels experience no lateral force because they can't take much lateral force at all. The rear wheel of a modern deep-dished bicycle wheel is so weak in the left to right position that it can barey wishtand a force of 200 N before collapsing. This is nowhere near what the centrifugal force on the bike in a steep corner is and therefore we know empirically that it supports it in some other mode.

 

A simple force diagram will solve your dilemma.

 

 

[Johan Bornman]

 

Cut cut cut cut 

 

Without proclaiming to be an expert on the forces at play with a rotating wheel' date=' my only comment would be that if the wheel is rotating fast and you are trying to steer more than a fraction of a degree, I think that you should then be more worried about a couple of other forces which will suddenly become relevant:

 

1 - Gravitational force which will accelerate your body towards the ground, followed soon thereafter by...

2 - Frictional force between your body and the ground.  Note - this force will be affected by the roughness of the tar

3 - if you are really unfortunate there may be an additional impact resulting in extreme deceleration.

 

Of course, none of these forces depend in the slightest on which wheels you are using.....

 

The "gyroscopic" force I would think is largely responsible for the fact that the bicycle tends to stay upright when travelling in a straight line (note that it is generally easier to ride "hands-free" at faster speeds), but any significant "steering" at high speed is a recipe for disaster. 

 

 

 [/quote']

 

Mark, convensional wisdom and lore isn't always the truth, as this case proves.

 

Gyroscopic forces play no role in bicycle balance.  A rider balances on his bicycle like a cleaner balances a broom on the palm of his hand - by riding into the fall so that the centre of gravity is restored to the position directly underneath it.

 

Go away from your PC for a minute and go balance a broom.

 

Notice how you push the base of the broom (in your hand) to the point directly underneath its centre of gravity. It falls left, you move left, it falls forward, you push forward and the same for the other two "dimensions".

 

On a bicycle the problem is simpler, since you only have to worry about on plane , the left right-place. You cant fall forwards or backwards unless your's is a unicycle.

 

As you ride and you start to overbalance to the left, you steer left and whoopee, your CoG is underneath your head again.

 

OK, now for gyro forces. For a moment, consider a bicycle with very, very little gyro forces playing on it. Your son's bike has less gyro than your MTB because it is smaller. It is also slower. Your son's mall scooter with Rollerblade wheels have very little gyro forces, yet he zips through the traffic without thinking about gyro forces. Your rollerblades and finally, for the ultimate zero-gyro vehicle, your ice scates! All of these balance with balance.

 

Back to the gyro. Only a fool wil say there's no gyro force on a spinning wheel. The mere fact that you can hold a skewer in your hand, spin the wheel and release your grip on the skewer so that it merely rests in your hand, yet the wheel still hangs there, proves there is a gyro force on the wheel. Further confirmation is that you have to slowly turn in order to prevent the wheel from turning on the skewer and hitting your arm or torso, is further proof.

 

Note how the gyro force operates: you apply an upwards force to the skewer (wheel spinning clockwise) and the wheel turns (as in around a corner) to the right.

 

Now try and envisage this force on the bicycle itself and you'll see that it doesn't contribute to balance but to the wheel's tendency to straighten itself after being leaned into a turn.

 

I hope R2D2??the rocket scientist) will this time join in this discussion. Please do.