Interesting fact about a wheel.

[GSVR]

In one of my other threads I calculated that at 100 kph a 600mm diameter motorcycle tyre is doing approximately 884 rpm

When you put these numbers into the links below you will find the centrifugal force is huge.

http://www.msu.edu/~venkata1/gforce.htm

http://www.centrifuge.jp/cgi-bin/calc-e.cgi

Even with a reduced diameter to say the inside of the rim it would still be a large number.

[Badjelly]

Perhaps you really *should* be worried about your wheels!

[Steam]

For a radius of 300 mm and a speed of 885 rpm (100kph)
The G-force is 263.16 g units! Feck!

Apparently the relationship is non-linear, as when I put in 300kph or 2600 turns of the wheel per minute, I get a result of 2368g's. HOLY SPIT!
That's a lot of G's. I wonder at what point a wheel and tyre would come apart?
No wonder tyres have to be rated for certain speeds. The forces are huge.

[Finn]

In one of my other threads I calculated that at 100 kph a 600mm diameter motorcycle tyre is doing approximately 884 rpm

Hmmmm, maybe we should attach our engines directly to the wheel and get that sucker turning 14,000 rpm's.

[Patch]

Hmmmm, maybe we should attach our engines directly to the wheel and get that sucker turning 14,000 rpm's.

They already do - its called a propellor . . and it has wings

[GSVR]

This explains why a wheel is so hard to turn at higher speeds. But the faster you go the less you need to turn it so its also a good thing.

55rpm is the speed for 1g.

55 rpm times 1.884 metres (circumference) equals 103.62 metres per minute or 6217.2 metres per hour (6.2 kph)

Calculations

D = Tyre outside diameter (600mm for example)
Pi = 3.142 approx
Speed of motorcycle = 100kph

First lets get the distance travelled by the tyre in one revolution. Its the circumference which is Pi times the Diameter. All distance measurements will be in metres so 0.6 times 3.142 equals 1.8852 metres

With one revolution of the tyre the motorcycle travels 1.8852 metres.

If the motorcycle is travelling at 100kph what does this equal in metres per second?
100 kilometres = 100 times 1000 metres = 100000 metres
1 hour = 60 minutes = 3600 seconds
100000divided by 60 = 1666.666 mtres per minute (will use this to show RPM of tyre)
100000 divided by 3600 = 27.7777

At 100kph the motorcycle is doing 27.78 metres/sec.

If we divide the distance for one revolution of the tyre into the distance it covers in 1 minute we will get the RPM at 100kph.
1666.66 divided by 1.8852 = 884.08

Tyre is revolving at 884 RPM when the bike is travelling at 100kph

[Mikkel]

For a radius of 300 mm and a speed of 885 rpm (100kph)
The G-force is 263.16 g units! Feck!

Apparently the relationship is non-linear, as when I put in 300kph or 2600 turns of the wheel per minute, I get a result of 2368g's. HOLY SPIT!
That's a lot of G's. I wonder at what point a wheel and tyre would come apart?
No wonder tyres have to be rated for certain speeds. The forces are huge.

The acceleration, a, in a circular motion with a given speed, v, and radius, r, is given by:

a=v^2/r - so yes it's not linear, it's a potential relationship.

Don't underestimate the size of the wheel though - has a big impact!

As long as the wheel is balanced you shouldn't get any trouble with it coming apart. However, balancing something so that it's capable of doing e.g. 120,000 RPM requires very high precision. Take a turbine in a turbo - they typically operate at 100,000 - 200,000 RPM.

For car tyres there are speed ratings which indicate how high a speed they are certified to work at. E.g. V up to 240 km/h and Z over 240 km/h.

[Mikkel]

They already do - its called a propellor . . and it has wings

The propellers on an airplane revolve at rather less than 14,000 RPM.

Propeller

Turboprop

[onearmedbandit]

For car tyres there are speed ratings which indicate how high a speed they are certified to work at. E.g. V up to 240 km/h and Z over 240 km/h.

Bike tyres have speed ratings as well.

[yod]

this thread is far too relevant and informative

can someone PD it please?

[pritch]

Years ago I read that you should always ride with valve caps fitted as the centifugal forces generated at high speed can be enough to unseat the valve and deflate the tyre. Which event could create an "interesting" riding experience.

If the figures quoted here are correct, and I have no intention of checking them, it's is easy to see how such a thing might happen.

And I will be check the caps are tight before I head off next

[Mikkel]

Bike tyres have speed ratings as well.

I'd expect as much - I'm just not familiar with the ratings (are they the same).

Years ago I read that you should always ride with valve caps fitted as the centifugal forces generated at high speed can be enough to unseat the valve and deflate the tyre. Which event could create an "interesting" riding experience.

If the figures quoted here are correct, and I have no intention of checking them, it's is easy to see how such a thing might happen.

And I will be check the caps are tight before I head off next

I'd say you'd have to go fucking fast for that to happen - but indeed, why take a chance? Send Mythbusters an email - would be interesting to see. I guess they might take a motorcycle wheel and indeed rotate it at 14,000 RPM with the cap off to see if it deflates...

Different issue effects maxium prop speed at the is the speed of sound. Exceed that at the tips and you have a problem.

Indeed - the aerodynamics when approaching the sound barrier becomes quite complicated.
However, it's not just the rotational speed of the propeller - it's the resultant speed, vR, of the planes airspeed, vP, and the tangential (rotational) speed, vT, that can't exceed the speed of sound.

vR^2 = vP^2 + vT^2 < (344 m/s)^2

[johan]

Any ideas how much the radius of the tyre would increase at 100kph due to the gforce pulling it out?

Check out the rear tires on these guys. The radius is increasing like 40 cm when the tires start to rotate.
http://www.youtube.com/watch?v=Ls_ob...eature=related

[Mikkel]

Any ideas how much the radius of the tyre would increase at 100kph due to the gforce pulling it out?

At the top of the wheel yes - not at the bottom where they contact the ground. Besides IIRC Top Fuel dragsters run a fairly low pressure on the rear tyres...

Doubt it would be even measurable on a motorcycle even at speeds exceeding 250 km/h.

[Mr Merde]

At the top of the wheel yes - not at the bottom where they contact the ground. Besides IIRC Top Fuel dragsters run a fairly low pressure on the rear tyres...

Doubt it would be even measurable on a motorcycle even at speeds exceeding 250 km/h.

From my understanding these cars run at something like 8psi when staging but due to the burnout and the run the pressure goes up substantially. Something to do with the heat generated and the expansion of the air due to the heat.

As to this thread.

A question.

How does the mass of the wheel feature into all these calculations?

From personal experiencve of using non factory wheels on one of my bikes I found that the acceleration, deceleration and handling of the bike dramatically increased due to a reduction of the inertial mass of the wheels.