Does the hub/axle hang from or stand on the spokes ?

[Lounge Lizard]

A thread that discussed bridge building (and the spoke topic) was closed - I did not see why, but looks like it had some 'too personal' remarks.

 

Problem is, it was very interesting and I would still like to know the mechanics.

 

I am obviously not an engineer but it almost sounded if the one story had merit.

 

1) Does a bike wheel stay in shape because the pressure (rider weight) on the hub/axle is less than the tension in the bottom spokes ? i.e. the hub/axle stands on the spokes ? in line with the pre-tension principle used in bridge building (concrete reinforcing)? This implies that (provided the weight vs spoke tension is correct) a stationary wheel will not collapse if only the bottom half has spokes (?)

 

or

 

2) is the rider weight as pushed onto the hub/axle supported by the spokes in the top half of the wheel ? which implies that the stationary wheel will not collapse if the only the top half has spokes (?)

 

or

 

3) is the combined tension from ALL the spokes in play ?

 

of wat de f*& gaan nou eintlik aan met die wiel ?

[LazyTrailRider]

Hubs hang on spokes. That's the *really* short answer.

[Zeps]

A properly built wheel neither hangs nor stands but rather 'suspends' in a vacuum as it were

[Guest Big H]

Ssssa..... Johann B ..... vat hulle!!!!!!!

[The_Break]

Hubs hang on spokes. That's the *really* short answer.

 

A hub niether hangs nor rests, rather it is pulled equally outward in all direction when it is in the unloaded (i.e. no rider) condition.

 

When you load the wheel the top and bottom spokes then increase and decrease their tension equally and respectively, whislt the left and right spokes increase their tension equally, yet are all still under an effective pull or tension force (corrected). The actual variation is a nice smooth positively offset sinus shaped graph as you move around the wheel with mean at the unloaded tension.

 

If this was not the case the spokes would be loose and the wheel would fall apart.

 

That is the basic way a wheel works anyhow.

Edited December 15, 2010 by The_Break

[Zeps]

Oom dit lyk my JB het hierso 'n 'ally' hier in die_breek

[eggsovereasywithteandtoast]

Are those hanging or standing on her chest

Edited December 15, 2010 by eggsovereasywithteandtoast

[The_Break]

Why is she smelling her armpit?

 

I think it was to get that old man so excited cause damn it made him dance funny!

Edited December 15, 2010 by The_Break

[Lounge Lizard]

A hub niether hangs nor rests, rather it is pulled equally outward in all direction when it is in the unloaded (i.e. no rider) condition.

 

When you load the wheel the top and bottom spokes then decrease their tension equally, whislt the left and right spokes increase their tension equally, yet are all still under an effective pull or tension force. The actual variation is a nice smooth positively offset sinus graph as you move around the wheel with mean at the unloaded tension.

 

If this was not the case the spokes would be loose and the wheel would fall apart.

 

That is the basic way a wheel works anyhow.

 

Now this is the confusing part :-

...top and bottom spokes then decrease their tension equally

How can the tension in the top decrease - when one applies weight ? i.e. pull on the hub side end of the spoke, surely this will increase the tension ?

[Lounge Lizard]

Are those hanging or standing on her chest

 

now watch it ! boys... you will get this thread going the wrong way (or is it right way) and ADMIN will close it under the 'porn' statute.

[Minion]

When you load the wheel the top and bottom spokes then decrease their tension equally, whislt the left and right spokes increase their tension equally, yet are all still under an effective pull or tension force. The actual variation is a nice smooth positively offset sinus graph as you move around the wheel with mean at the unloaded tension.

No, that is wrong. The load is carried almost entirely by a reduction in tension in the bottom spokes. There is almost no change in load on the upper spokes. This is unequivocal and is back up by basic structural mechanics analysis and experimental results. A sample of these analyses may be read below:

 

Bicycle Wheel as Prestressed Structure - Abstract from Journal of Engineering Mechanics. Clearly states that bottom spokes carry virtually all the load.

Bicycle Wheel Spoke Patterns and Spoke Fatigue - Paper from ASCE Journal of Engineering Mechanics. Page 10 has a diagram that shows the measured strains on a spoke throughout its entire rotation: peak strains occur at the bottom.

Finite Element Analysis of a Classical Bicycle Wheel - Shows the detailed stress distribution. Andrew D. Hartz, Senior Mech Eng, Raytheon Engineering

 

Here are two diagrams extracted from the sources, showing the spoke strains caused by an imposed load on a prestressed wheel:

Edited December 15, 2010 by Edam

[The_Break]

Now this is the confusing part :-

...top and bottom spokes then decrease their tension equally

How can the tension in the top decrease - when one applies weight ? i.e. pull on the hub side end of the spoke, surely this will increase the tension ?

 

Newton taught us this. For every action there is an equal and opposite reaction. I.e. if you press at the top of the wheel the bottom of the wheel is pushed back equally as hard by the ground. As the wheel's rim will also want to form a slightly ovalized shape as it is "squashed" it tends to want to pull the horizontal spokes as it tries to do this.

 

Tension in the spokes means you are trying to lengthen the spokes. This can be seen as the hub "pulling" the spoke in one direction and the rim/nipple "pulling" the spoke in the opposite direction. If you now push the rim/nipple toward the hub, you effectively "pull" less and thereby decrease the tension. Note: decrease the tension but not make it zero or negative. It is this constantly "positive tension" that keeps a wheel strong.

[The Saint]

Wouldn't Newtons third law apply here?

[The Saint]

The_Break beat me to it

[The_Break]

No, that is wrong. The load is carried almost entirely by a reduction in tension in the bottom spokes. There is almost no change in load on the upper spokes. This is unequivocal and is back up by basic structural mechanics analysis and experimental results. A sample of these analyses may be read below:

 

Bicycle Wheel as Prestressed Structure - Abstract from Journal of Engineering Mechanics. Clearly states that bottom spokes carry virtually all the load.

Bicycle Wheel Spoke Patterns and Spoke Fatigue - Paper from ASCE Journal of Engineering Mechanics. Page 10 has a diagram that shows the measured strains on a spoke throughout its entire rotation: peak strains occur at the bottom.

Finite Element Analysis of a Classical Bicycle Wheel - Shows the detailed stress distribution. Andrew D. Hartz, Senior Mech Eng, Raytheon Engineering

 

Here are two diagrams extracted from the sources, showing the spoke strains caused by an imposed load on a prestressed wheel:

 

 

Now you going to confuse the hell out of everyone. This is a right pulling spoke showing strain. I have tried to keep it simple and have used a straight (radial) spoke configuration.

[Minion]

Now you going to confuse the hell out of everyone. This is a right pulling spoke showing strain. I have tried to keep it simple and have used a straight (radial) spoke configuration.

The basic pattern of the results i.e. top spokes carry no load, bottom spokes carry almost all the load applies to all spokes. The first diagram shows results from 4 spokes from multiple positions. The actual values vary, but the overall pattern is consistent.

Edited December 15, 2010 by Edam