Advice with MTB wheel/rim

[Johan Bornman]

Well JB I no longer disagree with you regarding the stress distribution in the spokes of the wheel. It is clear from the FEA that that the wheel deforms and expands and this expanding is countered by all the spokes. therefor the force is evenly distributed between all the spokes expect the ones where the force is applied.

 

 

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs187.snc4/37696_452208935559_641460559_6609133_6568016_n.jpg

 

There is a very small amount of higher stress in the top side spokes but this is minimal. if the elasticity of the spokes are greatly increased then this higher stress does have a role but in a normal wheel setup it is negligible

 

I am aware that there has been several simplification done to the model but i am under the impression that it demonstrate the principal of a wheel and spokes very elegantly.

 

B) so we learn

 

Aag jy is so 'n slim kind.

 

Nice to see that you also picked up the rim expansion. I usually don't talk about that until the concept is firmly grasped. The rim expands because it is deformed by the load at the bottom. If you do the spoke-pluck experiment and have perfect tonal perception, you'll pick this up. However, I don't get caught out with that one often since I know how to pick my figths and don't challenge musicians or piano tuners. Besides, the latter are usually blind and can be swindled quite easy.

 

If I may paraphrase your conclusion then: The loaded hubs stands on the bottom spokes and doesn't hang from the top spokes.

 

May I have permission to use your picture in my presentations? Mine is simplistic and was done before the days of colour.

[Bike Lore]

You are more than welcome. if you pm me your email i will send you high res ones.

 

But if you use them please note that the one that i have posted above is of 3 principle stress which is wrong to use if you are interested in tension. I use it because of it illustrate the argument and it has artistic value. here is the 1 principle model with pre-stress in the spokes.

 

 

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs204.snc4/38554_452229310559_641460559_6609439_1995136_n.jpg

 

note that the horizontal spokes has the highest amount of stress due to the deformation of the wheel. they are the most likely to brake.

 

If I may paraphrase your conclusion then: The loaded hubs stands on the bottom spokes and doesn't hang from the top spokes.

 

 

i would rather say that the load is carried/absorbed by the bottom spokes by reliving there tension. but that is just how i see it.

[goatman]

Hannes,

 

The Hope Pro 2 standard alloy freehub body is quite soft, so it is best to use more expensive cassettes like Shimano XT or SRAM PC 990.

The reason is that these cassettes have an alloy spider on the largest 4 or 5 cogs (forgive me if my terminology is not correct) so the cogs don't dig into the splines of the freehub body.

Cheaper all steel cassettes like SRAM PC 970 wear into the splines of the hub; making removal of the cassette somewhat of a mission (I've been through that experience)

Hope do a steel replacement freehub body whch is heavier but rather expensive.

I would use Stan's yellow rim tape instead of Velox cloth if it is an option. By adding a Stan's Olympic valve you have a tubeless compatible wheel. That's how I run my Stan's Flow on the rear.

This is slightly off topic but just Hope the info helps!

[Weight Weenie]

The tape and valve is allot better than strips IMO, cheaper, lighter and doesnt perish.

[Bike Lore]

Hannes,

 

The Hope Pro 2 standard alloy freehub body is quite soft, so it is best to use more expensive cassettes like Shimano XT or SRAM PC 990.

The reason is that these cassettes have an alloy spider on the largest 4 or 5 cogs (forgive me if my terminology is not correct) so the cogs don't dig into the splines of the freehub body.

Cheaper all steel cassettes like SRAM PC 970 wear into the splines of the hub; making removal of the cassette somewhat of a mission (I've been through that experience)

Hope do a steel replacement freehub body whch is heavier but rather expensive.

I would use Stan's yellow rim tape instead of Velox cloth if it is an option. By adding a Stan's Olympic valve you have a tubeless compatible wheel. That's how I run my Stan's Flow on the rear.

This is slightly off topic but just Hope the info helps!

 

darn!! already ordered the wheel. thanks for the tip. will go investigate. but can one remove the velox tame and install the stans yellow tape later?

[Bike Lore]

If I may paraphrase your conclusion then: The loaded hubs stands on the bottom spokes and doesn't hang from the top spokes.

 

 

Hi JB. sorry but I am back to disagreeing with this statement. it is amazing how many problems i solve while exercising. the loaded hub definitely does not stand on anything and does hang from the spokes and i will explain why.

 

there are 2 superimpose stress systems in the wheel. the first is caused by the riders weight pushing the hub to the ground. and the second is due to the deformation of the wheel.

 

lets analysis the first system. we know from newtons laws that if a body is subjected to a imbalance force then it will accelerate. consider that the hub does not accelerate we can simplify the system to the following diagram.

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs267.snc4/39666_452340510559_641460559_6613154_4880622_n.jpg

the downward force that is caused by the riders weight must be counter and equal to reaction force. or else the hub will start to accelerate to the bottom.

 

therefore any spoke with an upward vector will contribute to the reaction force as illustrated by the below diagram:

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs247.snc4/39666_452340505559_641460559_6613153_3306120_n.jpg

therefore it is clear that the vertical most spoke will carry the most force and the other will decrease as there vector components change. please note that only spokes in tension can contribute to the holding of the position of the hub.

 

the second system, due to the reaction force the forces on the rim can be simplified to the following diagram:

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs247.snc4/39666_452340500559_641460559_6613152_2791038_n.jpg

where yellow is the reaction force caused by the weight of the rider and the pink is the earth being very stubborn and not moving. the result is that the wheel deforms. due to the spokes in the wheel having a fixed length it will resist this deformation.

 

if you superimpose the forces on to each other you should be able to see why the tension in your wheel stays ruffly the same. expet for the sopkes that are at the contact aria. it can also be seen that all the stress in the hub is on top and to the sides not the bottom. the 3rd Principal stress method is excellent in indicating compression.

 

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs187.snc4/37696_452208935559_641460559_6609133_6568016_n.jpg

therefore i conclude that the hub is hanging in a web and the bottom spokes give up there tension due to the deformation of the wheel in which case the hub remains where it is because it is still a balanced system.

[Weight Weenie]

I remember a very famous gravitationally advantaged individual who once said that Tubeless is over-rated. That really made me think.

 

Haha yes, UST ie thick sidewall and strong bead hook

[Johan Bornman]

note that the horizontal spokes has the highest amount of stress due to the deformation of the wheel. they are the most likely to brake.

 

 

Not quite. You can't load them enough to break them in tension. The deformation of the rim will not go that far, no matter what you do. Have a look at my photo of the accident wheel. The rim breaks first. Spokes break from fatigue, never in tension.

 

 

i would rather say that the load is carried/absorbed by the bottom spokes by reliving there tension. but that is just how i see it.

 

I agree, I was just being provocative in my "standing on the bottom spokes" statement. I usually go on to define "stand" and then I used this very statement of yours.

[Johan Bornman]

Hi JB. sorry but I am back to disagreeing with this statement. it is amazing how many problems i solve while exercising. the loaded hub definitely does not stand on anything and does hang from the spokes and i will explain why.

 

there are 2 superimpose stress systems in the wheel. the first is caused by the riders weight pushing the hub to the ground. and the second is due to the deformation of the wheel.

 

lets analysis the first system. we know from newtons laws that if a body is subjected to a imbalance force then it will accelerate. consider that the hub does not accelerate we can simplify the system to the following diagram.

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs267.snc4/39666_452340510559_641460559_6613154_4880622_n.jpg

the downward force that is caused by the riders weight must be counter and equal to reaction force. or else the hub will start to accelerate to the bottom.

 

I think you should be looking at Newton's other law, for every action there is an equal and opposite reaction etc....

 

Therefore your green arrow should emanate from the hub and point downwards (the load) and the yellow arrow emanate from the road and point upwards. The force is applied from the hub to the road and from the road to the hub. The top spokes are not part of that equation. The only reason they do end up in the crossfire is because the rim changes shape, but to understand the concept, we can safely ignore that at first. In my previous post I explained and elaborated on "stand."

 

 

 

therefore ....cut cut cut cut

 

 

Lets sort out the premise before we build on that.

[Gatiepie]

If the weight is not hanging from the top spokes, why is it possible to make a wheel with fish gut as spokes and ride it?

 

I remember as a child there was a bicycle like that (with gut for spokes) in the science exhibition of the Potchefstroom University (in the Spinnekop Gebou) and I have always used that as a reference when trying to understand different forces working on an object. But these principles are very vague in my head since it's been 17 years since I attempted to study structural engineering.

[Wyatt Earp]

I could be wrong but in Newtons law/experiment the apple didn't levitate.

[goatman]

darn!! already ordered the wheel. thanks for the tip. will go investigate. but can one remove the velox tame and install the stans yellow tape later?

 

Hannes,

 

Yes, the Velox tape can be removed easily.

Your LBS should have a roll of the 25mm diameter Stan's yellow tape to fit your rim so you can ask them nicely and they should tape the rim up for you:

For ZTR Olympic, ZTR 355, ZTR 355 29er (21mm) or For ZTR Flow, Flow 29er, Arch, Arch 29er only (25mm)

• Weight per Rim 7g (25mm)

• Can do 5 rims with one roll (if you buy your own roll you can order 4 more rims )

 

Then you just need to buy the correct Stan's Olympic valve, fit that and away you go:

This is a custom Presta valve stem to be used with our ZTR Rims only! It will not seal in a Mavic UST rim. This valve stem features a removable valve core which allows for easier application of our tire sealant.

 

• This valve stem is specifically for the Olympic, ZTR 355, ZTR 355 29'er, Arch, Arch 29er, Flow, Flow 29er. No other valve stem will fit!

[Bike Lore]

Hannes,

 

Yes, the Velox tape can be removed easily.

Your LBS should have a roll of the 25mm diameter Stan's yellow tape to fit your rim so you can ask them nicely and they should tape the rim up for you:

For ZTR Olympic, ZTR 355, ZTR 355 29er (21mm) or For ZTR Flow, Flow 29er, Arch, Arch 29er only (25mm)

• Weight per Rim 7g (25mm)

• Can do 5 rims with one roll (if you buy your own roll you can order 4 more rims )

 

Then you just need to buy the correct Stan's Olympic valve, fit that and away you go:

This is a custom Presta valve stem to be used with our ZTR Rims only! It will not seal in a Mavic UST rim. This valve stem features a removable valve core which allows for easier application of our tire sealant.

 

• This valve stem is specifically for the Olympic, ZTR 355, ZTR 355 29'er, Arch, Arch 29er, Flow, Flow 29er. No other valve stem will fit!

 

wow thank goatman. will defiantly do that. just need to get my self a valve.

[goatman]

wow thank goatman. will defiantly do that. just need to get my self a valve.

Pleasure Hannes.

The valves don't come cheap at round about R100 a pop....(don't quote me on that price though!)

The valve cores are replaceable.

In my opinion it is better to use proper UST or Tubeless ready tyres with Stans rims as these tyres have a different bead design to normal tyres. These tyres also tend to be more expensive....especially in South Africa.

This bead then fits better into the bead socket interface ("BST") that Stan's rims use.

Bead Socket Technology

 

* By eliminating the bead hook and lowering the sidewall by 2-3mm we reduce the weight of the rim. Some of this material can be used in the center part of the rim making it stronger and stiffer.

* The curve of the rim sidewall is the same shape as the bead of the tire so they fit together like a ball and socket joint. This design will help reduce the strain on the tire bead while creating a tighter seal.

* By lowering the sidewall of the rim we also reduce the mechanical leverage the tire has on the rim. This will make the rim stiffer and last longer by eliminating flexing that can cause cracking.

* With these short sidewalls the tire should not hit the rim and pinch flat as often as standard rims, either with or without tubes. This design will allow you to run lower pressures and use 4mm more of the tire than ever before. The tire will have larger air volume giving you better traction.

[Johan Bornman]

If the weight is not hanging from the top spokes, why is it possible to make a wheel with fish gut as spokes and ride it?

 

Fish gut, provided it is specc'd to have a similar tensile strength as stainless steel, make for a perfectly good spoke.

 

Spinergy does this with their Kevlar spokes.

 

The wheel is supported by reducing the tension in the bottom spokes. So, lets say it is a flimsy rim and you have three spokes involved in the load affected zone (in other words, the wheel squashes flat like in Hannes' picture over a span of three spokes), then those three spokes collectively take up half your weight.

 

Example. Spokes are typically tensioned to 1000N. Thus, over three spokes, you have 3000N of tension and you can compress those spokes up to 2999.9999N before the spokes will go slack.

 

You weigh say 100kgs and your bike has two wheels. Thus 50kgs on the back wheel or 500N. 3000-500=2500N Per spoke that is 833N of tension remaining in each spoke before it goes slack.

 

That's how fishgut can support a wheel. The challenge is to find gut strong enough and find a method of affixing it to the hub and rim.

 

If you use a stronger rim (which is just a beam), then you'll involve more spokes and take even less tension away per spoke.

 

A wheel is a pre-stressed structure and therefore the spokes can support a compressive load up to the point where they go slack.

[Johan Bornman]

I hope i can explain this correctly but a bolted assembly works with pre-tension in the bolts. the joints it makes are a preloaded joint and if you pull on the plates that are begin joined you reduce the compression force on that joint between the plates. if you increase the force the load in the joint becomes less and less up to the point where your force is equal to the preloaded force in the bolts. After this the tension in the bolts will start to increase not before. Therefore if you would like to know how strong you need design your bolts you need to know how much preload you put in. if you design force is below the preload force your bolts will never see cycle loads and thus never suffer from fatigue that is the beauty of a bolted assembly.same goes with your wheel the spokes are preloaded but deu to the design you don't need to pre-load the spokes bejond the requierd force.

 

 

 

I don't see it like that. If you bolt two flanges together and pull on them, you put a load on the bolt that is in addition to the pre-load. The total tension in the bolt increases.

 

The total compressive force between the flanges decreases up to the point where it equals the tension in the bolts and then the compressive force is zero.

 

If you want to determine you strong (tensile) to make the bolts, you have to decide the sum total of the pre-load the load.

 

What am I missing here?