Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Help understanding transfer of torque from hub to rim

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Help understanding transfer of torque from hub to rim

Old 04-17-21, 07:09 PM
  #1  
Symox
Senior Member
Thread Starter
 
Join Date: Jul 2020
Posts: 300

Bikes: '07 Specialized Roubaix Comp Triple, '12 Gravity Fixie, '21 Liv Rove 4, '06? Giant EB Spirit

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 140 Post(s)
Liked 59 Times in 46 Posts
Help understanding transfer of torque from hub to rim

Got a copy of Jobst Brandt's classic "The Bicycle Wheel" - great book but some sections I've reread several times to understand.

One section that I still cannot understand is the following:

" As the chain turns the rear wheel sprocket it exerts torque on the hub. Torque is expressed in terms of a force and the length of the lever on which it acts. In the bicycle the force and lever are the tension in the chain and the radius of the sprocket. Spokes are flexible and cannot transmit torque by acting as levers, so they transmit torque from the hub to the rim by becoming tighter and looser. The lever arm is the distance by which the line of the spoke misses intersecting the centerline of the rear axle. The force is the total change in tension among the spokes, some of which become tighter, and some looser. "

The main concept I cannot understand is in this sentence: "Spokes are flexible and cannot transmit torque by acting as levers, so they transmit torque from the hub to the rim by becoming tighter and looser." I get it that the spokes will compress or stretch based on torque and that they cannot transmit torque by acting as levers since they are flexible. What I don't get is how the change in spoke tension transmitting to the rim causes the wheel to turn.

The reason I even care about this is I'm trying to understand the effect of flange diameter on torque transmission and if a more tangent spoke with a larger diameter flange leads to more efficient transfer of power.

My head hurts now
Thanks for the help
Symox is offline  
Old 04-17-21, 10:47 PM
  #2  
oldbobcat
Senior Member
 
oldbobcat's Avatar
 
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 3,392

Bikes: '79 Gios, '80 Masi, '06 Felt, early '60s Frejus

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
Liked 104 Times in 77 Posts
When you apply forward pressure to the cranks, the chainring pulls the chain. The chain pulls the rear wheel cog. The cog pulls the hub flange. The hub flange pulls on the spoke. The spoke pulls on the rim and the bike moves forward. Something as narrow and flexible as a spoke can't push a rim forward, it can only pull. Under power only the pulling spokes are tensioned. But don't confuse this with supporting the bicycle. The weight of the bike plus rider is supported by the spokes at the top of the rim. The hub is literally hanging. Of course, the rest of the spokes prevent the hub from swinging like a pendulum. And under power, the trailing spokes keep the hub from winding up. The hub always rotates at the same speed as the rim.

Likewise, a disc brake decelerates the hub, so the pull is in the opposite direction.

As for flange height and cross pattern, within normal parameters you're probably splitting hairs. Generally, the stiffer and lighter the wheel, the more quickly it accelerates. Larger flanges, shorter spokes, and more spokes make a wheel stiffer. Larger flanges and longer spokes also make the wheel heavier. And longer spokes make the wheel less stiff. As for the cross-pattern, you have to consider the angle of pull from the flange and the spoke count. Two-cross on a 24-spoke wheel is like 3-cross on a 36-spoke wheel. And there's flange height. The spoke length on a low-flange 3-cross wheel is more equivalent to spoke length on a high-flange 4-cross wheel.

I once built 4-cross rear wheel around a 36-hole high flange hub. It felt more sluggish than 3-cross. My bet is any efficiency of the more direct tangential pull was lost in the weight and flexibility of longer spokes.
oldbobcat is offline  
Likes For oldbobcat:
Old 04-17-21, 10:59 PM
  #3  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 14,920

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2925 Post(s)
Liked 1,197 Times in 842 Posts
Spoke are springs in a manor of speaking. A thinner spoke will have more stretch then a thick one (and this is why butted spoked wheel tend to suffer from less broken spokes over time)

I wouldn't be too wrapped up in "efficient transfer of power" as it relates to a tangentally laced rear wheel. Now a radially laced one is a really poor application. Basically the more a spoke is at a 90* angle to the lever arm that the hub acts as, WRT the axle, the more efficient the spoke will be at passing along the force to the rim. However the differences are rather minor between, say, a 4x and a 3x lace pattern. Both provide a geometry that has been proven to be adequate for millions of bikes over many decades. This is why i say don't fret the tiny details of proven designs too much.

Now there's far greater factors that affect wheel performance like spoke tension, spoke gage, spoke count, rim stiffness and spoke bed strength, aero slipperiness, tire/rim matching, tire pressures. And all these pale in comparison to the rider's conditioning and fit let alone fitness.

Jobst has had rather strong opinions and not all are worth too much energy. His book does lay a good foundation for thought but one can get lost in the engineering claims. Just because one can measure a thousandth of an inch easily does not mean it has great value in real life. Andy
__________________
AndrewRStewart
Andrew R Stewart is online now  
Likes For Andrew R Stewart:
Old 04-17-21, 11:06 PM
  #4  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 2,833

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1056 Post(s)
Liked 254 Times in 191 Posts
Imagine lying on a prone bike holding a spoke. You can reach out to the front wheel. You want the bike to move. Do you hold the spoke near the center of the hub and try to use the stiffness of the spoke to push the rim around? Of course not, because the spoke is not a very stiff lever.

Spokes exert force on the wheel in one way only: by tension. Not by acting as a lever. Put another way, there are spokes that work just fine that are made of ultra high strength fiber. They look like a string. When installed, they transmit torque just fine.
WizardOfBoz is offline  
Likes For WizardOfBoz:
Old 04-17-21, 11:44 PM
  #5  
Trakhak
Senior Member
 
Join Date: Jan 2005
Location: Baltimore, MD
Posts: 2,676
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 869 Post(s)
Liked 609 Times in 361 Posts
I wonder how Brandt would have explained the forces at work in a rear wheel composed entirely of radially oriented spokes, where the only practical constraint is the strength of the hub with respect to resisting the tendency of the spoke heads to rip out of its flanges.
Trakhak is offline  
Likes For Trakhak:
Old 04-18-21, 12:15 AM
  #6  
Symox
Senior Member
Thread Starter
 
Join Date: Jul 2020
Posts: 300

Bikes: '07 Specialized Roubaix Comp Triple, '12 Gravity Fixie, '21 Liv Rove 4, '06? Giant EB Spirit

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 140 Post(s)
Liked 59 Times in 46 Posts
Thanks for the excellent explanations!
Symox is offline  
Old 04-18-21, 12:20 AM
  #7  
Symox
Senior Member
Thread Starter
 
Join Date: Jul 2020
Posts: 300

Bikes: '07 Specialized Roubaix Comp Triple, '12 Gravity Fixie, '21 Liv Rove 4, '06? Giant EB Spirit

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 140 Post(s)
Liked 59 Times in 46 Posts
Originally Posted by WizardOfBoz View Post
Imagine lying on a prone bike holding a spoke. You can reach out to the front wheel. You want the bike to move. Do you hold the spoke near the center of the hub and try to use the stiffness of the spoke to push the rim around? Of course not, because the spoke is not a very stiff lever.

Spokes exert force on the wheel in one way only: by tension. Not by acting as a lever. Put another way, there are spokes that work just fine that are made of ultra high strength fiber. They look like a string. When installed, they transmit torque just fine.
but the spokes pull on the rim at close to a 90 degree angle, wouldnít that just compress the rim not rotate it?

im almost getting it
Symox is offline  
Old 04-18-21, 09:43 AM
  #8  
oldbobcat
Senior Member
 
oldbobcat's Avatar
 
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 3,392

Bikes: '79 Gios, '80 Masi, '06 Felt, early '60s Frejus

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
Liked 104 Times in 77 Posts
Originally Posted by Andrew R Stewart View Post
Jobst has had rather strong opinions and not all are worth too much energy. His book does lay a good foundation for thought but one can get lost in the engineering claims. Just because one can measure a thousandth of an inch easily does not mean it has great value in real life. Andy
Mavic, Zipp, Enve, Bontrager, etc., have engineers and computer programs to figure all this stuff out. If the rear bicycle wheel is a problem to be solved, they will solve it, not a hobbyist wheel builder or bike shop mechanic. If it is indeed a problem to be solved.
oldbobcat is offline  
Old 04-18-21, 09:45 AM
  #9  
oldbobcat
Senior Member
 
oldbobcat's Avatar
 
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 3,392

Bikes: '79 Gios, '80 Masi, '06 Felt, early '60s Frejus

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
Liked 104 Times in 77 Posts
Originally Posted by Symox View Post
but the spokes pull on the rim at close to a 90 degree angle, wouldnít that just compress the rim not rotate it?

im almost getting it
Yes, but the rim, being rigid, doesn't compress, so the force is vectored. Another reason not to overthink it.
oldbobcat is offline  
Likes For oldbobcat:
Old 04-18-21, 09:59 AM
  #10  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 14,920

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2925 Post(s)
Liked 1,197 Times in 842 Posts
Originally Posted by oldbobcat View Post
Mavic, Zipp, Enve, Bontrager, etc., have engineers and computer programs to figure all this stuff out. If the rear bicycle wheel is a problem to be solved, they will solve it, not a hobbyist wheel builder or bike shop mechanic. If it is indeed a problem to be solved.
Solving something that the basic engineering work was published in 1896 is not what I would call a study to get worked up about. Oh, there's the millions of millions of wheels built with that 1896 work by AR Sharp that have proven the tangentally and tensioned spoked wheel works in real life too. Sorry but I have better things to get all tangled up in then what has been proven over and over. Andy
__________________
AndrewRStewart
Andrew R Stewart is online now  
Old 04-18-21, 10:02 AM
  #11  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 14,920

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2925 Post(s)
Liked 1,197 Times in 842 Posts
I'll add one more opinion- Today's wheel engineers are working on the materials, manufacturing, not the foundational engineering. And that big aspect of any product meant to be purchased, the marketing needs (which can be greater then that thousandth of an inch I referenced). Now I'm 3 and out. Andy
__________________
AndrewRStewart
Andrew R Stewart is online now  
Old 04-18-21, 12:16 PM
  #12  
davidad
Senior Member
 
Join Date: Feb 2009
Posts: 6,491
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 519 Post(s)
Likes: 0
Liked 125 Times in 105 Posts
Originally Posted by oldbobcat View Post
When you apply forward pressure to the cranks, the chainring pulls the chain. The chain pulls the rear wheel cog. The cog pulls the hub flange. The hub flange pulls on the spoke. The spoke pulls on the rim and the bike moves forward. Something as narrow and flexible as a spoke can't push a rim forward, it can only pull. Under power only the pulling spokes are tensioned. But don't confuse this with supporting the bicycle. The weight of the bike plus rider is supported by the spokes at the top of the rim. The hub is literally hanging. Of course, the rest of the spokes prevent the hub from swinging like a pendulum. And under power, the trailing spokes keep the hub from winding up. The hub always rotates at the same speed as the rim.

Likewise, a disc brake decelerates the hub, so the pull is in the opposite direction.

As for flange height and cross pattern, within normal parameters you're probably splitting hairs. Generally, the stiffer and lighter the wheel, the more quickly it accelerates. Larger flanges, shorter spokes, and more spokes make a wheel stiffer. Larger flanges and longer spokes also make the wheel heavier. And longer spokes make the wheel less stiff. As for the cross-pattern, you have to consider the angle of pull from the flange and the spoke count. Two-cross on a 24-spoke wheel is like 3-cross on a 36-spoke wheel. And there's flange height. The spoke length on a low-flange 3-cross wheel is more equivalent to spoke length on a high-flange 4-cross wheel.

I once built 4-cross rear wheel around a 36-hole high flange hub. It felt more sluggish than 3-cross. My bet is any efficiency of the more direct tangential pull was lost in the weight and flexibility of longer spokes.
The wheel stands on the spokes.
davidad is offline  
Old 04-18-21, 12:19 PM
  #13  
davidad
Senior Member
 
Join Date: Feb 2009
Posts: 6,491
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 519 Post(s)
Likes: 0
Liked 125 Times in 105 Posts
Originally Posted by Trakhak View Post
I wonder how Brandt would have explained the forces at work in a rear wheel composed entirely of radially oriented spokes, where the only practical constraint is the strength of the hub with respect to resisting the tendency of the spoke heads to rip out of its flanges.
He wouldn't because it is not practical.
davidad is offline  
Old 04-18-21, 12:22 PM
  #14  
Symox
Senior Member
Thread Starter
 
Join Date: Jul 2020
Posts: 300

Bikes: '07 Specialized Roubaix Comp Triple, '12 Gravity Fixie, '21 Liv Rove 4, '06? Giant EB Spirit

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 140 Post(s)
Liked 59 Times in 46 Posts
Thanks everyone. Iím not trying to solve anything just understand the physics behind it to help make choices in hobbyist wheel building.
Symox is offline  
Old 04-18-21, 01:16 PM
  #15  
Trakhak
Senior Member
 
Join Date: Jan 2005
Location: Baltimore, MD
Posts: 2,676
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 869 Post(s)
Liked 609 Times in 361 Posts
Originally Posted by davidad View Post
He wouldn't because it is not practical.
The practicality is limited only by the strength (resistance to cracking) of the hub flange. (A young mechanic at a shop where I worked forgot to take into consideration the need to calculate the lengths for crossed spokes for the rear wheel for the first set he built, so he went ahead and built the rear wheel radial on both sides. Last I heard, he had a couple of thousand miles on that wheelset.)

Ten years earlier, I worked in a shop with an engineer who amused himself by building wheels with all clockwise (pulling) spokes on one flange and all counterclockwise spokes on the other. He used hubs with large-diameter bodies (Phil or Durham or Weyless) to avoid twisting the hub body, barber-pole style.
Trakhak is offline  
Old 04-18-21, 01:49 PM
  #16  
cyccommute 
Mad bike riding scientist
 
cyccommute's Avatar
 
Join Date: Nov 2004
Location: Denver, CO
Posts: 23,993

Bikes: Some silver ones, a red one, an orange one and a few titanium ones

Mentioned: 121 Post(s)
Tagged: 1 Thread(s)
Quoted: 4103 Post(s)
Liked 1,595 Times in 975 Posts
Originally Posted by davidad View Post
The wheel stands on the spokes.
What does a spoke stand on? It’s not attached to the rim other by tension. The wheel is a tensegrity structure that hangs from the spokes just like this toy.



The upper platform isn’t “standing” on the two gray chains. Those only serve to stabilize the structure. The upper platform is hanging from the short black chain.

Similarly, the spokes of a wheel aren’t standing on the rim. The rim is free to slide up and down the spokes. There’s no compressive forces on the spokes from the rim. Let’s reduce the rim and spokes to (almost) their simplest form. Just a spoke (well 2 spokes), a hub, and a bit of rim. You can see in the picture below that the rim hangs from the hub through the spokes.



If you turn the system over, the hub can hang from the rim by the spokes.



However, if you put the hub on a hook and try to make it hold up the rim, the rim won’t stay up. It slides down the spokes to the hub. In a system where the wheel stands on the spokes, the rim should move in either configuration.




And, in fact, you can push the rim up off the spokes (if you hold it in position) when the hub is held in position.



Brandt has said that the wheel stands on the spokes because compression increases as tension decreases. But he is wrong in his analysis. However, while tension and compression are opposing forces in terms of direction of force, they aren’t the opposite of each other. Drive a stake into the ground, i.e. compress it. Now pull it out of the ground, i.e. put tension on it. You can push it but you can’t pull on it at the same time. If compression is removed, the object isn’t in tension. Compression has to go to zero before tension can start to ramp up.

On a bicycle wheel, just because the tension decreases due to compression of the rim, that doesn’t mean that the spoke is compressing. The whole system is still under tension and like the tensegrity toy, the wheel hangs from the top spokes. The bottom ones only stabilize the upper spokes.
__________________
Stuart Black
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
cyccommute is offline  
Likes For cyccommute:
Old 04-18-21, 02:03 PM
  #17  
oldbobcat
Senior Member
 
oldbobcat's Avatar
 
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 3,392

Bikes: '79 Gios, '80 Masi, '06 Felt, early '60s Frejus

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
Liked 104 Times in 77 Posts
Originally Posted by Andrew R Stewart View Post
Solving something that the basic engineering work was published in 1896 is not what I would call a study to get worked up about. Oh, there's the millions of millions of wheels built with that 1896 work by AR Sharp that have proven the tangentally and tensioned spoked wheel works in real life too. Sorry but I have better things to get all tangled up in then what has been proven over and over. Andy
Probably why they spend more talk and energy on aerodynamics and weight than the brilliance of the tangential pull of their spoke patterns.
oldbobcat is offline  
Old 04-18-21, 04:13 PM
  #18  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 14,920

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2925 Post(s)
Liked 1,197 Times in 842 Posts
Originally Posted by davidad View Post
The wheel stands on the spokes.

I have to break my rule here due to a new aspect of this thread...

IIRC Brandt's book uses this model to make the math easier to deal with. My understanding is that we hang from the rim's upper section, like two hammocks. I really like this model as it fits with my feeling the flow of rolling over the road. Andy
__________________
AndrewRStewart
Andrew R Stewart is online now  
Old 04-18-21, 05:19 PM
  #19  
Kimmo 
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Posts: 9,107

Bikes: https://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=152015&p=1404231

Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 1157 Post(s)
Liked 429 Times in 309 Posts
Originally Posted by Symox View Post
The reason I even care about this is I'm trying to understand the effect of flange diameter on torque transmission and if a more tangent spoke with a larger diameter flange leads to more efficient transfer of power.
Given that you occasionally see a full radial rear (admittedly they usually have like 96 spokes), it's not a huge consideration, unless maybe the wheel in question is going to experience an unusual degree of torque. It doesn't take much tangentiality to provide an adequate lever on the spoke, since even the lightest spokes are often heavier than necessary for tensile loads (except perhaps in very low spoke count wheels) - there's a minimum size dictated by the need to withstand the twist of tensioning.

So the smaller the flange diameter, the more any torque applied to the hub stretches and loosens the spokes, but the effect is almost negligible. If you want to ensure durability, as Brandt has no doubt impressed upon you, paradoxically enough, you want lighter spokes with more elasticity, helping to ensure that any give in the system is confined to the stretching and slackening of spokes, rather than elbows flexing or what have you.
Kimmo is online now  
Old 04-18-21, 05:51 PM
  #20  
Troul 
:D
 
Troul's Avatar
 
Join Date: Oct 2013
Location: Mich
Posts: 3,806
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked 835 Times in 611 Posts
Originally Posted by Symox View Post
The main concept I cannot understand is in this sentence: "Spokes are flexible and cannot transmit torque by acting as levers, so they transmit torque from the hub to the rim by becoming tighter and looser." I get it that the spokes will compress or stretch based on torque and that they cannot transmit torque by acting as levers since they are flexible. What I don't get is how the change in spoke tension transmitting to the rim causes the wheel to turn.

My head hurts now
Thanks for the help
In a general way of explaining: One section of spokes in the wheel give-way, bound tension; while the other section of spokes in the wheel go as straight as they can, achieving as much tension they're capable of. The "round" rim shape you see is going "egg" shaped from the spokes exchanging energy levels.
__________________
-Oh Hey!
Troul is offline  
Likes For Troul:
Old 04-18-21, 08:57 PM
  #21  
Kimmo 
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Posts: 9,107

Bikes: https://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=152015&p=1404231

Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 1157 Post(s)
Liked 429 Times in 309 Posts
Regarding whether a wheel stands or hangs, what about Brandt's measurements? No detectable increase in tension of any spokes in a loaded wheel, only a decrease in tension in the bottom spokes. If you accept that as fact, how can you possibly say it hangs?

IMO this counterintuitive conclusion serves to illustrate that most of us fail to understand just how clever this tensegrity structure is, almost entirely failing to appreciate that the tension is a structural component.

I'd be interested to see if Brandt's results would be mirrored in the tensions of leading and trailing spokes in a torqued wheel... No increase in tension of trailing spokes would thoroughly confirm Brandt's view, although I'm not sure the opposite would necessarily invalidate it.

Anyway, I reckon it's pretty safe to say that it's a lot more complicated than many folks imagine. A wheel stands on its lower spokes in the sense that these are the only ones experiencing a change in tension. Go figure.

Last edited by Kimmo; 04-18-21 at 09:03 PM.
Kimmo is online now  
Likes For Kimmo:
Old 04-18-21, 10:07 PM
  #22  
cjenrick
Senior Member
 
Join Date: May 2020
Posts: 263
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 94 Post(s)
Liked 77 Times in 58 Posts
some folks use bigger spokes for the pulling spokes in order to do something,

i have a wheel like that out in the garage, Mavis SSC 280 gram sewup rim, tied and soldered also, don't know how to get solder to stick to stainless, it must just cling to the wore used for the tie.

is it to give you more snap?

if that is what the mind thinks, then mission accomplished.

can you see the different gauge spokes? who cares, the only thing of interest here is the Mavic titanium freewheel which they made for maybe three weeks, you don't see those growing on trees, good for that, who wants a frewheel that wears out in two weeks and has slop develop in the bearings that go click click while you go up the hill? not to mention the stripped mangled Ti when you try to remove it, so there is stays.

Last edited by cjenrick; 04-18-21 at 10:39 PM.
cjenrick is offline  
Old 04-18-21, 10:51 PM
  #23  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 14,920

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2925 Post(s)
Liked 1,197 Times in 842 Posts
Originally Posted by Kimmo View Post
Regarding whether a wheel stands or hangs, what about Brandt's measurements? No detectable increase in tension of any spokes in a loaded wheel, only a decrease in tension in the bottom spokes. If you accept that as fact, how can you possibly say it hangs?

IMO this counterintuitive conclusion serves to illustrate that most of us fail to understand just how clever this tensegrity structure is, almost entirely failing to appreciate that the tension is a structural component.

I'd be interested to see if Brandt's results would be mirrored in the tensions of leading and trailing spokes in a torqued wheel... No increase in tension of trailing spokes would thoroughly confirm Brandt's view, although I'm not sure the opposite would necessarily invalidate it.

Anyway, I reckon it's pretty safe to say that it's a lot more complicated than many folks imagine. A wheel stands on its lower spokes in the sense that these are the only ones experiencing a change in tension. Go figure.

I'm not sure I can explain my thoughts well enough for some to understand. My thoughts are just those, not some engineering treatise. But here goes. The rim has for all intent a fixed circumference so when the rim deforms from the loads that gravity produces, and the bottom spokes lessen their tension, the rim wants to also deform elsewhere away from the hub. Other spokes see increased tension. If the overall spoke tensions are high enough this deformation is within the elasticity of the rim and the rim returns to it's previous shape. The spokes that see increased tensions are not the bottom ones but some are the spokes above the hub. I have played with a spoke tension gage and seen this when pressing the wheel against the ground while another person gaged the spoke tensions. No I didn't record the differences between the bottom and upper spokes but we did see the tension changes.

I believe it's well known that if the spokes are not fully tensioned they will relax as they pass through the bottom, enough to have nipples loosen. If a hub stands on the bottom spokes how can this relaxing of tension happen, as many have said how can you push on a rope? Now a old time wagon wheel with non compressible spokes does stand on the bottom spokes, or maybe better said the spokes are not under tension so the hub can't hang from above.

As I also mentioned I have read others smarter then I who say for the math purposes it is awkward to have a negative tension so Brandt's equations "pretend" the bottom spokes support the hub.

Regardless of my thoughts or other's too I still feel that the tangental and tensioned wheel is pretty well proven a design and pretty much most all the later "engineering" has more to do with product differentialization (sp?) which is a marketing aspect, not a basic first principle engineering one.

I've just about used up my ability to write about this. Andy
__________________
AndrewRStewart
Andrew R Stewart is online now  
Old 04-18-21, 11:05 PM
  #24  
cyccommute 
Mad bike riding scientist
 
cyccommute's Avatar
 
Join Date: Nov 2004
Location: Denver, CO
Posts: 23,993

Bikes: Some silver ones, a red one, an orange one and a few titanium ones

Mentioned: 121 Post(s)
Tagged: 1 Thread(s)
Quoted: 4103 Post(s)
Liked 1,595 Times in 975 Posts
Originally Posted by Kimmo View Post
Regarding whether a wheel stands or hangs, what about Brandt's measurements? No detectable increase in tension of any spokes in a loaded wheel, only a decrease in tension in the bottom spokes. If you accept that as fact, how can you possibly say it hangs?
Because the tension change is spread out over many spokes. A decrease in tension of the bottom spokes is what would be expected in a system that is under tension and one where the spokes arenít attached to the rim. That change in tension may be present in the upper spokes but the magnitude of the tension change is small so that it quickly becomes unmeasurable.

IMO this counterintuitive conclusion serves to illustrate that most of us fail to understand just how clever this tensegrity structure is, almost entirely failing to appreciate that the tension is a structural component.
The idea that the wheel stands on the spokes isnít counterintuitive. We are used to seeing wheels where the vehicle stands on the wheels. Nearly every car wheel, buggy wheel, wagon wheel, and ox cart wheel stands on the wheel. The wheel is under compression. The real counterintuitive part is the idea that the weight hangs from the spokes. Tensegrity structures mess with your head because we see so few examples of them. Many people, looking at that Lego tensegrity structure assume that the long chains are the structural units. However, they arenít. If weight is put on the structure, the long chains slacken and the structure becomes unstable. The long chains are important but they arenít the most important element. Just like the bottom spokes are important as well but they donít carry the load.

The problem is that Brandt made some wrong assumptions and was too stubborn to admit it. Hereís what he said in The Wheel

A wheel with wire spokes works the same as one with wooden spokes except that the built-in force in its spokes is different. In a wooden-spoked wheel, force is transmitted from the ground to the hub by compressing the bottom spoke. This spoke becomes shorter as it furnishes the upward force to the hub. As in a wooden-spoked wheel, the bottom spokes of a wire wheel become shorter under load, but instead of gaining in compression, they lose tension. With the same load, the net change in force is the same for both wheels. The algebraic sum of negative and positive forces (compression and tension) is the same.
First, the spokes of a wire wheel donít get shorter. The rim rides up on the spoke. The rim deforms and becomes oblate. Yes, the spokes undergo decreased tension. The real problem is that he assumes that the opposite of compression is tension and vice versa. But they arenít. They work in opposite directions but arenít opposing forces. A lack of tension doesnít mean a increase in compression. Thatís somewhat counterintuitive as well.


Anyway, I reckon it's pretty safe to say that it's a lot more complicated than many folks imagine. A wheel stands on its lower spokes in the sense that these are the only ones experiencing a change in tension. Go figure.
I agree that the spokes on the bottom of the wheel undergo a change in tension. But thatís because the rim is deforming not because the spoke is being shortened through compression. The spoke remains the same length. Nothing is pushing on it to shorten itís length. Hereís another thought experiment. Remove all the spokes on 1/2 of the wheel. Put the wheel in the bike with the spokes above the hub. The bike can be balanced (but not ridden) in this configuration. You could probably even get on the bike and load the wheel.

Now spin the wheel so that the spoke are on the bottom. The bike wonít stand up. The spokes would poke through the bottom of the rim putting the spokes in compression and they will just bend. They could hold no weight. Maybe Iíll do the experiment sometimes.
__________________
Stuart Black
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
cyccommute is offline  
Likes For cyccommute:
Old 04-19-21, 03:15 PM
  #25  
davidad
Senior Member
 
Join Date: Feb 2009
Posts: 6,491
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 519 Post(s)
Likes: 0
Liked 125 Times in 105 Posts
Originally Posted by Andrew R Stewart View Post
I have to break my rule here due to a new aspect of this thread...

IIRC Brandt's book uses this model to make the math easier to deal with. My understanding is that we hang from the rim's upper section, like two hammocks. I really like this model as it fits with my feeling the flow of rolling over the road. Andy
Gerd Schraner in his book "The Art of Wheel Building" he states that the wheel stands on the spokes.
It doesn't mater weather the spokes are wood, or steel rods or steel wire under tension the load on the axle pushes down on the spokes and loads they by compression.
davidad is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.