Lacing triple cross 28h

[tctyres]

Originally Posted by Mark McM

It is true that when a flange breaks with radial spokes, then it is likely that several adjacent spokes will be released. But that's more of an issue with the whether the hub is designed for radial spoke loads. But that's still a moot point, because if the spokes on the other flange are crossed, then the radial spokes experience no additional loads due to wheel torque.

If this were true, there would be no nds failures, and there are. The hub transmits torques across it.

Please explain where these torques come from. The wheel bearings separate the wheel/hub form the rest of the bike and pass virtually no torque loads between the wheel and the fork/frame. Unless there is an additional coupling between the fork/frame and hub (such as disc or drum brake), then there is no significant spoke loading due to torques.

A torque is F*l = m*a*l. Change m or a, and the torque changes. Put another way, the torques come from the additional mass and accelerations associated with the loading. Cross and mtb riding requires instantaneous accelerations that are higher than a road bike. A loaded touring bike imparts extra torque from the extra mass. Brakes, chains, instantaneous accelerations on the wheel (positive or negative), associated with the road (e.g. potholes) all impart torques on the wheel.

The rim is supported by the spokes, with only short spans between the spokes. The rim can not flex if the spokes don't flex, so the stiffness of the spokes will greatly affect the stiffness of the assembled wheel. Grab the two ends of a spoke, and try to stretch it. You'll find that the spokes are far stiffer than any rim.

Also consider this: The heaviest spokes weigh about 230 grams for 32 spokes - but for many wheels, the total weight of the spokes is about half of that. The weight of the lightest rims is about 280 grams - but most rims weigh far more than this. If you were to take a few dozen grams off of the rim on the average wheel, and add extra spokes equal to the same weight, I guarantee the wheel will have more lateral stiffness.

The weight of the metal is irrelevant. A double walled rim is a hollow tube. A tube is hollow to increase its strength to weight. Furthermore, the discussion is on lateral strength so the lengthwise stretching is irrelevant. A set of spokes will flex inward/outward with hard pedaling. This why a brake can rub on a hard effort if the clearances are tight. If I had said radial or tangential, you'd be correct.

[oldpotatoe]

If you were to take a few dozen grams off of the rim on the average wheel, and add extra spokes equal to the same weight, I guarantee the wheel will have more lateral stiffness.

Of course..how to make a lighter, stiffer wheel? Light rim and sufficient spokes BUT that doesn't 'look' good on the LBS floor..marketeers make low spoke count wheels by increasing the rim weight a BUNCH(to make them reliable, sorta) and then use 18 spokes. BUT a little math...subtract 200 grams from that rim and add 14 spokes(32), which weigh about 3.5 OUNCES(120 grams or so)..but loses LBS and coffee shop points.

For right above..OMG..battle of the equations...

YOIKES!!

[ergott]

Torque is applied when driving the hub (rear wheel) and as a result accelerating the rim or braking at the hub and as a result a negative acceleration of the rim.

I'd like to see a picture of a 3X laced 28 hole wheel that has spoke overlap.

[tctyres]

Originally Posted by oldpotatoe

For right above..OMG..battle of the equations...

YOIKES!!

Sorry! I was trying not to ... but it happens.

[Lewis Moon]

I lace my 28s 3x all the time and have never had a problem. Perhaps if you have small flanges and the wheel is laced at less than optimal tension you might have overlap issues, especially on the NDS where the tension is the lowest.

[Lewis Moon]

Originally Posted by oldpotatoe

Of course..how to make a lighter, stiffer wheel? Light rim and sufficient spokes BUT that doesn't 'look' good on the LBS floor..marketeers make low spoke count wheels by increasing the rim weight a BUNCH(to make them reliable, sorta) and then use 18 spokes. BUT a little math...subtract 200 grams from that rim and add 14 spokes(32), which weigh about 3.5 OUNCES(120 grams or so)..but loses LBS and coffee shop points.

For right above..OMG..battle of the equations...

YOIKES!!

I don't know why, but low spoke count wheels just look wrong to me. The same with "grouped" spokes. Give me a set of 28 - 32 wheels, Sapim DB spokes, DT hubs and Archtype(ish) rims any day. I'll ride them from gravel to hill climbs...and I'll have three sets shod with different tires for the same price as a set of fancy carbon wheels.

[oldpotatoe]

[QUOTE=ergott;2512596]

I'd like to see a picture of a 3X laced 28 hole wheel that has spoke overlap.

[ergott]

not 28 spokes

[ergott]

If 28 3X was an issue I would have run across it long ago.

[Mark McM]

Originally Posted by tctyres

If this were true, there would be no nds failures, and there are. The hub transmits torques across it.

Spokes don't need torque loads to break The largest loads experienced by spokes are usually vertical loads (particularly when hitting bumps), and these can be sufficient to break spokes without the contribution of torque loads.

The hub only transmits torque loads if the spokes provide torsional stiffness. Since radial non-drive side spokes provide no torsional stiffness, they can't carry torsional loads, so torque is not transmitted across the hub. (Conversely, if the drive side spokes are radially laced, as on some Mavic Ksyrium wheels, the drive side spokes carry no torsional loads, and all torque is transmitted across the hub to the crossed non-drive spokes.) This is covered by several publications on wheel dynamics, including The Bicycle Wheel by Jobst Brandt.

Originally Posted by tctyres

A torque is F*l = m*a*l. Change m or a, and the torque changes. Put another way, the torques come from the additional mass and accelerations associated with the loading. Cross and mtb riding requires instantaneous accelerations that are higher than a road bike. A loaded touring bike imparts extra torque from the extra mass. Brakes, chains, instantaneous accelerations on the wheel (positive or negative), associated with the road (e.g. potholes) all impart torques on the wheel.

This is a tremendous reach. The wheel is a very small portion of the entire mass of the bikes. Plus, the wheel torques experienced are only those requred to accelerate the hub and spokes (the tire and rim are directly accelerated by ground contact forces), so those torques are very, very small (which is why I said "pass virtually no torque loads between the wheel and fork/frame). These torques are too small to have any meaningful effect on the spokes.

Originally Posted by tctyres

The weight of the metal is irrelevant. A double walled rim is a hollow tube. A tube is hollow to increase its strength to weight. Furthermore, the discussion is on lateral strength so the lengthwise stretching is irrelevant. A set of spokes will flex inward/outward with hard pedaling. This why a brake can rub on a hard effort if the clearances are tight. If I had said radial or tangential, you'd be correct.

Spokes support the rim by their lateral bracing angle. Clearly, without the spokes, a wheel whould have no lateral strength/stiffness at all. When a wheel is flexed laterally, the spokes are on either side are either stretched or 'compressed' (shortened by de-tensioning). The lateral movement is therefore constrained by the stretching/compressing of the spokes. As this article on wheel flex shows, even wheels with the stiffest rims have lateral flex, caused by spoke flex:

https://www.slowtwitch.com/Tech/Debu...ness_3449.html

From the article:

When someone comments that their race wheel isn’t stiff enough, what they likely mean is this: Their wheel has too much lateral rim stiffness and not enough lateral spoke stiffness. That’s the big secret! You may feel compelled to say, “A-ha!”

How often do riders complain of their shallow-section aluminum wheels not being stiff enough? I don’t know about you, but I almost never hear that – short of a wheel with spokes that are far too loose. The reason you never hear that is because most aluminum wheels have relatively high spoke stiffness and relatively low rim stiffness. Think of wheel with 32 spokes of 2mm diameter, laced to a 20mm deep alloy rim – that’s a lot of spoke material and not much rim.

[tctyres]

Originally Posted by Mark McM

Spokes don't need torque loads to break The largest loads experienced by spokes are usually vertical loads (particularly when hitting bumps), and these can be sufficient to break spokes without the contribution of torque loads.

The vertical load is mainly constant as the weight of the rider + frame doesn't change appreciably over the course of a ride. Hitting a bump is vertical but can cause a torque if there is an acceleration off the vertical plane, and there almost always is.

The hub only transmits torque loads if the spokes provide torsional stiffness. Since radial non-drive side spokes provide no torsional stiffness, they can't carry torsional loads, so torque is not transmitted across the hub. (Conversely, if the drive side spokes are radially laced, as on some Mavic Ksyrium wheels, the drive side spokes carry no torsional loads, and all torque is transmitted across the hub to the crossed non-drive spokes.) This is covered by several publications on wheel dynamics, including The Bicycle Wheel by Jobst Brandt.

A torque can be transmitted across a hub with radial non-drive side spokes. This is the issue as to why they break. If the torque is transmitted, those spokes cannot support it either leading to elastic flexure or plastic failure. There aren't other options with a radial lacing. For a cross-laced wheel, the torque can be transmitted to the rim, which is where the rider wants it.

This is a tremendous reach.

Ha! Using the definition of a torque is a reach. I guess if you don't know physics, it might seem like it.

The wheel is a very small portion of the entire mass of the bikes. Plus, the wheel torques experienced are only those requred to accelerate the hub and spokes (the tire and rim are directly accelerated by ground contact forces), so those torques are very, very small (which is why I said "pass virtually no torque loads between the wheel and fork/frame). These torques are too small to have any meaningful effect on the spokes.

The average acceleration of the wheel is the average acceleration of the bike. If you're thinking only about the wheel, that's the problem. The wheel rotates over the ground (no-slip condition) and translates the hub.

Spokes support the rim by their lateral bracing angle. Clearly, without the spokes, a wheel whould have no lateral strength/stiffness at all.

The bracing angle is tiny, so transmits little force laterally.

[dddd]

Originally Posted by tctyres

...The bracing angle is tiny, so transmits little force laterally.

All of the lateral force that a wheel sustains is from the product of spoke bracing vector and the multiple spoke's relative inelasticity.

These forces can be quite substantial, certainly enough to bend the rim outright but for the effective later bracing provided by the spokes.

Also, the bracing angle on the drive side has to provide a balancing equal force to the better-braced non-drive spokes, which may help one to visualize how substantive that the forces are.

[cribbit]

Is this thread now a battle between wheel and equations porn?

[oldpotatoe]

Originally Posted by cribbit

Is this thread now a battle between wheel and equations porn?

Oh yeah? Take this.

What's scary is one or both of these guys will look at this and know what it means..

[Mark McM]

Originally Posted by tctyres

The vertical load is mainly constant as the weight of the rider + frame doesn't change appreciably over the course of a ride. Hitting a bump is vertical but can cause a torque if there is an acceleration off the vertical plane, and there almost always is.

The vertical load can be magnified when hitting a bump to a very large value (consider - hitting a sharp edge bump can compress the tire enough to pinch flat it, which takes a very large instantaneous force). But perhaps more importantly, the vertical force only affects a few spokes near the LAZ (Load Affected Zone) at the bottom of the wheel, whereas torques are distributed nearly evenly across all crossed spokes.

Originally Posted by tctyres

A torque can be transmitted across a hub with radial non-drive side spokes.

As stated before, no torque is transmitted across the hub with radial non-drive side spokes. The reason is explained in the book "The Bicycle Wheel" by Jobst Brandt. The rest of the world agrees with this, and here are some examples:

Sheldon Brown's guide to wheel building says that radial lacing the non-drive side spokes can sometimes be an advantage because then these spokes experience no torque loads:

https://www.sheldonbrown.com/wheelbu...ml#half-radial

Here is an paper on the Williams Cycling web site, featuring an analysis of spoke loading with different lacing patterns. They also conclude that radial non-drive spokes transmit no torque:

http://www.williamscycling.com/asset...e%20Lacing.pdf

The Wheel Fanatyk blog also says this about radial non-drive spokes:

There must be a million road bikes with 24 hole rear wheels. Most of them have radial patterns on the non-drive side for style and aerodynamic bling. Radial can transmit no torque until a tiny windup. Since the drive side, crossed pattern is rotationally stiffer it carries the torque load before the poor non-drive side gets a chance. It’s not unwilling, just too slow. The rear wheel’s left side is completely unable to assist for torque loads. All it can do is carry vertical weight, for which the whole unit is grateful.

And you don't have to take their word for it, you can verify it with your own test. Take a bike with a rear wheel that has radial non-drive side spokes and put the drivetrain into it's lowest gear ratio. Have a friend clamp the rear brake (to keep the wheel from turning) and stand on the forward pedal with the crank horizontal to generate a torque load on the wheel. On the drive side, pluck spokes on both sides at the top of the wheel and listen for the tone they make - the pitch of these tones with vary with spoke tension. Compare the tones on each spoke with and without torque applied to the wheel. You should find that tones of drive side trailing spokes increase in pitch under torque load (increase tension), while the tones of drive side leading spokes decrease in pitch (decrease tension), but there should be no change in tone in the radial non-drive spokes (no change in tension). If the non-drive side spokes don't change tension, they are not transmtting torque loads.

Originally Posted by tctyres

The average acceleration of the wheel is the average acceleration of the bike. If you're thinking only about the wheel, that's the problem. The wheel rotates over the ground (no-slip condition) and translates the hub.

The translational acceleration at the hub from the wheel weight is also very small, and besides, translational accelerations don't generate torques.

Originally Posted by tctyres

The bracing angle is tiny, so transmits little force laterally.

This very obviously can not be true. The tire & rim are only connected to the rest of the bike by the spokes. Therefore all forces (lateral, vertical, and torsional) between the hub and rim must be transmitted by the spokes, and only by the spokes.