open topic, for anything cycling related.
Just a stupid question from a not-very-technically-adept commuting/recreational cyclist, about spokes:
On a rear wheel, the number and crossover of spokes should be greatest (to provide greater strength / structural integrity) on the side of the wheel that has the cassette i.e. the "driven" side).
Wandering through a bike shop the other day I noticed an essentially random arrangement of "stronger" vs "weaker" spoke configurations for the two sides of the rear wheels on a range of road bikes. i.e. some had a larger number of spokes (and more cross-lacing) on the cassette side of the wheel, and some had more on the non-cassette side of the wheel.
Do some bike shops put together wheels/bikes arse-around without realising it? Does the "sided-ness" of rear wheel spoke lacing simply not matter? Am I missing something blindingly obvious such as the bikes with fewer spokes on the cassette/driven side being chunkier/stronger spokes?
I’m certainly no expert when it comes to wheels, however as I understand it, the number of spokes and spoke placement of any given wheel depends on the rim design and strength.
In most instances it requires for the the cross laced spokes to be on the non drive side to offset the twisting action on the hub caused by the pressure on the drive side.
There again I have no doubt that a more expert explanation would be forthcoming if this question was asked in "The Shed"
I can add nothing, apart from:
A, Like everything else in cycling, it's all about fashion.
1.370" x 24 tpi - what sort of stupid standard is that?
Half Radial lacing is done to prevent the spokes on the NDS from breaking because of fatigue. 2:1 lacing patterns are used to even up the tension on both sides of the rim, The NDS is usually much lower (usually 50-65% for me) than the DS on a properly dished wheel. Lower spoke counts mean a lower tolerance to spoke tensions as each spoke takes up a bigger load. To achieve a ridable low spoke count wheel, the rim needs to be fairly stiff which usually means that they are heavier. Has anyone seen the 200g rims that were around when 36 and greater spoke counts were the norm? I dare someone to ride one of those rims with today's spoke counts
the main reason for today's lower spoke counts is stronger, rather than heavier rims.
for an equivalent L-R spoke count, the spokes on the drive side must be tensioned more. i also don't understand why there isn't a higher spoke count on the drive side - probably just due to a desire for symmetric rim holes?
Which is why a light alloy rim is 383g vs the 200g from years back... Technology must be going backwards
This is to even up the tension on both sides of the wheel, The tension on the NDS is lower because the rim is dished to one side. Sometimes you can break spokes on the NDS because the tension is too low (letting the spoke move alot, causing it to fatigue where it crosses), if you use less of them you can bring the tension up without effecting the dish or the tension on the other side (which may already be too high). You could also lace the wheel half radial and that will also solve the problem, not by increasing the tension to the same as the DS, but removing the cross where the spokes rub/fatigue. I've never had problems with breaking spokes on the NDS, but I'm not the hardest on my wheels
Hope this helps
My fulcrum 5 has 2 to 1 lacing, ie 2 drive side spokes for every offside spoke. I like the design because rear wheels are weaker on the drive side because of dishing as well as the drive torque unwinding them.
The actual problems (as far as a shop building one up a random), is that the spoke count is now a multiple of 3, instead of a multiple of 2, and the hub has 2 to 1 drillings as well. ie I have a 27 hole rim, and a 27 hole hub. Virtually all hubs and rims sold to builders have multiples of 2. Required a wheel builder of factory scale who either builds (or can commission) a decent run of rims and spokes with the correct drillings.
The wheel is faster with less spokes, because the spokes thrash the air as they go over the top of the rotation. At my usual commuting speed the spoke head is doing 80 at the top.
I've never broken a spoke on any cross laced wheel mid spoke where they were bent over each other. Its always the j-bend or at the nipple. thats also reflected in the practice of using double butted spokes - I have a set on the rear of my MTB (32 spoke, 3 cross) at the moment, which wouldn't be feasible if cross lacing was fatiguing them.
Just wondering: is it just the hub that's drilled all funky? Could you hypothetically do the same thing with a 36h rim and a 48h hub? Or 18 and 24 or whatever? Not that I can think of any compelling reason to do that rather than just buy a set of Fulcrums (and I suspect that 48h hubs are very much a specialty item anyway)...
When I've had spokes fail in the middle (there was a thread about this recently) they were just sitting in a shed and didn't fail where they crossed over. Dodgy spokes would seem to have been the problem there. All my in-use failures have also been at the ends.
I was going to post a similar answer to SA.
Like everything else in cycling, if it is not to be found at the altar to St Sheldon it probably isn't very important.
Actually they've changed the spec of the wheels between when I researched them, and when I needed them (and thus pressed the trigger). Mine are actually 24 spoke rears (16 and 8 ). Probably easier to recreate with a 32h or 48h hub if you had to. Whether or not some of the last levels of detail matter, I couldn't say.
I assume your running disk brakes? I'm not 100% sure but I read somewhere that disk brakes affect the tension of a wheel. You are not supposed to lace a disk wheel radial for this reason. I've never had issues with cross laced wheels either... Sheldon Brown does mention this in his article about wheelbuilding, if you want a more in depth explanation see that (why half-radial prevents spokes from being broken)
I was also recently debating this question as I noticed a Shimano Ultegra wheel radially spoked on the drive side and cross spoked on the NDS. As radial spokes are not good at transferring drive (or braking) force between the hub and rim, it seems that a beefy hub is required as the drive force must transfer across the hub to the NDS or whatever you would call it in this case. The wheel feels solid enough as I did 75km on it today. My Bontrager wheel is the opposite with radial spokes on the NDS.
That actually is design is actually quite clever. The forces in the spokes produced by the torque are quite low compared to the static forces of spoke tension and the load forces that occur when the wheel is occasionally laterally loaded. The drive side experiences significantly high forces not because of the torque of the drive but due to the unsymmetrical dish of the rear wheel. Making the higher loaded drive side spokes radial is actually very an efficient use of the available strength.
So... it begs the question...
Whatever one's pet theory is regarding the pros/cons of radial versus cross-laced spokes on the driven and non-driven side of the wheel, the fact remains that there seems to a random assortment of configurations in bikes sitting on the shop floor, including within the same brand of bike, and sometimes even the same (or very similar) wheelsets used across those bikes.
Does it just not matter?
Or is there dissent amongst wheel manufacturers as to which side needs to be stronger?
That would be true, except for the fact that both 6700s and rs80s are fully cross laced on the rear, and that particular ultegra hub probably can't be laced any other way because its straight pull and there is no way for the spokes to exit radially from that particular hub. Possibly darryl confused straight pull with radial.
When you cross lace the wheel, only half the spokes resist drive torque, and if you made half of them radial on a 20 spoke rear wheel, you'd be down to 5 spokes resisting drive forces.
There is no optimal design, and depends on the ratio of fast riding to climbing or hard starts, and the weight of the rider. Gears produce torque multiplication in various degrees, and climbing up a hill in a lower gear produces more torque at the hub and thus spokes than the same pedal force and cadence riding along a flat road in a taller gear.
Riding fast along a flat road, cycles the spokes through load more frequently, and exposes them to more load when striking surface irregularities (and usually will strike more of them per journey due to simply eating up so much more road).
http://www.bikeradar.com/gear/category/ ... t-08-27765
Here are some radial laced rears. Maybe they're their not around anymore. I don't know I don't keep abreast with the latest and greatest.
A 1.8mm spoke has a ultimate strength strength of around 340kg. So with 5 spokes you are talking over 1.5 tonne of ultimate tensile strength capacity! (The pre-load would use up a certain percentage of this) Either way I wouldn't worry about breaking a spoke base of drive forces.
Yeah they are gone now. I don't think they had a particularly bad reputation for the ultegra versions, so its obviously not a terrible arrangement, but hopelessly painful for spoke supply when a repair is needed. I take back my observation about darryls observation skills and apologise.
That is the perfect optimal for a perfect spoke that has not gone through assembly and not been nicked, tool damaged, or is probably not in fact sitting in a typical hub hole, and doesn't have a j-bend on it or a thread cut in the nipple end, or a straight pull rivety head thingie on it, and is mounted such that all force is applied entlrely along its axis, which simply cannot be true of a drive transmitting crossed spoke.
I can bend a broken off spoke with my hand to tie it away if I apply the force at 90 degrees. ie their strength is proportional to the angle the force is applied at. if you have less you have to lean them over further to resist the drive forces, and the more you lean them over, the less well they do the weight bearing forces. Lastly they can't be cycled at 50% of their yield strength without shortly failing (ie all of the spokes of a wheel would fail if the spokes are reaching 50% in service pretty quick), and low spoke count wheels can see 1 spoke doing nearly all the work during its turn in the cycle.
The one shown above by Human909 is like mine - also about the only Ultegras that are 10s only. Had to buy the only wheel we could find in Wangaratta as the free wheel on my daughters Kyserium jammed solid and we were doing the rail trail.
Disc and rear hubs must have a cross lacing on at least one side to prevent the rotary forces imposed by the drive/braking collapsing the wheel.
It is not strictly necessary to have the crossing on the drive/brake side but if it isn't then the hub shell must be strong enough to handle the assymetric forces involved.
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
London Boy 29/12/2011
Spokes almost never break due to high tension, they mostly break due to being under tensioned. This is the reason for 2:1 lacing on the rear wheel as it is much harder to under tension the NDS spokes when they are almost equal tension as the DS spokes.
Spokes have almost all the strength in tensile/compressive directions and very little in shear and bending directions. Low tension causes these shearing and bending forces, usually around the hub flange where most spoke breakages occur.
Thats not strictly true. Spokes like any long thin steel wire/rod have very hight tensile strength and negligible axial compression strength and bending stiffness. Shear strength should be approximately similar to tensile strength.
Not really. Low tension causes unloading and loading of the spoke which then rubs, bends and fatigues. Its the fatigue that is the problem not the bending or shearing which is SIGNIFICANTLY lower that would cause breakage.
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