Two different spoke gauges - same flange (rearDS)?

[Look585]

Suppose in one hand you have 7 DT Aerolites and 7 DT Aero Comps in the same length. In the other hand, you have a 28h rear hub and rim that need drive side spokes in that very length.

Would you lace a drive side rear with two different spoke gauges? Would the heavier gauge spokes be leading or trailing? Heads in or heads out?

Or, just spend $25 on 7 more aerolites/aerocomps and do it "right"?

Discuss...

[11.4]

Buy the right spokes. The two gauges will interfere with each other in several ways. Your wheel won't be stable, you'll have regular spoke retensioning issues, and you put additional strain on the rim and hub.

[cachagua]

I'm not quite seeing where the problem would arise. Can you say more about that?

[oldpotatoe]

Suppose in one hand you have 7 DT Aerolites and 7 DT Aero Comps in the same length. In the other hand, you have a 28h rear hub and rim that need drive side spokes in that very length.

Would you lace a drive side rear with two different spoke gauges? Would the heavier gauge spokes be leading or trailing? Heads in or heads out?

Or, just spend $25 on 7 more aerolites/aerocomps and do it "right"?

Discuss...

Or spend some $ on DT Comp or Sapim Race spokes..for the RH side..28h.

I wouldn't mix spoke gauge/type on drive side rear. I seldom if ever lace rear, drive side, with thin spokes unless the rider is like buck-20 max weight,and maybe not even then, IMHO, of course. And lace 3 cross.

[Black Dog]

I'm not quite seeing where the problem would arise. Can you say more about that?

Different gage spokes will elongate different amounts under the same load. Not a stable situation.

[cachagua]

Different gage spokes will elongate different amounts under the same load. Not a stable situation.

Trying to mentally walk through this, I can see where you'd get fluctuating torques on the hub and variations in tension here and there in the wheel, but I think they wouldn't be more than the usual dynamics from accelerating, braking, and cornering that every rear wheel lives with happily.

Or put another way: the force applied to other parts of the wheel *by* the different elongation of the thinner and thicker spokes -- the *effect* of the different elongation -- would be quite small compared to the whole mix of load variations that make up the world the wheel lives in. It wouldn't increase those variations to any level that'd cause trouble in the wheel, even over time.

When I read the original post, I thought "Yeah, I'd do it". But maybe that's naive? I'm open to further explanation--

[Gummee]

You've got the spokes. Try it and see. Worst case, you'll need to relace the wheel. Best case, it'll ride nicely

That said, I'd do the heavier spokes as pulling spokes.

Life is short. Experiment

M

[Black Dog]

Trying to mentally walk through this, I can see where you'd get fluctuating torques on the hub and variations in tension here and there in the wheel, but I think they wouldn't be more than the usual dynamics from accelerating, braking, and cornering that every rear wheel lives with happily.

Or put another way: the force applied to other parts of the wheel *by* the different elongation of the thinner and thicker spokes -- the *effect* of the different elongation -- would be quite small compared to the whole mix of load variations that make up the world the wheel lives in. It wouldn't increase those variations to any level that'd cause trouble in the wheel, even over time.

When I read the original post, I thought "Yeah, I'd do it". But maybe that's naive? I'm open to further explanation--

I am talking mostly about the effect of lateral loading. If there is one side of the wheel that has spokes of different gauges then the heaver gauge spokes will transfer more force than that lighter spokes. This effective focuses the force on 1/2 of the spokes on that side of the rim, this on the side of the rim that is already at higher tension. I suspect that this would lead to cracks at these holes.

[cachagua]

Yes, I think we're seeing just about the same thing: that the relative "unstretchiness" of the thicker spokes would load their spoke holes more heavily. And yes, it'd be where the load is higher anyway... probably that's how that wheel would eventually die, but how much sooner would it die (i.e. would cracks appear) than if all spokes were the same?

H'mm. Would the increase in force at drive-side trailing spoke holes be a percent? Two? Five? Hard to see it being much more than that. And how much increase, over the static force of the build tension, does a hard acceleration produce? Especially an out-of-the-saddle sprint where the acceleration torque is combined with a lot of lateral force... seems like that'd have to be orders of magnitude more than the ∆ from the odd spokes.

Anyway, idle speculation. I'm *thinking* about building wheels because I'm not *building* wheels, which is dumb because I've got half a dozen I need to build! All the same, thanks for the insight and discussion.

[Black Dog]

Best way to know is to build em and ride em. They will certainly not explode any time soon! Hard to say about the % differences without measurement or good engineering calculations. Fun thought experiment though.

Yes, I think we're seeing just about the same thing: that the relative "unstretchiness" of the thicker spokes would load their spoke holes more heavily. And yes, it'd be where the load is higher anyway... probably that's how that wheel would eventually die, but how much sooner would it die (i.e. would cracks appear) than if all spokes were the same?

H'mm. Would the increase in force at drive-side trailing spoke holes be a percent? Two? Five? Hard to see it being much more than that. And how much increase, over the static force of the build tension, does a hard acceleration produce? Especially an out-of-the-saddle sprint where the acceleration torque is combined with a lot of lateral force... seems like that'd have to be orders of magnitude more than the ∆ from the odd spokes.

Anyway, idle speculation. I'm *thinking* about building wheels because I'm not *building* wheels, which is dumb because I've got half a dozen I need to build! All the same, thanks for the insight and discussion.

[Mark McM]

Buy the right spokes. The two gauges will interfere with each other in several ways. Your wheel won't be stable, you'll have regular spoke retensioning issues, and you put additional strain on the rim and hub.

I'm not sure I understand what instability you are talking about. Many wheels are already built with non-symmetric spokes, and they are perfectly stable. Dished wheels have spokes that pull at the rim differently angles, yet these wheels can be perfectly stable. Many dished wheels use differential lacing (thicker spokes on the drive side, thinner spokes on the non-drive side), but these wheels can be perfectly stable. Many dished wheels are built with triplet lacing (1 spoke on the non-drive side for every 2 spokes on the drive side), and these wheels can be perfectly stable.

If you mix different gauge spokes, the two main affects will be:

- The wheel stiffness will be less than if all thick spokes were used, but more than if all thin spokes were used.

- More of the load will be concentrated on the thicker (stiffer) spokes. It is true that this will increase the propensity of breaking spokes or cracking rims, but only if the wheels are close to the limit breakage/cracking already. If the rim is stout and an adequate number of spokes are used for the load and are already well below the breakage/cracking threshold, the wheel with mixed spokes will probably stay below the limit.

On another practical matter, using thin spokes on the drive side can be more problematic, because the lack of torsional stiffness makes them twist-up easily when tightening, making it more difficult to tension and true the wheels.

[cachagua]

Using thin spokes on the drive side can be more problematic, because the lack of torsional stiffness makes them twist-up easily when tightening, making it more difficult to tension and true the wheels.

I like the technique where you build a rear wheel with no tension at all on the non-drive-side, and get the drive side 100% trued first -- then you only have to mess with the nds spokes, and they're at lower tension so less problem with windup.

Did someone here turn me on to that, some years back now? Anyway it's a great technique -- you put all this time and sweat into the drive side, and you look and go "jeez I'm only halfway done", and then you pull the rim to the center and suddenly the wheel just HAPPENS! Very satisfying.

[oldpotatoe]

I like the technique where you build a rear wheel with no tension at all on the non-drive-side, and get the drive side 100% trued first -- then you only have to mess with the nds spokes, and they're at lower tension so less problem with windup.

Did someone here turn me on to that, some years back now? Anyway it's a great technique -- you put all this time and sweat into the drive side, and you look and go "jeez I'm only halfway done", and then you pull the rim to the center and suddenly the wheel just HAPPENS! Very satisfying.

Used to be taught by Tim Breen, when he was a DT wheel pro certifier when he worked for DT in Grand Junction...maybe 15+ years ago. I tried it, this old dog couldn't do it.

[Gummee]

Used to be taught by Tim Breen, when he was a DT wheel pro certifier when he worked for DT in Grand Junction...maybe 15+ years ago. I tried it, this old dog couldn't do it.

So how far off-center do you need to build the wheel to be able to pull it into dish with the NDS spokes?

M

[cachagua]

When you get some tension on the drive-side spokes, the rim is directly over the hub flange -- all the nds spokes are just flopping, they're attached to their nipples but no tension at all. You have to get the rim exquisitely round and true at this stage, and you have to kinda guess how tight to make the drive-side spokes, since you're not going to touch them once you start on the non-drive side. --Which I admit I've messed up a few times, and had to de-tension the nds and make an adjustment on the drive side. There's supposed to be a formula, but different flange spacing, different gauge spokes, different lacing patterns on the two sides, et cetera -- intuition works just about as well.

I wouldn't necessarily recommend it for a shop setting, because in reality, it's more complicated and finicky. But I only build wheels for myself, any more, so I like it. Half the reason I build wheels at ALL is that it's complicated and finicky.

[dgauthier]

Or, just (. . .) do it "right"?


Didn't you just answer your own question? What's the appeal of doing it "wrong"?

Futzing with wheels is time consuming. I would do it whichever way minimized the need to touch the wheel again. And that'd be the "right" way...

[oldpotatoe]

So how far off-center do you need to build the wheel to be able to pull it into dish with the NDS spokes?

M

Don't remember, a fair amount since the RH side is true, round, tensioned..then pull over to dish, which does raise the RH side tension a bit.

BUT back to the OP.... .3mm spoke difference, thickness of bladed part. .9mm vs 1.2mm..doesn't mean a lot..maybe use the thicker ones on pulling spokes..

Or, like I said, use DTComp or SapimRace on RH side.

[Look585]

Thanks for the thoughts / musings / insights everyone.

Even knowing its not ideal, I might just do it anyway.

In my brain, the "sum-of-forces" physics argument says that they system has to be in equilibrium. Perhaps the thicker spokes and their corresponding holes and sections of rim are bearing a larger %age of the force, but I'm not convinced of that, at least when the wheel is idle. When you start adding dynamic forces to the rim and hub, that need to be transmitted via the spokes, it gets way more complex. And I barely passed Physics 1 at university.

What I do think is that the tensioning process will be confusing, as each driveside spoke will need to be turned more (then less) than its neighbors.

To limit my choices, the DS flange has been laced previously and the pulling/trailing spokes are "outside" and the pushing/leading spokes are "inside". I'd convinced myself that spokes oriented "inside pulling" have the hardest job and should be the thicker ones.

Finally, as to why: I have the spokes hub and rim waiting and 7 is an odd number to have lying around leftover. Aero Comps (what I'd use if I were buying fresh) are expensive, moreso when purchased piecemeal, and even moremoreso when purchased at the LBS.

[oldpotatoe]

Thanks for the thoughts / musings / insights everyone.

Even knowing its not ideal, I might just do it anyway.

In my brain, the "sum-of-forces" physics argument says that they system has to be in equilibrium. Perhaps the thicker spokes and their corresponding holes and sections of rim are bearing a larger %age of the force, but I'm not convinced of that, at least when the wheel is idle. When you start adding dynamic forces to the rim and hub, that need to be transmitted via the spokes, it gets way more complex. And I barely passed Physics 1 at university.

What I do think is that the tensioning process will be confusing, as each driveside spoke will need to be turned more (then less) than its neighbors.

To limit my choices, the DS flange has been laced previously and the pulling/trailing spokes are "outside" and the pushing/leading spokes are "inside". I'd convinced myself that spokes oriented "inside pulling" have the hardest job and should be the thicker ones.

Finally, as to why: I have the spokes hub and rim waiting and 7 is an odd number to have lying around leftover. Aero Comps (what I'd use if I were buying fresh) are expensive, moreso when purchased piecemeal, and even moremoreso when purchased at the LBS.

Not true. Altho the 'number' on some sort of spoke tension meter will be different, you are still trying for the same and equal tension on the RH side spokes. All about 100-110 kgf.

[dsillito]

I agree, just do it! What is the worst that could realistically happen? I bet you won't tell as much difference as you think in building them. It is easy to overthink.

I know it isn't the same, but I broke a spoke on a rear wheel once, and the only bladed replacement spoke the LBS had in the right size was way, way thicker then the others. I used it anyway, and haven't had to think about it since, which has been about 10 years now. Yes...I know...it is only one spoke, but it is the only quasi-relevant experience I have with mixing gauges on the same side.

Good luck.

[Look585]

What I do think is that the tensioning process will be confusing, as each driveside spoke will need to be turned more (then less) than its neighbors.


Not true. Altho the 'number' on some sort of spoke tension meter will be different, you are still trying for the same and equal tension on the RH side spokes. All about 100-110 kgf.

Hmm. I'm thinking that 1 turn on a 14/15g spoke will impart more tension than 1 turn on a 14/17g spoke as the 14/17 will stretch slightly more per turn. This might be true theory but irrelevantly small in practice.

[Mark McM]

In my brain, the "sum-of-forces" physics argument says that they system has to be in equilibrium. Perhaps the thicker spokes and their corresponding holes and sections of rim are bearing a larger %age of the force, but I'm not convinced of that, at least when the wheel is idle.

True - the tensions required to make the wheel true and round will be the same regardless of the spoke thickness.

When you start adding dynamic forces to the rim and hub, that need to be transmitted via the spokes, it gets way more complex. And I barely passed Physics 1 at university.

This is also true. As the wheel is loaded and the components start to flex, the distributions of the load will be affected by the relative stiffnesses of the components. If the spokes are different thicknesses, the wheel reactions will be slightly different (but not enough for the rider to notice) and the thicker (stiffer) spokes will flex a little less and bear a slightly larger amount of the load. But unless the wheel is under-designed, it probably won't make a real world difference.

What I do think is that the tensioning process will be confusing, as each driveside spoke will need to be turned more (then less) than its neighbors.

Theoretically, the nipples on the thinner spokes will have to be turned a little bit more than the for the thicker spokes for the same reaction. But the difference between the thin/thick spokes will be less than the difference between the right/left spokes on a dished rear wheel. Since wheel truing is an iterative process anyway, it will all come out in the wash.

To limit my choices, the DS flange has been laced previously and the pulling/trailing spokes are "outside" and the pushing/leading spokes are "inside". I'd convinced myself that spokes oriented "inside pulling" have the hardest job and should be the thicker ones.

Your conclusion is correct, but actually for a completely different reason. Spokes fail due to fatigue, not from overload, so it is the cyclic stresses (i.e. the changes in tension) that matter the most. The cyclic stresses come from two sources: The largest is the weight bearing loads, from the rider's weight, which primarily causes tension decreases in a few spokes near the ground contact point; much smaller are the stresses from torque loads, in which tension increases in the "pulling" spokes are about equal to the tension decreases in the "pushing" spokes. When these two are loads are combined, the greatest cyclic loads occur in the "pushing" spokes, in which the tension decreases due to the weight loads and torque loads combine. Since we also know that load distribution also depends on relative spoke thickness, and that thinner spokes experience a smaller percentage of the loads, we can shift some of the cyclic tension changes on the "pushing" spokes to the "pulling" spokes by using thinner spokes for the "pushing" spokes.[/QUOTE]