Touring - Differential spokes

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NoReg
11-04-06, 09:24 PM
One theory about wheel dish is that it helps to use two gages of spokes in order to allow amore equal degrees of tension to be used given the different rigging angles of the spokes. I am building my first dfront disc wheel, and I was wondering if that thinking was ever applied to this particular case. So I'm guesing that would be 14 gage on the dsic side and 16 on the other side (16 is smaller right?).

My normal touring wheels are all dishless, I could have a situation where the front wheel was dished and the rear wasn't.

Monoborracho
11-05-06, 06:49 AM
Not sure what you mean by "more equal degrees of tension" Tension is measured in pounds, or pressure (taking the area of application into account).

The grade or type of steel does not determine the stress that is on it.

Stress=pressure=pounds per square inches = pounds of force divided by the cross sectional area of the smallest part of the spoke.

With different types of spokes, you could, in theory, tension each spoke till it was equally stessed as a percentage of its maximum rating. But why would you want to go to so much trouble?

NoReg
11-07-06, 11:20 AM
One of the wheel makers that has building info recomends this for rear wheels, forget who it was though. The theory is that a large part of the problem with dished wheels is that the side with the lower slope, therefore lower stress is not very tight compared to the other side (which would be the freewheel/cassette side for the rear, or the disc side for the front). As a result the low tension spokes tend to get loose, and truing or tension problems set in, then maybe spokes break. His view was that this often gets blamed on the loads imposeed by the wheel being dished. But in his view the root of the problem is that the wheel loosens as a result of the tension on one side being too low. If different gage spokes are used then there is a better chance of the wheel staying tight.

"The grade or type of steel does not determine the stress that is on it."

No but gage of the spoke is the wire thickness not it's grade.

"Stress=pressure=pounds per square inches = pounds of force divided by the cross sectional area of the smallest part of the spoke."

Right, so a thinner spoke is working closer to it's limit when under the same force than a fatter spoke. It get's more stretched out and is more likely to stay tight. Or so the theory goes.

seeker333
11-07-06, 04:18 PM
My normal touring wheels are all dishless, I could have a situation where the front wheel was dished and the rear wasn't.
Your rear wheel is not dished? What kind of hub are you using?

Using a conventional cassette hub, the wheel ends up dished as a result of building up the wheel so that the tire is centered between the chainstays. This is unavoidable. You can reduce the dish a bit with an asymetrically drilled rim. I think there are some specialty hubs/wheels available (ritchey?) where the left flange is located further right than the Shimanos, this would reduce dish too.

A front disc wheel is not dished nearly as much as a normal cassette rear wheel. Spoke tensions are less disparate between left and right sides. It ends up closer to a rim brake front wheel than a rear wheel.

seeker333
11-07-06, 05:15 PM
After consulting the SpoCalc hubs section I see that the Ritchey wheel is most likely a dishless rear wheel.

I wouldn't mind having some of these hubs - i could quit using those velocity rims with the crappy joint.

NoReg
11-07-06, 10:43 PM
All Phil 36-h f/w hubs are "asymmetrical flange" design (i.e., equal spoke length with standard rim)

I have heard that some 145 tandem/touring hubs are dishless. It may be that the 165 hub is both dishless and has the better rigging angles. The rigging angles I read, aren't necesarilly all that great on the 145s, but at least they are the same. And if you look at the thread I have on diferential spokes, you can read the argument that says that equalising the strain may well be the more important issue than getting better angles.

seeker333
11-08-06, 12:49 AM
If you're using phil hub then your wheel is not dishless, which is the case with 99.99% of all rear freewheel or cassette hubs.

The purpose of an assymetric flange (diameter) is to reduce to a single spoke length requirement and/or make spoke holes more accessible for repairs on a disc hub. I have these on some DT hubs - on mine this actually worsens dish on the rear, but improves it on the front (disc) hub.

The only way a rear wheel is not dished is if both hub flanges are spaced equidistant from center of hub. To get this geometry the left flange must be located 5-8mm to the right of the normal location on a cassette hub. This is basically what ritchey does, combined with asymetric drilled rim.

In the attached jpg, the figure on the left is not dished - the spokes form a diamond or rhombus. This is what spokes look like on rim brake front wheel, viewed from end of bike.

The figure on right IS dished. It takes its name from the fact that the shape resembles a dish (as in dishwasher). This shape is typically what you see on all rear wheels. Single speed and gear hub rear wheel can be made dishless since they don't require the right hub flange to be moved radically towards the center to accomodate the cass/fw.

http://www.bikeforums.net/attachment.php?attachmentid=29373&stc=1&d=1162972136
dish.jpg

tomn
11-08-06, 07:59 AM
[QUOTE=seeker333]If you're using phil hub then your wheel is not dishless, which is the case with 99.99% of all rear freewheel or cassette hubs.

All except the 145mm tandem cassette read hub. It is dishless, symetrical with equal diameter flanges, and uses equal length spokes. I have it on my touring single. Big, heavy, and bullet-proof. Buy the way, I bought it because I got such a deal that I couldn't pass it up. I thought that it wouldn't be such a trick to spread each dropout 5mm. It's only 5mm after all. Boy was I wrong!

NoReg
11-08-06, 10:41 AM
There are lots of non-dished gear hubs. Ok so having hashed out the non-question stuff, is there anyone out there who can answer the question?

Monoborracho
11-08-06, 12:09 PM
What was the question? The only question I see in your post is whether 16 is smaller than 14?

seeker333
11-08-06, 03:48 PM
Buy the way, I bought it because I got such a deal that I couldn't pass it up. I thought that it wouldn't be such a trick to spread each dropout 5mm. It's only 5mm after all. Boy was I wrong!
Yeh, I'd never drop 5 bills on a hub either. Or even a hubset.

Maybe you should try cold-setting that frame with some 2x4s so you don't blow a hernia or lose a finger the next time you pull the wheel out.

Size always matters.

Ok so having hashed out the non-question stuff, is there anyone out there who can answer the question?

You have not stated your question clearly, thus the answers you receive are unsatisfactory.

If you ask a wheelbuilding question (in the touring forum, instead of more appropriate and effective mechanics forum), and state you have a dishless wheel, then naturally anyone who's built a few rear wheels is going to be curious how you accomplished this somewhat incredible feat - since this is the most elusive goal of every rear wheelbuilding effort.

At least you now understand dish as applied to building wheels - my ms paint skills were not wasted!

The only builder I know of who uses different spoke gauges is dave at speeddream. I don't really buy his theory supporting this practice. I think its mostly a line he uses to get people to buy \$\$\$ wheelsets. Everybody needs a gimmick is business, that seems to be his.

Why don't you post your question in the bike mechanics forum with Sheldon in the title. He is a regular contributor to that forum and has experience with unusual bike topics. A large section of his website is devoted to wheelbuilding. Calvin at Park is also extremely helpful and knowledgeable and also offers sound advice.

Or, you could save some time and frustration and just get some wheelsmith db spokes and build the wheel. I think i could have built one in the time its taken me to answer your posts. Maybe not, i'm slow and particular.

Millions of front disc wheels have been successfully built and run without imploying some obscure mixed gauge spoke strategy. Yours most likely will too provided you get the spoke tension somewhere between 70 and 130 kgf. In other words, make em kinda tight. If you start rounding off nips they're too tight.

If you want to do this right and have a high tolerance for mind-numbing arduous tasks, get a park tensiometer and you can achieve uniform spoke tensions to a target +/- 5%.

Bottom line - a front disc wheel builds nearly the same as a front non disc wheel, and these are not hard to build up well using inexpensive standard parts.

tomn
11-08-06, 05:46 PM
Maybe you should try cold-setting that frame with some 2x4s so you don't blow a hernia or lose a finger the next time you pull the wheel out.

I should have been more clear. The strain was cold setting the frame, not trying to force in a hub that was 10mm to large. I used a Park tool made for that task, but it was an unbelievable struggle.

Tom

NoReg
11-08-06, 06:17 PM
"One theory about wheel dish is that it helps to use two gages of spokes in order to allow amore equal degrees of tension to be used given the different rigging angles of the spokes. I am building my first dfront disc wheel, and I was wondering if that thinking was ever applied to this particular case."

That's the question, though I admit there isn't a question mark. There are quite a few people around here in the touring section who know bike mechanics also. Build their own bikes from scratch and so forth. Touring is it's own thing, with it's own pattern of wear on wheels. Probably half the questions here are technical bike set-up questions, and they don't get the brush-off because they weren't put before hte grease monkey crowd.

You are somewhat answering the question if you refer to this as an obscure method, since if nobody does it, has heard or it, or can comment on it (on topic), how necesarry can it be. Might still be a better way.

LWaB
11-09-06, 03:41 AM
It is fairly common to use thinner spokes on the offside of a rear wheel, compared to the drive side. Usually 1 gauge size difference (15=1.8mm vs 14=2.0mm) is enough difference in cross-sectional area. Plenty of durable wheels are built with the same diameter spokes on both sides though. Suit yourself Peterpan1 but I probably wouldn't bother.

NoReg
03-10-07, 10:35 AM
Here is another approach to the same problem:

http://www.hewittcycles.co.uk/_bikefittingsite_new/reviews/articles/Touring_6.jpg

They use a mix of straight gage and butted. They win a lot of UK awards for best touring wheels from the look of their site.

Niles H.
03-10-07, 04:56 PM
I agonized over this one myself for a while.

The elasticity of the spokes plays a role, too. 15-gauge spokes can maintain their tension through a wider range or cycle of motion. A 14-gauge spoke is more inelastic. It's easier for it to cycle out of its range and lose tension completely. Complete loss of tension is very undesirable.

There is also this somewhat tricky point: thinner-gauge, more-elastic spokes on one side might allow slightly more side-movement of the rim in relation to the hub, in the direction of the more-inelastic side -- which (it appears to me at the moment at least) might potentially allow the more-inelastic side to lose more tension, than if the other side did not allow this movement.

Elasticity on both sides seems to be valuable (up to a point, or within a certain range, at least).

Sheldon Brown, Jobst Brandt, and Gerd Shraner might be good sources of further information on this.

Personally, I would use triple-butted spokes on both sides, and check with a good, experienced wheelbuilder about the gauges.

If you find out anything definitive, or further, on this one, please post. I'm interested in finding out more about it too.

One aspect that is clear to me is that you do not want the spokes to lose tension, even very briefly, through their stress cycles while riding: Their lifespans are much shorter if this happens.

Also, triple butted spokes have the great advantage of more-fatigue-resistant, thicker-gauge wire at the flange end.