Bicycle Mechanics - No 3x in 28H???
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09-17-05, 11:28 AM
I just heard from someone that I con't build a 3-cross wheel with only 28 spokes. :( She proceeded to explain why, but the phone was staticy. Can I not build a 28-spoke wheel in 3-cross? Why or why not?
If I'm stuck with 2-cross...how does one do it? I've only ever built 3x. Is it over-under or under-over? How much less strong is a 2x than a 3x? These will be dishless wheels.
09-17-05, 12:17 PM
By crossing more spokes, the spokes become closer to tangent with the hub flange, which means less vertical stress on the flange. It doesn't necessarily mean the wheel is any stiffer or handles 'windup' any better. I'm not sure if this applies to 28h wheels or if a couple more spokes need to be lost but here's my guess as to what she was explaining:
At certain points as spoke count decreases and distance between them on the rim increases, the number of spokes one *can* cross to place the spokes at proper angles to the hub flange will decrease. For example, on a 48h wheel you cross 4 spokes to get the same spoke angle on the hub as you would with 2x on a 24h wheel. If you cross too many spokes and the angle is too close to tangent (say you tried 4x on a 24h wheel), the spokes don't clear each other at the bend. No good.
09-17-05, 12:21 PM
that makes sense--so how does one build 2x? are the trailing spokes over-under or under-over?
09-17-05, 12:39 PM
No reason to do any different than you would building a 3x, I'd imagine. All my wheels to date have been 3x and 4x (BMX type stuff) so I couldn't say for sure, but Sheldon Brown's site on wheelbuilding (http://www.sheldonbrown.com/wheelbuild.html#side) seems to be in agreement. :)
09-17-05, 01:29 PM
If you try to cross too many spokes, the spokes going one way from the flange will cross over the holes for the spokes that go the other way. It's actually possible to build a wheel that way if you put all of the spokes in the hub before you start crossing them and laceing the rim. I'm thinking that replacing a broken spoke would require the use of words that only bike mechanics are allowed to say.
09-17-05, 01:34 PM
"that makes sense--so how does one build 2x? "
Same way as with the others. You just use shorter spokes and after lacing up all the spokes in one direction like on Sheldon's site just quoted, you twist the hub and lace up a spoke in the opposite direction to hold the twist in place. The only difference at at this stage is the spoke you install crosses only 2 others before going into the rim instead of 3. I have yet to see any quantified numbers on any performance differences between 2x vs. 3x.
"are the trailing spokes over-under or under-over?"
I usually like the pulling spokes going under-over. Meaning they come out from inside the flange and go over the spoke they cross. Seems to cause fewer problems with rubbing the derailleurs under lots of load like hillclimbing. I used to mill my hubs down on a lathe to get the freewheels as close to the spokes a possible for minimal dish and the under-over lacing causes less rubbing when tolerances are tight. Some people mention spoke-damage if the chain gets caught between the spokes & largest cog, but I haven't had any issues with that with proper adjustment.
I ride a home built 3X 28h front wheel, no problems, DT Hugi 240 S hub, Revolution spokes, DT RR 1.1 rim. With this build there is no interference with the spoke heads.
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