Bicycle Mechanics - Wheel build turned out loose wheel
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12-17-07, 06:25 PM
Good day. I am building up a new franken road bike, and I found that I needed a new rear wheel since:
a.) the rear cassette on this one was nearly toast (and I don't currently have the tools to swap it, nor am I likely to have the needed tools any time soon).
b.) too many spokes were missing for my liking, and could not be replaced without removing the cassette.
I had out back a hub with intact spokes and cassette that I had taken out of a rim a number of years back (I can't figure out why I did that), but since these both come from the same size wheel (an old 27" steel wheel) I figured I ought to be able to swap them around and build up a whole new wheel.
Well, after trying and retrying, I finally get it put together right (as best as I can figure) according to the instructions on sheldon browns website. However, it is way too loose. In order to get it taught, I need to tighten it to the point where the spoke ends would rip through the inner tube. I can not figure out what I am doing wrong here. I compared the spokes and they seem to be of identical length.
What am I doing wrong here?
Joshua A.C. New
12-17-07, 06:47 PM
The dimensions on the hubs are different, which means that the spokes you have are too long. Which sucks, cuz you're going to have to buy a whole new set of spokes, which will cost some $36, and all you'll have is a 27" steel wheel.
The relevant dimensions are the distance to the wheel center from the flanges and the distance to the center of the flange holes from the axle center.
I'd suggest downloading the full version of Spocalc (http://www.damonrinard.com/spocalc.htm) and seeing if your hubs and rims are in there. Then you'll know how long your spokes should be.
The tool to get apart a freewheel or freehub (http://www.performancebike.com/shop/profile.cfm?SKU=12775&subcategory_ID=4203) is usually like $3.50, by the way.
12-17-07, 06:50 PM
There are several things that could account for the spokes being too long:
1) The hub flanges on the hub you had out back have a larger flange diameter (distance between centers of opposite spoke holes) than the old hub, resulting in a shorter distance from the hub spoke holes to the rim spoke holes.
2) You may have laced the wheel 2-cross instead of 3-cross,
3) The ERD of the old 27" rim may not be the same as the ERD of the replacement 27" rim.
There are critical dimensions you need to measure on the hubs and rims (http://www.damonrinard.com/spocalc.htm#MeasureHubAndRim) in order to determine the correct spoke length for the lacing pattern you want to use. Once you have these dimensions you can plug them into spocalc ( http://www.damonrinard.com/spocalc.htm).
Are the old and new hub holes the same distance from the center?
Are the old and new spokes the same length?
Are you sure you laced it correctly?
Do you have a hand grinder of some sort?
12-18-07, 06:21 AM
I believe sheldon's instructions are for a 3X wheel, the wheel you had may have been 4X, which would definitely account for the long spokes. You can try relacing it 4X and see what happens, lots of hassle for a franken wheel, however.
12-18-07, 09:05 AM
You figured wrong, as you have discovered. Each rim has its own diameter. one 27" wheel is not the same dimensions as another. Easiest solution is to buy a cheapo 27" wheel. More difficult: measure the parts you have and get the correct length spokes.
12-18-07, 01:06 PM
Thanks guys. As it turns out, lacing it 4x instead of 3x made all the difference in the world. I think I tried 4x before to no avail, but I think I was screwing up and putting the wrong spoke in the wrong hole the first couple of times (very likely, since I kept making stupid mistakes even with the 3x method the first number of times). But it worked this time, so thank you for suggesting it. Now I just have to finish tensioning and truing that bad boy.
Thanks once again.
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