# Bicycle Mechanics - building my first wheel - spoke length longer is better?

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

antchen
10-23-08, 11:43 PM
I just used sapim's spoke calculator and it's giving me

hub, gear , nongear
front, 293, 291
rear, 291, 292

Does this mean 292 is the right spoke length for me, or should I go one up to 294? (assuming I put in all the numbers right)

Torchy McFlux
10-23-08, 11:51 PM
Gear, nongear?

Use a different spoke calculator. I like DTSwiss's:
http://www.dtswiss.com/SpokesCalc/Welcome.aspx?language=en

antchen
10-23-08, 11:55 PM
i chose to use sapim's because i'm building a disc brake hub onto a 'road' rim and thought that the flange offset might cause a need for different length spokes. i didn't see on the other sites the ability to add measurements for the hub-end to flange distance

Torchy McFlux
10-24-08, 12:04 AM
i chose to use sapim's because i'm building a disc brake hub onto a 'road' rim and thought that the flange offset might cause a need for different length spokes. i didn't see on the other sites the ability to add measurements for the hub-end to flange distance

All rear hubs have offset flanges. Hub-end to flange is kind of a weird method. Most calculators use center-to-flange measurements. It's not hard to figure out.

antchen
10-24-08, 12:09 AM
right..

the point of my post is to find the right spoke length to buy, not which calculator to use.

given the recommendations and assuming that i used the calculator correctly, I want to know if 292mm is the right spoke length for me or if 294 is better.

Torchy McFlux
10-24-08, 12:18 AM
right..

the point of my post is to find the right spoke length to buy, not which calculator to use.

given the recommendations and assuming that i used the calculator correctly, I want to know if 292mm is the right spoke length for me or if 294 is better.

A wheel composed of a hub with offset flanges and a symmetrical rim normally requires 2 different lengths of spokes.
If you entered your hub and rim info into the calculator and can't intuitively figure out the result, then I'd suggest that the calculator isn't a good one.
Maybe if you mention the hub and rim models or measurements, someone could give you a definitive answer.

dabac
10-24-08, 03:04 AM
When in doubt, round down.
Having the spokes sitting perfectly flush with the bottom of the nipples is neat, but there is little, if any strength to be gained by achieving that last bit of perfect fit.
OTOH using spokes that are too long will expose you to the risk of running out of thread before you've reached the recommended spoke tension, and that'll compromise wheel durability far more than a few empty threads in the nipples will.

hub, gear , nongear
front, 293, 291
rear, 291, 292

I don't get that gear, nongear reference, but given the choice(and assuming 2 mm increments) I'd go for front 292/290, and 290/292 rear.

I would consider using 292 all round a bit of a gamble, but less so than 294.

Retro Grouch
10-24-08, 05:55 AM
Spokes have to be pretty close to right or you're likely to have problems. Essentially you only have about plus or minus 1mm to work with.

If your spokes are too long you may run out of spoke threads before you can get them up to tension. Too short, unless they're way too short, might not show up right away. If the spoke isn't long enough to reach all the way to the knob the ultimate problem can be broken nipples.

dabac
10-24-08, 07:12 AM
...... If the spoke isn't long enough to reach all the way to the knob the ultimate problem can be broken nipples.

I don't know about that, the only way I've ever broken a nipple/or seen one broken(apart from rounded tool flats) is with the flange sheared right off.
I've never seen one pulled apart along the cylindrical mid-section, regardless of whether it has had a good thread engagement length or a short one.

antchen
10-24-08, 02:56 PM
thanks for the replies guys! I think i'll have to remeasure everything and try running it through the calculator (or calculators..) again. I'm trying to lace 32H disc brake hubs to 32H Ambrosio Excellight SSCs so I was expecting this to be tough as a first try at wheel building.

I really want to get the spoke length right because I want to build my wheel with sapim cx-rays which would be an expensive loss if I ordered the wrong length!

For disc brake hubs laced to a symmetric-eyelet rim, do you typically end up with a 2mm difference in the spoke length? Intuitively, I would guess so, but hearing some definitive answers from others' experience would be a relief!