spoke length question
 

My spoke length calculator tells me I need 260.07mm spokes in front and 259.65 on the NDS rear and 258.51 on the DS rear.

How much of a compromise am I taking if I use 259mm spokes for all three?

FYI, I am using a SONdelux hub in the front with a 32h Mavic XM719 rim. In the back I'm using a Shimano FH-M770 hub with a 36h XM 719 rim. I'm using the Mavic spoke calculator.

Paul

Three variables to consider.

1- is the calculated length the minimum, maximum or optimum. Optimum means the spoke will reach to less than 1mm short of the top of the nipple when the wheel is finished.

2- how much over travel is available in the spoke and nipple thread, or how far above the top of the nipple can the spoke go if it's too long. Typically this is 2-3 millimeters, but varies with brands.

3- are you building hollow rims where spokes going beyond the nipple don't matter, or single wall rims where you'd have to grind off any excess.

Answering those questions for yourself will tell you how much fudge factor you have in either direction, and which is the best size to go with if you don't want to deal with two.

Generally I prefer to use only 2 spoke lengths, the sa;e for left rear and front, and usually 2mm shorter for right rear. That's no big deal because I usually also use a stouter spoke on right rear, ie. 14/16 for right rear, and 14/17 for left and front.

you should redo the calculations and measurements.

on shimano hubs, there's usually a 2mm difference between NDS and DS for non-disc rear hubs.

Assuming we are aiming for the screwdriver flat of the nipples on the rear wheel:

36H
3X

R = 536
r-left = 44.0
r-right = 45.0
c-left = 35.30
c-right = 22.10

SL-Left = 259.11
SL-Right = 257.44

As AEO indicated you end up with 259.00 and 257.00


=8-)

Go 258 on all three. It will work fine and make replacements easier to carry on the bike.

Does anyone know if the Shimano published specs are to the center of the flange? Based on my actual meaurements, it looks to me like the c-left and c-right dimensions are to the outside edge of the flange.

FB: This is a box rim with probably 4mm from the top of the eyelet to the second wall. I do have some room if the spokes are too long.

In any event, it looks like the Mavic calculator gives about 1mm or so longer than the UBI or Musson calculator regardless of the numbers.

I found a place near me (Excel Sports) that sells individual spokes, so my need to stay with one length is lessened. I'll probably go with 260mm and 258mm (Excel only offers even lengths at this size).

Paul

I measured an Ultegra 6600 hub the other day and found the Shimano published numbers a little off from what I measured. I agree with you, the published numbers appear to be to the outside of the flange rather than the center. The good news is that this makes no practical difference to the spoke length. If you run your spoke length calculation with the different dimensions you will see that you get about the same spoke length for the published numbers as with your measured numbers.

Campy does the same...I just subtract 1.6mm and get center of flange...but overall...it really isn't a deal killer.

=8-)

It doesn't matter either way. If you figure that a 10-15mm difference generates a 2mm spoke length change, another 1-2mm either way is going to make a difference of a fraction of that, or within the spoke length rounding anyway. Flange diameter and nipple circle diameter are the more critical dimensions.

I actually never thought of that. I like the idea. Thanks.