Getting incorrect results from spoke length calculator

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mornview

mornview

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I've built dozens and dozens of wheels and never had my trusty spoke length calculator steer me wrong, but I recently tried lacing up a Bendix Aviation manual 2-speed hub to a Sun Ringle CR-18 (ISO 590) rim. For a 3x lacing pattern the calculator recommended me 275.4mm spokes, which I ordered, laced up, and found that I ran out of threading on the spokes before I even got any tension on the spokes. So I tried another spoke length calculator that re-affirmed the results of the first one. I then tried two other (more detailed) calculators which recommended 271.7mm spokes. I took the spokes down to the LBS, had them cut them (and rethread them) down to size, and I'm able to get some tension on there, but they're still at least a couple mm too long.

Now, I know how to measure a hub/rim; I am not concerned that that is the issue here. What I am wondering is this - the Bendix manual 2 speed hub has a HUGE flange, bigger in diameter than anything I've laced up before. I believe I've heard that large flange hubs should be laced 2x. I've always laced 3x for strong wheels. Could the hub's large flange diameter (79.3mm I measured) be causing the errors in the spoke length calculator? Is there any way to remedy this? Should I just scrap the idea of going 3x altogether? And would there be any significant loss in wheel strength by going 2x?

Thanks!
 
I think the measurement you are using for the hub is wrong. I don't build rear wheels 2X, but depending on your riding style it could work out just fine. Cant you just take a measurement of a spoke you have and adjust it the amount you need and swap them out for correct ones? I dunno man, good luck though!
 
CrazyDave said:
I think the measurement you are using for the hub is wrong. I don't build rear wheels 2X, but depending on your riding style it could work out just fine. Cant you just take a measurement of a spoke you have and adjust it the amount you need and swap them out for correct ones? I dunno man, good luck though!
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I certainly can (and most likely will) continue going down the trial and error route; I'm just curious if there is something about my hub/rim/lacing pattern combination that is causing me to get incorrect results.
 
clamdigger said:
Using the ISO 590 or the ERD 580 with the calculator ? I don't know at this point what you have to work with, but spoke nipples can be found in different lengths.
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The rim's ERD is actually 578mm; that's what UniversalCycles' website lists it as and that's what my measurements have always come up as.

I'm using Wheelsmith 2.0 straight-gauge spokes along with Wheelsmith 14g brass nipples. That combination has never steered me wrong before either.
 
1.) Could be the spoke nipple length, you are using, which matters a lot & needs to be considered. 2.) Be sure you use actual measurements in Millimeters to both the rim diameter, the hub flange diameter, offset, & width measurements. 3.) Maybe the spoke holes on the Bendix are "deeper" into the flange than most average hubs, which would make a big difference..
 
Hmm, I suppose the spoke nipples could have something to do with it, but, again, these spokes/nipples are the same ones I use on every build and have never had a problem.

I can't help but feel it has something to do with the rather sharp angles that a 3x pattern causes when the flange is such a large diameter.

The spoke holes are something to consider, but, if anything, I would say this hub's flange feels paper thin compared to other hubs I work with.
 
Not the width of the flange, the distance the spoke holes are from the top of the flange edge towards the axle. Look at another hub and you can see what I mean. As I remember, the bendix big-flange hubs had spoke holes drilled waaay below the outside edge of the flange (towards the axle) Checkitout..
 
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That's probably why the holes are drilled so far away from the flange edge.
 
CrazyDave said:
A paper thin flange on a kickback?! This just keeps getting more intresting.
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Not a kickback, but a Bendix manual 2-speed.

And paper-thin was a bit hyperbolic, but I'm coming up with a 2.5mm flange thickness on most of my other coaster brakes (including my Bendix kickbacks) and the Bendix manual's flange is a half a millimeter thinner. That said, I'm not concerned about the flange failing me or anything; I'm just not used to working with a thinner flange.
 
SILVERKINGPC said:
Not the width of the flange, the distance the spoke holes are from the top of the flange edge towards the axle. Look at another hub and you can see what I mean. As I remember, the bendix big-flange hubs had spoke holes drilled waaay below the outside edge of the flange (towards the axle) Checkitout..
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Ah, I see what you mean now. And going off of my memory I'd say you are correct, but now that I have the hub in my hands and I am measuring it, it looks like the holes are exactly the same distance from the flange as my single-speed hubs (1.8mm). That would've been a good explanation, though.
 
Well, I took the hub, rim, spokes, and spoke nipples into the LBS today, let them do their own measuring, and they came up with the exact same results (171mm). They couldn't figure it out either. Judging by how much of a difference cutting 4mm off the spokes the first time made, I estimated I'd need another 2mm taken off the spokes. I've laced it back up and I'm nearly done tensioning it and it looks like I hit the nail on the head. I have no idea what is throwing the calculations off, but I'm just happy to have this thing properly laced up finally :D.
 
SILVERKINGPC said:
Not the width of the flange, the distance the spoke holes are from the top of the flange edge towards the axle. Look at another hub and you can see what I mean. As I remember, the bendix big-flange hubs had spoke holes drilled waaay below the outside edge of the flange (towards the axle) Checkitout..
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Scrolling thru this thread, that's the first thing i thought, too. You don't want the flange diameter; you want the pitch circle diameter. If there's a decent bit of space between the spoke holes and the flanges' edges, then yeah, that could do it.

Thin flanges and modern spokes, to me, call for some spoke washers. That'd help with the elbows at the flange, but it wouldn't help your miscalculations in spoke length.

Aside from the idea that your pcd might be markedly smaller than the flage diameter, Kenny was onto something with the nips issue. DT spoke nipples are markedly different in terms of nip length, but thread depth is the same or at least very similar.

FWIW, i ran your numbers through the EDD calculator, and i caught the same figure as you did the second time--271.7mm. Weird. I'm curious to know what the real culprit is....sounds like you'd have been best with 270s?
 
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Good call on spoke washers; that thought never crossed my mind as I've never needed them before, but these bends near the flange don't look too good.
 
I used 268 with 4 cross. They were originally usually laced 4 cross. Not as strong as 3 cross but they have withstood 30 mile cross country races with out a problem. I also used used 265 spokes from an old mountain bike along with the old long 19mm brass nipples and done them 4 cross. This works great, just don't get a stick in your spokes because they will be sheared off.

4 cross, used 265mm spokes with long brass nipples. I still run this on a klunker.
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I use 3 spoke length calculators to determine my spoke length. You get different results with each one. Sometimes I use a 4th one. I have never used the one you used. If one calculation is way off I toss that out and kind of use judgement for an "average". I use digital calipers to measure the hub width and hole to hole diameter. If you are having custom spokes made (which I find cheaper than getting a set of already made ones if you go to the right guy) then have them threaded for 16 mm nipples. You could use 12, 14 or 16 mm spoke nipples to adjust the right length. This fudge factor has so far worked for me. Buy a set of each length nipple. I have rebuilt two Bendix manual 2 speeds and don't like either one. They are kind of grindy, have a tremendous amount of back pedal to engage the brake (which increased to even more back pedal in low gear), easily bent axles, poor braking and are hard to adjust. After the rebuild I put the wheel on a bike without the shift toggle and push in the shift pin with a small screw driver. If the bike shifts, then I know it can be adjusted to work, usually a hair trigger on the adjustment but the screwdriver test gives me confidence to keep trying to get it to shift right. I think this clunkiness is the reason they didn't make the manual 2 speed for very long. Every time you remove the rear wheel for a flat or whatever, you have to go through the adjustment dance. The non drive side cone adjustment can easily become too loose if you are not careful with the number of turns you put on the brake arm when reassembling, which if you take the wheel off and adjust the cones with the brake arm will make you have to readjust the shift setting. I bend my axle Klunking and straighten it by tapping on the nut. I have now given up straightening it and just ride it, hopefully it won't ovalize any parts soon? Most of these I have seen have bent axles. Be careful screwing the shift pin into the small fitting when rebuilding to a void stripping the extremely fine threads. One of my friends did this on his Bendix manual rebuild. I still enjoy Klunking with this but you really have to pay attention to the pedal location and anticipate braking as you can bottom out your brake stroke and still not engage the brake. With a bigger chain wheel this is not quite as bad, but them you can't single track with one.
 
Good review of the Manual and automatic Bendix hubs US5.....thanks man!
 
That's a long way out. Did you measure the spokes you ordered originally. Maybe they were supplied incorrectly or miss labeled.
 

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