lacing a wheel

[PIGEON]

I don't know if this is the right place to post this but as there doesn't seem to be a tech subforum I'll just put it here.

I want to lace a disc hub to a 28" rim. I already have the hub and rim, but now I need some spokes. I'm having some difficulties determining the correct spoke length, and I'm hoping someone here can help me verify the results I get.

Now first let's make sure I'm using the correct dimensions. I'm using the wheelpro spoke calculator, and I measured the hub like this:

I also measured the effective rim diameter (inside diameter + 2x the thickness of the material) which in my case is 592mm.

When I enter these data into the spoke calculator, it comes up with these results:

This raises a couple of questions: should I lace the spokes cross 2 or cross 3? Should I round the numbers up or down? And I know in theory the spokes on the disc-side should be shorter, but can it really be this different? I mean a difference of approximately 2mm seems like a lot.

Any help, tips, tricks and such will be greatly appreciated!

 

[Tad]

Sorry I can offer no practical advice other than to check out Sheldon Brown, his website has an article on wheel building if I remember correctly.

 

[cchris2lou]

2mm is not a lot when choosing spokes . it is best going for longer ones as your nipple will have a better hold of your spoke .

 

[one-eyed_jim]

C and D should be measured from the centre line of the hub:

http://www.wheelpro.co.uk/spokecalc/hubs.jpg

so subtract your measurements from 50mm

Lace 3x. I normally round down. 1.5mm difference is in the ballpark for the two sides, but correct C and D first - you may find you get a different result.

I usually try a few different calculators to check for discrepancies if it's a combination I haven't built before. The DT Swiss one usually does pretty well - but note that it adjusts for nipple length.

 

[PIGEON]

That's a very good point one eyed jim, I wasn't sure about how to measure C and D, I thought the purple line in the image wasn't in the centre but upon closer inspection I realize it is.

so I should actually enter the numbers in red in this image:

Now the calculator comes up with these numbers:

the pros and cons of both rounding up and down are obvious, I want as much thread in the nipple as possible, but I don't want the end of the spokes piercing my inner tube.

I checked out Sheldon's article on wheel building earlier. That, amongst others, made me feel confident I could do it. I don't know now though, it's a hassle with all the numbers! I hope I can get the spoke length correct, I'm still fairly confident I can pull off the more practical part.

 

[one-eyed_jim]

the pros and cons of both rounding up and down are obvious, I want as much thread in the nipple as possible, but I don't want the end of the spokes piercing my inner tube.

If the spokes protrude a little, it's not a big deal. In a typical box-section rim the inner tube can't come into contact with the spoke sitting deep inside the rim section - the rim tape keeps them well separated.

A bigger problem with getting the spokes too long is that the bottom end of the rolled thread on the spoke can jam on the nipple, making it impossible to tighten the spoke. That's why I normally round down on length.

http://i32.photobucket.com/albums/d7/k4 ... ipples.jpg

As long as you have decent thread engagement, that's generally good enough. If the spoke comes somewhere between 1mm short of the bottom of the nipple slot to 1mm proud of the nipple head, I'm happy. That's about a 3mm margin. You could probably get away with a bit more either way. Spokes are often sold only in even lengths anyway.

I checked out Sheldon's article on wheel building earlier. That, amongst others, made me feel confident I could do it. I don't know now though, it's a hassle with all the numbers! I hope I can get the spoke length correct, I'm still fairly confident I can pull off the more practical part.

It's half the battle! If you start with the right parts, the wheel almost builds itself...

It pays to check the rim diameter above all - it's by far the biggest measurement, and has the most risk of error.

 

[PIGEON]

Thanks, I'll make sure to double check the rim diameter!

For now, assuming the rim diameter I entered is correct, the DT calculator comes up with the exact same numbers as the wheelpro one. Nice!

So rounding down to even numbers with no decimals, I'd need 282 and 280, correct?

 

[Xesh]

So rounding down to even numbers with no decimals, I'd need 282 and 280, correct?

I normally round up myself. In this case I'd use 283/281 spokes. But then I use a different spoke calculator with different measurements.

 

[one-eyed_jim]

For now, assuming the rim diameter I entered is correct, the DT calculator comes up with the exact same numbers as the wheelpro one.

That probably just means that they use a common formula...

Of course the trigonometry should be the same for all calculators, but its the assumptions that can lead to discrepancies. Not everyone defines ERD in the same way, for example, and some calculators compensate for nipple length, hole diameter, flange thickness, etc...

So rounding down to even numbers with no decimals, I'd need 282 and 280, correct?

Right. If you're feeling lazy, you'd probably get away with 280 (or 281 if they're available) both sides.

The Wheelpro site says:

"Treat the calculated spoke lengths as maximums"

I'll make sure to double check the rim diameter!

Have a read of the pdf file on the Wheelpro site that deals with rim measurement. It seems that his definition of ERD isn't quite the same as yours - though there's not much difference.

http://www.wheelpro.co.uk/spokecalc/calc-measure.pdf

 

[FluffyChicken]

Spoke Calulator I normally use (based on spocalc) http://lenni.info/edd/
came up with this

Complete wheel data
Hub

* My hub, undefined
* Right flange ø: 61
* Left flange ø: 61
* Centre to ø: 18.5
* Centre to ø: 33.5
* Spoke hole ø: 2.5

Rim

* My rim
* Effective rim ⌀: 592
* Offset spoke bed: 0

Spoke length
for 36 spokes
Cross Right Left Tension L/R
0 264.9 266.4 55%
1 266.9 268.4 55%
2 272.7 274.1 55%
3 281.3 282.7 55%
4 291.6 292.9 55%

So I would use 280 and 282 (as they usually come in the even number sizes. 1.3 mm for the lenght of the nipple is no a lot compared to teh expense of topping out on the nipple)

for 12mm nipple btw.