26 11 2012

Well…that was interesting….

On bringing the fatsno/marge lite up to tension I found the spokes too short to fill the nipple. As I mentioned previously I used the freespoke calculator, did a lot of reading around and I measured everything except the ERD on the rim by vernier gauge and confirmed the dimensions. I built this combo 3 cross, brought the tension to within 5kgf of 100kgf on the drive side (quite a bit less, but still consistent, on the disc side….which sort of surprised me), it was perfectly dished, spokes were all bent carefully around the flanges etc, with 263mm spokes – nothing funky going on.

But the spokes ended well below the shaft/head of the nipple on the disc side and only just came into the head on the drive side. The on-line wheel build programs suggested that 263mm would be ideal for my build…263.1 left 262.6 right from freespoke for example.

For a primer on why this is not acceptable, see Wheel Fanatyk: Wheel Building Tip No. 9 – Succeed with Alu Nipples.

So, nothing for it but to take it apart and build it up with 264mm spokes.

With 264mm spokes, on the higher tension/drive side, the spokes are 0.5mm away from the ‘top’ of the nipple and come to the bottom of the nipple slot on the disc side. The wheel is perfectly dished and within 0.1mm lateral and vertical (other than the welded joint area, a given), 100kgf/ within 5kgf on the drive side.

Unless there is something I don’t know about going on with the ERD ( I will go and measure this on the rim destined for the front wheel) the calculator isn’t calibrated for aluminium nipples….for brass nipples, 263mm would be fine IMO/FWIW, but not for my wheel build standards!

Oddly enough, if you plug the ERD and measurements into the DT swiss calculator, you pop out….264mm. So, my question is, did Surly cut out the middleman (reminds me of the ‘name your fingers’ song my 2 year old sings….) and in giving the ERD of 543.5 allow us to calculate the spoke length easily on standard spoke calculators that do not allow offset spoke-nipple hole dimensions etc.

Of course, *nothing* mitigates against slight errors on wheel builds – after all you are relying on lots of measurements and in some instances manufacturing tolerances/measuring differences of a mere 0.1mm at every stage could easily lead to a different ideal spoke length.

Nothing can substitute for experience.

On poking around the web, I found an interesting discussion on bikefroums and this informative post from someone called Drew Eckhardt.

(In answer to a question about whether you can compensate for too-short spokes with longer nipples)

“No – that’s exactly the problem here.

The wheel builder used nipple length to finish the distance between hub and rim and nipples are not as strong as spokes, especially when the nipples are made out of aluminum.

Longer nipples would provide more threads below the rim; but those don’t make the nipple strong enough to hold up where it goes through the rim without a spoke’s reinforcement.

Longer nipples should only be used when when the rim configuration results in the spoke wrench flats ending up inside the rim instead of outside where they’re useful for truing. To provide the most tolerance for spoke length and rim diameter variations this in turn dictates using a longer nipple with the same amount of thread you have with a 12mm nipple (Sapim) or spokes that have longer thread (via a spoke threading machine).

DT spokes have 9mm of thread (it might actually be 9.5; but lets use 9mm for discussion purposes)

DT nipple slots are 1mm deep.

Measured to the top of the nipple DT 12mm nipples have 8mm of thread, 14mm 9mm, and 16mm 10mm.

With the 12mm nipple you have 1mm remaining before the spoke runs out of threads and nipple stop turning when your reach the top, or 2mm past the slot. If we assume that you’re allowed to go 1mm below the slot (I wouldn’t since the nipple is narrower there) that provides +/- 1.5mm of tolerance. With spokes coming in 2mm increments some rim + spoke combinations will let you choose a size that ends at the slot for +2/-1mm of spoke length tolerance or +2mm / -4mm of ERD variation or a size that ends at the top of the nipple for +1/-2mm of spoke length tolerance or +4/-2mm of ERD.

With the 14mm nipple you have 0mm remaining at the top, or 1mm past the slot for +/- 1.0mm of tolerance. You might be able to aim for the slot itself; or you might be stuck aiming for 1mm below the slot for +2/-0mm of tolerance.

With the 16mm nipple you have 0mm remaining at the bottom of the slot and +/- 0.5mm. Some rim + hub + spoke brand combinations won’t work at 2mm increments because you need to aim for the bottom of the slot with 0 tolerance for long spokes / small rims or 1mm short of that with 0 tolerance for short spokes or big rims.

That’s not viable with alloy nipples where spokes that are too short result in broken nipples.”





3 responses

26 11 2012

Long nipples are inadequate compensation? It’s a cruel world.

29 11 2012
Ford Bailey

Why not use brass on those wheels ?

2 12 2012

You could compensate for long nipples though…
Alu vs brass. Probably just because I haven’t used brass nipples for years, no need to really. Clearly weight is not a major player when the tyres are 1200g, but as long as you build the wheel well Alu nips last as long as they need to .

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