Spoke calculator: Which one do you trust?

antikythera

Hi folks,

My front wheel's braking surface feels decidedly concaved (no wear indicators that I can see). So I plan to rebuild it but I'll need to build with new spokes because I'm changing the brand of rim (different ERD).

Since I'm planning to use Sapim spokes I checked against their calculator as well as a bunch of others from the web. However the Sapim has ±7mm variation compared with any other results? Worst still, it gave me different lengths for front and rear wheels even though I'd entered the same data for both (fixie with track hubs).

So far none of these calculators return exactly the same values usually varying within 1mm. But that the Sapim calculator is significantly different from the others concerns me and given how much a box of spokes is, I really want to get this right!

So can anyone suggest spoke calculator that they have confidence in? Should I just ignore the Sapim results?

2Phat4Rapha

Try my database if you like, http://www.wheelingwrinklies.co.uk/WB/WB.html. The SLC is accurate but is based on 12mm nipples. ERD is assumed to be level with the bottom of the nipple slot.[/url]

antikythera

2Phat4Rapha wrote:

Try my database if you like, http://www.wheelingwrinklies.co.uk/WB/WB.html. The SLC is accurate but is based on 12mm nipples. ERD is assumed to be level with the bottom of the nipple slot.[/url]

Thanks for that, tried it and not sure about the results though: +20mm?

The average result I'm getting is for 290mm spokes using the following:

ERD: 601.5 (ambrosio excellence, 32H)
Hole diameter (PCD): 66 (Goldtec track hubs)
Hub centre to flange (CTF): 36

Built in a 3x pattern.

The ±1mm variation I can excuse given computation rounding and the like, but a 7mm variation and now 20mm?

2Phat4Rapha

Sapim seem to be speccing Nipple Seat Diameter rather than the Effective Rim Diameter. Without knowing the thickness of your rim at the nipple holes as their calculator asks for I can't be precise but if I assume 2mm they say 292mm, I say 290mm. ERD is the most sensitive of all the dimensions, just a small difference can have a big affect on the final length.

The method I describe for measuring ERD is slightly different than Sapim's but that doesn't mean that either of them are wrong. You just have to be careful with each SLC that you match what you measure with what their particular formula expects.

So, assuming that the Excellence rim is 601.5 ERD and that it really is the ERD and not the NSD, 290mm (actually 290.46) is the length.

So not sure where you're getting 20mm difference from or even 7mm. PM me if you like.

I've looked up your dimensions for both rim and hub and they are correct (spoke holes are 2.4mm on the hub).

2Phat4Rapha

Just as a follow up, I've tried DT's SLC and one other, both of which round up to 291 which I'm guessing you might have trouble sourcing so I round down to 290.

ps, I calculate to the end of the spoke ideally ending up flush with the bottom of the slot in the nipple head, 12mm nipples.

Nuggs

I've always used the DTS calculator with no problems at all.

antikythera

Thanks 2Phat4Rapha,

I'll try again on your calculator and then on the Sapin one once I have the rims in my hand. I appreciate confirmation that 290mm sounds like the way to go