Originally Posted by
danmyersmn
Now that I have picked up a truing stand (and a dish tool and tension meter that came along) I am looking at trying my luck at my first set of wheels. I am having some difficulty with picking the correct spokes. Well I should say that the online calculators I have tried have given me similar information but the problem is if I should go up or down in the spoke length.
I am going to be using Ultegra 6500 32h hubs and Sun M13-II rims. I plan to use a 3 cross pattern. Nothing fancy, just get through my first build with success.
Using 2 different calculators I come up with:
Calculators are: Edd (DT Swiss)
Front
Crosses Spoke length left Spoke lenght right Tension ratio L/R
3 299.1 (299) 299.1 (299) 100%
Rear
Crosses Spoke length left Spoke lenght right Tension ratio L/R
3 297.9(298) 296.3(297) 52%
It appears Rose Bikes DT Swiss Alpine III is a great price for spokes so that is what I was looking at. Any other better deals for a good spokes? The problem I am running into is the length options. I can get 296 and 298 but not 297 or 299. Can anyone confirm that I could likely go with 298mm spokes for the front and for the rear use 298/296?
No. In the front wheel:
With 298mm spokes you risk broken nipples if ERD was based on spokes ending at the nipple slot bottom and the calculator did account for stretch.
With 300mm spokes you risk running out of threads if ERD was based on spokes ending at the nipple top and the calculator did not account for stretch.
Buy your rims, insert spokes in opposite holes, thread nipples to the slot bottoms, measure across the elbows using a caliper, and add double the spoke length. Repeat 90 degrees away. If the numbers don't match do the two 45 degree increments between those. Average. That's ERD.
Drop that into spocalc.xls which doesn't account for spoke stretch.
For spokes 1.8mm (15 gauge) in the butted section subtract 0.5mm front and rear drive side. For 1.5mm (17 gauge) take off 1mm front and DS, 0.5mm NDS.
Use judgement. A spoke more than 1mm shorter than that number won't make it through the spoke bed, will load the nipple in tension, and the nipple may break (will break if it's aluminum). A DT spoke 2.5mm longer with a DT 12mm nipple will run out of threads.
If spocalc.xls calls for 299 and your choices are 298 and 300, round up to 300 to end at the top of the nipple because rounding down puts you 1mm below the slot. When the calculator spits out 298.3, truncate and use 298.
Please advise if I am way off. I read a few other threads and they all appear to indicate that the length has some leeway too it.
Thank you!
You have about -1mm, +2.5mm of tolerance assuming the ERD measurement was aiming for the nipple slot and calculator accounts for spoke stretch.
If it was aiming for the nipple top and accounts for stretch, it's -2mm, +1.5mm
Aiming for the nipple top not accounting for stretch, it's -2.5mm, +1.0mm
With spokes coming in 2mm increments, rounding 1mm in the wrong direction risks problems. Measure then use a calculator where you can see the formula so you know whether it's accounting for stretch under tension.