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Spoke Length Calculation

Posted: Wed Apr 03, 2019 1:34 pm
by Afnole16
First time wheel building, I need help finding the spoke length for a new wheel build. I am using Pro Wheel Builder calculator.

DT Swiss 350 J Bend
LB 55mm deep, 25mm wide

Re: Spoke Length Calculation

Posted: Wed Apr 03, 2019 2:47 pm
by Jugi
According to LB's product description, effective rim diameter (ERD) is 530mm for RRU55T02 and RRU55C02. If possible, I would measure the actual ERD on the rims from multiple locations. But a millimeter less or more in diameter only affects the spoke length by 0,5mm, so it's most likely a question of rounding up or down.

247 or 248mm sounds about right for DT Swiss hub flange dimensions, radial pattern and 55mm rim. I'd suggest to triple check the outcome with DT Swiss's calculator and the Edd calculator.

Are you building a rear wheel as well? A rim brake front wheel is very simple in construction as flange spacing is symmetric and a radial pattern can be used. A rear wheel is asymmetric in all variations and spoke pattern can be different for drive side and non-drive side. The basic principles for calculating spoke length apply, you'll just most likely end up with different lengths for the sides.

Re: Spoke Length Calculation

Posted: Wed Apr 03, 2019 2:47 pm
by Weenie

Re: Spoke Length Calculation

Posted: Wed Apr 03, 2019 2:49 pm
by alcatraz
1. Decide upon your nipples. Observe how far their threads extend inside the rim. This will affect the "effective rim diameter" erd.

2. Use the dtswiss spoke calculator.

Ask here before you order the spokes, to verify the lengths. When using the dtswiss calculator the hub geometry should be spot on and nearly foolproof.

Re: Spoke Length Calculation

Posted: Thu Apr 04, 2019 3:31 am
by Afnole16
I’m on a budget cause I’m going to be a father this year, is it possible to do on the rear wheel 14 mm nipple and 12mm every other nipple with different spoke length?

Re: Spoke Length Calculation

Posted: Thu Apr 04, 2019 4:57 am
by Jugi
Everything is possible but why would you want to do that? A spoke has the same price tag for all common lengths. Nipples are the least expensive part of a wheel.

Are you implying you already have some spokes or nipples which seem to almost fit this build? It's always best to use the optimal lengths and spoke patterns. Anything else just transforms into problems, eventually.

Re: Spoke Length Calculation

Posted: Thu Apr 04, 2019 9:40 pm
by Afnole16
It was an odd number that was going to run extra for spokes being cut and rethreaded. But if I use a 14mm nipple, it allows me to use even number and no extra costs

Re: Spoke Length Calculation

Posted: Thu Apr 04, 2019 10:32 pm
by biwa
My impression is that the manufacturer specified ERD is likely to be slightly different from the actual ERD, maybe by 1~2mm? I wonder what the acceptable range is for such variation..

Re: Spoke Length Calculation

Posted: Fri Apr 05, 2019 8:13 pm
by Afnole16
Front Wheel

Re: Spoke Length Calculation

Posted: Sat Apr 06, 2019 5:27 am
by alcatraz
Double check the hub geometries with vernier calipers.

Double check that the 530 erd is an accurate average by measuring two locations and using a nipple with similar head length. (By this I don't mean nipple length, but the length of the part that extends inside the rim. Two otherwise similarly looking nipples can have 2-4mm of this value. Calculating for the 2mm one and using a 4mm one will result in too short spokes.)

I'd double check the erd together with the rim seller. They usually know what value to use when you tell them the nipple you intend to use. (If you're talking to chinese they love pictures, so send a pic of the nipples)

Are you only building a front wheel?

Last time I used the dtswiss calculator the value came out 2mm shorter than another calculator and real world measurements told me the spokes should in fact have been 1-2mm longer. I did do everything custom though and calculated using dt aerolites which may have reduced too much.

If I had to do it again I'd try some different nipples/spokes in the calculator and observe the lengths. If it suggests 246/247/248 I'd go with 247. If it suggests 245/246/247 I'd go with 246.

I'm an amateur. If a wheelbuilder replies I'd pay greater attention.

Re: Spoke Length Calculation

Posted: Sat Apr 06, 2019 5:27 am
by Weenie

Re: Spoke Length Calculation

Posted: Sat Apr 06, 2019 4:09 pm
by MikeD
I wouldn't use the DT calculator unless you are using DT spokes and nipples because it has correction factors built in for DT spokes and nipples that may be applied wrong if you are not using their spokes and nipples. It also doesn't account for spoke stretch.

I like this one best because it accounts for spoke stretch. https://www.wheelpro.co.uk/spokecalc/