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Old 09-20-06, 04:04 AM   #1
TheBrick
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Spoke length please check

Hello all,

I am currently doing a fixed gear convertion and hence am building a rear wheel. I have repaced rims beofre but never built a wheel from scratch. I would like to check weather I have used http://www.recumbents.com/wisil/spokes!.asp corecly to work out spoke lengths for my wheel. I got 499 mm.
I would like to use this hub http://tinyurl.com/pwecj with this rim http://tinyurl.com/jkdkf. Please could some one just advice me on the correct spoke length.

Many thanks

T
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Old 09-20-06, 04:13 AM   #2
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I didn't try to calculate the spoke length but I can tell you for sure that, assuming you're building a 700c wheel, 499mm is wrong. The right answer will be closer to 299mm.
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Old 09-20-06, 04:30 AM   #3
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My guess is that you used the diameter of the hub instead of radius. Divide diameter by two before entering into the radius field.
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Old 09-20-06, 04:48 AM   #4
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Thanks guys. Ok just re did it and got 300.092 mm using an Inside Diameter of Rim = 622 mm. I was not sure what internal dimeter of rim to put. Is 622 mm correct?

Many Thanks

T
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Old 09-20-06, 05:35 AM   #5
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Quote:
Originally Posted by TheBrick
Thanks guys. Ok just re did it and got 300.092 mm using an Inside Diameter of Rim = 622 mm. I was not sure what internal dimeter of rim to put. Is 622 mm correct?

Many Thanks

T
The rim diameter you need is called the "ERD" or effective rim diameter and is the distance between opposite nipple seats. The 622 value is the bead seat diameter of any standard 700c rim and is not the same as the ERD which varies depending on rim design.

Sheldon Brown's web site has Damon Rinard's Spokecalc Excel program but it hasn't been updated in quite a while. It doesn't list the ERD for the new Mavic Open Sport but it does list it for the previous MA3 at 607 mm and the Open Pro at 605 mm. The DT web site also has a spoke calculator but that page seemed to be down this morning. Try it later.
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Old 09-20-06, 06:23 AM   #6
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HillRider: Thanks for the info. I did some googleing and found out the ERD of the Mavic Open Sport of 611 mm giving me a spoke length of 294.621 mm. Sound about right to you guys?

Many Thanks

T
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Old 09-20-06, 07:57 AM   #7
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That sounds much better.
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Old 09-20-06, 08:56 AM   #8
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Thanks HillRider. I shall get on and order the parts.

T
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Old 09-20-06, 09:19 AM   #9
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294mm for 36 hole, 298mm for 32 hole (rounded). 3x both sides.

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Old 09-20-06, 09:34 AM   #10
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Thanks tomacropod. I was thinking 36 spokes, I seem to always be able to bend a wheel. I guess it is my days when BMXing to much hopping around! Thanks for comfurming my calc
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Old 09-20-06, 09:40 AM   #11
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Quote:
Originally Posted by TheBrick
Thanks tomacropod. I was thinking 36 spokes, I seem to always be able to bend a wheel. I guess it is my days when BMXing to much hopping around! Thanks for comfurming my calc
If you need different spoke lengths for the front and rear wheels, but they're only off by a couple mm, just get all the same length, choosing the longer one. Having spokes 1 or 2 mm off is usually not a problem, since the nipple heads are recessed in most good rims, and the rim tape will protect the tube from the slight protrusion of the spokes.
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Old 09-20-06, 10:56 AM   #12
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Originally Posted by moxfyre
If you need different spoke lengths for the front and rear wheels, but they're only off by a couple mm, just get all the same length, choosing the longer one.
Never buy spokes long. When rounding off round down. If the spokes are long you may run out of threads when approaching the target tension. This is especially important for the driveside rear spokes having highest tension on the bike. A mm short is much better than a mm long.

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Old 09-20-06, 10:59 AM   #13
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Quote:
Originally Posted by Al1943
Never buy spokes long. When rounding off round down. If the spokes are long you may run out of threads when approaching the target tension. This is especially important for the driveside rear spokes having highest tension on the bike. A mm short is much better than a mm long.

Al
Whoops... you're absolutely right. Err on the side of short spokes. What was I thinking? Do what I mean, not what I say
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Old 09-24-06, 01:07 PM   #14
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Thanks everyone. I built the wheel up on sat and every thing is purfect. All I need to do nown is finish off painting the frame and I will have my fixie!!
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