Author Topic: spoke length calculator  (Read 3346 times)

Offline nick1973

  • Funky Chicken
  • ****
  • Posts: 61
spoke length calculator
« on: December 14, 2013, 09:39:26 AM »
hi all
what's the best spoke length calculator  to use?
or what's the best way to work out what size you need , as some of the calculators i have looked at don't always have the hub/ rim combination you are looking for

any help appreciated

cheers
nick

Offline DaddyCool

  • Deathtrucker
  • ********
  • Posts: 843
Re: spoke length calculator
« Reply #1 on: December 14, 2013, 01:40:15 PM »
Hi Nick,
it is much better to have an equation with all the measurements included, so you are not dependent on which hubs/rims are in the list...
You need to know:
a=distance of the flanges in mm
b=flange diameter in mm (measured from hole to hole)
c=number of crossings of the spokes (zero for radial lacing)
d= number of spokes
e=diameter of the rim in mm (measured where the nipples are, often given as "ERD": effective rim diameter)
Then you have to calculate this (use Microsoft Excel for example):

Spokelength=square root(0,25*(a^2+b^2+e^2-(2*b*e*cosine(pi/180*720*c/d))))-1,5

I have found this equation somewhere in the web. The -1,5 was found empirically by me, it was more accurate for my wheels... It should give you a length about plus minus 0,5 mm.

I hope this helps.

Offline Revig

  • Cliffhanger
  • *******
  • Posts: 444
Re: spoke length calculator
« Reply #2 on: December 14, 2013, 02:26:08 PM »
Hi Nick,
it is much better to have an equation with all the measurements included, so you are not dependent on which hubs/rims are in the list...
You need to know:
a=distance of the flanges in mm
b=flange diameter in mm (measured from hole to hole)
c=number of crossings of the spokes (zero for radial lacing)
d= number of spokes
e=diameter of the rim in mm (measured where the nipples are, often given as "ERD": effective rim diameter)
Then you have to calculate this (use Microsoft Excel for example):

Spokelength=square root(0,25*(a^2+b^2+e^2-(2*b*e*cosine(pi/180*720*c/d))))-1,5

I have found this equation somewhere in the web. The -1,5 was found empirically by me, it was more accurate for my wheels... It should give you a length about plus minus 0,5 mm.

I hope this helps.


that's the way, and you can avoid to make the calculation yourself by using these kind of spoke calculators:
http://www.sapim.be/spoke-calculator
http://www.bikeschool.com/tools/spoke-length-calculator


Offline nick1973

  • Funky Chicken
  • ****
  • Posts: 61
Re: spoke length calculator
« Reply #3 on: December 14, 2013, 11:41:18 PM »
thats great - many thanks for the help!
cheers
nick