# Measure Spoke Tension on BMX Wheel

I'm building a 20" BMX wheel. I want to check the spoke tension, I'm not sure how to do that accurately. It's a high flange hub laced 3x with 186mm spokes. Because of that, the cross is just off center and makes it difficult to get a centered reading with the tensiometer. (TM-1)

Anyone with experience build BMX wheels that could share some wisdom?

• Guessing, might be one of those situations you have to go by ear, or feel, or even finger pressure on the nipple key.
– Criggie
Apr 3, 2018 at 6:53
• With 3 cross (or likely any type of lacing) there's still some symmetry, i.e. groups of spokes which behave the same, so I'd just check that all spokes where center is at the same position have similar tension? Then again, I don't have a tensiometer but built a fair share of bmx wheels and it seems that if you and up with a rim which is round and doesn't wobble while at the same time there's no obvious off-sounding spokes, you're good to go. Apr 3, 2018 at 8:46
• I wonder if there's a market for a spoke tension meter that only needs a short piece of the spoke accessible ?
– Criggie
Apr 3, 2018 at 23:17
• I guess that the IceToolz spoke meter and the Wheel Fanatyk Tensiometer, a Jobst Brandt design, measure a shorter piece of spoke, although I don't find this in their specifications. However, they come with a hefty price tag compared to the TM-1. Apr 5, 2018 at 11:27

## 1 Answer

I have never build BMX wheels, but used the TM-1 a lot. There is no need to really center the meter on the spoke. The meter functions on the principle that if you apply a force perpendicular to a beam at the center of two support points, the deflection is dependent on the applied force F and on the force pulling in the axis of the beam, on the distance L between the support points (about L^3 ; L= 105 mm for the TM-1), on the beam diameter (about D^-4) and on the elastic modulus of the spoke material. The length of beam outside the support points is less important (except less than 5 mm).

You can check this by taking a common 28" bicycle wheel and take readings while moving the TM-1 from close to the nipple to close to the spoke cross.