Latest creation of a tool to check/calibrate spoke tensiometer. It’s pretty simple tool as below:
A piece of square tubing with attached digital scale at one end and bracket on the other which allows to (precisely) tension spoke and calibrate tensiometer.
The “scale end” is pretty self explanatory. Just a digital scale attached to tubing. On one side the scale has got soft aluminium plate, with drilled 2.5mm holes, to keep spoke head (pretending to be hub flange).
On the other end of the bar is a bracket which allows to put a tension by turning the nut.
Why did I make it? I bought tensiometer some time ago. The tensiometer is not from the well known company, but a cheap copy (£17), which however IMHO is made better than original(!). It came with a table of tensions and instructions how to correlate reading with spoke dimensions, but I didn’t trust it whatsoever. So the calibration tool is a really cheap project, but effectively making even cheap tensiometer equal to fancy “blue one” ;-). The most expensive is the scale, which is around £15. Rest is just a square tubing (£4) and a couple of bolts to put it together.
Now the real life example. Smashed 650B wheel (bent rim). I ordered a replacement rim – DT Swiss G540, and decided to not reuse old spokes (2.0mm), but instead go for 2.0/1.8 butted ones.
On the rim you can read: “maximum spoke tension 1200N”, which is around 122kg. I set up the jig and I tested both spokes. Ordinary 2mm spokes ~122kg tension – reading from tensiometer 28.5. Butted 2.0/1.8, same tension – reading around 25.5-26.
There you go. Still, probably the most important, is to have as close to equal tension around the wheel as possible, but is nice to know where the limit is, as “tight” wheels are not going out of true that easy. Not mentioning, that to me the tension scale (reading the deflection from the tensiometer) looks logarithmic (I need to check it). Anyway, let’s simplify. That means, if let’s say, 40kg is 15 reading from tensiometer and 60kg is 20 doesn’t mean that 80kg will be 25 (20+5).