Wheelbuilding - Spoke tension nerd question

[PpPete]

I usually build either 36 spoke or 32 spoke, and by carefully following Roger Musson's advice I'm happy to say that despite wearing out any number of rims over the course of 20, 000 miles or so, I have yet to break a spoke on ANY of the wheels I've built (or indeed have any breakages reported to my by friends I've built for.)

I'm challenging my wheel-building skills on this latest set though:
Bitex 106 hubs, Kinlin XR26 rims
28 spoke double butted Sapim Race on the rear
24 spoke CX-Ray on the front.
Weight with rim tape 1675g which I'm quite pleased with.

I've read that the Kinlin rims will take up to 130kgf of spoke tension, and as I'm no lightweight and the load is spread through fewer spokes I figured I'd aim for between 120kgf and 130kgf (on drive side rear/disc side front), as opposed to my usual 100kgf rule of thumb.

I recently saw a youtube video (can't find it now) that suggested rechecking wheel trueness and tensions after mounting and inflating a tyre to maximum pressure. I've never done that before, but as I'm still waiting on the frame to arrive I thought I'd try it. I expected tensions to be slightly lower, but to my huge surprise they are now around 30kgf less on average!

I'm now wondering whether I need to up the tensions still further, and recheck/increase the tensions on all the other wheels on my various bikes.
Any thoughts from the more experienced wheel builders?

 

[the snail]

Any thoughts from the more experienced wheel builders?

Throw the tension meter in the bin and tighten the spokes til they make a nice pinging sound when you puck them. I don't think rider weight is particularly significant, and if your wheels are reliable that suggests the spoke tensions are somewhere in range of values that work fine?

 

[rogerzilla]

A wired-on tyre shouldn't affect tension by very much at all, as the constricting effect of the air pressure is counteracted by the outward pull on the bead seat. A tub does constrict the wheel a fair bit when inflated, but I doubt you're using tubs.

Any inflated tyre has a tendency to straighten the wheel (i.e. the wheel becomes more true) but this won't affect average tension.

How long did you leave between checking tensions without and with the tyre on? Some wheels can creep a bit as the spokes settle, although this shouldn't happen with good components (the ancient thin-flanged Sturmey-Archer alloy hubs are bad for this) and technique.

I would shoot for correct tension without the tyre, personally.

 

[fossyant]

Sounds like you can already build wheels well, so go with your usual tension. I assume you aren't going radial spokes in the front !

 

[PpPete]

Sounds like you can already build wheels well, so go with your usual tension. I assume you aren't going radial spokes in the front !

Nope - I might have done, but this is disc brake set up

A wired-on tyre shouldn't affect tension by very much at all, as the constricting effect of the air pressure is counteracted by the outward pull on the bead seat. A tub does constrict the wheel a fair bit when inflated, but I doubt you're using tubs.
Any inflated tyre has a tendency to straighten the wheel (i.e. the wheel becomes more true) but this won't affect average tension.

No, not using tubs. But both with inner tubes and set up tubeless (sans sealant for testing purposes) the reduction in average tension was at least 20% immediately, reversible when pressure reduced and repeatable on two rims of same brand but different hole numbers, different spokes, and both Michelin and Schwalbe tubeless-ready tyres. I shall be checking other rim/tyre combinations in due course....

I would shoot for correct tension without the tyre, personally.

Yes that's kind of my thinking, because if go for the correct tension with inflated tyre then a +20% when tyre removed risks taking them into Euler buckling...

Throw the tension meter in the bin and tighten the spokes til they make a nice pinging sound when you puck them.

I built several sets of wheels by ear before I got a tension meter. Trouble is, I have a cloth ear, so it had to be a joint venture with Mrs P calling out which were flat and which were sharp