spoke tension question

[e-rider]

how much does spoke tension decrease when the tyre is inflated?

manufacturers state that no attempt to compensate for this is necessary when building a wheel but if optimal tension is say 1100N and the spoke tension decreases by 10% then surely it would be wise to over tension slightly - obviously I have no idea how much tension decreases, I could run some tests measuring before and after fitting the tyre, but if someone on CC knows then that would be easier. I suspect that it's minimal really.

 

[Biker Joe]

I don't know for sure but I would imagine that, the tensions recommended by the manufacturer, would be taking the reductions in tension into account when a tyre is added.
Increasing the tensions recommended would be running the risk of compromising the rim around the nipples (Micro splits?).
As I say, I don't know this for certain.
Spoke tension reduction also depends on what the final tyre pressure is.
I'm just trying to think this through. I'm no expert.

 

[e-rider]

I don't know for sure but I would imagine that, the tensions recommended by the manufacturer, would be taking the reductions in tension into account when a tyre is added.
Increasing the tensions recommended would be running the risk of compromising the rim around the nipples (Micro splits?).
As I say, I don't know this for certain.
Spoke tension reduction also depends on what the final tyre pressure is.
I'm just trying to think this through. I'm no expert.

Indeed. Mavic, for example, quote the same recommended spoke tension for most of their road rims, and it's obvious that some of their rims are a lot stronger than others! So, does this mean the recommended spoke tension is with or without tyres fitted? This is never specified. However, if you send a rim back to Mavic with cracks around the eyelets they might/will be quick to say that the spoke tension was too high and that they wont replace it under warranty, and yet the information they provide to the wheelbuilder is very poor indeed.

I aim to operate in the region of 800-1100N for the rear wheel and 1000-1100N for the front - however, in every build there are always a few spokes that fall both below and above this range. The spoke holes next to the rim join are often problematic, requiring either very low or very high (or both) tension to compensate for a poor join.

 

[e-rider]

to answer my own question; after a few tests I can say that spokes lose approx. 80 N when the tyre is inflated to 120 psi