9Kg (or 90N I assume) is quite "stiff" spring, but not unreasonable I suppose for a 130KG load and you definitely should see some sag to speak of with your rider weight 105Kg.

Most up-rated springs I've heard of people using tend to be 80N, and the odd rider using 90N, but that's with a new shock, such as Ohlins for example. Most people who change out the OE spring go for a progressive like Hyperpro, not heard of anyone changing for a linear rate? I think a 90N spring would ask too much of the already suspect OE Sachs' shocks damping ability!

What spring did they fit?

The other catch is that a 90N spring might have been calculated correctly and be fine for your weight, but if it was longer than stock, then you could end up with no sag even with no preload as you have found (because it would have been excessively preloaded when fitted to the shock body). Are you sure your suspension chaps fitted the correct length spring?

Oh, by the way... Hi and welcome to the forum!

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