So just an update on this, in case it’s of any use to anyone. I got the spring today, the soft (black) one which is apparently 35 lb/in or as near as damn it 4Nm. (£25 plus postage from TF Tuning)
OD of both springs is 29mm, so that’s all good – weight is about 195gms, the Ti spring is 145gms.
Compared to the Ti spring the free length is 310mm as opposed to 305mm so I tried it as it is, without shortening.
For me, at around 67kgs in riding gear, I reckon it’s pretty much perfect straight out of the box, running no mechanical preload and no air preload. With the original spring, although I really liked the forks, I had to run negative air preload – ie. compress the forks and then bleed air from the preload valve in order to get anywhere near 20-25% sag. Hardly surprising, as the standard spring is, as far as I’m aware, 6.9Nm or about 61 lb/in.
Anyway, I’ll have a better idea after a decent run out, not just a quick razz around but so far it’s all looking good and has cheered me up on yet another dark, wet day.