The fork oil change on my 2004 niner was overdue and I decided that this time I would look closer at pre-load setting. I have always considered the harshness over ripples and bumps to be down to the fork design. The full stroke of the forks is 140mm and with pre-load adjusters at minimum and a full tank, 40mm of that is taken up with the weight of the bike. With my 100kg / 15.75 stone aboard, that takes up another 15mm. The initial spring compression, forks extended, is 25mm with the fork cap in place. Therefore, the spring compression, bike upright, is 25mm+40mm = 65mm.
When I removed the springs, I noticed they were dual rate. As far as I know, they are standard springs - I bought the bike at 13,000km / 8,000 miles. Their length is 350m, the same as quoted on JBX pages. So what do they look like when compressed by 65mm? Using some threaded studding, the pictures show that the softer rate is fully compressed at just 300mm. Basically, the spring acts as a stiff linear type.
In order to meet recommendations from various sources for sag with my 100kg aboard, in the past Ive set maximum pre-load. I have now set pre-load at minimum and will increase it should I find it necessary.
<p><p>BSA C15T, Ducati 200 Elite, Villiers Cub Trials Bitsa, Ariel Huntmaster, AJS 650 CSR, Sunbeam S7, Suzuki 650 Katana, Honda 400-4, Bultaco 350 Sherpa, Cotton Minarelli, Fantic 303, Yamaha SRX 400, Yamaha 550 Virago, Kawasaki ZZR 1100,
 Fantic 305,
Yamaha TDM 850 '91
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Yamaha TDM 900 '04. Ducati 200 Elite (again and now completed restoration), Yamaha SRX-600
Bulldog
