Front Fork preload advice please (35mm Showa)

[graeme]

Hello to all,
I built a 450 single using a Moretti frame.
The recommended forks are 35mm Showa from a Honda NSR 125. (And triple clamps).
The static sag is 20.6mm, loaded (me sitting on it) is 46mm. That seems to me to be somewhere I would expect, bit too much loaded sag (10mm)
Pot holes and hard breaking they compress enough for the front guard to touch the exhaust header (if doing a left turn slowly, not in a straight line)
I know I need to trim the front guard (fender), or preload the fork springs perhaps 20mm with a spacer or short springs.
I assume the correct fix is to fit heavier or progressive springs,,, this is where I start to cry poor....
Any ideas or suggestions ?
I used 318cc of 15w oil and left 130mm air gap.
Heavier weight oil ?

Regards
Graeme

[blethermaskite]

Graeme, front fork springing has so many variables its a bit of a minefield......so here's my simplistic answer.....put a couple of 20mm spacers in to preload the springs and see what that does.
Cheers, George

[IanHood]

I'm with George, try 20mm spacers. Heavier weight oil might slow down the compression but won't stop it.

Ian

[graeme]

Thanks for the reply George and Ian, that was my thoughts too.
Will turn a couple of spacers and try them.
Graeme

[Hiya9612]

Thanks for the reply George and Ian, that was my thoughts too.
Will turn a couple of spacers and try them.
Graeme

Have a look at this website: https://www.peterverdone.com/archive/lowspeed.htm
It gives a lot of technical information about the relative weights of different fork oils, it's not quite as simple as we might think.

As has already been said, spring preload should sort your sag setting out, I have read that 30mm is around the optimum loaded sag (rider onboard). I've used a thick wall plastic pipe as it's cheap and easy to cut to different lengths, you can always turn a couple of metals ones once you're happy.

Good hunting
Phil

[graeme]

Thanks Phil
Now my head hurts (re your link)
Graeme

[graeme]

20mm preload seams to have sorted it,
Thanks to all for comments.
graeme