Oil Height: Simple Question

[andoman]

With regards to oil height in my Sachs forks (2011 EC 300):
Does a little change go a long way or does it take a big change in height to feel much difference?

I'm trying to soften things up and would like to minimize the number of fork on and off iterations required to get it right.

Also, I searched and can't find a minimum oil height for my Sachs units. Any one got that number? I don't want to take too much out.

Thanks in advance.

[Jakobi]

I think 140mm air gap (fork collapsed no spring) is the max. You could also try going to a thinner oil. Even with 10weight Silkolene RSF Racing oil and 135mm air gap, stock 4.2 rate springs I could never use the last 2 inches of travel in my Sachs.

[swazi_matt]

Originally Posted by Jakobi

I think 140mm air gap (fork collapsed no spring) is the max. You could also try going to a thinner oil. Even with 10weight Silkolene RSF Racing oil and 135mm air gap, stock 4.2 rate springs I could never use the last 2 inches of travel in my Sachs.

Yep 140 is max, and i dont think you can use the last 2-3cm of travel on the sachs, it bottoms before then (there will always be some chrome showing at the bottom of the sachs)

What you can do is start at 140 and then using a syringe just add 10cc of oil at a time through the air bleed holes until it stops bottoming. but in all honesty you can make huge improvements in the sachs performance (especially on square edge deflections) by getting them revalved

[Jakobi]

I didn't realise that Matt Is it the cart itself that that limits the travel before they bottom?

[swazi_matt]

yes i think it is the bottom out cone. I was also baffled but then i put the fork together without the spring (and with the bleed screw out - quite interesting how significant the air spring is) and pushed it down and it stops a bit above the bottom

So also to answer the topic question, the air gap has more effect on the bottoming of the bike as a result of the air spring, so make sure your seals are not leaking or your handling will be off

[andoman]

I've had them revalved by LTR and he set the oil at 130. I just took out a bit so I'm right at the min oil level. After a quick ride, it feels noticeably better, but I'm still not using the last 2-3 inches of travel.

Thanks for the info.

[Jakobi]

See if you can go a thinner oil next service. Makes a decent difference in action too!

[swazi_matt]

2-3 inches is about 5-7cm, seems a bit high if you know you have hit something hard, but if you have been riding without any major hits it should be about right.

I am pretty sure that the sachs bottoms with only a bit more than an inch of fork still exposed. next time you have the forks off, just remove the spring, open the bleed hole and push the forks down and see where it stops

[GMP]

Some forks, depending on their internal volume, respond well to subtanks. WP43s are an example. They basically function as a speed sensitive variable air gap. You can run a max oil level, and at low fork speeds or short travel impacts(trail trash) greatly reduce the progressive air spring effect.

Andoman, what are you trying to soften up? If its trail trash I would first try and reduce preload as much as possible. A stiffer spring with 1 - 2mm, just to keep it from rattling around will feel better than a soft spring all jacked up. Same applies to the shock.

[andoman]

It's a little more plushness over rocks that I'm trying to achieve.
Spring is correct for my weight and has only 4mm preload.
I know that the oil height affects primarily the last 3rd of the travel but that it will affect a little up top, too. And it has always bothered me leaving unused stroke that I couldn't get to bottom no matter how big the hit.
The forks are real close as they came back from Les. I'm just looking for perfection. I would try a lighter oil, but I still have plenty of clicks left on both rebound and compression.
Thanks again for the input.