oil heights again

[georgieboy]

Yes it is discussed many many times before but lately i have done this experiment and it came up with questions.
The experiment was: filling up the fork with oil without the spring and see how easily i cld compress it. Fill it up a little more etc etc.
I started with 100mm, i marked with a ty-rip the distance, then 90mm, 80mm, 70mm and hardly noticed a difference.
So the question is: do manufactures just quess the oil heights or is there a systemetic calculation done?
In above cases i was able to collaps the fork to almost bottoming distances. Go figure when i land a jump what happens.
So i wld say they are a little conservative with oil heights.

 

[NEMX305]

I know the oil height affects the "air spring", but i thought the height had more to do with where the bottoming cones come into play.? Tim

 

[georgieboy]

nobody else wants to comment on my experiment?
So am i right about the oil heights that they do not make a great contribution afterall, or do i miss something here completely?

 

[Jaybird]

Your experiment is done with no fork springs?

If so, why?

 

[terry hay]

Georgie
The air spring is complementary to the coil spring and there is a combined spring force that creates the overall effect. The changes in oil volume although hard to feel by just pushing are immediately apparent when riding the bike. Your experiment was conducted without the coil spring and you would have to compensate for the lost volume of the spring to get the full effect of the pressure differential between fully extended or fully compressed. The oil height is determined by two extremes. Too low and air will be drawn into the cartridge creating cavitation. Or as someone else mentioned you may affect the capability of the bottom out cone. Too high and you will create "hydraulic lock". Obviously there is a minimum and maximum level with a little safety margin built in. Everything in between the two levels allows for a tuning variable.
Regards
Terry

 

[georgieboy]

no springs, i am not that heavy (wink)
How much cc's wld a spring take, so i can take that in consideration.
But maybe i just have to fill it up to much and just experience the locking motion while riding.

 

[georgieboy]

O sorry to clarify it a little. I didn't ride without the springs. I just took a leg and pushed it a little.

 

[joereitman]

My 03 KX250 had a stock height of 110mm. Upon rebuild and revalve (check valve to replace mid valve) went to 100mm. It still needs just a touch more resistance to bottoming off hard flat landing jumps. I have read 80mm is ok. Is the change to 90mm from 100 going to effect it much, or should I just go to 80mm? Thanks.

 

[marcusgunby]

go in 10mm increments, 20mm is alot.

 

[joereitman]

Thanks- will do.