What's wrong with antidive that it's no longer used in motorcycles and a lot of people just disable it.
While in theorie it all sound great.
First we'll have to decide what is a good choise in suspention,
if you have ever driven a kart you know you can do without, but you'll need a good flat road and stop drinking because it's killing your kidneys, so we want a suspention that is soft so we can ride comfortable.
But it also needs to be firm in some way so you don't loose contact with the road, bounce away or bottom out when driving through a pothole.
In the end this is an impossible task but you have different tools for different problems.
That in combination with your personal feeling of a good ride will get you about where you should be.
Now back to the antidive units
In the eightys they had a good thought, what improves handeling the most?
A stiff frame, yeah but if you can't do that? Constant the same geometrie!
And how can you reach that ideal?
Well....think along...usually when riding in a straight line on a perfect road your suspention sits at 'race sag'
When the road is getting worse your unsprung mass is bouncing a bit up and down, while your sprung mass goes in a straight line forward.
The average of the bouncing should be the 'race sag' point.
But when you accelerate this supersoft suspention would bottom out at the rear, and in the front when braking.
So you need some damping in the system to reduce the rebound and to prevent fast movement.
This is the thought behind the antidiveunit, soft suspention that is firm when braking (because it's blocking/reducing oil flow)
this makes cornering much better because you go where you steer (instead of globally going in that direction, correcting when you go along)
Here immediately begins the trouble:
when braking the superstiff suspention wouldn't allow bumps in the road anymore and your bike would 'jump' over bumps,
thus loosing contact.
So they added another valve that opens up when there is a sudden pressure increase.
Now doesn't this sound like the perfect suspention? Because of the antidive your geometrie stays the same, thus steering very accurate and the rest of the time you have a nice and soft front end
To complete this fantastic technological breakthough, the antidiveunit was produced with 3 settings to set the initial brake pressure before the antidive came into action.
What went wrong then?
There is something that you english speaking people call stiction.
This is the fact that when parts are standing still the initial movement costs more energie than keeping the movement going.
So in the end the bike is supersoft and then when braking it's very firm on good tarmac,
But when you hit a bump in the road the stiction keeps the valve just long enough closed to let your bike jump up (before it opens up) and let you make a short wheelie when braking (not an advisable idea, probably your front wheel is standing still when you hit the road again)
So years later eveybody has removed 'that crap', very simple just remove the brake part. (or more)
Test stiction yourself
If you have your forkleg without spring lying flat, move the inner tube, and feel that starting point.
there is a little 'shock' when the initial movement starts. This is stiction.
It can be reduced by better materials (or worn ;) smarter constructions etc.
ps. if you don't have that fork tube handy, it even works with a toy car, just place it on a smooth surface and try to push it forward, if you start of with the intention of not hitting it but really pushing it you can feel/see it.
So what now?
We could start removing it, but there are more paths you can go by.....
First I must tell ya, my main reason for pursuing this was that I wanted to keep the looks as original as possible.
Ok first again the picture of the antidiveunit
|1. Inner Cylinder
2. Fork Hydraulic Oil
3. Brake hose
4. Brake Pressure
7. Anti Dive Adjuster
8. Fork Outer Tube
|As you see on the picture there is a piston that fist exactly in the Control valve, thus closing off the passage when braking, there is a strong spring pressing the piston back and by the settings on the antidive units you alter the preload and thus the braking pressure the valve starts to move.
The control valve also has a spring that keeps it in position, and when you hit a bump and the pressure rises the spring will be depressed opening up the oil passage
What can we do to improve all this?
The Piston is, when in place narrowing the oil channel a bit
(in combination with the mounted brake part, may be disconnected)
Because of stiction however, the control valve will always open up too late, so what if we lower the control valve .25mm ?
Considering this I thought of a way to improve the overall action, and the best solution I could come up with was altering the piston, but leaving the initial idea intact.
I also considered to remove the piston spring and replace it with a piece of thread and altering the 3 way setting into 3 way inbound damper.
Both of these goals are reached, but untested, because I have to finish my bike first.