Thu Dec 5 16:26:34 1996 - Message No. 252
From: Martin Franz <100265.3434@CompuServe.COM>

Subject: RE: front fork, oil, air..


Hi Micha !
>>>blocking front wheel after filling in air
hmmm, "again idealy" increasing the pretension of the fork should not cause harm
on braking. There is an explanation (which is at least compatible with MY
feelings of adding air):
the air in the @ fork is only _supporting_ the work of the steel spring. If you
add now air, the steel spring, in its "normal driving" position, is more
extented and therefor less resistant. Suspension is now done more by air
pressure than steel spring pressure. Air is much more compresible than steel
(spring). Conclusio :-)): a hard brake will let your fork dive deeper now
(measured from the higher normal position), as the main resistans still comes
from the steel spring.

For offroad driving, this is nice, as the fork is more "sensitive". On the
street, it is "wobbly"...

As I said before, diving is bad. While the dive, there is less force on the
road, reason: the spring "stores" those energy. So, while the dive period, there
is a high probability, that your front wheel blocks. 

>>> Is it only because of the more "direct" operation of the brake while you
>>> have additional time to release a bit of brake power when your fork is
>>> diving? 
no. From starting pulling the brake, throughout the "dive" period, you can't
give full power to the brake. the shorter the dive is, and the better it is
reduced by harder damping, the faster you can give full break power. The added
air makes the dive longer and deeper, if your are not used to it and expect to
give the full power early, you will easily block your front wheel.

On optimal conditions, with socia, going 100km/h, full break, it is nearly
imposible (after the dive) to block the front wheel, the brake is too weak to do
that (okay, kill me for that last sentence, but I tried that several times).
Alone, not a big problem to do, maybe more a problem to survive :-)))

Before the 12.000km oil change, I experienced similar problems, as I had to add
some air, to not get "at the end of the suspension" when going with socia. The
bike felt very "hoppy", brake performance and handling on speeds over 80km/h
degraded heavily.  The oil at 12.000 removed most problems, only with (my :-)))
socia, there where some handling problems, so I exchanged oil again with
16.000km (harder grade). I also increased pretension of the rear spring and put
the rear damping to "very hard": optimal handling/breaking with socia, very good
handling at high speeds on "bad jumpy roads", good on "unmounted" roads, real
bad handling on "real" abroad. Everything is only a compromise...

Ah year, not to forgett to mention: very often are handling problems not caused
by the suspension system, they are caused by old, worn out  tires. Changing
tires sometimes saves
a lot playing around with the suspension. Own experience.

have a nice slide, Martin
P.S. if you wanna try more air, better use a T-tube and a daytona pump, think,
that both are available at Hein gerike. Its not wise, to drive with different
pressures left/right, the fork easily stucks then.
Last not least, the air pressure will always increase while biking, simply
because the fork gets hot. okay, and I promise, to not get too theoretical next
time.



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