Re: [ST] Fork Oil Question

["Rick & Joyce" <rnjwes@xxxxxxxxx>]

> I'm up for my 12k mile service in about 600 miles. I don't have
the money to
> invest in the racetech fork upgrade (much as I'd like to).
However, several
> people have talked about using a heavier weight oil instead of
the standard
> weight to improve rebound/compression damping.

Peter,
I posted the following last fall:
"Decided to experiment with fork oil levels to see if any
improvements could be made.  I settled on raising the level from
the factory recommended 145mm to 125mm using 10w fork oil.
Preload was backed off to the first mark.  I just rode ~1300
miles on the TRAP Rally in eastern Oregon and the front end is
better in every respect!  With less preload, the initial fork
response is softer, soaking up washboard surfaces and small bumps
nicely.  As the forks compress, the rate increases and nose dive
under heavy braking is greatly reduced---all for the price of a
quart of fork oil."

YMMV.  For the record, my riding weight is ~190 lbs.

In response "Scott Friday" asked:
> Why did you decide to raise the level in addition to changing
> the weight of the oil? Why not just change the oil only? Does
> that also affect the damping?

My response:
"It's a trick I learned years ago with a GS650.  On that bike I
added 10% more oil & the improvement was dramatic.  Raising the
oil level reduces the volume of air in the fork tube and provides
a rising (spring) rate as the air is compressed.  I tried 10%
with the Sprint (500ml = ~100mm oil level) but it was too much,
limiting the fork travel.  The increase in oil viscosity (from
7w) was more a matter of availability, though I'm happy with the
slight increase in damping. . .  I'd be careful with viscosity
increases.  On my Trophy, I switched from the factory's 10w-20 to
15w and while the bike felt better in the twisties, it was pretty
harsh for normal riding.  Switching back to 10w with a little
extra oil volume was much nicer."

My guess is the 15w would have been fine if I were heavier.

Hope this helps,
- -Rick in Oregon
'01 Sprint ST

Politics is supposed to be the second oldest profession.
I have come to realize that it bears a very close
resemblance to the first.
- -Unknown



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