[ST] Fork Oil Heights, Pre-Load and Front Sag

[Rich Hartwick <hartwick@xxxxxxx>]

I have been working on the ST for the past week or so with
the front suspension.  Just wanted to share the info I have
so far.  First thing to do was change the fork oil.  This is
a 00 ST, purchased new this past March, with only 6,000
miles on it, most of it with a quick trip to Florida with my
son to check out colleges.  Actually, I am getting the bike
ready for another trip down, as he is starting in mid-August
at Florida State, and we are biking down two-up on the
Sprint.  As I got older and smarter, I told him to ship his
stuff down ahead, and we would go on the bike alone.

As with virtually every Hinckley Triumph I have heard of,
the factory oil levels were low.  I found 170 mm oil level
(145 mm recommended in the manual).  At least they were both
about even.  Sucking out the old oil, and rinsing several
times with small amounts of fresh oil, I ended up with 140
mm of 15W.  RaceTech recommends 125 mm of 15W, but with
their recommended 0.95 kg/m springs, vs. stock 0.65's.
Personally, I have always found RaceTech recommendations on
oil heights, sag and spring rates to be a little "over the
top" for normal street use.

I took some time to measure pre-load and sag, and found the
following - the sag is for my svelte 200 lbs (150 lbs me, +
50 lbs of jacket - no wait, 190 lbs me, 10 lbs jacket, you
get the picture)

Top Fork Nut distance:

mm             Lines          Sag mm
15 mm          3 L          25 mm

17 mm          3 1/2+      30 mm

18 mm           4 L           40 mm


The factory manual recommends 15 mm of pre-load for a
single, normal rider.   I had a problem here, as the manual
also states a front travel of 127 mm.  Using the rule of
thumb of 1/4 to 1/3 of the travel for sag, that would put
the recommended front sag at 32 mm - 42 mm, or supposedly 3
1/2 to 4 Lines showing.  RaceTech recommends 32 mm, which is
consistent with their more aggressive settings of 1/4 of the
front travel.

Test riding the bike using 17 mm of pre-load (about 3 1/2
Lines), I found two things.  First, the 15W oil is too
stiff, giving too much compression damping, even in 85 deg F
temperatures (forget when it hits 20 deg F in upstate NY
here).  Rebound is probably OK, but the suspension felt a
little stiff and slow to respond, but definitely firm.  Not
awefully bad, but a little too much.  Secondly, I found I
could sense the stability differences on the Interstate
between the 15 mm and 17 mm pre-load.  Here is the
inconsistency - I would have thought that the 3 1/2 Lines,
or even 4 Lines showing on the pre-load, would have given me
about the right sag.  However, I found the bike noticibly
twitchy at the 3 1/2 Line setting, and much more stable at
the recommended 15 mm - 3Line position.  Rock stable in
fact, even with gusting trucks and such.   This would mean,
I assume, that the factory spec of 15 mm preload gives an
abnormally shallow sag - can this be right?  The front on
this bike has fairly small trail values, with only, what, I
recall 92 mm of trail.  This is a very small number, and I
could feel the difference in stability between the various
sag values.  Mind you, I have not monkeyed witht the rear
sag, leaving it at the stock setting for a single rider.
None of the front settings were scary, just noticible in
terms on their effects on, mostly, straight-line stability.

One question I have then is, has anyone else measured their
front sag with stock springs?  Either I am mis-measuring (I
used a tie-wrap, and measured the difference from a fixed
point on the triple-clamp with the front wheel in the air,
vs. my full, normal weight on bike, balanced by somone
else).  In other words, 25 mm of sag seems too little - less
than 1/4 of the front travel.

Beyond the sag, and thus the trail values, I also decided
the 15W oil as too stiff.  I pulled it out tonight,
replacing it with 145 mm of 10W - I will let the list know
the results when I give it a good test run tomorrow.  Except
perhaps for the race track, my opinion is 15W is too stiff.
The manual recommends Showa SS8, which I am not sure of, but
am certain it is below 10W, probably around 7.5W.  I am not
a big fan of the Race Tech Gold Valve cartridge emulators.
I know many will disagree with me here.  However, in this
case, if I wanted to take the time to put them in, they
would probably benefit, as then I could release the
compression, and use the thicker oil to modulate the
rebound.  My past experience with them is that they are just
too much pain the neck to set up properly, and that changes
in oil weight accomplish 90% of what they can do, with a lot
less hassle.  That is just my opinion though.  We will see
when we get done optimizing the forks, assuming I don't
totally screw them up in the process.

Anybody with any front sag measurements for stock setups
(and be honest on the weights here - nobody will tell).   My
numbers seem off, despite checking them again.

Rick Hartwick
00 Sprint ST


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