TECHNOLOGY STORIES BIKE INFO, GEOMETRY ... - Vintage Trek

STP
Are you a rider who would love full suspension, but
you’ve decided to wait until the bikes get lighter? Wait
no more! At a mere 4.10 pounds (1860 grams), including
the frame and shock mounting hardware, the Trek
STP frame is lighter than many hardtail race frames.
The acronym STP stands for Soft Tail Pro. A Soft
Tail is a suspension bike without pivots, where the
frame flex provides rear wheel travel over bumps. Pro
geometry is the successful design Trek uses on high
end race bikes. This design provides increased handling
performance at higher speeds. Put them together with
another Trek acronym, OCLV (see pages 4-8), and you
have one fantastic full suspension racing mountain bike.
STP suspension features
The STP offers 35mm of rear wheel travel, or about 1
1/2”. This travel is controlled by a RockShox SID rear
shock. The shock is placed with a very low leverage
ratio, so it does not take much pressure in the shock to
provide adequate preload. This low leverage ratio also
allows the shock’s damping to do an excellent job, so the
suspension action is not readily noticeable. Basically,
the bike feels like a hardtail in steering, pedaling, and
uphill performance. The difference comparing the STP
to a high-end racing hardtail is that the STP offers
more comfort and extra rear wheel traction. Not a bad
combination of features.
Why not just put a suspension seatpost in a hardtail?
It’s true that a suspension seatpost offers some comfort.
However, few suspension seatposts provide a lot of
travel. And none of them help you when you stand.
There are those suspension seatposts that provide a
lot of travel. This can add lots of comfort, like any suspension.
However, most suspension seatposts use pretty
basic suspension, without much opportunity for tuning
beyond simple preload. Another issue is that the same
movement that provides comfort also allows too much
motion between the seat and the bottom bracket.
Moving the seat up and down by an inch or two detracts
from your pedaling power. In some cases, the motion of
the saddle can aggravate your lower back, since with
a suspension seatpost the angle changes between the
back and thighs during the suspension stroke.
Last, allowing the seat height to change during cornering
or other maneuvers reduces rider control. Some
seatpost advocates argue that on tough sections a rider
stands up anyway, but when standing the seatpost is no
longer providing suspension.
With the STP, the suspension works full time, seated
or standing. There is a generous amount of suspension,
yet the distance from seat to bottom bracket (as well
as the seat to bars) is fixed for pedaling efficiency. And
with a RockShox SID rear shock, the suspension is
highly tunable.
Compared to pivoting suspension systems
There can be several objections to full suspension.
Most prevalent of these are loss of frame rigidity, added
weight, increased frame noise and/or maintenance, and
reduced pedaling efficiency. In each of these categories,
the STP compares favorably to a hardtail. Most of these
issues are generated by pivots, in either designing the
frame for the pivots, or the result of pivot wear.
No Noise- Noise, or maintenance to avoid or eliminate
noise, is eliminated since there are no pivots to squeak
on an STP.
No Flex-As pivots wear, they can allow unwanted frame
10
Trek 2002 Tech Manual
flex. As the frame flexes laterally and torsionally, the rear
wheel can come out alignment with the front of the bike,
and this makes the bike steer poorly. Again, the STP has
no pivots to allow flex, so steering is just like a similarly
designed hardtail. All the time.
No added weight- Although the STP has the weight of a
rear shock, the use of an OCLV carbon composite frame
balances out the shock weight. Even with the shock in it,
the frame weighs barely over 5 pounds. While this isn’t
the lightest frame on the market, it’s within a full water
bottle of that weight.
No pedal bob- Since the seatpost and the bottom bracket
are rigidly fixed, there is no change in seat height, and
no loss of pedaling efficiency. Since the bottom bracket
can move relative to the rear wheel, it can be argued that
energy will be lost due to excitation of the shock. That
is, as you move your mass up and down when pedaling,
the shock will be compressed slightly. This does take away
some pedaling energy. But this energy loss is certainly
no greater than without suspension, when you have to
deal with bumps coming directly from the rear wheel to
the saddle.
Frame details
The STP has 2 water bottle mounts, just like a hardtail.
It has a replaceable derailleur hanger. Of course,
the STP also has top routed cables to keep the controls
free from muck-induced friction.
STP suspension setup
As a starting point for adjusting the suspension on an
STP, we recommend setting the forks for about 15% sag
(12mm), and the rear shock at about 25% sag (6mm).
This will provide a good race feel.
To make it easier to set an STP up for a test ride, a
shop can use body weight. Try using a setting in the
rear shock of 1/3 your body weight in pounds in the
main spring, and 1/2 of that in the negative spring.
Adjust the damping in 2 to 3 clicks from minimum.
Body /Preload Body /Preload
Weight Main Neg Weight Main Neg
LBS PSI PSI KG ATM ATM
100 33 16.5 45 2.3 1.1
110 36 18 50 2.5 1.3
120 40 20 55 2.7 1.4
130 43 22 60 3.0 1.5
140 46 23 65 3.3 1.7
150 50 25 70 3.5 1.8
160 53 26.5 75 3.7 1.9
170 56 28 80 4.0 2.0
180 60 30 85 4.2 2.1
190 63 31 90 4.5 2.3
200 66 33 95 4.8 2.4
210 69 35 100 5.0 2.5
220 73 36 105 5.2 2.6
230 76 38 110 5.5 2.7
240 79 40