BOS Kirk 2015 User manual

Model Year 2015
User Manual
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Terms and conditions
BOS MTB offers warranty on its products on the following terms:
BOS MTB guarantees to the original purchaser that the BOS product for which they received this
warranty is free from defects in material and workmanship for one year from the date of original
retail purchase. A proof a purchase will be asked for any warranty claim. This warranty is not
transferable to a subsequent purchaser.
Wear and tear parts such as dust seals, O-rings, bushings, rear shock mounting hardware,
stanchions, threaded parts and bolts are not covered under this warranty.
Terms
This warranty is subject to legal jurisdictional or warranty rights of the country where it has been
originally purchased, which will prevail if different from the terms herein listed.
Limits
BOS MTB cannot be liable for any loss, inconvenience damages, whether direct, incidental,
consequential, resulting from the use of its products, local legislation prevailing.
Warranty exclusions
This warranty does not cover the following cases:
• Damage to products resulting from improper assembly other than listed below
• Products that have been modified by the owner or a third party
• Improper use
• Damages resulting from an accident, crash under any circumstances
• Invalid servicing procedures and servicing time frame not respected
• Replacement of the original parts by parts from others manufacturers
• Products whose serial numbers has been altered, defaced or removed.
Warranty procedure
The owner should always refer to an approved BOS center for any warranty claim. A proof a
purchase is compulsory for any warranty claim. Otherwise the warranty claim will not be
considered. Always contact BOS MTB warranty department before returning any products that
may fall under this warranty. If “the faulty parts” do not fall under warranty, the customer will be
charged for any costs in respect with warranty such as transport and package back and forth.
Warranty

Thank you for purchasing a BOS KIRK shock. Your shock has been assembled specifically for one bike - yours! - which means that
the internal valving and the air chamber volume are adjusted for your bike. The correct mounting kit is also provided with the
shock.
Your KIRK shock is delivered with the correct mounting kits for the bike specified while ordering.
Check the mounting direction
By referring to the compatibility table, available on the BOS MTB website : http://www.bosmtb.com.
Refer to the bike’s user manual
To follow the specific shock mounting procedures of your bike.
3.1 AIR PRESSURE
Before using the shock, you must set up the air pressure based on your weight and your bike’s rear suspension
geometry.
Refer to the compatibility table on BOS MTB’s website, in the download area on http://www.bosmtb.com for the
base recommended air pressure.
Connect a pump equipped with a precise dial to the Schrader valve located on the side of the upper part of the body,
and inflate at the recommended pressure.
CAUTION
Never try to disassemble your shock. Limit yourself to the instructions given in this manual. This shock is pressurized, for your
own safety, do not try to open it. You also risk damaging the shock and its internal mechanisms as well as voiding your
warranty.
Contact an authorized service center for any maintenance operation.
Air Valve
1. Introduction
3. Settings
2. Assembly

11mm
3.2 EQUALIZING AIR CHAMBERS
In order for your shock to function correctly, you must equalize the air chambers after setting your pressure.
To equalize the chambers, the shock must be mounted on the bike.
Place the travel checker O-ring at 11 mm from the seal of the shock, sit on your bike, and slowly compress the suspension until
the seal comes into the O-ring. Let the suspension slowly extend to its full travel. Slowly cycle the shock 15 times over the first
11mm of its travel to complete the equalization.
3.3 SETTING YOUR SAG
The sag is the amount of travel used by your suspension from your weight on the bike. It has to be set up by adjusting the air
pressure.
BOS recommends a sag percentage of 30 to 35 %.
The bike manufaturer may also indicate a percentage of SAG. Please refer to your bike’s user manual for this value. If the
manufacturer recommendation differs from ours, you should test the bike on the trail at different sag values to find the right
amount for your riding style.
How to measure and set your sag
Slide the travel checker O-ring up to your shock’s dust seal.
Sit on your bike (if possible dressed with your riding outfit) feet on the pedals - horizontal position, and let the suspension
compress under your weight. Get off the bike without pushing on the suspension any more, extend the rear suspension to its full
travel by pulling up the saddle, and measure the distance between the O-ring and the seal. This distance allows you to check the
percentage of SAG obtained with the current air pressure. To convert the distance into percentage, refer to the table below.
Length x travel (mm)
200x51
200x57
216x63
222x69
SAG (%)
30
35
30
35
30
35
30
35
Shock travel (mm)
15
18
17
20
19
22
21
24
If the sag is not correct, adjust the air pressure in 15 PSI steps. Equalize the air chambers after each adjustment.
Too much SAG: increase the air pressure.
Not enough SAG: reduce the air pressure.
11 mm

3.4 HYDRAULIC SETTINGS
The KIRK shock is a three-ways adjustable shock, which means there are three types of damping adjustment:
rebound, low-speed compression and high-speed compression + a lock out lever that affects low speed compression
only. Your shock’s base setting (internal) is set up for your bike’s geometry when you purchase the shock. We use
five basic settings which cover the majority of bikes on the market. If a different setting is necessary for a given bike,
we will develop it.
The purpose of damping adjustments is to use all the shock’s travel without bottoming-out (or only very
occasionally), to give grip to the rear wheel, to stop the bike stalling out in holes, and finally to maintain a good
chassis position. Below you will find the base settings for all shocks. Then it’s up to you to analyze its performance on
the trail and adjust the settings to suit your riding style. Do this carefully and methodically, step by step. Only change
one setting at a time and only by a few clicks. If it’s OK, note the setting and type of terrain. If you get confused with
the settings, return to the base settings and start again.
Low-speed compression (A) and low-speed compression lock out lever (B)
The low-speed compression (A) affects the shock’s performance in compression over small bumps or through the
beginning of the travel and low-speed shocks (like whoops).
Harden the low-speed compression (by turning the knob clockwise) on rolling terrain with big compressions and
kickers.
Soften the low-speed compression (by turning the knob anti-clockwise) on steep gradients.
The lock out lever (B) acts on the low-speed compression and affects the shock’s threshold. It is useful to lock it out
on pedaling sections and uphills to maintain the bike’s balance.
High-speed compression (C)
The high-speed compression acts mainly on harsh hits (jump landings, rough rutted sections). It should be soft
enough to get all the travel without bottoming-out. If, on a given track, you bottom-out frequently, harden the high-
speed compression by turning the knob clockwise. However, don’t get hung up on bottoming-out if it only happens
once or twice during your run. You risk setting your shock for 3% of the course and losing effeciency on the other
97%.
If your shock doesn’t get full travel, soften the high-speed compression by turning the knob to anti-clockwise.
Rebound (D)
The main factor in adjusting the rebound is the position of the bike. A bike shouldn’t be “sunken down” all the time,
although the back does need to be fairly low. Adjusting the rebound will allow you to maintain this balance.
If you feel like the back of the bike is pushing you forward on a slope or when braking, slow down the rebound (turn
the knob clockwise). It can be useful to accompany this adjustment (especially if the problem persists) by softening
the low-speed compression slightly (by turning knob A counter-clockwise).
However, if the bike seems too low at the back and/or the front end has a tendency to drift offline, speed up the
rebound (turn the knob anti-clockwise).
C
D
A
B

Base settings (regardless of internal shock setting):
Please refer to the chartlist available to download at bosmtb.com for specific pressure and setting suggestions for your bike and
weight.
3.5 AJUSTING AIR VOLUME
The progressivity adjustment featured on the Kirk, allows you to adjust the air spring rate on the last third of strok. Thus, if you
have found satisfying settings (air pressure and hydraulic) on the first half of the stroke, you can adjust the feel of the last
millimeters of travel.
The most frequent and simplest cases are:
The shock has an overall setup to single out comfort and grip, and the bikes sits low: by increasing the end-stroke rate you will
get a better control of the chassis through the shock and avoid bottoming out. The rate curve should be more progressive
(increasing at the end) by adding o-rings.
The overall setup of the shock is more responsive, with a chassis balance high. By decreasing the end stroke rate by removing o-
rings, you can make sure that you use all the travel.
This setting is adjusted by adding or removing O-rings placed inside the air can.
We suggest you to go about the set-up step by step. First add or remove two O-rings, then fine-tune the setting with one O-ring
at a time. Adding one O-ring in the chamber increases the end of stroke spring rate by 2%.
Usually, the correct setting is between 0 and 4 O-rings. However, the range can go up to 10 O-rings depending on the bike. The
installation procedure can be found on the following page.
Low-speed compression: 15 clicks from the fully closed position
High-speed compression: 12 clicks from the fully closed position
Rebound: 12 clicks from the fully closed position
ATTENTION
BOS has worked hard to develop our compression curve, which allows the KIRK shock to maintain the balance of the bike,
as well as giving good response, and improving handling. BOS recommends setting up the bike with a fast rebound to
keep the chassis balanced, and avoid the bike sitting low in its travel. This will make the bike less nervous, and more
comfortable.
The feeling of «fast» or «slow» rebound will differ from one rider to another. Thus it’s difficult to define it precisely. We
advise you to define your own range of correct rebound - the range of settings between «too fast» and «too slow». Then,
always choose a setting in the faster part of that range, for example the three last clicks (counterclockwise) on a range of
nine.
Only use O-rings provided by BOS. The dimensions and the material are specifically chosen for this purpose.
WARNING
IMPORTANT
To start your adjustment, turn the knob clockwise until it stops (clicks = 0). Then count the clicks while turning the knob in
the counterclockwise direction.

Procédure
Place the head of the shock in a soft-jawed vice
(figure 1).
Lightly tighten the vice jaws to prevent damaging the
shock.
Note your shock pressure, taking into account the
loss of pressure when connecting your pump. Slowly
deflate the shock. The shock body will retract slightly.
Unscrew the air can (a) while keeping the body (b) in its
initial position (figure 2).
Remove the air can (figure 3)
Insert the O-ring(s) from the body side of the shock
(figure 4) and put them in position. Make sure that
the O-ring(s) do not block the hole in the shock.
Align the air can (a) sticker with the rebound knob.
Replace the air can by screwing back by hand until the
stickers align to ensure the proper torque (image 6). If
the stickers do not align when the air can is hand tight,
reinflate and equalize the shock air chambers (chapter
3.2) then finish tightening the air can.
Reinflate the shock.
Mount the shock on your bike.
Equalize the shock air chambers (chapter 3.2).
Before tightening the vice, make sure the jaws grip a
flat surface and are not touching the rebound knob.
WARNING
The shock body must not be unscrewed. The air can
is unscrewed by hand without additional tools.
5
2
6
a
4
b
3
1
WARNING

Service
It is compulsory to clean your shocks immediately after every use! Nothing is worse for your shock’s seals than dry mud.
It is very simple to clean your shocks: wipe off the body and the seal with a clean, soft rag. Occasionally lube the stanchion (with
fork oil). Warning: Do not under any circumstances use degreaser, solvent, or any abrasive material.
If you power wash your bike, do not point the hose toward the seals! It will only push the mud inside the seal and get it stuck
between the body and the seals and scratch your stanchions.
Cleaning
Oil service
Full service
Recreational use
After each ride
Once per year
Every two years
Racing use
After each ride
Twice per year
Once per year
3. Maintenance11
Caution :
We recommend doing the oil service and full service at a BOS approved center. Only the BOS approved centers are able
to identify and appraise a damaged or worn part, especially in case of shock or wear on structural elements such as the
body, the mounting kits, and the shaft.

What is the basic set up?
Your shock has been set up for your bike, with a specific internal valving and air chamber volume. It is delivered with a pressure
of 80 to 100psi. You can find all the information about standard settings for your bike in the chartlist on the BOS website
bosmtb.com.
There is air leaking when I connect the high pressure pump, what can I do?
Check that your pump is correctly connecting to the valve shell. Make sure that the Shrader valve core is correctly tightened.
My shock is too stiff on the first inches of travel and / or the rebound is very fast. What can I do?
The two air chambers are not correctly equalized. Check out chapter 3.2 to see how to equalize your air chambers.
I added/removed anti-volume O-rings. Once reassembled, the shock stickers are not aligned. What can I do?
To be sure that the stickers will be correctly aligned, the rebound knob must be perfectly aligned with the air can stickers when
you start to screw the air chamber back in place. Check out chapter 3.5.
My shock has a slight negative travel. Is that normal?
The air spring of the KIRK is designed to obtain the best sensibility on the first inches of travel. As a result, on some types of
bikes, you may notice some negative travel.
Where can I purchase original stickers and valve cap?
You can purchase these items through your approved BOS center, or on the BOS store on bosmtb.com.
I noticed some play between my shock and the frame, what can I do?
Check that your mounting hardware is torqued to your manufacturer’s specifications. If it is, the rear shock mounting hardware
must be replaced. Contact an approved BOS service center, or connect on bosmtb.com.
My shock is compressing when I deflate it, is that normal?
When you deflate your shock from the air valve, you are only deflating the positive air chamber. The negative air chamber is still
pressurized and pulls on the shock’s shaft. If you want to avoid this, deflate step by step (30 to 40psi), and balance the air
chambers between each step (5 to 6 slow compressions and extensions over the first 11mm of the shock’s travel).
My shock makes a whistling or clicking sound when I compress it.
These sounds are normal to the functioning of the hydraulics when the rebound or low-speed compression circuit is closed or
almost closed. Check your settings and bring them closer to the base settings in your product’s user manual to reduce this noise.
For any other questions, please visit our FAQ page at http://www.bosmtb.com/ faq.html or send a message to
[e-mail]
4. FAQ11