Tapered stacks are commonly used in dirt bike suspensions. This page will take a brief look at adjusting tapered stacks. (more later)
Picture 2 shows a single stage tapered compression stack on a KYB 46mm shock piston.
Picture 2
Target specific damping ranges
It's been said that changing a shim located at the top of a tapered stack will target the low speed damping range to a greater degree than the high speed range, and that changing a shim located at the bottom of a tapered stack will target the high speed damping range to a greater degree than the low speed range.
Table 5 shows a comparison between two tapered shim stacks.
Stack v6 has the 26.20 & 24.20 shims removed.
stack v5
stack v6
11-04-05
40.20
40.20
04 RMZ 250
38.20
38.20
stk251s
36.20
36.20
34.20
34.20
32.20
32.20
28.20
28.20
26.20
0
axiom: changing a shim located at the bottom of a tapered stack
targets the high speed damping range
24.20
0
22.20 b
22.20 b
ips
dyno forces
v5 (lbs/in)
ips
dyno forces
v6 (lbs/in)
lb diff
% diff
10
211
10
199
-12
94%
20
293
20
277
-16
95%
30
375
30
356
-19
95%
40
456
40
434
-22
95%
50
537
50
513
-24
96%
60
617
60
591
-26
96%
70
696
70
669
-26
96%
80
774
80
748
-26
97%
90
852
90
826
-26
97%
100
929
100
904
-25
97%
Table 5
Table 6 shows another comparison between two tapered shim stacks.
Stack v7 has the38.20 shim removed.
stack v5
stack v7
40.20
40.20
38.20
0
axiom: changing a shim located at the top of a tapered stack
targets the low speed damping range
36.20
36.20
34.20
34.20
32.20
32.20
28.20
28.20
26.20
26.20
24.20
24.20
22.20 b
22.20 b
ips
dyno forces
v5 (lbs/in)
ips
dyno forces
v7 (lbs/in)
lb diff
% diff
10
211
10
193
-18
91%
20
293
20
270
-23
92%
30
375
30
348
-27
93%
40
456
40
427
-30
93%
50
537
50
505
-32
94%
60
617
60
583
-33
95%
70
696
70
662
-34
95%
80
774
80
740
-34
96%
90
852
90
819
-33
96%
100
929
100
898
-31
97%
Table 6
Conclusion: chart 14 shows the damper force changes to be linear, indicating they each target the low and high speed to about the same degree.
This conclusion is based on changes to a single stage tapered stack. We will run more tests on both single and two stage tapered stacks in upcoming pages.
Chart 14
It's also been said that a tapered stack is more "progressive" than a strait stack.
Table 7 compares the tapered stack from above with a strait stack.
stack v5
stack v8
40.20
6 - 40.20
38.20
0
36.20
0
34.20
0
32.20
0
28.20
0
26.20
0
24.20
0
22.20 b
22.20 b
ips
dyno forces
v5 (lbs/in)
ips
dyno forces
v8 (lbs/in)
lb diff
% diff
10
211
10
200
-11
95%
20
293
20
282
-11
96%
30
375
30
365
-10
97%
40
456
40
448
-8
98%
50
537
50
531
-6
99%
60
617
60
614
-2
100%
70
696
70
697
2
100%
80
774
80
781
7
101%
90
852
90
864
13
101%
100
929
100
948
19
102%
Table 7
Chart 15 shows that the tapered stack is not more "progressive", but is in fact less progressive.
The strait stack (pink) starts slightly lower and ends higher.
