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   Valving Info 107
 

 

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.

          Chart 15

 

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  valving info
valving 001
valving 002
valving 003
valving 004
valving 005
 
  complex stacks
complex shim stacks
 
  more valving info
valving 101
valving 102
valving 103
valving 104
valving 105
valving 106
valving 107
valving 108
valving 109