| Valving Logic Discoveries
- "If you run a test and it confirms your hypothesis, you have taken a measurement. If you run a test and it doesn't perform as expected, you have made a discovery!"
- At valvinglogic we specialize in dyno and pressure testing. Each year we perform hundreds of fork and shock dyno tests. And as you might guess, things don't always turn out as expected.
- These 'discoveries' started back in 2005, about 3 weeks after I received the dyno. As time permits I will put some of these discoveries here, in no particular chronological order.
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a) ips = in/sec, dyno test velocities
b) force = lbs, all forces are lbs
c) comp = compression
d) reb = rebound
e) mv pist = fork midvalve piston or shock main piston
f) bv pist = fork base valve piston
g) ca pist = shock compression adjuster piston
h) ls = low speed (force or velocity)
i) hs = high speed (force or velocity)
j) gas force = gas force from nitrogen pressure or fork inner chamber spring
k) drag force = drag force from seals, orings and piston band
l) c force = compression force from the shock mv pist with gas force, drag force and ca force removed
m) ca force = compression force from the shock compression adjuster with c force, gas force and drag force removed
n) ca % = percent of force coming from the compression adjuster
Pressure testing allows us to break down the compression forces into:
- c force (from mv pist)
- ca force (from cadj)
- gas force
- drag force
This allows us to see:
How much force from mv pist
How much force from ca pist
How much beginning force
How much ending force
Where do they cross
SHOCK REB WASHERS, 2016-2018 WP SHOCK
We tested several different variations of shock rebound washers and got surprisingly different results. All tests have the same stock rebound stack.
Comparing reb force at 2ips, 5ips, 40ips
1) 3160, reb force = -61, -125, -1050
2) 3162, reb force = -65, -138, -1130
3) 3163, reb force = -69, -142, -1157
4) 3165, reb force = -73, -153, -1187
5) 3161, reb force = -74, -157, -1269
6) 3164, reb force = -72, -160, -1375
SHOCK LOW SPEED COMPRESSION, 2016-2018 WP SHOCK
Tests 2389, 3092
We revalved a shock for 17 XCF 450 for XC. We have used this build many times with good results. However, the rider was not happy. We dyno and pressure tested the shock and found it was lacking low speed compression force.
It's hard to see the lack of ls comp force looking at overall dyno numbers (that's why we missed it in the first place).
Comparing overall comp force at 1ips, 2ips, 5ips, 50ips
2389, good oall comp force = 38, 56, 99, 607
3092, lacks ls comp force = 34, 52, 98, 602
percent difference = 89%, 98%, 99%, 99%
Once we pressure tested we were able to compare c force only and it shows an obvious lack of ls c force at 1-2ips.
2389, minimum ls c force = 20, 38, 79, 506 (force from mv pist)
3092, lacks ls c force = 10, 25, 70, 505
percent difference = 49%, 66%, 89%, 100%
Once we bumped up the ls numbers at 1-2ips the shock worked great.
The rider said "shock works fantastic. Works everywhere, rocks, single track, high speed woops. Rear feels pillowy. Does everything better than 3092."
SHOCK COMPRESSION ADJUSTER FORCE, 2016-2018 WP SHOCK
Tests 3075 and 3130.
When pressure balancing a shock we shoot for 13% of the compression force coming from the compression adjuster (that is, ca force with mv force, gas force and drag force removed). Different compression adjusters have different ca force curves.
The goal is to control the low speed compression force for both c force and ca force. In this case we will also look at the ca % through the velocity range to get an idea of how much work the ca pist is doing.
Comparing ca force at 1ips, 2ips, 5ips, 50ips
3075, stk comp adjuster
c force = 22, 45, 91, 498 (force from mv pist)
ca force = 0, 0, 4, 81 (force from ca pist)
ca % = 0%, 0%, 4%, 14%
3130, diff comp adjuster
c force = 28, 51, 103, 513
ca force = 1, 3, 11, 69
ca % = 4%, 6%, 10%, 12%
The low speed ca % is much higher for 3130. The ca force number difference looks small but the percentage difference shows ca force increasing 275% at 5ips (11/4 = 2.75). And with 3130 if you just increased ca force at 1ips to 2 lbs, the ca% would be 7%.
SHOCK - NO TWO SHOCKS ARE ALIKE, EXAMPLE, 2005 KXF 250
Tests 40, 147
First thing we noticed dyno testing shocks was that 'no two shocks are alike'. Here is one example from 2005.
We dyno tested two stock 05 KXF 250 shocks, both had 40-50 hours.
Comparing oall comp force at 5ips, 50ips
40-used, oall comp force = 153, 727
147-used, oall comp force = 164, 699
percent difference = 107%, 96%
Comparing oall reb force at 5ips, 50ips
40-used, oall comp force = -81, -1151
147-used, oall comp force = -76, -1094
percent difference = 94%, 95%
SHOCK FORCES CHANGE AFTER SERVICE, EXAMPLE, 2005 KXF 250
Tests 40, 147
Continued from above. We took the same two shocks and serviced. Changed oil, new piston orings and band, shaft bush and seal, torque 300 in/lb.
Notice that the two shocks are still different, even after service.
Comparing oall comp force at 5ips and 50ips
40-fresh, oall comp force = 183, 844
147-fresh, oall comp force = 182, 819
percent difference = 99%, 97%
Comparing oall reb force at 5ips and 50ips
40-fresh, oall comp force = -84, -1163
147-fresh, oall comp force = -89, -1227
percent difference = 106%, 106%
Notice the shock comp and reb force increased after service. Comparing 147 at 50ips
147-used, oall comp force = 699
147-fresh, oall comp force = 819
percent difference = 117%
147-used, oall reb force = -1094
147-fresh, oall reb force = -1127
percent difference = 112%
This is a huge difference. You would need a significant shim change to get 12-17% increase in force. And this was achieved just by grinding the nuts, servicing the shock and re-torquing.
SHOCK FORCES CHANGE WITH NUT TORQUE, EXAMPLE, 2005 KXF 250
Tests 147-300, 147-150 (300 and 150 in/lb torque)
Shaft nut torque can affect the oall comp and reb force.
Comparing oall comp force at 5ips and 50ips, 300 lb/in vs 150 lb/in
147-300, oall comp force = 182, 829
147-150, oall comp force = 189, 797
percent difference = 104%, 97%
Comparing oall reb force at 5ips and 50ips, 300 lb/in vs 150 lb/in
147-300, oall reb force = -89, -1227
147-150, oall reb force = -88, -1162
percent difference = 99%, 95%
If you revalve a shock and replace 2 shims the change in force might be 5%. But in the case of the 05 KXF 250, just disassembling and reassembling the shock can change comp and reb force 12-17%.
All shocks are different and some will have the comp and reb force decrease after service. There is no pattern. So after servicing a stock shock the rider may need to readjust the clickers to dial the bike in.