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2/15/2024
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Bedford, NS, CA
Anyone ever dyno a KYB rear shock?
I did one today, mine, off a 13 KX450, didn't seem like the compression adjusters were doing anything, so we threw it on our shock dyno.(we have a car race shop)
Both low and high speed comp adjusters did nothing from full soft to full stiff.
Only thing that changed anything was rebound adjuster on the bottom, and it affected compression more than rebound, especially low speed.
Very odd. We took it apart and can find nothing wrong. Can it be that we didn't use enough shock speed? We went to 20 in/sec, which is very high for the auto world.
This is comp adjusters only, almost zero change.
20in/sec seems low, restacker calculates at higher speeds...
I would guess actual speeds, especially for pro riders are significantly higher, if a jump has 2 seconds of hang time, that's 1 second of gravity accelerating the bike toward the ground from the jump apex, giving a speed of 9.81m/s with the ground, or roughly 3 times lower that for shock speed, so 29m/s or 130in/sec.
Race cars don't jump!
I think you are right, but I would have expected to see a little change with the clickers at low speed, especially on the low speed circuit.
Below is the graph when I swept the rebound clicker on the bottom, has a huge affect. Blue is rebound only.
The rebound clicker controls oil flow past the piston on extension, the compression clickers control the oil flowing into the reservoir on compression, the bladder's pressure can have an effect on oil flow into the reservoir, what was the bladder's gas pressure?
I think it was low, the dyno said it was 85 PSI, but we didn’t check the bladder specifically.
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Not sure what Kawasaki's spec is, I'd guess 160-170psi, it would be interesting to see the difference in compression damping.
Once I rebuild it, and set correct pressure, I will dyno it again and see if it changes.
The rebound clicker will affect both the rebound and compression, because as stated, it's a bypass hole around the piston. It has no check valve properties that will prevent flow in the compression direction.
If I'm not mistaken, gas pressure on most KYB's is spec'd around 150#.
Yamaha's spec is 142psi...
20in/s is only 500mm/s?
Using data acquisition potentiometers when riding, my max comp speeds are 3000-5000mm/s. So 500 would barley get the low speed circuit to work.
True, the KYB comp adjusters do very little and are mainly for fine tuning. KYB adjusters can very as well with some doing more than others, reason is the inconsistent manufacturing of the comp adj piston. You can change the diameter of the 11mm shim that rests on the HS adjuster spring bigger which will give your HS adjuster more range. But looks like you got one with excessive bleed on the comp adj piston.
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