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High Speed/Low Speed Compression Dampening

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I've seen quite a few written attempts at giving a good description/explanation of the effects of adjustment of high speed compression dampening (specifically, modern rear shock vs. low speed). Frankly, none are very good. Low speed is easy for me to feel and understand, but with my limited opportunities to ride, I've never had time to test/experiment much with high speed adjustments. Any experts care to enrich and enlighten?

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Someone posted THE best laymans explanation of the high and low speed compression about a year ago. Unfortunately, it was lost when TT had a database problem. If you're out there, please post again.

In general though, think about the vertical travel of the rear wheel in relation to the horizontal travel. For instance, a square edged rock that is 6" high will make the rear wheel travel vertically 6" in a horizontal distance of 0". This is an example of high speed compression. Landing from a big jump, on the other hand, may cause the rear wheel to move 8" vertically, but this may be over a horizontal distance of 12", resulting in a much lower ratio, or shock shaft speed, which is an example of low speed compression.

While maybe not the best explanation, I hope it helps.

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Low speed and high speed are just two simple divisions of how fast a shock or fork is being compressed, (and sometimes it may refer to rebound). It's a matter of velocity or what some refer to as "rod speed".

It's like the difference between someone coming up and giving you a big push to that of someone whacking you with a hammer. One is very slow, almost gradual, the other is very sudden and sharp.

But both low speed and high-speed movements can take up little or huge amounts of travel. In general, landing most jumps and falling out of the sky and hitting the ground is a low speed movement. Small ripple bumps and sharp edge corners and such, like rocks, are often in the high-speed range. Drive your car up a sharp curb at 60MPH and you'll know what a high-speed movement feels like.

You can also look at this as a matter of frequency, given that any vibration is a just a collection of cycles. Fast and short vibrations are usually high-speed, which means, arm pump and hand pain is the result of high-speed movements.

In the reality of tuning suspension, however, low speed and high speed doesn't cut it since there is a range of velocities that we deal with, all of which have to be examined and tuned accordingly. This means you're dealing with a spectrum of movements such as ultra low-speed, low speed, mid-speed, high speed and ultra high speed.

In most modern suspension, there are the means (damping circuits) to manage each of these, and with some knowledge each can be tuned to work up the ideal feel.

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A couple of good explanations, including the MXA article. Of particular interest are a couple of references I've seen which also relates high speed damping to ride height. Some have said that increased HSD increases ride height and vice versa. Dirt Bike magazine compared HSD to a "relief valve" which affects ride height. ???

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