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slow 5 foot drop to flat.

is it a low speed event, or high speed event concerning fork travel? or is it a bit of both?

this will probably bring about some debate. but, i hope it will also create some much needed information that may help answer many of the questions people post about low-speed vs. high-speed events, and how to tune for them. below are the circumstances that have prompted me to create this thread.....

recently i made some stunts. one of them was intended to be a drop to tranny, but my tranny ended up being too short and not steep enough, so it ended up being a slow drop to nearly flat landing. little did i know, i had also created a perfect (and repeatable) testing grounds for setting up my suspension for hucks. well, even with 25% sag this drop eats nearly all the travel on my solo air totem.

so is it a high-speed event, or is it low-speed?
 

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Elitest thrill junkie
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Low speed, unless you hit a sharp rock during the landing, then it's both.
 

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If your using nearly all your travel then this would be a high speed event as the high speed compression adjuster on totems or an rear shock with one is for large impacts and only effects a certain percentage of the last end of the travel if that makes sense, low speed is for repeated small bumps and pedal bob and the like.
 

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Jayem said:
Low speed, unless you hit a sharp rock during the landing, then it's both.
Incorrect. Landing a drop is a high speed compression event. This is straight from Darren at Push:

PUSHIND said:
Pedaling, braking, some g-outs, and rider weight shifts = low speed at the damper
Jumps, drops, bumps, and heavy g-outs = high speed at the damper
What's frustrating, Jayem, is that you're still giving out wrong information, even though Darren has already set you straight in this thread:
http://forums.mtbr.com/showthread.php?p=5320822
 

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bad mechanic said:
Incorrect. Landing a drop is a high speed compression event. This is straight from Darren at Push:

What's frustrating, Jayem, is that you're still giving out wrong information, even though Darren has already set you straight in this thread:
http://forums.mtbr.com/showthread.php?p=5320822
STOP....... STOP............. STOP!!!
There is not place here for your facts. The internet is for hearsay an inuendo ONLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

All fun and games aside, as this is related to another post from the OP, just keep in mind that EVERY high speed event will start and end in the low speed range...and of course we can all find the type of jump (high rider speed, long linear take off, and good landing slope that nearly matches you trajectory) where you supension barely compresses at all and would be a 'low speed event' ...but the majority of landing are not of this type.
 

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davep said:
STOP....... STOP............. STOP!!!
There is not place here for your facts. The internet is for hearsay an inuendo ONLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Whoa. You're right, you're right. I have no idea what I was thinking. What I meant to say was my brother's friend knows a girl who dated a guy who did a 5 foot drop to flat once (reportedly it was "wicked" and he was very "stoked") and he said it was a low speed event.
 

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davep said:
All fun and games aside, as this is related to another post from the OP, just keep in mind that EVERY high speed event will start and end in the low speed range...and of course we can all find the type of jump (high rider speed, long linear take off, and good landing slope that nearly matches you trajectory) where you supension barely compresses at all and would be a 'low speed event' ...but the majority of landing are not of this type.
I am pretty much on board with this... you can't have a high speed event without low speed events occurring along with it.

It sounds like your particular situation is generating relatively high speeds, but you should also consider the total duration of the event. A 5 foot to flat is a pretty large amount of energy to absorb. Your legs absorb some of it and in the process, stretch out the total duration of time that the suspension is compressing.

Anyways, without knowing anything else about your situation (riding technique, bike, terrain, etc, in other words, take this for what it is worth) I would turn up LSC 1-2 clicks and HSC 2-4 clicks. But you also need to look at how your bike handles the rest of your riding.... what works on a drop to flat might not be so nice anywhere else.
 

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bad mechanic said:
This is straight from Darren at Push:
There are a couple "straight from darren at push" things that he's screwed up. Remember how he was franitically claiming that Fox RL forks had no compression damping circuts? He went on with this for a long time, then quietly reversed his position. I am convinced that Darren's claim of measuring the "highest velocity impact" during a drop is the result of what I said above, a lower shaft speed event combined with a higher shaft speed event (a+b=c). There's no way around it. Gravity is 9.8 m/s^2, you can do the math as I have, to find out how fast the shaft has to move when the bike hits a 100mm vertical rock at 40kph. The speed is significantly higher, there's just no way around it. You'd have to fall 9.8 METERS (huge!) to have a shaft velocity of 9.8m/s when you land, so the higher you drop, the higher the speed gets, yet you can easily achieve those shaft speeds during bump impacts. Now, this doesn't mean that a low speed event is defined by a certain speed, because within the realm we can have quite a bit of variance, in terms of chassi-stability, pedal-bob, and so forth, so a drop could be "higher speed" than those, but when compared to hitting a bump where the wheel has to move quickly at 20mph, it's "low-speed".

Go read more literature on the subject, as I have. Darren lumps "bumps, drops, g-outs, and jumps" all together. Yes, Darren tried to "set me straight" on this, but unfortunately I've read a lot more material than just Darren's.

I gotta say, that goes against everything I've read and experienced. Those can have some radically different shaft speeds. It's also interesting that I only bottom my marocchi forks (when the oil level is too low) on things like jumps and drops, whereas for sharp bumps the fork almost never gets that far in the travel. These forks don't have crap for low-speed damping, as you know.

You're going to have to change how you think shocks work if you believe Darren on this. In any case, damping is provided by an orofice and the damping increasing as a result of the square of velocity. If the fork or shock is bottoming out on a drop, it's because the velocity is simply not high enough to provide enough damping, hence it's a lower speed impact than what the damping is set for. Of course that's a little too simplisitic: increasing the low-speed damping should force more oil through the high-speed circut and provide more damping through the low-speed circut. Yes, the high speed circut will most likely be working in this case, yet if you just increased the HSC it's still going to bottom because again the velocity is not sufficient to create enough damping through the LSC port. Closing off the LSC port is the answer, and after the HSC has initialy blown off it restricts the flow in conjunction with the LSC, to provide enough damping to hopefully slow/stop it.
 

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unless you have nearly no damping and spring rate and your travel simply stops because you smash into the bottom, the last portion of a near full compression hit is going to be lsc, and the beginning will always be hsc.

stating a drop is just lsc is completely ignoring the beginning of the travel.
 

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So Jayem you think Darren is basing his whole suspension theory on a drop with a rocky landing that he measured, and ignoring all the other data that would prove you right, so he can have internet bragging rights...?

Your theory doesn't seem to take into account all the different variables, mostly rider input. Darrens tests are affected by every variable, and are quite hard to argue with, unless it is a big conspiracy to fool MTBR members.
 

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Jayem said:
There are a couple "straight from darren at push" things...
1. I'm will NOT be drawn into another one of your pointless suspension arguments.

2. Darren has real world telemetry backing up his statement. Theory must match results, not the other way around.

3. Because Darren was wrong on a feature a fork had once, doesn't mean everything he says now sits under a shadow. Plus, if you're going to play that game, how many times have I seen you be wrong? Not that you'll admit it.

4. Yes, I'm going to believe the suspension professional who runs a highly regarded suspension tuning shop on this.

5. Finally, you can have two very different shaft speeds, and still have them be high speed events.

With that, I won't be posting in this thread again.
 

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Jayem said:
There are a couple "straight from darren at push" things that he's screwed up. Remember how he was franitically claiming that Fox RL forks had no compression damping circuts? He went on with this for a long time, then quietly reversed his position. I am convinced that Darren's claim of measuring the "highest velocity impact" during a drop is the result of what I said above, a lower shaft speed event combined with a higher shaft speed event (a+b=c). There's no way around it. Gravity is 9.8 m/s^2, you can do the math as I have, to find out how fast the shaft has to move when the bike hits a 100mm vertical rock at 40kph. The speed is significantly higher, there's just no way around it. You'd have to fall 9.8 METERS (huge!) to have a shaft velocity of 9.8m/s when you land, so the higher you drop, the higher the speed gets, yet you can easily achieve those shaft speeds during bump impacts. Now, this doesn't mean that a low speed event is defined by a certain speed, because within the realm we can have quite a bit of variance, in terms of chassi-stability, pedal-bob, and so forth, so a drop could be "higher speed" than those, but when compared to hitting a bump where the wheel has to move quickly at 20mph, it's "low-speed".

Go read more literature on the subject, as I have. Darren lumps "bumps, drops, g-outs, and jumps" all together. Yes, Darren tried to "set me straight" on this, but unfortunately I've read a lot more material than just Darren's.

I gotta say, that goes against everything I've read and experienced. Those can have some radically different shaft speeds. It's also interesting that I only bottom my marocchi forks (when the oil level is too low) on things like jumps and drops, whereas for sharp bumps the fork almost never gets that far in the travel. These forks don't have crap for low-speed damping, as you know.

You're going to have to change how you think shocks work if you believe Darren on this. In any case, damping is provided by an orofice and the damping increasing as a result of the square of velocity. If the fork or shock is bottoming out on a drop, it's because the velocity is simply not high enough to provide enough damping, hence it's a lower speed impact than what the damping is set for. Of course that's a little too simplisitic: increasing the low-speed damping should force more oil through the high-speed circut and provide more damping through the low-speed circut. Yes, the high speed circut will most likely be working in this case, yet if you just increased the HSC it's still going to bottom because again the velocity is not sufficient to create enough damping through the LSC port. Closing off the LSC port is the answer, and after the HSC has initialy blown off it restricts the flow in conjunction with the LSC, to provide enough damping to hopefully slow/stop it.
Your wrong....

When dealing with shock absorbers one talks about frequency....

A sine wave with a frequency off say 90 per minute is a slow speed event.

A square wave has a very high frequency since to model the extreme requires high frequency terms in a fourier series...

The impact caused by hitting the ground is essentially a square wave....

The impact caused by rolling over some rollers is a low speed impact...

Shaft velocity is not a measure of the impact frequency it is a measure of the damped response to the impact frequency.
 

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LAKESNAKE said:
So what damper shaft velocity, in inches per second, constitutes a "high speed event" ?.

That may help clarify things (at least for me anyway).
A high speed event may result in very low shaft velocity, or it may result in high shaft velocity...

The highest shaft velocity will result when the input frequency matchs the resonant frequency of the system.
 

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Jayem said:
There are a couple "straight from darren at push" things that he's screwed up. Remember how he was franitically claiming that Fox RL forks had no compression damping circuts? He went on with this for a long time, then quietly reversed his position. I am convinced that Darren's claim of measuring the "highest velocity impact" during a drop is the result of what I said above, a lower shaft speed event combined with a higher shaft speed event (a+b=c). There's no way around it. Gravity is 9.8 m/s^2, you can do the math as I have, to find out how fast the shaft has to move when the bike hits a 100mm vertical rock at 40kph. The speed is significantly higher, there's just no way around it. You'd have to fall 9.8 METERS (huge!) to have a shaft velocity of 9.8m/s when you land, so the higher you drop, the higher the speed gets, yet you can easily achieve those shaft speeds during bump impacts. Now, this doesn't mean that a low speed event is defined by a certain speed, because within the realm we can have quite a bit of variance, in terms of chassi-stability, pedal-bob, and so forth, so a drop could be "higher speed" than those, but when compared to hitting a bump where the wheel has to move quickly at 20mph, it's "low-speed".

Go read more literature on the subject, as I have. Darren lumps "bumps, drops, g-outs, and jumps" all together. Yes, Darren tried to "set me straight" on this, but unfortunately I've read a lot more material than just Darren's.

I gotta say, that goes against everything I've read and experienced. Those can have some radically different shaft speeds. It's also interesting that I only bottom my marocchi forks (when the oil level is too low) on things like jumps and drops, whereas for sharp bumps the fork almost never gets that far in the travel. These forks don't have crap for low-speed damping, as you know.

You're going to have to change how you think shocks work if you believe Darren on this. In any case, damping is provided by an orofice and the damping increasing as a result of the square of velocity. If the fork or shock is bottoming out on a drop, it's because the velocity is simply not high enough to provide enough damping, hence it's a lower speed impact than what the damping is set for. Of course that's a little too simplisitic: increasing the low-speed damping should force more oil through the high-speed circut and provide more damping through the low-speed circut. Yes, the high speed circut will most likely be working in this case, yet if you just increased the HSC it's still going to bottom because again the velocity is not sufficient to create enough damping through the LSC port. Closing off the LSC port is the answer, and after the HSC has initialy blown off it restricts the flow in conjunction with the LSC, to provide enough damping to hopefully slow/stop it.
I am not going to try to re-create the math now, so take this however you wish, but I about 4 years ago I, too, was convinced that a drop was a low speed event, and had the math to show it. IIRC, I was comparing velocity attained durring a 4' drop to a reasonable estimate of the velocity needed for a 26" wheel to clear a square edged bump a little smaller and slower than you describe. According to my calculations, the drop was much slower. In some thread I argued for pages about this. At some point, somebody finally spotted the flaw in my math (it was embarrassingly simple, and I could not believe it had not been spotted earlier). I was wrong. The speeds were actually in the same ballpark.

Of course, it really depends on what you consider a "high speed hit", but a 4 foot drop to flat was comparable with some pretty fast velocities produced with square edged hits. Now, a 100mm square edge @ 40kmp is clearly a pretty hard and fast hit, and was a bigger hit than the ones I/we were using to calculate velocities for square edged hits, but I think we can agree that square edged hits a lot slower and smaller than the one you describe would still be in the realm of high speed compression adjustments.

You'd have to fall 9.8 METERS (huge!) to have a shaft velocity of 9.8m/s when you land,
I'm not sure how you are getting this. Correct me if I am wrong, but to find the velocity of a falling object after falling a given distance, the formula is v = sqrt(2*a*d)

If you fall 9.8 meters, then v = sqrt(2 * 9.8 * 9.8) = 13.86 m/s when you hit the ground.

Dropping 1 meter, you are going 4.43 m/s.

I believe you need to drop around 5 meters (to flat) to be going 9.8 m/s when you land. Still an absurdly large drop, but my point here is that I think you math is off.
 
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