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High Speed, Low Speed Compression

11K views 22 replies 14 participants last post by  Turveyd  
#1 ·
I have just bought some Rock Shox Lyric forks, they have adjusters for high speed and low speed compression. The instructions don't really tell me much about these adjustments. In the real world what do they mean? What is good about have a hard or soft, high or low speed compression?
 
#4 ·
The two adjustments cover just about what they're labeled for...damping for when the shock is being compressed at a slow rate or a fast rate. Though usually associated with big or small hits, it depends more on the speed at which the shock is being compressed and how fast the suspension is cycling in its movement. You can be hitting lots of small bumps at a relatively low speed and this is where low speed compression would play the biggest part in controlling the shock...like a bumpy technical section where you have to slowly pick you way through small ledges, rocks, and turns to negotiate you way through. On the other hand, if you were hitting small bumps, rocks, and other smaller trail obstacles at fairly high speed, the suspension would be cycling rather fast, and this is where the high speed compression would control shock action. High speed compression is usually most noticeable when flying through a rock garden at a decent speed, even if the rocks aren't giant boulder sized.
 
#6 ·
Low and High Speed compression damping, given a constant spring rate of resistance, effect the compression action in two basic ways:

Firmer high speed damping increases progressive rate compression resistance. Resisting bottomout, larger bump compliance, brake dive, and wallow.

Firmer low speed damping increases falling rate rate compression resistance. Resisting smaller bump compliance, brake dive, and wallow.

Both reduce compliance to bumps. Adjust to the minimum required for your sense of confident and stable handling, pedaling, and braking.
 
#7 ·
I'm curious about this too. I'm getting ready to buy the Lyrik Solo Air, and I've never had compression settings on a fork before.

Scenario:

I'm heavy at ~240lbs

Bombing down 3rd divide in Downieville. I was to reduce brake dive but keep the fork active to smooth out the trail. How many clicks for hs and ls compression?

What do you guys normally run with your compression?
 
#8 ·
bullit71 said:
I'm curious about this too. I'm getting ready to buy the Lyrik Solo Air, and I've never had compression settings on a fork before.

Scenario:

I'm heavy at ~240lbs

Bombing down 3rd divide in Downieville. I was to reduce brake dive but keep the fork active to smooth out the trail. How many clicks for hs and ls compression?

What do you guys normally run with your compression?
7 clicks high speed, 4 clicks low speed, except on Tuesdays, then 1.5 clicks more. :D

Seriously, get your air pressure right, then add compression as needed for the feel and ride you want. There are too many variables for someone else's setup to work perfectly for you.

If you are just looking for a starting point, Ok, as was mentioned, you start with minimum compression, and dial it up from there.
 
#9 ·
derby said:
Low and High Speed compression damping, given a constant spring rate of resistance, effect the compression action in two basic ways:

Firmer high speed damping increases progressive rate compression resistance. Resisting bottomout, larger bump compliance, brake dive, and wallow.

Firmer low speed damping increases falling rate rate compression resistance. Resisting smaller bump compliance, brake dive, and wallow.

Both reduce compliance to bumps. Adjust to the minimum required for your sense of confident and stable handling, pedaling, and braking.
He's talking about a fork, so progressive rate and falling rate are not applicable. They depend on having a changing leverage ratio on the rear suspension.

On a fork, raising the low speed damping will reduce bobbing when pedaling out of the saddle. It will also prevent sudden brake dive. The fork will still compress under braking if the brakes are held for a length of time, but the movement will be slower.

Raising the high speed damping will make it harder to bottom out. It will also give mid- stroke support, which means reducing any tendency to go too far into travel from sudden sharp bumps.
 
#10 ·
Steve from JH said:
He's talking about a fork, so progressive rate and falling rate are not applicable. They depend on having a changing leverage ratio on the rear suspension.

On a fork, raising the low speed damping will reduce bobbing when pedaling out of the saddle. It will also prevent sudden brake dive. The fork will still compress under braking if the brakes are held for a length of time, but the movement will be slower.

Raising the high speed damping will make it harder to bottom out. It will also give mid- stroke support, which means reducing any tendency to go too far into travel from sudden sharp bumps.
You are describing the effects of falling and rising damping rate increases. The cause of those effects is what I posted above. It doesn't matter if it's a fork or leveraged shock. (In the big picture there is leverage to the fork from CM inertia swinging around both axles and any linkages between including arms and legs).

Of course the falling or rising rate damping effect is blended with the natural progression of the spring and any linkage effects. For example: extreme falling rate platform damping such as propedal falls off in resistance rate as speed increases and the rising rate of the low speed damping and spring takes over at higher fork stansion (or shock shaft) travel. So you get a falling rate transition to rising rate of resistance though total compression travel.
 
#12 ·
Basically to attempt atleast to keep it REALLY Simple!!

Low Speed, you'll want this as near to off as possible or you'll feel all of the small bumps and big bumps more, add a bit if you want a stiffer fork to taste ( all the way OFF for me ), it'll let you tune out fork bob!!

High Speed, this is when you jab your front brake on and your bike dips forwards very fast or hit something big, then lets you tune out the dive as such, I run quite a bit of this as I hate brake dive.

I only ride XC / Trail centre stuff!!
 
#14 ·
Turveyd said:
Basically to attempt atleast to keep it REALLY Simple!!

Low Speed, you'll want this as near to off as possible or you'll feel all of the small bumps and big bumps more, add a bit if you want a stiffer fork to taste ( all the way OFF for me ), it'll let you tune out fork bob!!

High Speed, this is when you jab your front brake on and your bike dips forwards very fast or hit something big, then lets you tune out the dive as such, I run quite a bit of this as I hate brake dive.

I only ride XC / Trail centre stuff!!
Running low speed all the way off will cause a wallowing fork. You want to run it low enough where you're still getting the small dump absorption you want, but the fork will still be well taut, controlling pedal bob, and controlling fork dive.

Brake dive isn't a high speed event. The shape of a bump will dictate if it's a high or low speed event, not the size of the bump.

Turveyd, I'd suggest increasing your LSC and decreasing your HSC.
 
#15 ·
bad mechanic said:
Running low speed all the way off will cause a wallowing fork. You want to run it low enough where you're still getting the small dump absorption you want, but the fork will still be well taut, controlling pedal bob, and controlling fork dive.

Brake dive isn't a high speed event. The shape of a bump will dictate if it's a high or low speed event, not the size of the bump.

Turveyd, I'd suggest increasing your LSC and decreasing your HSC.
Agreed :thumbsup:
 
#16 ·
bad mechanic said:
The shape of a bump will dictate if it's a high or low speed event, not the size of the bump.
Not just the shape, but the speed it's encountered. Also due to the shape of our front wheels (circles around 26" diameter) smaller bumps generate lower fork speeds than a larger bump of the same shape and speed.

Having said that, small bumps are not low speed events. Anything bumpier than rolling ground is a high speed event.
 
#17 ·
If you're riding your bike and you encounter something that makes your fork change position nearly instantly, its a high speed event..

For example, if you hit a bump going 22 fps (about 15mph), and you hit the brakes enough to compress your fork 50%, you might travel ~ 250 inches (20 feet) to use 50% of your travel. Low speed event.

If you hit a 4 inch tall, 6 inch long bump, it'll use 50% of your travel. You just blasted 50% of your travel over 6 inches of riding. High speed event!

Ideally, you want a lot of low speed compression that magically turns into a mild amount of high speed compression (enough to deal with your biggest hit) once you hit anything. This would give a dive free, small bump compliant fork. This is impossible, but you want to work in that direction.

Spring rate plays a bit role too.. but at some point you kinda have to ignore all that and just play with settings until you find something that works. If you thoroughly understand how both settings actually function on the trail, their ideal settings dont matter too much. In reality, the HSC and LSC circuits overlap heavily. The "LSC" knob will have a big impact on the actual high speed damping function.
 
#18 ·
One Pivot said:
Ideally, you want a lot of low speed compression that magically turns into a mild amount of high speed compression (enough to deal with your biggest hit) once you hit anything. This would give a dive free, small bump compliant fork. This is impossible, but you want to work in that direction.
Impossible?
Hell no, that's exactly what shimmed dampers do.
 
#19 ·
bad mechanic said:
Running low speed all the way off will cause a wallowing fork. You want to run it low enough where you're still getting the small dump absorption you want, but the fork will still be well taut, controlling pedal bob, and controlling fork dive.

Brake dive isn't a high speed event. The shape of a bump will dictate if it's a high or low speed event, not the size of the bump.

Turveyd, I'd suggest increasing your LSC and decreasing your HSC.
Any LSC causes nerve damage ulnar bla bla what ever it is, I have to run that all the way off with low volume fat tires.

HSC tames the fast drop through the travel air forks suffer with, which I hate.

Haven't got HSC on either of my forks at the moment, Reba's to short travel wise to suffer from brake dive and the RC41 Fighter is linear enough to not need it.
 
#20 ·
Steve from JH said:
He's talking about a fork, so progressive rate and falling rate are not applicable. They depend on having a changing leverage ratio on the rear suspension.

On a fork, raising the low speed damping will reduce bobbing when pedaling out of the saddle. It will also prevent sudden brake dive. The fork will still compress under braking if the brakes are held for a length of time, but the movement will be slower.

Raising the high speed damping will make it harder to bottom out. It will also give mid- stroke support, which means reducing any tendency to go too far into travel from sudden sharp bumps.
just FYI - air springs are rising rate by nature (air spring curve is far from linear... it's exponential), so in fact, an air sprung fork does in fact have a rising rate... that's why on a rear susp, a falling rate linkage combined with an air shock can provide near linear rate... then there's variable volume shocks like the Fox DRCV (DCRV?) shock from Fisher/Trek... but that doesn't apply to forks.
 
#21 ·
Some forks, have bigger air chambers, what counts is the air chamber volume which is left when the fork is fully compressed, cause your compressing say 150mm's of stroke into that space.

So although there all rising rate some don't rise as fast, Marz AM2's for instance used to drop through the travel like is wasn't there then ramp up and only really do anything in the last 20mm's or so. Or atleast that's how they felt.
 
#22 ·
Turveyd said:
Some forks, have bigger air chambers, what counts is the air chamber volume which is left when the fork is fully compressed, cause your compressing say 150mm's of stroke into that space.

So although there all rising rate some don't rise as fast, Marz AM2's for instance used to drop through the travel like is wasn't there then ramp up and only really do anything in the last 20mm's or so. Or atleast that's how they felt.
Yes, the weak mid-stroke of air forks. This is one of my biggest dislikes with them.
 
#23 ·
Dougal said:
Yes, the weak mid-stroke of air forks. This is one of my biggest dislikes with them.
Magura's I've ridden are really nice, very linear and coil like, my RC41 fighter although old is also very Linear and fine, mates got 170mm RS something or anothers okay I'm heavier than him, but touch the brakes and feels like I'm going over the bars, scarey!!

Dunno if the DT Swiss forks are still RC41 like, but like Magura's to much money for my taste.