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Discussion Starter · #1 ·
I have SR Auron 35 Boost fork (130mm, four spacers in the air chamber), and no matter what I set the compressions to, I can't "see" any difference.
I thought I would not bottom out as much (or at all) if I go from fully open to fully closed high speed setting, but when I tried unscfientifically testing it today by jumping/falling from one say 20cm step at various speeds, the fork always compressed exactly the same.
Same story with the low speed. When I just push on the handlebar, it feels exactly the same open vs closed.

ALSO, when trying to set the SAG, the fork always compresses different amounts despite me trying to sit down in the same way, slowly, into the same position etc. It can easily differ by 5mm every time. I understand there is variability, but this much? That's weird, isn't it?

Am I doing anything wrong, is the fork bad, or?...
 

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Are you adjusting the compression or rebound? Compressions is typically adjusted by the PSI in the shock. The dial adjustment, either locks out the fork (the knob is typically on top) or the dial on the bottom of the fork adjusts how quickly the shock decompresses or rebounds.

if you are adjusting the rebound, you will not see any difference in how the fork the compresses.
 

· since 4/10/2009
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your expectations about what those adjustments do isn't quite right.

first, when setting sag, you're going to get a little variability. you cannot make your body position absolutely identical every time, no matter how much you think you can. that's one variable. stiction in the fork is another one that's going to affect this. part of this is why sag is really only a starting point. you have to ride the bike like usual to decide if you want more or less pressure in the fork.

the compression adjusters also aren't really going to do what you're currently thinking. high speed compression isn't going to do much of anything for drops or single hits. when you are talking about the "speed" of the compression, you want to think about the frequency. so high speed will make a difference for things like fast, chattery sections of trail. washboards, chattery rocks or roots, that sort of thing. low speed compression is going to affect very low frequency compressions like the sorts of compressions you'll get from pedaling. I'm not talking about pedal-induced bob that might manifest on some rear suspension designs (though low speed compression damping CAN tune this out). I'm talking about the slow compressions from shifts in body position. On a fork, the push/pull on the bars that you might do when you're cranking at a climb would be a good example of this. You're probably not going to be able to replicate this kind of input in a static situation.

again, with these settings, you're going to have to RIDE the bike to see changes.

the "ride off a curb" test is something you can use to check rebound adjustments. But still, you actually have to ride the bike on the trail to get a real verification of whether a given setting works for you.

The proper way to address these is to ballpark the air pressure and ballpark the rebound setting in a parking lot or such. you can use sag to help ballpark the air pressure, but you don't have to. there are other ways to play with this. use the curb test to ballpark your rebound. Then go ride your "test track" to see what you think about those settings. This is where you check for the suspension bottoming out, is the rebound too fast or too slow, etc.

Don't mess with compression settings until you get your spring rate figured out. And then, only mess with one compression setting at a time. figure that out, THEN move on to the next one.

the more clicks you have in your adjuster knob, the more difficult it will be to tell a difference between them. sometimes it can be helpful to "bracket" the settings so you know what the extremes do, before you start trying to find a more intermediate setting that's to your liking. On various forks I've used over the years, I tend to prefer the compression adjusters to be at or near the lightest possible settings.
 

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Discussion Starter · #5 ·
@Harold
I don't know, at this point I don't understand anything anymore. I read several different articles about compression and what I gathered is that:
high speed compression: how much a fork compresses during fast hits like roots, drops etc. (fast being the speed at which the fork compresses, not the speed of the bike).
low speed: pedalling, braking etc.

What I've read thus far almost universally say that if you completely open a compression setting, the oil moves around freely, not slowing the fork down, so, logically, it compresses more.
 

· since 4/10/2009
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@Harold
I don't know, at this point I don't understand anything anymore. I read several different articles about compression and what I gathered is that:
high speed compression: how much a fork compresses during fast hits like roots, drops etc. (fast being the speed at which the fork compresses, not the speed of the bike).
low speed: pedalling, braking etc.

What I've read thus far almost universally say that if you completely open a compression setting, the oil moves around freely, not slowing the fork down, so, logically, it compresses more.
it doesn't really change HOW MUCH the fork travels. not directly, anyway.

what it does is change how quickly the fork compresses. you use air pressure to adjust how far the fork travels for a given hit (with the damping fully open). more compression damping MIGHT have the effect of reducing the amount of travel you use in certain conditions, but in other situations, it won't. how quickly the fork compresses does depend some on how fast you're riding, but it also depends on the shape of the impact. drops, especially smaller ones like your 20cm step, are going to be relatively slow because it's a single impact and you are using your arms and legs to attenuate the impact, as well. chatter is probably a better example of where more high speed compression damping is more noticeable because successive hits come quickly. with square edges and some speed, the impacts will be sharp and the restricted fluid movement of more high speed compression will result in less compression of the fork.

a particularly big drop will speed up fork compression so that the high speed damping settings might make a difference. but a single small one? not a good test.

this is why at a certain point, you need to take your suspension setting adjustments ON THE TRAIL and get out of the parking lot/yard/whatever more controlled area you're using. I don't generally bother touching compression damping knobs until after I've ridden a bit.
 

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Discussion Starter · #7 ·
Ok, so uh, if I leave say high speed compression completely open, it will compress faster, resulting in softer ride through say a lot of big roots, stones etc.?
If that's the case, isn't it best to just keep it "open" all the time and never touch it? What's the point of having the control anyway?
 

· since 4/10/2009
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Ok, so uh, if I leave say high speed compression completely open, it will compress faster, resulting in softer ride through say a lot of big roots, stones etc.?
If that's the case, isn't it best to just keep it "open" all the time and never touch it? What's the point of having the control anyway?
I'll come back to the chatter example because it's a difficult situation on suspension.

especially when the chatter is fairly big stuff, you have the risk of your suspension packing up before the next hit, which means that you have less to work with on each successive hit. rebound is an obvious component in this equation because a faster rebound will reset the suspension before the next hit. what's less obvious is that by slowing down the compression, the suspension doesn't have to travel as far to return for the next hit. there's a risk of clamping down on compression damping too much such that the hits feel harsh. so there's a fine balance.

high speed compression damping can also help with bottom-out resistance on single, sudden, sharp hits. I'm not talking about drops so much, but rather cases where you're hauling and you hit a janky square-edged rock/root. big impact, lots of energy, VERY sudden compression forces. Because the fluid is moving more slowly due to the resistance from the damping circuit, more of the compression energy is transferred to heat.

you're getting to a point, honestly, where the differences get very fine and subtle. the more adjustments you have, the more sensitive you need to be to feel a difference between them. and this is also why telemetry units like the shockwiz exist...to help people make sense of some of this stuff. and custom tuning exists because the max/min options on these adjusters don't always work for everyone, and some folks need/want adjustment options outside of those limits.
 

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Discussion Starter · #10 ·
Um let's go back and explain what does chatter mean to a non-native speaker, please.

yes you are trying to use sag as a way of setting your fork.
Pump some air in (use recommended pressure for your weight) then go ride. Adjust the air pressure accordingly to the effect you want on the ride.
Then come back to compression settings.
The problem is that when I pump some (yes, some, not too much) air in the SAG is suddenly way below 25%. That's the problem.
 

· since 4/10/2009
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Um let's go back and explain what does chatter mean to a non-native speaker, please.
sharp, high-frequency impacts. can be low amplitude stuff (that big tires can be good at absorbing) but can also be higher amplitude stuff that really gives your suspension a workout. like I said earlier, riding speed can absolutely be a factor here. ride slowly enough and it's no big deal. but add speed to the equation and the suspension is constantly working, diving well into its travel and immediately extending.

lots of very long, chattery descents in my area.

The problem is that when I pump some (yes, some, not too much) air in the SAG is suddenly way below 25%. That's the problem.
The absolute number of sag isn't what matters. What really matters is that the spring supports your weight and is responsive to the terrain. It just so happens that for most people, the sag they wind up with is within some range (which might differ from one fork to another). so sag is really only sorta useful to put you into a ballpark. you'll likely need to adjust from there. it's similar to how some say to set up your fork to the weight recommendation and adjust from there. the problem arises when people set sag as though that's the be-all setting. it's not like that. it's just a starting point.

My MRP fork came with a card that gave a range of pressure settings at a given weight depending on how you like it to feel/perform. My fork has a dual air system so I can set positive air spring and negative air spring pressures independently. I've had rockshox in the past, and RS likes to use sag (they even print sag charts on the stanchions). I had a wren fork in the past, also, which was the biggest PITA to set the air springs because you had to count the damn pump strokes. it made fiddling and making small adjustments a royal pain. you had TONS of control, but replicating the same settings was a nightmare.

if you're having problems with fine tuning the pressure in the fork, then that begs the question of what pump you're using. with a good shock pump, you should be able to make some pretty fine adjustments to fork pressure. if you overshoot your goal, that's why there's typically a bleed valve. it's often easier to overshoot the target pressure and then back off with the bleed valve.
 

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Discussion Starter · #12 ·
It's just that I kept reading that when the SAG is too low, you supposedly don't use as much travel as you should. Obviously it's important not to bottom the damn thing out, but I want to have a comfortable ride in terrain too.
 

· since 4/10/2009
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It's just that I kept reading that when the SAG is too low, you supposedly don't use as much travel as you should. Obviously it's important not to bottom the damn thing out, but I want to have a comfortable ride in terrain too.
sortof.

I mean you don't necessarily have to use all your travel all the time. but there's also an element here of whether your bike suits your terrain. If you think the suspension feels pretty good, but there's a lot of travel that you're not using, then the issue probably has less to do with your suspension settings and more to do with the fact that you're overbiked for the terrain you're riding. you can also underbike (though that's a lot less common these days) such that in order to avoid bottoming your suspension, you have to make it so firm that it rides like crap in the other direction. I remember this being super common when I was a noob rider in the 90's and early 2000's. overbiking is a lot more common these days.
 

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Discussion Starter · #14 ·
Yesterday I ended up releasing all air from the fork only to find out it ended up halfway through the travel. It turned out some air managed to get into the leg, somehow. I released some of that by carefully sticking something between the leg and the wiper, but at that point I was like wait a minute, this is not normal, and after some considerations, I decided to dismantle the fork to check whether everything was ok. Apparently it wasn't.
First of all, this is what came out after just 500km (most of which was not ridden in mud or horrible conditions). I mean the bike is pretty much new.
1947015


My old 2011 Epicon had almost clean oil/grease in it after 2000km.
This is really weird.
I immediatelly though how the hell can that much crap get inside on a new fork? WTF?

But then I removed the outer legs and found out the piston in the air chamber was completely stuck solid inside, and I had to hammer it out with a pipe. What the hell?
Fortunately no obvious damage was done, presumably because the piston is plastic. After cleaning everything I slipped it back in and easily pushed it all the way to its place and back, so it's all good.

How the hell can this happen? Could it be due to me bottoming the fork numerous times two days ago when I went to a bike park that is on a pretty steep hill?

Also, can the zero effect of compression be related to the piston being stuck?
 

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Sounds like somebody has been doing the noobie mistake of sticking things in their wiper seals too often to release air and damaged the seals causing crap to get in. Hate to say it but your fork is probably ruined if that much dirt got in, the insides of the stanchions will be scratched to hell.
 

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I have no experience with Suntour but I'm interested to see how this mystery is solved. For my Fox and Manitou forks, when I adjust the compression, I can definitely feel the difference just by pushing on the handlebars.
 

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Probably just sloppy seal tolerances or they dried up sitting on a shelf too long. Suntour's top of the line forks are well built, but they also make cheap low quality forks. I suspect some of their oem forks are cutting corners to save money. Sounds like new dust seals will set you straight. SUntour makes forks for DVO and some others I believe. They do put out reliable good quality forks but to get that level of quality with the ST brand you probably have to buy their aftermarket top tier options.

As far as set up goes, I completely ignore sag. It will be whatever it will be. I like forks set up so I only get full travel on hardest hits which causes many rides to not produce full travel. Forks I've owned with independent HSC have to be compressed fast to feel a different. Like you said, it's not about the impact, it's about how fast the damper shaft moves. Parking lot test with fast sharp compressions should produce a different. I usually like open HSC. If much HSC is needed the spring rate is probably too soft.
 

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Discussion Starter · #19 ·
I'll know more once I receive the damn seals and reassemble the thing back. I'll also completely swap the greasy weirdness inside for proper amount of real oil. What came out of the fork didn't see anywhere near enough.
 

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Not uncommon for forks to come without enough oil. Iv'e seen it with fox and rockshox over the years. I've seen bearings that were essentially dry from the factory too. The amount of slop in the bike industry is kind of frustrating considering the prices we pay. I guess skimping on 10ml of oil for every fork saves enough money at scale? Or there's such poor QC no one is paying attention. Whatever it is, it's all too common .
 
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