Skipping - suspension set up question

DirtyMike · Apr 19, 2009

dhkid said:
if you think about what he said for setting up rebound, setting it by compressing then trying your best to make your body a dead weight, you are going to need very very fast or close to no rebound damping to get it to oscillate.

he does say there that most people run their rebound way to fast, which i dont agree with at all. most people have a fear of running fast rebound, which is just stupid.

This is funny, Most bikes that come in the shop I find are way under damped ont eh compression, and WAY over damped for rebound.

I have always looked at rebound like this, its what is holding your tire on teh terrain, ifs its too slow, your going to load up, and basically shorten your travel, lower your effective sag, and change the Geo on your bike through the Stutter, too fast, and youll be topping out, and bucking.

I keep mine pretty fast, I slow it down just enough to keep it from bucking, stick to the terrain like mad...without limiting the ride.

Steve M · Apr 19, 2009

top_dog said:
But the bit about the suspension not coming back past the sag point and not over oscillating does sound pretty right. You'd want the bike to return to a steady state ASAP.

Unfortunately I'm somewhat partial to the Chris porter way of thinking...

500psi

No it doesn't sound right, and if you run/like BOS stuff, you don't exactly agree with his "who cares about compression because we got SLOW REBOUND BABY!" ideas, since BOS obviously do care a LOT about compression damping and don't slow the rebound down to such silly speeds. If the suspension doesn't extend past the sag point (what is "over oscillating"? Either something oscillates or it doesn't), it's AT BEST critically damped, and much more likely to be overdamped, both in a technical and a layman's sense. And that's making the gross simplification of a rigid body mass, which a rider isn't.

top_dog · Apr 19, 2009

Socket said:
No it doesn't sound right, and if you run/like BOS stuff, you don't exactly agree with his "who cares about compression because we got SLOW REBOUND BABY!" ideas, since BOS obviously do care a LOT about compression damping and don't slow the rebound down to such silly speeds. If the suspension doesn't extend past the sag point (what is "over oscillating"? Either something oscillates or it doesn't), it's AT BEST critically damped, and much more likely to be overdamped, both in a technical and a layman's sense. And that's making the gross simplification of a rigid body mass, which a rider isn't.

Forgot I have to speak like a bloody mechanics lecturer with you around

oster_oops:

The 'who cares about compression, slow rebound' is wrong clearly, but I was talking more about the 'over oscillating' which I would define (in this context) as oscillating past the neutral point or under damped in proper speak.

I believe Porter is right in saying the correct amount of rebound damping is when it is critically damped, which even the most anti-Porter (ie. you) must agree with.

Steve M · Apr 19, 2009

top_dog said:
Forgot I have to speak like a bloody mechanics lecturer with you aroundoster_oops:

The 'who cares about compression, slow rebound' is wrong clearly, but I was talking more about the 'over oscillating' which I would define (in this context) as oscillating past the neutral point or under damped in proper speak.

I believe Porter is right in saying the correct amount of rebound damping is when it is critically damped, which even the most anti-Porter (ie. you) must agree with.

As I said, no, I don't agree with that. Why "must" I? Besides the fact that critical damping comparisons are irrelevant and inaccurate because of the fact that the rider isn't rigid, nor even a nonlinear spring/damper system of its own accord, a mathematically underdamped setup isn't necessarily unstable anyway, due in no small part to the existence of compression damping, as well as the feedback loop that is the rider.

buckoW · Apr 20, 2009

Muttely said:
so what settings are we talking to get a nice hard setup on a DHX?

You can't get a stock DHX anywhere near to what I was talking about.

buckoW · Apr 20, 2009

DirtyMike said:
Sounds a little freeridish on your setup, but thats not neccessarily a bad thing. Alot fo that really has to do with your riding style, on a wide open full blown haul ass DH coarse, you probably going to want a bit more sag, for when you find those little holes you want to keep your wheels on the ground, instead of skipping of them from topping out.

If you sat on my bike you would think it is as far from a "freeride" setup as possible. My bike feels "dead" in the parking lot. I ride "wide open full blown haul ass DH coarse" all the time. I live in the Alps and build trails and tracks for a living. I said AROUND 30% meaning that I change it for what I am riding. I may hit a stunt or 2 and throw a table here and there but what I ride mainly is as downhill as it gets.

Last year I built a trail at a resort with nothing but g-out berms next to a very steep and tech trail (that I also built) with suspension setup in mind during the build. The steep trail requires lower levels of compression to get the grip and the g-out trail needs as much compression as you can find. I am lucky to have a suspension sponsor (Suspension Center) and a couple different tunes on a couple different shocks for different tracks. The kind of setup I am talking about is definitely not a freeride setup or anywhere close to a stock setup.

I don't want my bike to go into every little hole. I understand what you mean about your setup. I rode similar setups for years. My brother hates the feel of my bike but then one day his bike wasn't running and I took out my 6" bike and he rode my DH bike. He hated it first run and by the end of the day he said it was cheating to have so much traction and stability. It is a rougher ride at slow speeds but when you open it up the suspension begs you to go faster.

buckoW · Apr 20, 2009

Whoops said:
wheeeeeeeeeeeee.

So glossing over the finer points of suspension harmonics, Q factors and attenuation rates....

As far as the general point goes... I think most people get what 'over sprung and over damped' means.... and even if not will get what I mean by a suspension setup that tracks or skips the ground.

That given... the question is - - does it require a level of confidence/skill/particular riding style to benefit from the skipping stone approach compared to the tyre-on-the-dirt mode? Based on the above comments, I have a feeling it does, and I don't. I think it takes a little time to get comfortable on the new setup but if there is too much compression then there is too much.

Will have a play on the weekend, but I have a feeling I'm probably going to stick to the old setup. Go into it with an open mind and give it a chance. It will take some time to get used to it.

(counter point - perhaps there are a number of setup's to induce skipping... some of which are catastrophically uncontrollable, some of which are [not withstanding a loss of traction] controllable enough... guess I'll find out.)

Hey Whoops

What shock are you going to try and run more compression?

It all depends on the speeds. Lots of compression will "skip" at slower speeds but once you get it up to speed the skipping stops and "the tyre-on-the-dirt mode" starts. It is all about how hard you are pushing and setting the bike up accordingly. It is all about understanding the compromises and limiting them as much as possible.

Basically, unless you have a speed sensitive setup you are setting up your suspension for certain speeds and impacts. What if you start going faster on 20% of the track than your preferred setup was tuned for? Then you are making a compromise on 20% of the track for the other 80% that feels good. Going further, what if you are really pushing your bike hard on 50% of the track (like g-outs so bad you are dragging both heels on the ground) and the other 50% is super steep and technical where you can't finesse the ground enough? Do you run more or less compression? Do you run high rollers or spikes? It is all about the making as little a compromise as possible.

Until you do back to back runs on differently tuned shocks it is hard to understand how a "hard" setup could be good but the fact that there is no spiking and it slows you down earlier in the travel lets you charge harder, IMO.

nowlan · Apr 20, 2009

I dunno, over the years my tire pressure increases and so does my suspension set up. Less Rebound in my rear travel, more compression in my fork. I personally found that it takes a certain level of skill to ride with a super stiff suspension set up though, but it for sure is alot faster IMO.

Muttely · Apr 20, 2009

right, so my 40's are running maximum preload, and a ****load of compression, and my DHX air chamber is at minimum size, with 200Psi in the piggy, and my stadnard 350 spring on... all feels nice and firm! will be testing it all this weeek in the evenings, though first thing i notice is it holds its geo better riding around the streets, sits up rather than sagging strupidly, its porbably sagging 25% on the rear now? and the same up front.

norbar · Apr 20, 2009

nowlan said:
I dunno, over the years my tire pressure increases and so does my suspension set up. Less Rebound in my rear travel, more compression in my fork. I personally found that it takes a certain level of skill to ride with a super stiff suspension set up though, but it for sure is alot faster IMO.

Your Tire pressure increases over the years? :shocked:

I don't see a real benefit here unless you run some superlight tires that float on lower pressures.

nowlan · Apr 20, 2009

norbar said:
Your Tire pressure increases over the years? I don't see a real benefit here unless you run some superlight tires that float on lower pressures.

Ahh its generally easier to ride with less tire pressure, say 23 psi then around 30psi. U roll alot faster and let loose easier, i dunno maybye im doing it all wrong. And to be honest I dont even really understand your reply.
I was just trying to say that " I " found riding an overall tighter set up takes a bit of getting used to.

norbar · Apr 20, 2009

nowlan said:
Ahh its generally easier to ride with less tire pressure, say 23 psi then around 30psi. U roll alot faster and let loose easier, i dunno maybye im doing it all wrong. And to be honest I dont even really understand your reply.
I was just trying to say that " I " found riding an overall tighter set up takes a bit of getting used to.

It just sounded like you put in the same bucket higher tire pressure and higher damping levels on your bike. If you slam your bike on with to low compression your bike may get unstable but if you slam your bike (ON GOOD TIRES) with low pressure I don't see any reason it would. From what I see actualy most people run too much tire pressure.
Also you roll faster on lower pressure? And let loose easier? It's the other way around

Steve M · Apr 20, 2009

norbar said:
It just sounded like you put in the same bucket higher tire pressure and higher damping levels on your bike. If you slam your bike on with to low compression your bike may get unstable but if you slam your bike (ON GOOD TIRES) with low pressure I don't see any reason it would. From what I see actualy most people run too much tire pressure.
Also you roll faster on lower pressure? And let loose easier? It's the other way around

I've found over the years that I've had to run the tyres firmer and firmer too. The harder you push them in corners (and the heavier you are), the more pressure you need to keep them on the rim (esp if you run tubeless).

nowlan · Apr 20, 2009

norbar said:
It just sounded like you put in the same bucket higher tire pressure and higher damping levels on your bike. If you slam your bike on with to low compression your bike may get unstable but if you slam your bike (ON GOOD TIRES) with low pressure I don't see any reason it would. From what I see actualy most people run too much tire pressure.
Also you roll faster on lower pressure? And let loose easier? It's the other way around

We are on the same page I believe.

ChrisKring · Apr 20, 2009

Socket said:
I've found over the years that I've had to run the tyres firmer and firmer too. The harder you push them in corners (and the heavier you are), the more pressure you need to keep them on the rim (esp if you run tubeless).

And to keep the knobs from squirming when you are railing a corner.

DirtyMike · Apr 20, 2009

Socket said:
I've found over the years that I've had to run the tyres firmer and firmer too. The harder you push them in corners (and the heavier you are), the more pressure you need to keep them on the rim (esp if you run tubeless).

ChrisKring said:
And to keep the knobs from squirming when you are railing a corner.

To add on the Tire pressure, I have also come to realize over the years, that no matter what The back end is going to be squirrly in the loose. So lower your rolling resistance and go for it, least in the back that is. For the front, I run around 30 ish, depending on the trails, and what I intend to do.

buckoW · Apr 21, 2009

I too have had to run higher pressures in the last couple of years to resist rolling over in the corners.

Avy Rider · Apr 21, 2009

The faster a rider becomes, the less forgiving his bike set up becomes. That's the price you pay for being on the edge but the rewards can be worth the aches and pains afterwards.

I can imagine that many of the guys who have claimed that Avalanche shocks are "way over damped" now understand why that is. They were valved to be ridden much faster than the average human being is willing to go. That's why Craig insists that you are very honest about your riding abilities when you are having it set up.

William42 · Apr 21, 2009

yah, I'm running 75 PSI on DP maxxis casings cause I corner so hard.

Just kidding, I was just trying to be cool, but I've noticed I've been bumping up the rear little by little lately, I used to be at 32, now I've made it up to 35 with no definite end in site.

Kanye West · Apr 21, 2009

Avy Rider said:
The faster a rider becomes, the less forgiving his bike set up becomes. That's the price you pay for being on the edge but the rewards can be worth the aches and pains afterwards.

I can imagine that many of the guys who have claimed that Avalanche shocks are "way over damped" now understand why that is. They were valved to be ridden much faster than the average human being is willing to go. That's why Craig insists that you are very honest about your riding abilities when you are having it set up.

That I disagree with. Even going mach speeds I couldn't get his valving "for my weight" to feel acceptable and not spikey and unpredictable. Unfortunate because those are some of the best shocks made.

Kanye West · Apr 21, 2009

If the rebound is critically damped to not oscillate above the sag point, then there HAS to be an appropriate/matching amount of compression damping, or you will be bottoming out constantly. One of the tuners (BOS or Mojo) had the theory that for every compression setting there is a correct rebound setting. I seem to remember that not sitting well with some people, but I think they're exactly dead on with that.

Basically, if the rebound is critically damped, then the compression needs to be as well. That setup has it's purposes, but it's not a be-all-end-all setting. I think of that as a high speed tune, kind of like a desert tune vs. a woods tune for a dirt bike (I think I've used that analogy on here before, but it really seems to sum up the suspension setups I see for tight stuff vs. wide open stuff in the DH world).

I find it funny how nobody is ever really looking for "DH plush" as much as "DH stable" these days, and the bike setups are slowly turning into huck settings, while the hucksters are looking for things to be more plush and more progressive (which I think is somewhat dangerous for that purpose with the massive accumulated rebounding forces on bottoming). It makes sense though, modern day DH shredders are really just bouncing off the little stuff and staying over it and hucking their way down DH courses, meaning gapping stuff up, prejumping and stepping down features, and generally only concerning themselves with the biggest and most upsetting features on a course.

Muttely · Apr 21, 2009

OH MY GOD.

went up the local on my session, running these new hard suspension settings, and jesus ive never been so fast through the entire track, cornering was faster, and the final very rough section, i just flew down, probably 15 seconds faster than with slurpy settings. and i mean the 15, i almost cried.

ChrisKring · Apr 21, 2009

It was Mojo that stated that compression and rebound damping needed to be linked and was all on one adjustment. While somewhat correct for the reasons stated above, a bicycle rider puts a lot of rider induced loads into the suspension and therefore it may be desireable to keep the adjustments seperate. The biggest reason I can think of to limit suspension adjustment is to keep the hack from "tuning" a really poor setup and thinking it was the fault of the equipment.

norbar · Apr 21, 2009

Socket said:
I've found over the years that I've had to run the tyres firmer and firmer too. The harder you push them in corners (and the heavier you are), the more pressure you need to keep them on the rim (esp if you run tubeless).

Hmm I may not yet be on that level but I think it also depends heavily on the tires. Now I run 1.3kg tires (each) but I think the main reason for my tires keeping with under 20psi pressures is my ridiculously low weight (well now it's better at 70kg but still I'm far from a beefcake). I wonder If I will change when I step up my game or will I keep it as I don't even feel that much float when I push my light XC bike with on lower pressure.

BTW. With all the talk about mojo. They did a great job with my DHX Air and I haven't touched it since.

Kanye West · Apr 21, 2009

When the bike is weighted with the rider (and wheel on the ground, say from landing a drop or going through a g-out) you probably only want it to return to the sag point on rebound and not come back with enough speed that it goes above that and provides one more thing for the rider to compensate for. No numerical analysis behind that one really....

Steve M · Apr 21, 2009

The whole critical damping idea is a bit silly anyway, bikes don't just have the sprung mass of the rider to deal with, there's also that of the wheel when the wheel isn't in constant contact with the ground, which is obviously far less than that of the rider... and the fact that most damping settings (with the exception of the DHX's rebound, at least up to 2007) aren't linear anyway. I am of the opinion that theorising about "critical" rebound damping doesn't actually stand to provide any benefit to anyone. It's especially worth noting that rebound damping is usually about 3x the rate of the compression damping, meaning you typically wouldn't have both directions anything like critically damped, or even the whole range in one direction critically damped. There is a reason why most high-performance dampers have more or less quadrilinear damper rates (bilinear in both compression and rebound), and it's because compression and rebound strokes require different things for maximum performance.

Kanye West · Apr 21, 2009

Critical damping is necessary, but it sounds to me like you're thinking of OVERdamping. There is a quantifiable difference.

Kanye West · Apr 21, 2009

Whoops said:
Nope (and I do know the difference)... but I had thinking of the zero travel (unsagged) position as being where the fork should return to (as-close-to-critically-as-i-could-judge) rather than the sag point, which makes more sense and probably means (if all the posts above are right) that I had it under-damped.

Again - will try out this weekend and see how fast I am (a.k.a. how many crashes I don't have).

Sure, if the wheel is unweighted or off the ground. If the wheel is weighted by the rider and on the ground, the damper should be bleeding off momentum on the rebound stroke that would otherwise let it go above the sag point, and cause more oscillating (in a perfect setup with no other variables at all).

It's actually very easy to set up most modern shocks to be fast up to the sag point and slow above, or vice versa. I have a couple valved cleverly utilizing that idea and they track VERY nicely skimming over snotty stuff that would otherwise buck me off the bike.

ChrisKring · Apr 21, 2009

Whoops said:
I think I get it now. Just want a data acquisition kit (or just time to get out and ride the damn bike).

We just need to give DW or Profro a e-beatdown until they give up their sources of the linear transducers that they are using on the dataq systems.

Or you can buy this (the system that PUSH uses):

http://www.racetech.com/page.aspx?id=37&menuid=96

http://www.racetech.com/shockclock/Testing_SC_PDA.htm

TESTING with the SHOCKCLOCK PDA
<testing with the shockclock.doc> 2-21-05

Kicking - One of the most common symptoms of poor rear suspension is "Kicking". There are two major reasons for kicking (and it's not what most people think). Most people head for the Rebound Adjuster and slow the rebound down. They think the suspension is compressing and then recoiling uncontrollably. The truth is that 99% of the time Kicking is caused by either:

The suspension is TOO SOFT. The suspension runs out of travel, still has energy, loads the frame and deflects off the bump. This happens on the COMPRESSION SIDE of the bump, not the rebound.

The suspension is TOO STIFF. It doesn't use enough of the travel because it has too much resistance to moving (damping most of the time but also could be spring) and it deflects off the bump. This also happens on the COMPRESSION SIDE of the bump.
About 1% of the time kicking is caused by TOO MUCH Rebound Damping. The suspension "packs down" because there is not enough time between bumps for it to return to it's normal ride height. This means the spring is compressed and the next bump has to overcome this initial force before it compresses. This is a minor "kick" compared to the previous 2 causes.
The problems with test riding:

1. The first problem with human testers is we typically find what we are looking for. If we believe the problem will be fixed by whatever change has been made we will typically feel that it's better, whether it actually is or not. This is one of the reasons why people are still cranking in rebound adjusters.
Oh, by the way, when does anyone ever crank the rebound back out? My experience, never. After all why would they want it to kick again? We commonly find rebound adjusters set at 2 or 3 clicks out from all the way in. It kicked again and they "fixed it" again by slowing down the rebound some more.

If you really want to check this one go out and ride your bike with the rebound adjuster backed out. Obviously, you need to ride with caution. What you will find is that the bike is plusher and the traction might be way better (especially if you're riding on hard-packed) and the bike feels a bit "loose". BUT it doesn't kick! Hmmmmmmm.

2. As far as bottoming is concerned we have found that perhaps 50% of riders can tell if the front end is bottoming but 95% CANNOT tell if the rear is bottoming.

Analysis
From the Main Menu select "View". The first screen is the Bottoming Tab. This displays Soft and Hard Bottoms. The standard setting for Soft and Hard Bottoms is 90 and 95% of the Maximum Available Travel. This is good most of the time. The idea is; Soft Bottoms are OK but you're getting close, and Hard Bottoms are not OK.

The Bottoming Tab will display the number of Soft and Hard Bottoms that have occurred during the entire recording.

The conclusions are simple. If it's kicking and you have Hard Bottoms make it stiffer. If it's kicking and you don't have Hard Bottoms, make it softer.

If you want a more advanced analysis use the "Peaks" feature. The places we have found that have many problems are either where we are using the most travel or where the highest shaft velocities are occuring.

If you want to view the top 10 greatest uses of travel, select the "Peaks" button. It will display the Travel Peaks in decending order, showing the amount of travel used and the time in the recording when it occurred. If you want to see whether it is high speed or low speed, toggle the "joy stick" on the PDA up. This will display the Velocity graph for the same time frame. For dirt bikes you can consider anything over about 0.5 M/s as high speed.

To change back to the Travel graph, toggle the joy stick down.

To see the top 10 highest velocities select the "Velocity" Tab. If you want to see the Travel View for this time frame, Toggle the joy stick up. You will notice that many times the greatest velocities do not occur at the same places the maximum Travel is used (though sometimes they do).

Note on a common misconception:
Many people think the suspension should bottom once per lap. Where did that come from? Think of this; your bike is setup perfectly, no bottoming, great balance, good feedback, good traction, good feeling of control, etc. and you go to a track that doesn't have big jumps or perhaps is pretty smooth. What are you suppose to do, make everything so soft you bottom once a lap? You'll find yourself riding a mush bucket that's hard to control.

By the way, you might want the suspension to bottom, maybe even more than once a lap. You may find the compromise that handles the biggest stuff is just too harsh on the rest of the track and the trade-off isn't worth it. Properly setup suspension is still a compromise. Gold Valves satisfy a very wide range of conditions, but even they are a compromise.

If you are not using all the travel you can make it softer. This doesn't mean you have to make it softer. Keep in mind that just because your suspension isn't bottoming it doesn't mean it is the best it can be. Remember, "The best you've ridden is the best you know."

Stay Tuned,
Paul Thede

Steve M · Apr 22, 2009

Hacktastic said:
Critical damping is necessary, but it sounds to me like you're thinking of OVERdamping. There is a quantifiable difference.

Who says it's necessary? What condition are you actually basing that on? And exactly what issue is caused by mathematically underdamped systems (in rebound)? I know what the difference between critical damping and overdamping is, in fact I spent nearly all of last year writing a thesis on the interaction between bicycle suspension and rider.

Critical damping means close to nothing in the bike sense. It's a mathematical ideal for dealing with singular step inputs to a rigid body, single degree of freedom system. It does NOT take into account repeated or random inputs, or any kind of desired response other than returning to static as fast as possible. And that's in addition to the fact that the rider isn't rigid, your damper isn't linear in either direction, your compression isn't the same as your rebound, etc etc ad infinitum. It's just an ignorant argument.

jsk14 · Apr 26, 2009

I'm just speaking out of observation, I'm not a racer, but i like to ride fast as possible, and when i had my lyrik on, i definitely benefited from oversprung(23%)/overdamped set-up. I ran about 50% low-speed damping, and almost 100% highspeed damping. Even though you lose alot of sensitivity, when you go into a rockgarden, or a steep section and you hit a rock abruptly you will be thankful for the damping preventing you from going OTB.
Now, i run 28% sag on my totem which i consider to be proper, but i blew through the travel on it by just pushing it down on it in the parking lot. After a dozen runs. I put the compression max for low/high speed, and it definitely ride better. I would go over the bar alot with low compression, and now i don't dive doing steep section or g-out as much.
It's all preference, and you have to balance brake dive/ sensitivity out. At the end of the day, its not about how it feels in the parking lot. I use all of my travel all the time, but it's never harsh.

Skipping - suspension set up question

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