Compression and rebound damping

[oldskool]

Some help getting my head around this concept please.

Someone over the weekend said the reason my son keeps coming off so often is because his front rebound is too soft (does this mean too quick?) so the bars kick around in his hands over bumps. Someone else posted on KB that a reason ppl were having trouble on whoops was because the shock was set with not enough rebound damping soooo

So I've made this little model and am requesting some answers from you experts as to what happens when you tweak the different settings. To start with what each setting does in theory and an example of what kind of terrain the adjustment is good for. I'll make animations with all this data once agreement has been made to which explanation for each setting is most accurate.

There are other factors I haven't included such as oil weight, spring ratings, rider weight and ability, and someone even suggested the size of the wheels have a bearing, but lets keep this relatively simple and conceptual to the 4 settings I've included. (*afterburn: I guess spring preload should be included too)

Forgive me for the initial file sizes and for the simple animations but if this works out I'll make them a wee bit more accurate. Maybe once I have enough information to complete them, they'll be useful for future peeps battling with the concept.

Hopefully the animations are self explanatory. The numbers 1,2,3 are there to describe the front and back kick height if required.

[Brian d marge]

For a start ,

95 % probably know enough to be dangerous ( including me)

There are some highly Qualified people on here ,

IMHO

Set up your SAG first
from that find out if you spring rate is correct for the rider

then set everything to middle

Depending on the bike , depends on the adjustment you can make

but for me I like my bike set up with rear bias , and a slower rebound rate so that the front sort of skips across the tops of the whoops ( you ok with the terms high speed low speed comp/rebound ) ?

Hopefully this will set the ball rolling

Stephen

[oldskool]

Set up your SAG first
from that find out if you spring rate is correct for the rider

then set everything to middle

Depending on the bike , depends on the adjustment you can make

but for me I like my bike set up with rear bias , and a slower rebound rate so that the front sort of skips across the tops of the whoops ( you ok with the terms high speed low speed comp/rebound ) ?

Hopefully this will set the ball rolling

Stephen

I think definitions are a good idea.

Please amend where needed:

Slower Rebound rate = Harder (in the screw adjustment settings?)
SAG = Where the bike sits loaded with rider weight?
Rear Bias = Rear compression is softer than Front?

[cheese]

You need to go talk to Danger. Take a box of beer with you and have a chat!

[vifferman]

Ack Shirley, this thread is a good one for ALL bike types, not just off-road.
I'm having some problems setting my bike up - the front is (or will be fine, once the springs and dampers are refettled by CKT) as it has only preload adjustment, but setting up the rear is problematic. Thank goodness I didn't get the next model of shock, which has three-way damping adjustment.
There seems to be a lot of confusion amongst bikers over the terms, with many thinking preload makes the suspension harder or softer, whereas in reality although it may feel like that's what it's doing, as I understand it it's basically adjusting two things: the amount of load it takes to begin to compress the spring, and - to some extent- the ride height (and therefore attitude and handling/steering dynamics of the bike).

The thing that got me confused when tuning the suspension by feel (apart from not testing it on exactly the same piece of road after each adjustment) was that the effects can feel the same. When the rebound damping is too soft, the suspension can rebound too quickly, causing the wheel to feel 'hoppy'. If the rebound damping is too hard, the suspension returns too slowly, which could be interpreted (if you have an uneducated/uncalibrated butt like mine) as making it feel like it's underdamped because it's bouncing off bumps because the damping is binding up the suspension action. If you throw the wrong spring rate into the mix, and lack of springing or too much (as in my case) can make it feel like the damping is all wrong.

A similar thing can happen with compression damping: too little (especially if the suspension is undersprung) and there's not enough resistance on big bumps. Too much, and the suspension is being strangled and can't absorb impacts.

Then there's high-speed and low-speed damping, which for the lay person might be better thought of as damping for big and little bumps (although that's not technically correct).

It's all a bit confusing!

[scott411]

ill let the more educated explian the whole system to you,

but they way i remember what H and S means on rebound damping is, H is full in, so the hole is closed, meaning less oil passes though so more restriction so more rebound damping,

[K6K]

I think definitions are a good idea.

Please amend where needed:

Slower Rebound rate = Harder (in the screw adjustment settings?)
SAG = Where the bike sits loaded with rider weight?
Rear Bias = Rear compression is softer than Front?

Rebound - This stops the suspension 'spring' from springing back after it has been compressed.
Soft = less rebound so the spring will return to its original extention faster. Less rebound can make the bike like a pogo stick
Hard = more rebound so the after the spring has been compressed on a bump the rebound slows the rate of return to the springs original extension. Too much rebound can make the suspension 'pack down' where successive bumps don't allow enough time for the spring to return to its orginal extension.

Compression damping is the opposite of rebound.
Soft = less force to compress the shock or fork - easy to bottom out
Hard = More force to compress the shock or fork - hard to bottom out

In addition you can have high speed and low speed compression damping which is the short sharp bumps versus slower compression (rolling hills maybe?)

SAG setting - This is the difference between the rear wheel off the ground and rider sitting on the bike in full gear. This is adjusted by the tightening or loosening the spring on the rear. It is important to get this right first as this allows the suspension to be in it's optimal alignment at the start. If you have to use all the ajustment in the spring or wind it off completely you need to change springs.

Rear bias - not sure about this one.

[dino3310]

check out some of Robert taylors threads or chat to the man him self.

[Reckless]

Rebound - This stops the suspension 'spring' from springing back after it has been compressed.
Soft = less rebound so the spring will return to its original extension faster. Less rebound can make the bike like a pogo stick
Hard = more rebound so the after the spring has been compressed on a bump the rebound slows the rate of return to the springs original extension. Too much rebound can make the suspension 'pack down' where successive bumps don't allow enough time for the spring to return to its orginal extension.

Compression damping is the opposite of rebound.
Soft = less force to compress the shock or fork - easy to bottom out
Hard = More force to compress the shock or fork - hard to bottom out

In addition you can have high speed and low speed compression damping which is the short sharp bumps versus slower compression (rolling hills maybe?)

SAG setting - This is the difference between the rear wheel off the ground and rider sitting on the bike in full gear. This is adjusted by the tightening or loosening the spring on the rear. It is important to get this right first as this allows the suspension to be in it's optimal alignment at the start. If you have to use all the ajustment in the spring or wind it off completely you need to change springs.

Rear bias - not sure about this one.

Yes yes and yes, what he said!! finally someone who is not turning their rebound to the plus to get it to extend faster. LOL!!!

Set sags first and get springs correct this is most most important I have learned.
Compression: So imagine the clickers closing a hole where the oil passes. With compression u turn to the plus to close the hole and it hardens or slows compression by restricting the oil flow, to the minus and it speeds up compression or makes it faster or softer by flowing more oil through.
The rebound works the same but in effect opposite. You have to turn to the minus to open the hole so the oil passes though faster and lets it rebound faster. Turn it to the plus and it will restrict the hole and the fork will return slower.
Out the sandpit as a general rule I'd run softer compression and faster rebound for the whooops. You want the suspension (both ends) to absorb the whoop but be out and ready to absorb the next one. I have an O ring on my fork so I set the compression so I'm using most of the travel and the rebound so the fork snaps out fast enough to be ready for the next whoop without packing down but not so fast I can feel it chucking me in the air off the top of the whoop. Same with the rear, I reckon my bike is fairly well balanced at the mo, so what I do to the front I usually do to the rear(dunno if this is right though).
On clay you would probably want your compression harder as your going faster and jumping, so your rebound would be slower (to the plus) after landing that jump so the bike is not springing you off the ground again. I found this out by going to Ardmore with Sandpit settings. Flipping thing kept launching ma back into the air after a landing, that only lasted two laps before I came in and changed it.
re bias you don't want the back fighting the front, like the front feels good but the rear is kicking you in the arse. Generally the bike should react evenly in the pits and out on the trail.

Hopefully all Dangers phone hours to me have paid off and I at least understand the basics and he's not going to log on and make me look like a big mouth know it all! LOL!!! I have Robert Taylors suspension write up printed and bound as part of my manual I take out with me as well.
I just wish it would make me faster but age is a devil.

Now getting your son to understand and explain this is another matter. LOL!! I know ! 10 years karting with my boy, everything feels good even when you lie about making any changes LOL!!!!

[Brian d marge]

Are you able to download torrent?

I have 2 files which are road racing ones but are videos from a suspension course

Explains everything ,,,,

Ill find them and post em up just in case

Stephen

[Robert Taylor]

We have a motocross suspension tuning tips manual that covers almost every conceivable question. If anyone wants a copy please request by e-mail only to robert@crownkiwi.co.nz Please request prior to next Wednesday Sept 9 as I will be away in Sweden until the 21st September.

[oldskool]

We have a motocross suspension tuning tips manual that covers almost every conceivable question. If anyone wants a copy please request by e-mail only to robert@crownkiwi.co.nz Please request prior to next Wednesday Sept 9 as I will be away in Sweden until the 21st September.

Cool! Hate to ask but it has to be done..."Is this a freebie?"

[Ktmboy]

I have my rebound clicked a few to the + side for the sandy whoops. In laymans terms it stops the arse end coming back up too fast and giving me sore butt cheeks

That is as long as the sagg etc is set up ok.

That is the suspension sag not the arse sag!!

[Robert Taylor]

Cool! Hate to ask but it has to be done..."Is this a freebie?"

YES, rare as it seems.

[oldskool]

We have a motocross suspension tuning tips manual that covers almost every conceivable question. If anyone wants a copy please request by e-mail only to robert@crownkiwi.co.nz Please request prior to next Wednesday Sept 9 as I will be away in Sweden until the 21st September.

Thanks Dr Bob!!
Theres a lot of info in those files..almost 11Mb worth! I'll have a good read of it and see if I can translate some of it into rules for my programmer to wrestle with.