clarify damper comp/ext

  • Thread starter esoxhntr
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esoxhntr

1,291
Canada
ontario
i've been going under the assumption that:

higher compression values = more difficult to compress the shock
lower compression values = easier to compress the shock

higher extension values = more difficult to extended the shock
lower extension values = easier to extend the shock

so, if i wanted to maximize the amount of weight transfer to the front during braking i would use a combo of low front compression and low rear extension.

on the flipside, if i wanted less weight to rear on accell: stiffer front extension (higher front ext value) & stiffer rear compression (higher rear comp value).

am i correct in my assumptions? i've come across posts that seem to suggest otherwise when it comes to extension. ie. a higher value allows for "more" extension.
 
Your all good except you want to minimize the rate of weight transfer to the front under braking not maximize it. You also want to reduce body roll, not maximize it, as soft front comp and soft rear exp will do under braking.
 
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thanks again.

off topic but,

perhaps maximize was not the right word. however, i would argue that there are instances where you would want to increase transfer to front on decel: the vehicle understeers on corner entry. taking the weight off the rear can help rotate the vehicle. body roll can be mitigated with sway bars. of course, driving style depends on this.
 
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esoxhntr
thanks again.

off topic but,

perhaps maximize was not the right word. however, i would argue that there are instances where you would want to increase transfer to front on decel: the vehicle understeers on corner entry. taking the weight off the rear can help rotate the vehicle. try it on the trucks ;). body roll can be mitigated with sway bars. of course, driving style depends on this.
Click to expand...

I like the play on words "manage" and would consider that more of reducing the rate that the weight leaves the rear. lol :P trucks are built to be drivable with/without a load. The rear springs/dampeners are set up for that, but when taking the truck around a track unloaded if you want good times you need set up the suspension for it.

There are many factors to consider, it's always a give and take world of compromises.
 
When it comes to dampers I always try to think of them as working against the springs. So the stronger (higher value) the Extention or Compression Dampers the more countered the springs will be.

So...
If you want the car to "nose down" more in a decceleration then you would lessen the Compression Dampers (ie the nose is more inclined to compress). If you wanted the nose to stay down longer you would lessen the Extension Dampers so the nose doesn't rebound as fast.

Am I getting this right? It seems to work good on my tunes.

As an example:
I'm tuning my Yellowbird for Trial Mtn and I'm having a problem with the springs being too weak in the front, so I up the SR from 6.9 to 9. Viola! I can now start to trail break into corners without all the weight unloading from my back tyres. But now when I enter a rear wheel drift and counter stear to control it the front outside spring retaliates and off I go into a spin. So to counter that I up my Extension Dampers from 5 to 7 and my best lap time drops by over a second. Now to test if I need to up the Compression to see if it needs to be raised for a better balance.
 
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Don't confuse me Ronald. :D

You need to specify which Comp/Ext dampers you are talking about (Front or Rear)

I am going to assume you are talking Front Extension, raising from 5 to 7 makes the front extension dampers more resistant to 'extending'. When you step on the throttle, what happens? Weight gets shifted to the rear. By making it more difficult for the front to extend, you are keeping more weight on the front longer - resisting the natural tendency of the car to shift weight rearwards on accelleration. The result? Your front all of a sudden has more grip and you dont spin.

Part of to is too is your approach..perhaps not a problem just a different way of arriving at a solution is that you used spring rates in the front to combat the rear gettting to light on braking. Whereas I would have used the dampers.. stiffening the front compression and/or stiffening the rear extension. I am not sure which is right, or even if there is a right vs wrong.. but suspension tuning is all about balancing and when you change one thing, you affect another.
 
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Sorry, yes, I did mean the front Dampers in my example above.

esoxhntr
When you step on the throttle, what happens? Weight gets shifted to the rear. By making it more difficult for the front to extend, you are keeping more weight on the front longer - resisting the natural tendency of the car to shift weight rearwards on accelleration. The result? Your front all of a sudden has more grip and you dont spin.
Click to expand...

I have always thought about it like this: If I want less weight shift during decceleration then I strengthen the front. If I want less weight shift during acceleration then I strengthen the rear.

It never occurred to me that I could I could have less weight shift during acceleration by strengthing my front Extension Dampers. Man have I got a lot to learn.

Thank you exoxhntr and GrimmSinn for the help.
 
If you think of the car as a teeter totter maybe it makes it easier to visualize. excuse the crudeness of my drawings :D

fe............re
-----------
fc....^......rc

the dots are there just for spacing

In my mind the front compression setting has a relationship with the rear extension and the front extension with rear compression as opposed to front comp & front ext and rear comp & rear ext respectively.

I have always thought about it like this: If I want less weight shift during decceleration then I strengthen the front. If I want less weight shift during acceleration then I strengthen the rear.
Click to expand...

so we can see the above is partly true. by increasing the front compression on decel and rear compression on accel you achieve your results. however, it's only half the truth. you can use the opposite ends extension too.
 
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^^ Ahhh, that makes perfect sense. I'm adding that one to my Drivers Toolbox.

To continue the example I gave earlier... Because I increased my Extension Damper in the front I also increased the front Compression Damper for less imbalance between the two. But taking your paradigm into play I see that I also need to increase my rear Compression Damper.
Springs were 6.9/10.0, now at 9/10.
Comp were 5/5, now 7/5
Ext were 5/5, then, 6/5, now 6/6.
Is that about right?
 
That's my understanding also. When the weight shifts there is body roll, as the front dives while braking the rear is raised, while the opposite occurs when accelerating. Adjusting the dampeners front comp/ rear exp or front exp / rear comp is working on the forces applied on both ends at that given point (accell/decell) instead of one side at a time.
 
I see that I also need to increase my rear Compression Damper.
Click to expand...

you may or may not. take the car out for a spin. :D

i don't think it's a 1:1 relationship.. ie whatever you do to front ext you must do to rear comp. if you achieved the desired results then you achieved them.

i know a rule of thumb is to change the setting on the end that is affected first. ie. if you're oversteering, change the rear. if you're understeering change the front. if that's not enough or it affects driveability in other situtations negatively, you also have the other end to adjust.
 
My rule of thumb for damper tuning is that for whatever values you feel necessary, keep the front and rear extension value the same. I do this because it equalizes the speed of weight shift which makes handling predictable, having them offset produces a bipolar car going into corners. Adjusting the compression dampers to separate values can have negative effects also but primarily tend to be most noticeable on cold tires, once heated, having a front spring with lower compression than rear tends to equalize on handling.
 
^^ Excellent explanations.

Now another question. I hope this isn't hijacking the thread, but GrimmSinn you mentioned frequence. Could you explain what you ment by that? Is it the same as what Dr Beckman talks about in his "Physics of racing"? I'm trying to understand driving and tuning from this paradigm but I don't understand it well enough.

In my Fireblade because the front and rear have equal weight and almost identical suspension settings the front and rear have the same frequency, right? But in my Yellowbird because the rear is so light compared to the front and the suspension settings are so desperate the front and back have vastly different frequencies, right?

I have alot of questions about frequency. Just like "mediation" once I understand the word from a drivers definition it takes on whole new meanings and connects to everything else I know about driving.
 
I like to do my best to balance the suspension mathematically, then use that as a starting ground to tune the suspension according to feel. I never like starting with the default settings as much of it appears to be relatively generic and certainly not optimum. That's just me and how I like to tune, however tuning methods are very subjective.
 
budious
My rule of thumb for damper tuning is that for whatever values you feel necessary, keep the front and rear extension value the same. I do this because it equalizes the speed of weight shift which makes handling predictable, having them offset produces a bipolar car going into corners. Adjusting the compression dampers to separate values can have negative effects also but primarily tend to be most noticeable on cold tires, once heated, having a front spring with lower compression than rear tends to equalize on handling.
Click to expand...

I will have to disagree with you. During weight transfer to the front (decel), the front extension plays NO or extremely limited role (bumps). During weight transfer to the rear (accel), the rear extension plays NO or extremely limited role (bumps). Therefore, having different front/rear extension values should not affect how a car behaves on corner entry or exit.

The only time I can see vastly different extension/compression settings between front and rear upsetting the vehicle is when the dampers are doing their other job, handling a bumpy track.

Just my opinion. :)
 
Ronald6
^^ Excellent explanations.

Now another question. I hope this isn't hijacking the thread, but GrimmSinn you mentioned frequence. Could you explain what you ment by that? Is it the same as what Dr Beckman talks about in his "Physics of racing"? I'm trying to understand driving and tuning from this paradigm but I don't understand it well enough.

In my Fireblade because the front and rear have equal weight and almost identical suspension settings the front and rear have the same frequency, right? But in my Yellowbird because the rear is so light compared to the front and the suspension settings are so desperate the front and back have vastly different frequencies, right?

I have alot of questions about frequency. Just like "mediation" once I understand the word from a drivers definition it takes on whole new meanings and connects to everything else I know about driving.
Click to expand...

I'm referring to the oscillation frequency of the springs based on spring rate/wheel rate and sprung weight.
 
budious
My rule of thumb for damper tuning is that for whatever values you feel necessary, keep the front and rear extension value the same.
Click to expand...

Because they're working against the the springs, shouldn't the Dampers be balanced against the spring rate? In my Yellowbird with its vastly different spring values shouldn't the Dampers also be different?
 
I'm my experience it's not important to mirror settings f/r. I would however avoid a lower expansion setting over compression on the same dampener though as that will induce bouncyness at times. Under accell it's mainly front exp and rear comp at work. Under braking front comp and rear expan.

Think of it like this

When braking the nose dives so your compressing the dampener. Increasing the compression setting increase the dampeners resistance to that compression or "nose dive" @ the same time while braking the rear end raises up or the rear dampener expands. Increasing the rear expansion setting increases the rear dampeners resistance to expansion.
 
Ronald6
Ok. Nevermind then.
Click to expand...

NP

Think of it like this the stiffer the spring, the higher the frequency, race cars are set up with a frequency around 2.2 any higher is considered too stiff. Sports cars that are meant to put around town are usually around 1.5 to 2.0 while economic boxes are around 1.3.

After dropping the weight and lowering the ride height I calculate the frequency of the springs to insure I get them stiff but not overdone or simply put too stiff. After that I can tune the dampeners according to the weight transfer under various load conditions. Using the sway bars to manage weight transfer in the corners or lateral weight transfer. I tune the camber/ toe then based on how I've manipulated the weight transfer under load conditions.

This is to get my starting point to tune according to how the car handles with what I consider a "balanced" suspension.
 
Ok, I get that (Two posts ago).But take the spring values into account: if the springs on the back are much stronger than the front then, not taking the dampers into account, the decel shift will be faster than an accel shift. Right?

When I accelerate in my Yellowbird the back end has stiffer springs so it resists the weight being placed on it. It will respond with stronger force in rebound because it was able to take in more energy. To compensate for that extra energy shouldn't the Dampers be stronger?

I always go back to this example. An old car with bad shocks. You press down on it and it continues to go up and down, "ee er ee er ee er." We've all heard it. The stronger the shocks the more force/weight that can be applied to them. When you do place that force on them you will need more counter force (Dampers) to halt the continuous motion.

I was trained by truck drivers and road engineers, not mechanics.
 
GrimSinn
After dropping the weight and lowering the ride height I calculate the frequency of the springs to insure I get them stiff but not overdone or simply put too stiff. After that I can tune the dampeners according to the weight transfer under various load conditions. Using the sway bars to manage weight transfer in the corners or lateral weight transfer. I tune the camber/ toe then based on how I've manipulated the weight transfer under load conditions.
Click to expand...

So Dampers are more for weight shifts and not to counter the "continuous motion" I described?

But more weight equals stronger springs. I'm confusing myself at this point.

Ok, stronger Dampers for load shift not for spring rate, even though spring rate is determined by weight. Got it.

To quote Bill Cosby, "Riiiight."
 
You guys are basically on the right track, but I thought I'd try to help with a basic overview.

The purpose of dampers are to dampen the coil and recoil of the springs, so that the car doesnt repeatedly bounce on the springs after the are initially compressed in a bump or turn or whatever.

See if this helps you to visualize things:

First imagine the wheelaxle(s) directly coupled to the cars frame without the shock absorbers, like a go-kart or child's wagon. Every bump in the road would set the car flying in a different direction, right?

So the obvious solution is to allow the wheel some travel so the chassis itself can remain as level as possible.

So we accomplish this using some sort of spring. For simplicity's sake, lets imagine the car as a box with each of its corners set upon a spring. Drop a weight in the box and what happens? The spring(s) compress then rebound, and then often compress and rebound again a number of times until the energy introduced by the weight is fully dissipated.

This where damping comes in. Dampers use the compression and expansion of (typically) hydraulic fluid to ensure that there is only a single cycle of compression and rebound of the spring, without over-stiffening the suspension, and defeating the whole purpose if introducing the spring in the first place.

Bottom line, damper settings should always be relative to the spring they directly affect. At least this is my understanding of them.
 
Ronald6
Ok, I get that (Two posts ago).But take the spring values into account: if the springs on the back are much stronger than the front then, not taking the dampers into account, the decel shift will be faster than an accel shift. Right?
Click to expand...

I'm responding to this from my phone so bare with me.

You can never really count out the dampeners

The springs will need to be stiffer where the most weight is supported. If your rear heavy the rear spring need be stiffer (but not too stiff) then the front (usually, this is not a golden rule and some people tune softer springs where it's heavy some cars have man spec softer front then rear while front heavy (I disagree), however tuning is very subjective, keep that in mind when taking advice). When decell the weight is shifted forward, I use the dampeners to counter the weight shift / reduce the body roll rate making the transfer less shocking (lol see what I did there) and more balanced.

In cornering I use the sway bars to manage the lateral weight transfer, making it stiffer where it's heavier.
 
Yellow Bird is rear engine and rear heavy. The stiffer springer supports a higher proportion of the car's weight distribution and receives less from the front the lighter front under acceleration. According to frequency though if the spring rates are in harmony, then applying the same damper strength to cancel out oscillation creates the same momentum change rate. Lighter spring handles less weight at same rate as heavier spring handles more weight with same dampers as I understand it, this is why I think having extension set front to rear at the same rate does yield better results if you have the proportion of the front to rear setup correctly.
 
Wow, explinations are flying like glitter at a Kesha concert. Lol.

Ok, one more try:
Springs are there to support the weight of the car. The spring strength/rate is proportional to the weight.
Dampers are there to counter the coil/recoil of the weight on the springs and are proportional to the spring strength/rate.
Roll bars counter lateral body roll.

So if I use Anti-roll bars to counter lateral roll, which counter longitudal roll? Dampers or springs? What I'm hearing is: Dampers mostly.
 
I adjust the dampers (shocks/struts) based upon two things:

1. Spring rate (which I base mostly upon the weight of the car); higher the spring rate the stiffer the dampers...

2. Over/understeer on throttle/off throttle.

-

If you have significant oversteer when releasing throttle, you should raise front bump (compression) and/or lower rear rebound (extension)... Do just the opposite for understeer...

If you have significant oversteer when hitting the throttle, you should lower the front rebound (extension) and/or rear bump (compression)... Again, just the opposite for understeer...

If you have oversteer or understeer on both of these, then adjust the springs (or camber, toe; in that order imo) to tune oversteer or understeer first.

I tune oversteer (or understeer) while cornering separately before tuning over/understeer while applying or releasing the throttle. For which, I adjust sway bars then springs, then camber.
 

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