Track: Shock Tuning Info

[JClark]

Jay Morris wrote this for Ground Control and Advanced Designs shocks a few years ago and is an awesome general summary for tuning shocks for road racing.

__________________________________________________ _______________

How to determine when to adjust your shocks

I would like to get one misconception out of the way; shocks do not need to be adjusted when you go to a different track! Sure, there probably is a bit of fine tuning that can help in a braking zone, or over a bump, but don’t fall into the trap of thinking that the shocks need the stiffness changed according to the perceived bumpiness of the course. Leave the car alone until you run some laps, get used to the tires, the weather, the traffic, the competition etc. If you have one of those race schedules where you only get one practice before qualifying, and you haven’t tested, don’t panic and start changing stuff. Wait until the last laps of practice and make some small changes, the driver doesn’t really even need to make a full lap after a quick adjustment. This type of thinking and approach is geared toward a realistic race team, not one from a magazine. Not everyone can test, (although everyone knows you should).

Before even considering any shock adjustment; the swaybars, springs and alignment must be very good, maybe not perfect, but you will never fix a racecar with shocks. If the suspension setup is not right, leave the shocks alone, adjusted to maybe “2” on compression and “-1” on rebound. Concentrate on the rest of the suspension, you must make the car fast before trying to go faster.

To be perfectly honest, the best thing to do is to just start changing adjustments, one end at a time, and see what happens.

During practice or a test day, have someone help you by taking notes and making adjustments. The driver stays in the car and does one or two laps maximum between adjustments. You may or may not want to record comments, but don’t be so picky and precise that you concentrate more on what you’re saying than what you’re feeling. Do a lot of laps and make a lot of big changes, starting with front compression changes. Start with the all the shocks set on neutral rebound (-1 or one turn out) and “1” compression, the softest, and then change the front to “3”. Skip “2”, because we’re trying to learn right now, not tune. You will feel the biggest difference as you come into turn, which makes sense because that is when the car is trying to compress the front shocks. Then try rear compression, see what happens as you come out of a corner, or hit a bump in mid-turn. Next, maybe try turning all the compression adjustments back to “1” and then tighten the rear rebound +1, all the way stiff and see what happens, then the front etc. It will soon start to be clear that when an adjustment is made at one end, it primarily affects the feeling from that same end, but also affects the other end of the car too. Pay attention. Like I said, there is no substitute for just driving around (laps), so do it!









COMPRESSION

Here is a BIG generalization:

Try to run as much front compression damping as the car and driver can stand

I will discuss some reasons and situations when you can’t or don’t want to run a lot of damping, but overall the cars seem to go fastest with a lot of low-speed compression damping, especially in front. It seems to help a lot in braking and turn-in, and doesn’t seem to hurt much anywhere else on the track.

Of course one clue that there is TOO MUCH compression is that the car won’t turn in (pushes), or stutters and hops under braking. Generally you can get away with very stiff front shocks, FWD or RWD, and nothing bad really happens, but always try turning the front compression down if the car is trying to push. If the compression is already set on “1”, and it pushes, check for suspension bottoming, wrong front springs, mismatched swaybars etc. All of these things must be perfect before trying to fine tune with the shocks. If the car persists in pushing, but it did get better as you turned down the compression, that does not necessarily mean that the shocks need to be valved softer. There are rebound adjustments that affect turn-in, but we’re only talking about compression adjustments for now.

If it turns out that the car is bottoming out the suspension in front, you cannot cure this by stiffening the shocks, perhaps reduce the symptoms, but never a cure. The car will still bottom out, it just will take a split second longer. Think of the shock compression adjustment as a split-second spring, the shock will make the car think that it has a stiff spring, but only for a brief moment. If the car is bottoming the suspension, your only options are to (ideally) increase the travel so it doesn’t bottom out, or install stiffer springs.

The same split-second spring characteristic that helps on the front of the car can cautiously be used to our advantage on the rear. On a RWD car, we can get a little bit of traction and security with a very slightly stiff degressive rear shock. This is a bit tricky, because if you go a tiny bit too far, the car will skate sideways every time you hit the gas. On a FWD car, stiff compression rear shocks are used to help the car rotate into a turn without skipping over bumps. Be very careful if you’re thinking about fixing an understeering racecar by reducing grip on the rear tires, it is always better to try to make the front end stick better.

REBOUND

Another BIG generalization:

A driver likes stiff rebound more than the car does.

Rebound tuning and characteristics are a bit tougher than compression because the forces are more gentle and gradual, and the adjustment results perhaps not so dramatic as compression. In theory, the primary reason for rebound damping, even for the whole shock itself, is to control the energy stored by the spring when it is compressed by the movement of the chassis. On racecars however, the shock is also used to affect and influence handling. I think of it as undercontrolling or overcontrolling the spring. Any time we don’t use enough rebound damping, we are not completely controlling the energy stored in the spring.


A severe example of this is big cars with a “floaty” ride, the floating sensation comes from the spring pushing the chassis back up too far after being compressed, because the shock didn’t slow down the release of energy. There are only a few situations where undercontrolling the springs can make a car faster. On a high horsepower RWD car, soft front rebound lets the chassis weight transfer to the rear tires out of tight corners, the car won’t feel as good in the fast corners, but lap times can be quicker. On a FWD car without a limited slip differential, using a very soft rebound setting can reduce the wheelspin of the inside front tire.

Try reducing the front rebound about –1/2 turn. As always, pay attention to if this helps, hurts or nothing. If now, or at any time the car starts to feel “floppy”, or seem like it leans real quickly, you may not have enough rebound damping. Conversely, if the car feels “tight”, but very sluggish, you may have too much rebound.

Of course how do you know that the car feels floppy, or sluggish or tight when you don’t have anything to compare it to? There is really no substitute for experience (laps) and paying attention to what you’re feeling. I don’t expect you to “feel” during qualifying or a race, but you really shouldn’t be paying attention to shock setup during a race anyway.

Undercontrolling the rear suspension is occasionally used, FWD and RWD, on cars with corner entry problems such as severe wheel hop or sudden transition oversteer. If it feels like the back tires start to lift off the ground whenever you brake hard, maybe that really is what is happening, especially possible on a car with very low unsprung weight. If this is happening, soften the rear rebound –1 turn and observe. Most often however, transition oversteer and wheelhop are cured with STIFF rebound settings, in particular on a heavy RWD car where overcontrolling the spring helps hold the chassis to the heavy unsprung weight. In essence you are temporarily holding the chassis to the suspension with a stiff rebound setting.

While increasing the rebound settings, at some point you may overcontrol the springs and the springs will not have time to relax between transitions, bumps or turns. This excessive overcontrol of the springs will actually cause the chassis to “ratchet down” to the bump stops. At first, the car might feel good, but as you get used to the settings, you will notice the car not coming back up after a bump. Excessively stiff rebound settings will always make the car slow to react and slow on the stopwatch, despite feeling secure and predictable.

Adjustment Summary:

Try to sneak up on a stiff compression setting to be used in the front, then try to use the minimum amount of rebound possible. More or less front rebound damping can be safely used to influence handling and transitions. It is not uncommon for the front shocks to have more low-speed compression damping than rebound (FWD and RWD). The rear compression damping will rarely be as stiff as the front. By paying close attention to how the car feels exiting the turns, you will arrive at the best setting, which should be less than you can tolerate, in order to leave a safety margin. Besides the exceptions noted earlier, the driver will be happiest with a little extra rear rebound damping and the car will feel better under braking.


Subject Summary:

There is no better way to learn how to make your racecar go fast than to teach yourself how. Every lap is just as important as every internet site and every book. Make test days fun, bring friends, food and drink. Plan ahead. It is okay to make two changes at once if you’re comfortable with it. There is nothing worse than getting to the end of a test day without getting enough done, you’re not an F1 team so don’t try to test like one.

My disclaimer:

Everything I have talked about is based on my own observations. I have not seen everything and I’m sure there are racecars that will not respond to my generic comments the way that you or I would expect. There is deliberately no mention of, or allowances for, damping effects on aerodynamics or vice versa.


Glossary:

Shock is a generic term for a racecar suspension damper, MacPherson strut or otherwise.

Damping is an engineering term for controlling or dissipating energy in a controlled manner.

Dampening is what happens when you wet your pants.

Degressive is the shape of a graph with a diminishing rate of change for Y plotted against X.

Digressive is when a discussion about shocks becomes a conversation about wetting pants.

Firm is a completely subjective term chosen because it sounds softer than “stiff”

Floppy is a completely subjective term chosen because it sounds wigglier than “tight”.

Overcontrolling is a word that I made up.

Undercontrolling is another word that I made up.



Respectfully submitted,

Jay Morris

[crAppAchic0]

Great info, sir!

[MikeyB.]

[Cavi Mike]

Good information. I would like to emphasize that this is for race cars only and that attempting to control rebound on a street car can be very dangerous. Race cars don't experience large undulations in the road like street cars and any time the spring isn't able to put the tire back on the pavement after a bump can easily throw a car way off balance. This is why 'drag' shocks say 'not for street use' in the warning.

[Moai]

Originally Posted by Cavi Mike

Race cars don't experience large undulations in the road like street cars

Ever hit an apex curb at 80mph? Guaranteed you haven't in your street car.
Might change your mind about setups.

[JClark]

LRP is twice as bumpy as any road I've ever driven on.

Eric- I have a much stiffer setup in the mail. No more floating like a Cadilac over curbing...

[Cavi Mike]

Originally Posted by Moai

Ever hit an apex curb at 80mph? Guaranteed you haven't in your street car.
Might change your mind about setups.

And just how many times have you spun out in the middle of a crowded highway amongst drivers who barely know the difference between the gas and brake pedals? Make sense now?

[Moai]

Originally Posted by Cavi Mike

And just how many times have you spun out in the middle of a crowded highway amongst drivers who barely know the difference between the gas and brake pedals? Make sense now?

Twice. Both times, driver fault. Had nothing to do with the suspension settings.
Dampening and/or rebound aren't going to crash your car by themselves. Your alignment will.

[Cavi Mike]

You're lucky to be alive.

I didn't say it would be by themselves, I just said it was dangerous and stupid to mess with rebound on a street car. There are way too many obstacles on a street compared to a race track to be messing around with rebound. There's a reason why the average adjustable shock doesn't have a rebound adjustment on them. If you want to continue to argue the point so every n00b on here thinks it's no big deal well, I tried.

[BoxerSix]

Originally Posted by Cavi Mike

You're lucky to be alive.

I didn't say it would be by themselves, I just said it was dangerous and stupid to mess with rebound on a street car. There are way too many obstacles on a street compared to a race track to be messing around with rebound. There's a reason why the average adjustable shock doesn't have a rebound adjustment on them. If you want to continue to argue the point so every n00b on here thinks it's no big deal well, I tried.

One of the smartest and more accurate posts i've seen on here in awhile.

Suspension setup is definitely not for the faint of heart. I've got a few programs I'm utilizing here to design the 962 suspension and the degree of sensitivity gone into such an area far exceeds what most people comprehend. Rebound is a dangerous setting to mess with if you don't know what's going on, what effects you are feeling from subtle changes, and how to make appropriate adjustments from that. Everything from suspension bushing deflection to sway bar progression affect rebound and if you don't know the variables you can get yourself into trouble VERY quickly.

This why every professional race team is very secretive with their suspension settings as the time an money invested in getting them right is huge...


I recon about 10 people max on this forum can actually used more than 50% of the info in that post......I know two of them definitely have posted here

[Moai]

Originally Posted by Cavi Mike

If you want to continue to argue the point so every n00b on here thinks it's no big deal well, I tried.

Wow. What a useless cock.

[crAppAchic0]

Well, suspension testing that involves that degree of 'stress testing' probably shouldn't be done on any public road. That's just my opinion.

You can tool around with any settings you want; it's _your_ car. But when dealing with any drastic changes, that's exactly what they are- drastic changes. Unless you know for sure, exactly what you're changing, either 'test' it somewhere where you can, or have someone who knows exactly what should be adjusted do the actual adjustment.