Setting bump and re-bound on shocks

[Andrew Jones]

I have just recived some new Koni double adjustable shock's for my FF1600 know I need some help. How do I know which way I should adjust the bump and rebound what type of handling will I get if I set each setting to hard or to soft.

[Bob Pearson]

I have been watching this thread with interest hoping someone else will reply, then we could all learn something, but so far it's only silence.
Dampers are a difficult subject, that is why people part with large sums of money to have their dampers set on 4 poster rigs at places like Dynamics, or pay to have a damper technician for the day.
Most drivers struggle to identify what damper changes they need, and it becomes worse with 3 and 4 way adjustable units.
The only advice I can give is to start with them on middle settings and move them either way and try to identify the feeling you are getting from the changes. It goes without saying that you must only do one change at a time.
Stiffening the bump has a similar effect to increasing the spring rate, i.e stiffer front more understear, stiffer back more oversteer, but those are very general things and not guaranteed.
You can increase the front rebound to hold the front of the car down longer after braking and improve your turn in.
You can stiffen the back bump to discourage weight transfer to the back and so reduce power on understeer.
You can soften all aspects of all your dampers in the rain to encourage more roll and so greater feel.
Things to avoid:
Too much rebound leads to corner jacking if you run over rumble strips. i.e the damper is depressed by the bump and cannot return before it hits the next bump and so the car gets gradually lower.

I don't know if that helps, but in the end you have two choices, pay for help or set about learning the feel of them yourself.

[Mark Benson]

There is a Haynes book called Competition Car Suspension by Alan Staniforth which goes some way to explaining all this.
It does help, but I find myself getting lost part way through each chapter, especially when he starts using equations that would frighten a Maths Professor.

Suspension is something we all know we need to get right, but take comfort in the fact that most of us mere mortals settle for tinkering on a test day and ending up using what feels right on the day.

[Mak]

Don't get to caught up in the set up on your car/dampers etc.. Learn to drive the car first and when you are close to the ultimate lap times start to play with your set up a bit. There is very little time found in setup (unless you are a million mile out) and loads in drivers. If you are always changing it you'll never learn how to drive it. (Remeber a little knowledge is dangerous)

[Stacy]

Originally posted by Andrew Jones
I have just recived some new Koni double adjustable shock's for my FF1600 know I need some help. How do I know which way I should adjust the bump and rebound what type of handling will I get if I set each setting to hard or to soft.

I was hoping Prodrive were going to pop in and explain all this, but in their absence..

Welcome to confusion! It's easy to adjust yourself into a blind alley and I've done so at some point, so while I'm no expert I'll profer my own views from my minimal experience. Your mileage may vary, and apologies if any of it is patronising or just rubbish - It's not meant to be, and if I have it wrong I'll be genuinely pleased to hear it so I can correct!

Anyway

1. Remember shocks control only the transitional reaction of the car, not the steady state cornering ie roll stiffness. By that I mean the shocks control the speed at which the load transfers, not the total load transfer, or the amount of ultimate roll from the load transfer.

2. Bump controls the unsprung mass's reaction to, well, bumps, and rebound controls the sprung mass's reaction to the spring change from the aforementioned. Therefore we can deduce we usually require more rebound than bump. With non-adjustables this figure is set at the factory, with adjustables you can change the ratio, not necessarily for the better.

3. The ratio of damping tends to stay the same front to rear, and in bump and rebound. What changes sometimes is the amount of overall damping from circuit to circuit.

4. To set them up from scratch, I set them all to almost soft. I then wind the bump up until the car starts feeling choppy and skipping on the surface, then wind it back a couple of clicks. I then wind on the rebound until you can feel the car jacking down after a set of corners or kerbs, then wind that back a couple of clicks. Then I'm done.. In reality my dampers don't change a lot now.

The object is to get the car into a zone where it's responsive without being twitchy, and soft enough without falling over any particular corner. Too much rebound has the car sort of wobbling up and down (can't think of a better word), and too much bump has a harsh ride with no compliance.

As for the tweaking, if you PM me your email address I'll send you a data sheet breaking down symptoms of corner entry/apex/exit and the bump/rebound changes necessary.

Of course once I've told you, I'll have to kill you. ;-)

Cheers

Stacy

[mattray]

Andy,

check your PM!

I will be happy to set your dampers up for you.

Matt