Fonzey

iTrader: (5)

Hi all, in a scenario in which both compression (bump) and rebound is independently adjustable, are there any general rules/guidelines with regards to the relationship between the two settings and the relationship between the spring rate and the damper settings?

For example, what should I change to reduce the "bounce" in the suspension after a dip in the road? What should I change to increase compliance for daily driving, what should I change when taking the car on track, etc.

I've got the BC Racing ER series as below:


My bump is adjusted by the **** on the bottom of the reservoir (1-32) and rebound adjusted on the top of the strut (1-32) so I could potentially have the bump maximum "soft" and rebound maximum "hard" for example.

Obviously I need to experiment for myself, but with 1024 combinations of settings available on each corner - it would be nice to have some basic facts/starting points first

MeisterR

The problem with this is unless you are very experienced in suspensions, 2-way adjustable can actually decrease performance when compared to 1-way adjustable system.

A "general" shot in the dark:
Sport car: Rebound to Bump Ratio (2:1)
Street car: Rebound to Bump Ratio (3:1)
You really will need a damper dyno to set that, or at least you will need to know what damping force each click are... otherwise it will be pretty hard to set this.

Unfortunately, i don't think I will be able to provide help unless I physically take the suspension from you, run it range through a damper dyno, and establish the damping force at each setting... it is hard to give you a starting point.

Also, 2-way adjustable are mainly design to adjust for track condition.
You can improve certain part of the track by using the adjustment, but you will decrease performance at other part of the track.

For example, you could increase compression to make braking into the paddock hill corner more stable at brand hatch, but you will find that you may lose some stability on the faster part of the circuit. 2-way and 3-way allow race engineer to adjust the suspension at track side base on the driver feedback and track condition, and it will be different at every track, on different day, by different driver...
It is the race engineer's job to get those info out of the driver (as most driver isn't very technically minded, they just drive) and adjust the suspension so the team ultimately win.

In your case, my only suggestion is to start in the middle and go up or down.
Without any data, your guess is as good as mine... or anyone else for that matter.

Let us know how you get on, and if there are any help i can provide just let me know.

Jerrick

Fonzey

iTrader: (5)

Thanks Jerrick, I appreciate that.

I wasn't expecting anyone to be able to tell me over the internet how many clicks I need for the optimal settings for all road/track conditions, I was more looking to find out what characteristics would be manipulated by the different adjustments.

I did some further google reading last night and found a high level summary which basically stated:

Compression manipulates the cars ability to grip but excessive compression damping can cause instability and poor ride quality on less than perfect surfaces.

Rebound manipulates the way in which the car reacts after a change in direction, acceleration or braking. Excessive rebound damping can prevent the suspension from fully extending again in quick succession of compressions causing the shock to eventually bottom out.

With that in mind, it seems that I should set both to full soft, then incrementally increase the hardness of compression until I feel the car crosses the threshold of stiff vs unsettled, then wind it back a couple of notches.

With compression sorted, I'll raise rebound to dial out excessive lean through corners and in braking zones.

MeisterR

Actually, the body movement of stiff vs unsettled is more affected by rebound.
Braking stability is more to do with compression.

And you really don't want to go to a higher than 2:1 on the rebound to bump ratio.

It is a difficult subject and really is difficult to adjust a 2-way suspension for road use because you are face with a lot of variable in an undefined layout.
As opposed to setting it up for a race day in a defined layout (track) and defined amount of variable (weather, surface condition, tyre compound, etc).

I am not sure how I can help on this because it is rather difficult to give any advice without solid data to work with.
This might be a case where you need to get some dyno data so you have a starting point.

Otherwise, the "butt dyno" is the only thing we have to rely on...
It isn't accurate or quantitive.... but it may be the only choice since there are nothing else to work with.

Go play around with the setting and let us know how you get on...
Base on what you feel and what you have done, I'll do what i can to assist but it may be difficult still.

Jerrick