Suspension question

[Mcalvert]

I am keen to revise the suspension on my 1991 De Dion Crossflow to improve turn-in, with at minimum new springs and dampers, upper wishbones and front ARB.

 

However, my car has never had a rear ARB fitted and I’m trying to understand what benefits adding one would bring. I understand that fitting a rear ARB would increase the overall chassis roll resistance, but can someone please explain the benefits of doing this via ARBs front and back rather than relying at one end only.

 

Thanks!

 

[R2D2]

Choosing spring rates is one of the most important decisions to make about adjusting the handling balance of a car and they need selecting with some care.

 

The main job of the spring is to allow the tyre to follow the road without the tyre unloading. The shock absorber also has an important part to play and interacts with the spring to give optimum results.

 

Another job of the spring system is to restrict body roll and it is fairly easy to calculate the spring rate needed to give a certain roll resistance. In general the springs needed to limit body roll to an acceptable degree are too stiff to allow the tyre to follow bumps in the road so generally an anti-roll bar is used to increase roll resistance by 25-50%. Adjustable anti-roll bars are also a convenient way of fine tuning handling balance.

 

What you really need to do is optimise the entire spring/anti-roll bar/shock absorber package.

 

Some people use less spring and more anti-roll bar others less spring and more shock absorber.

 

In general terms you are trying to adjust the pitch and roll resistance of the car

 

Increasing the front roll stiffness will tend to increase understeer and increasing rear roll stiffness will tend to promote oversteer but this is a very simplistic view.

 

Dynamic weight transfer is also important in terms of traction out of a corner and roll stiffness and dampers will also influence this behaviour.

 

You also need to consider tyres, tyre pressures and a few other variables.

 

I think the best thing to do is decide what improvements you are looking for and then find the best way forward by discussing it with people with similar cars.

 

A good road set up may be very different to a good track set up the they are not necessarily compatible.

 

You may well end up fitting a rear anti-roll bar but I am not sure that they are a essential in all circumstances.

 

 

 

[Mcalvert]

Thanks Chris - that makes a lot of sense and may help explain part of why my car tends towards understeer.

 

Does anyone have any recommendations towards good books on suspension theory that I could use to learn more of the basics?

 

Thanks - Michael.

[Kevin C]

for background, you might want to try

 

http://www.smithees-racetech.com.au/

 

http://www.dur.ac.uk/r.g.bower/PoM/pom/pom.html

 

cheers

 

kev