Anti roll bars and drop links

[Rich]

I've been looking into getting some adjustable front links made and have been asking Tony a few questions. I'm still abit confused about the subject and thought others might be as well, hence this thread.

 

From my understanding anti roll bars do exactly that, stop the car from rolling too much when cornering. Did abit of googling and came back with this for an explanation...is it correct Tony? Terminology is in American though.

 

Stabilizer bars are part of a car's suspension system. They are sometimes also called anti-sway bars or anti-roll bars. Their purpose in life is to try to keep the car's body from "rolling" in a sharp turn.

 

Think about what happens to a car in a sharp turn. If you are inside the car, you know that your body gets pulled toward the outside of the turn. The same thing is happening to all the parts of the car. So the part of the car on the outside of the turn gets pushed down toward the road and the part of the car on the inside of the turn rises up. In other words, the body of the car "rolls" 10 or 20 or 30 degrees toward the outside of the turn. If you take a turn fast enough, the tires on the inside of the turn actually rise off the road and the car flips over.

 

Roll is bad. It tends to put more weight on the outside tires and less weigh on the inside tires, reducing traction. It also messes up steering. What you would like is for the body of the car to remain flat through a turn so that the weight stays distributed evenly on all four tires.

 

A stabilizer bar tries to keep the car's body flat by moving force from one side of the body to another. To picture how a stabilizer bar works, imagine a metal rod that is an inch or two (2 to 5 cm) in diameter. If your front tires are 5 feet (1.6 meters) apart, make the rod about 4 feet long. Attach the rod to the frame of the car in front of the front tires, but attach it with bushings in such a way that it can rotate. Now attach arms from the rod to the front suspension member on both sides.

 

When you go into a turn now, the front suspension member of the outside of the turn gets pushed upward. The arm of the sway bar gets pushed upward, and this applies torsion to the rod. The torsion them moves the arm at the other end of the rod, and this causes the suspension on the other side of the car to compress as well. The car's body tends to stay flat in the turn.

 

If you don't have a stabilizer bar, you tend to have a lot of trouble with body roll in a turn. If you have too much stabilizer bar, you tend to lose independence between the suspension members on both sides of the car. When one wheel hits a bump, the stabilizer bar transmits the bump to the other side of the car as well, which is not what you want. The ideal is to find a setting that reduces body roll but does not hurt the independence of the tires.

 

I understand how these bars work but what about upgrading them to larger ones? In my other thread you weren't too sure about me upgrading the rear ARB without doing the front...why is this?

 

Now onto the drop links...the ones on the mondeo are very thin and are prone to snapping/bending...would upgrading these to thicker links that are not adjustable have any affect on how the ARB works? After seeing the plastic links on the pug 306 I'm thinking that strength is not an issue with these...right or wrong and why?

 

If I get adjustable links made what affect would increasing/decreasing the length have on the performance of the ARB? You said that longer links will produce less body roll and shorter links more...why is this? You also said adjustable drop links can be used to create oversteer on a FWD and this is a good thing...why?

 

What impact does shortening the links have on the ARB and the mounts/bushes...will they be under more strain?

 

How adjustable should they be, I know you said as much as possible but would an inch each end suffice or should it be more?

 

A few questions to be getting on with there!

[Tony]

Polar moment of inertia is a measure of an object's ability to resist torsion. It is required to calculate the twist of an object subjected to a torque. It is analogous to the area moment of inertia, which characterizes an object's ability to resist bending.

 

Think of it as this.... How do you think the car would react if you had 10psi pressure in the front and 50psi in the rear, against 50psi front and 10psi rear?

[Rich]

All those questions and you didn't answer any of them!

 

Polar moment of inertia is a measure of an object's ability to resist torsion. It is required to calculate the twist of an object subjected to a torque. It is analogous to the area moment of inertia, which characterizes an object's ability to resist bending.

 

Think of it as this.... How do you think the car would react if you had 10psi pressure in the front and 50psi in the rear, against 50psi front and 10psi rear?

 

To answer your question is this right?

 

10psi front and 50psi rear = Understeer

 

50psi front and 10psi rear = Oversteer

[Tony]

All those questions and you didn't answer any of them!

 

Polar moment of inertia is a measure of an object's ability to resist torsion. It is required to calculate the twist of an object subjected to a torque. It is analogous to the area moment of inertia, which characterizes an object's ability to resist bending.

 

Think of it as this.... How do you think the car would react if you had 10psi pressure in the front and 50psi in the rear, against 50psi front and 10psi rear?

 

To answer your question is this right?

 

10psi front and 50psi rear = Understeer

 

50psi front and 10psi rear = Oversteer

 

Other way round

[Tony]

Your question> "I understand how these bars work but what about upgrading them to larger ones? In my other thread you weren't too sure about me upgrading the rear ARB without doing the front...why is this?"

 

A: On cornering obviously the suspension compresses allowing the tyre to maintain maximum grip, the roll couple f/r is balanced, so if you deny the rear by upgrading the arb the tyres will rapidly reach their grip limits.

[Rich]

To answer your question is this right?

 

10psi front and 50psi rear = Understeer

 

50psi front and 10psi rear = Oversteer

 

Other way round

 

Seems I've misunderstood what under/over steer is.

 

If the rear feels like it's going to break away it's oversteer and if it's the front that's understeer?

 

Your question> "I understand how these bars work but what about upgrading them to larger ones? In my other thread you weren't too sure about me upgrading the rear ARB without doing the front...why is this?"

 

A: On cornering obviously the suspension compresses allowing the tyre to maintain maximum grip, the roll couple f/r is balanced, so if you deny the rear by upgrading the arb the tyres will rapidly reach their grip limits.

 

So you're saying that by upgrading one bar without the other this may cause more under/over steer, which obviously is a bad thing as you could end up spinning the car?

 

As oversteer is the rear tyres losing grip this is more dangerous as the rear can swing out causing the car to spin? If understeer occurs you could correct it more easily or take the corner wider?

 

What about the drop link questions or you doing one at a time?

[Tony]

Your question> "If I get adjustable links made what affect would increasing/decreasing the length have on the performance of the ARB? You said that longer links will produce less body roll and shorter links more...why is this? You also said adjustable drop links can be used to create oversteer on a FWD and this is a good thing...why?"

 

A: The OEM arb already has a small amount of preload on it, this preload is balanced front and rear to work in harmony with the torsional rate of the unmodified domestic car.

 

It's unlikely anyone would reduce the rate, more probable they would add preload in order to reduce overall roll or change the roll values in order to change the tyres grip limits, the arb's oem torsional strength has limits though so you cant go mad.

 

Corner-in during transition a FWD is subjected to a whole host of grip limitations, hence the understeer issues. By reducing the fronts "polar moment" it's possible to retain a better grip limit than the rear and evolve oversteer.

[Rich]

How do you know when you have reached the limit of the OEM ARB when fitting adjustable links?

 

So from what you're saying I should keep the front and rear ARB's standard (as only an uprated rear bar is available) and add adjustable links instead. This will help by allowing the front tyres to have more contact with the road when cornering?

[Tony]

The position of roll center at each axle determines how much weight transfer occurs through the mechanical components of the suspension at that axle. The position of the CoG relative to the roll axis determines how much roll moment is applied to the sprung mass.

 

This moment causes the sprung mass to roll under lateral acceleration. The roll will normally be resisted by the springs and dampers at each axle, and this will cause an additional weight transfer (i.e. additional to the mechanical weight transfer through the suspension links).

 

The total weight transfer over the whole car is determined by the CoG height and is non-negotiable, but these other details tell us where this weight transfer will occur, transiently and steady state and how much body roll will occur..... The body roll then determines what other geometry changes will occur.

 

It's reasonable to upgrade the rear arb assuming we have the ability to tune the front.

[hms]

1. Am I right in assuming that the length of the drop links, provided they are the same length side to side will make no difference to handling?

2. Adjustable drop links allow you to pre-load the ARB, so you could set the ARB up for a clockwise circuit with a few left handers, maximising the handling for the majority of right handers plus the ability to handle left handers, Correct?

I have a set of Steve Heath Adjustable rose jointed drop links, and have not touched them since they were fitted!

h

[Tony]

1. Am I right in assuming that the length of the drop links, provided they are the same length side to side will make no difference to handling?

2. Adjustable drop links allow you to pre-load the ARB, so you could set the ARB up for a clockwise circuit with a few left handers, maximising the handling for the majority of right handers plus the ability to handle left handers, Correct?

I have a set of Steve Heath Adjustable rose jointed drop links, and have not touched them since they were fitted!

h

 

1: Same length set at a relaxed state will offer whatever promise the ARB's said on the box.

 

2: Preloading the ARB's for circuits is common place, it's no different then camber stagger on the ovals.

[CIH]

With domestic American cars, I understand it's popular to have larger ARBs coupled with softer springs, allowing for a good ride quality (springs) but to also limit body roll on turn (ARBs). Though it's not 100% effective.