Anti Roll bars , sway bar , anti sway bar, what are they and what effect they have [Archive]

Davezj

22-12-2020, 11:08 PM

Ok so here is my take on the information contained in the video.
let me know if this does not make sense and will amend it.

Roll stiffness is the resistance to roll created by the stiffness of the anti roll bar fitted. More stiffness means less body roll.

Total Roll stiffness of the car is the combined roll stiffness at the front and back combined.

weight transfer is the shift in weight as a car corners.

the weight transfer is shared between the front and rear axel based on the relative roll stiffness of each axel. (important word is relative)

if you have a lot of roll stiffness at front of the car less at the rear, the front of the car will have to deal with more of the weight transfer. This means the front of the car will have less ultimate grip than the rear.

the roll stiffness front and rear is taken as a ratio and the weight transfer is applied to the car in the same ratio.

it is not the value of the total roll stiffness that governs the weight transfer it is the relative stiffness front to back.

you could have low total roll stiffness anti roll bars on the front and rear with the front twice as stiff as the rear the weight transfer will be twice as much on the front as on the rear.
you could have high total roll stiffness anti roll bars on the front and rear with the front twice as stiff as the rear the weight transfer will be twice as much on the front as on the rear.

the proportion of the weight transfer will be the same in both scenarios

the roll of the car will be different in each scenario above and will be more with the softer anti roll bars but the proportion of weight transfer will be the same front and back.

the total weight transfer is the always constant based on the weight of the car and the centre of gravity. you can't reduce the weight transfer by increasing the total roll stiffness front and back. you can reduce body roll by increasing total roll stiffness.
body roll is a visible manifestation of weight transfer, weight transfer is not a product of body roll.
gokart has weight transfer they do not have suspension and they do not have body roll.

front vs rear roll stiffness is more important than total roll stiffness.

so the point of antiroll bars is you can change the roll stiffness independently at each end of the car which changes the weight transfer.

if you increase the roll stiffness at the rear of the car, you move more weight transfers to the rear of the car so you have less weight transfer on the front. the front now has more grip and the rear has less grip which means you have more traction on the front than the rear.
the car is going to over steer more round a corner.

if you increase the roll stiffness at the front of the car, you move more weight transfers to the front of the car so you have less weight transfer on the rear. the front now has less grip and the rear has more grip which means you have more traction on the rear than the front.
the car is going to under steer more round a corner.

the roll stiffness of an anti roll bar change quickly with diameter of of the bar, the stiffness increases to the forth power, if you go from a 25.4mm bar to a 27mm bar the stiffness goes up by 27%

you can go to thick with anti roll bars and when you do you can experience something called Porpoising (dolphin coming up for air and going back under then coming up for air again and so on) this where you hit small bumber in the raod or track and the whole front and rear of the car dips and rises with no side to side difference. effectively both front wheels are locked together and both rear wheels are locked together, what one wheel does on the front the other wheel does on the front. but this is extreme behaviour.

Adjustable length drop links are used when corner weighting the car so once the car is set up you can connect the anti roll bar up so it does not put any tension on the anti roll bar. if tension is put on the anti roll bar then this will mess upset the corner weighting of the car.

this is just the basic gist of what is in the video, you are better off watching it to find out more but i have created this text version so i can understand it more.
in typing this out i have realised why my car likes to understeer more now than i remember it was.
i fitted a stiffer antiroll bar to the front and never got round to fitting the rear stiffer bar so that is still standard.
which means i have modified my car to make it worse by adding roll stiffness to the front which has moved more weight transfer to the front of the car making it understeer more. than it did from the factory an the VR4 was designed and setup to understeer from the factory. Understeer is easier to control and is safer setup than oversteer so that is the way the factory sets it up. also 4 wheel drive tends to promote understeer due to the way the 4 wheel drive pushes the car forward.

i will be fitting the stiffer rear anti roll bar i have to see what difference it make.

hope this help other get there head round anti roll bar setup.

if you see a mistake in the writeup let me know and i can correct it.