9 replies to this topic

[Evo One]

It is a common conception that a stiffer front anti roll bar will increase understeer - my experience is the opposite - what do you think?

[Kid Prozac]

stiffening the roll bar will increase the load transfer at that end of the car in cornering, however reducing the amount of weight transfer at the other end.

tyres offer different amount of grip depending on the amount of load applied, in general the more load you apply the less grip you get, a traction versus load curve is a curve not a straight line. ie if you were to add up all of the given tractions of the tyres when going through a corner it would be less than whne the car has equal load on all the tires.

so if you stiffen the front roll bar, you effectively take traction away from the front tires, leading to understeer.

what may be happening in your case is that your not using your tires to their full potential, so when you go round the corner and the load transfers, you may still be getting more traction and be in the portion of the traction curve where the traction is still increasing with load.

hope ive kinda helped, im only a second year degree student, im sure one of the poffesionals on here will be able to add more.

what kind of car is it your using?

when we started our formula student project the base car givens suspension set up was way out, and entailed a lot of rework with springs and bars.

it is also as i found out difficult to get slip circles, things that tell you about a tires traction available, from the manufacturers, we tried hard but ran out of time getting them, would have been useful as we were rally underusing our tires, formula renault slicks used to twice the weight and downforce on a 250kg car................

[Scoots]

Yeah, that's the common response. Increase stiffness in back, increase oversteer. Same with shocks and tire pressure. That's simplistic, but it's where it starts.

[Evo One]

"What kind of car are you using"

At the moment I'm using a Lancia Delta Integrale Evo which has a stiffer front anti roll bar than the earlier Integrale. Turn in is noticeably sharper with the Evo but both cars tend towards similar understeer. The Evo has a wider track and more suspension movement so I am sure that this is a contributary factor.


"what may be happening in your case is that your not using your tires to their full potential, so when you go round the corner and the load transfers, you may still be getting more traction and be in the portion of the traction curve where the traction is still increasing with load"

I don't think that is the case - I started racing in the early '70s and although I no longer race, on track days I can still mix it with pretty fast machinery ;)

[Ben]

Kid Prozac has made some good points. Another suggestion from me is that increasing roll stiffness will reduce roll angle and could therefore keep the camber angles of the wheels more sensible. For example you might be reducing a camber thrust effect that was causing some understeer.

It's difficult to say without knowing the vehicle, the tyres and what sort of driving you're doing. Remember that the theory that increasing front roll stiffness to increase understeer is a steady state theory and will be less valid if you start using it to explain big transient inputs.

Another thing we'd need to evaluate this properly is whether the cars FWD or RWD and what phase of the corner you're getting the problem.

Ben

[AutoDelta]

If you are talking about improving turn in then increasing front roll stiffness will always help, up to a point. This is because the outside front tyre is loaded up that much quicker than with a softer front suspension, although as already mentioned the ultimate grip potential will be lower once into the corner (all other things being equal) due to increased weight transfer.

When talking about improving road car handling we are almost always talking about improving transient response and wheel control (damping and camber control). Steady state is for the race track, where there are more long constant radius corners.

[Yelnats]

Evo One, I presume you are talking about your cars handeling on the road rater than a full race situation. If this is the case I doubt if you are extending the tires and car to their fullest, otherwise you would see both your tires and licence go up in smoke pretty quickly! My experience has been that road handling has very little to do with 'at the limit racing' due to numerous interferences we all encounter like trucks rounding corners in the wrong lane and children running out after their balls.

In my day I did some pretty fast motoring but never confused this with what I did on the track. So any comments about anti-roll bars based on road driving are more likely an observation of their effect on initial transient response rather than the few percentage change in ultimate grip that occurs on the race track.

[Evo One]

Yelnats - I am talking about track day driving but as it is a fairly high performance 4 wheel drive car (Lancia Delta Evolution with c. 270 BHP) things may well be different from normal.

[Yelnats]

You have a point about FWD being different but the principal is the same. A comment by another poster indicated that limited camber changes taking place with the stiffer anti-roll bars could be the causing reduced understeer. But comparing handling between two different cars even if they are a similar modle is a tricky business as there are so many other factors that come into play like tire types, state of tire wear, camber setups and subtle suspension geometry design changes.

[Evo One]

Thanks Yelnats - as you say there are many other factors that come into play.