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Principle of front anti roll bar?
Hasse - 22/12/08 at 06:56 AM

Can anyone please explain how they actually work?

As the caterhams use then, I trust they DO work, but how?

I can understand that the body roll is reduced when the inner wheel is lifted by the ARB during cornering, but why does this make my car go faster?

Is the reduction of front end grip just "reduced" to the same level as the rear end grip, if so, why is this good?

Is it making the car more balanced and easier to "feel" remaing level of grip before loosening it, or is weight somehow tranfered to the rear improving rear grip?

My car is a simple book car with std Escort rear axle and 1600 X-flow, built from scratch, but I´m thinking of adapting a Caterham ARB.

/Hasse

Mr Whippy - 22/12/08 at 07:26 AM

rather than me typing stuff about this...here's a linky that explains about it good enough

Custardtart - 22/12/08 at 09:10 AM

Well it made me 2 secs a lap quicker in a back to back tests at Anglesey.

sucksqueezebangblow - 22/12/08 at 09:15 AM

Front bar stiffens the front suspension, thus at the limit the rear (being more pliant) remains in full contact longer than the front thus generating understeer. So in effect front anti roll bar helps balance rear oversteer with some front understeer giving you a balanced car.

Ideal is to have a perfectly balanced chassis without them but they are often used to reduce roll (hence the name) and can tune out under and over steer as above.

smart51 - 22/12/08 at 09:48 AM

The other problem with an ARB is that they spring you back out of a lean a bit too fast. In an emergency lane change manoeuvre they can promote roll over on the second bend.

I had a saxo years ago and in tight left - right or right - left corners, there was a moment where it all went light before settling into the second curve. You were never sure quite what would happen in that moment but once it settled, it was fine for the rest of the corner.

BenB - 22/12/08 at 09:53 AM

It does exactly what it says on the tin.

IE prevents rolling (when the suspension on one wishbone moves up but the other side moves down) whilst not preventing "normal" suspension bump absorption (where one suspension doesn't move that much). If you had crazily stiff suspension you'ld get no rolling round corners but you also wouldn't have much in the way of suspension of damping.

procomp - 22/12/08 at 09:57 AM

Hi

The front roll bar also allows you to run softer front springs to aid ride quality whilst still being able to control the body roll. This keeps the suspension geometry in it's working area maintaining the front end grip. If no bar is fitted and excessive roll is taking place the geometry will not be in it's ideal working area.

Cheers Matt

MikeRJ - 22/12/08 at 12:07 PM

quote:
Originally posted by smart51
The other problem with an ARB is that they spring you back out of a lean a bit too fast. In an emergency lane change manoeuvre they can promote roll over on the second bend.

I had a saxo years ago and in tight left - right or right - left corners, there was a moment where it all went light before settling into the second curve. You were never sure quite what would happen in that moment but once it settled, it was fine for the rest of the corner.


That's far more likely to be down to knackered rear beam mountings on Saxo, or worn out/incorrectly matched dampers.

mcerd1 - 22/12/08 at 12:32 PM

quote:
Originally posted by MikeRJ
quote:
Originally posted by smart51
The other problem with an ARB is that they spring you back out of a lean a bit too fast. In an emergency lane change manoeuvre they can promote roll over on the second bend.

I had a saxo years ago and in tight left - right or right - left corners, there was a moment where it all went light before settling into the second curve. You were never sure quite what would happen in that moment but once it settled, it was fine for the rest of the corner.


That's far more likely to be down to knackered rear beam mountings on Saxo, or worn out/incorrectly matched dampers.


my 106 was a bit like that (unstable that is - I never rolled it) and it didn't have any ARB
I got 4 new dampers and 2 front springs (just OE spec) and that helped alot, but I always reconed that an ARB would have helped more
(mango/ macspeedy: what do you think - would the 106 be better with an ARB ? )

my brother has a near identical car with an ARB and its much more stable, but does seem to get alot more lift-off oversteer




oh and there is this site too: linky

[Edited on 22/12/08 by mcerd1]

Mr Whippy - 22/12/08 at 12:44 PM

once had the front bar link arm snap on a cavalier (due to rust) when exiting a slip lane on to a dual carageway, did a full 360 right down the middle of the road, woke me up thats for sure replaced both of them after that

britishtrident - 22/12/08 at 01:25 PM

quote:
Originally posted by smart51
The other problem with an ARB is that they spring you back out of a lean a bit too fast. In an emergency lane change manoeuvre they can promote roll over on the second bend.

I had a saxo years ago and in tight left - right or right - left corners, there was a moment where it all went light before settling into the second curve. You were never sure quite what would happen in that moment but once it settled, it was fine for the rest of the corner.


The fact it was a Saxo was the problem.

britishtrident - 22/12/08 at 01:34 PM

quote:
Originally posted by procomp
Hi

The front roll bar also allows you to run softer front springs to aid ride quality whilst still being able to control the body roll. This keeps the suspension geometry in it's working area maintaining the front end grip. If no bar is fitted and excessive roll is taking place the geometry will not be in it's ideal working area.

Cheers Matt


Spot on --- softer front springs lower the natural frequency of the front suspension and if the front suspension has lower frequency ( softer) than the rear suspensension car rides bumps better -- you tend not to get the bucking bronco effect. Or to put it another way the car settles back to its normal level ride more quickly after a bump..

britishtrident - 22/12/08 at 01:37 PM

quote:
Originally posted by Hasse
snip
My car is a simple book car with std Escort rear axle and 1600 X-flow, built from scratch, but I´m thinking of adapting a Caterham ARB.

/Hasse



The Lotus/Caterham ARB is likely to be too stiff --- something more like thickness of a ARB from the back suspension of a small FWD car.

Antnicuk - 22/12/08 at 05:39 PM

is a westy or caterham heavier than a book car then?

britishtrident - 23/12/08 at 08:16 AM

quote:
Originally posted by Antnicuk
is a westy or caterham heavier than a book car then?


From the start the Lotus Seven was designed with very soft springs the roll stiffness was mainly generated by the ARB, Book Locost and Westfield style cars for a lot of reasons use much harder springs so this affects the selection of the ARB.
With ARBs you start soft then try either adjustment to make it stiffer or stiffer (thicker) bars.

Adjustable ARBs can made a number of different ways.

C10CoryM - 23/12/08 at 06:13 PM

It seems that most car builders have gone for the softer spring, stiffer roll bar idea now. Probably more for comfort than performance, but even sporty cars seem to do this as well.

Long story short, as always it comes down to keeping the tires in contact with the road as much as possible. If the car in leaning in corners, you are probably losing the negative camber in the outside tires. So you need to either stiffen the coilovers which may make the tires lose contact with the road more often on bumps, or fit an ARB. The only drawbacks to ARBs are weight and stiffer wheelrate on single wheel bump (when only one wheel goes up the ARB has to twist).
This is basically how the ARB works. When the outside wheel goes up due to roll, the bar trys to stop it because the inside wheel is trying to do down. Result is higher roll resistance and less roll.
Cheers.

Antnicuk - 23/12/08 at 07:17 PM

i am in the process of making a stiffer bar for the front of mine, what is the best indication of the bar now being too stiff?

C10CoryM - 23/12/08 at 08:46 PM

quote:
Originally posted by Antnicuk
what is the best indication of the bar now being too stiff?


Understeer mostly. Also loss of contact over washboard roads. Too large of a swaybar basically negates the whole independent suspension thing on washboard roads.
Adjustable bars are a good thing while dialing the car in. Do not need to be anything fancy though.
Cheers.

Hasse - 26/12/08 at 12:27 PM

Thanks for all replies!

/Hasse