Do I need a rear anti roll bar?

[R500 CYA]

Just back from another great day at Goodwood, during which I asked the instructor to drive my car on a few fast laps and tell me what he thought:

 

It's a 1.6k SS, widetrack suspension, uprated springs, 6x13 ACB's, 500 kgs wet. But it understeers almost as much as a Vauxhall (there goes any help from F.A then!)

 

The instructor reckons it's because I don't have a rear ARB, which is allowing the back of the car to roll, reducing weight on the front and therefore creating understeer.

 

Sounds plausible but he races Formula Fords, so what does he know? What do real Caterham owners think?

 

It did help reducing the front tyre pressures by a few psi. I didn't try adjusting the springs but I'm not convinced it would help anyway.

 

Your thoughts please (especially you Arnie as I'm sure you have had to put a lot of effort in sorting this one out (tee hee) wink.gif

 

Nick

[FH]

Pinky,

Firstly - who was the instructor and how long did he drive your car?

Was he a wannabee racing driver/unsuccessful r/d or a technical person who happens to help out "Golbookeasyrmtrack" Limited?

 

Secondly - unless said instructor built/drives a seven, I think the responses you get from this site will be far more informative.

 

All IMHO

FH

blush.gif

 

 

Edited by - fullharness on 30 Apr 2001 22:36:34

[StewartG]

My experience is that you either don't need a rear arb or you need the weakest one available. My car seemed to handle best when the arb was broken (although I didn't know it) with better traction and drive out of corners. With a stiff arb, rather than absorbing the power and driving out of a corner the back end jumps sideways. As it can't roll it skips.

To sort out the understeer raise the back or lower the front.

[R500 CYA]

FH: Well he was introduced as a champion, drove the car for maybe 8 laps, and subsequently stuffed some poor chaps 911. Seemed like a nice bloke though! Definately thought the knowledge here would be superior (with o disprespect to him!)

 

Stewart, it sounds logical to raise the back (haven't got the ground clearance to lower the front), how do I do that(and can I paint the rear diff red and cover the dash in furry carpet?)

 

Cheers,

 

Nick

[Mike Bees]

As a rule of thumb adding roll stiffness at one end of the car reduces the grip at that end relative to the other end - so he's right in that adding roll stiffness at the back will help to cancel out the understeer. It might not be the best way of doing it - it might be better to reduce the roll stiffness at the front (smaller front ARB wink.gif), or to raise the back, or, or, or.... Was it understeering in the fast corners (Madgwick & No-Name)?

Any car can be made to understeer into Lavant.

 

Did you ride with the instructor? You'll get more understeer 2-up because the back sits lower & hence the steer effects of the DD-tube move further towards understeer territory.

 

What was the instructors driving style - was he braking hard and then jumping back on the throttle at the point of turn-in? Getting back on the throttle early takes weight off the front wheels and hence increases the tendency to understeer (Lavant is a really good place to trail-brake up to the first apex to avoid this).

 

Mike

[Alex Wong1697456877]

I'd agree with Stewart as I recently broke my rear ARB at the ring. The car seems more settled but the result is more understeer which is making it easier to hold onto the car at long corners when the power was trying to break the rears. If understeer is your problem, as already pointed out, a rear ARB should in theory help.

 

The easiest and cheapest way to change the handling of your car is with tyre pressures. The Seven is quite sensitive to a few psi more or less.

 

Alex

[Eugene]

Pinky,

I did a bit of research on roadholding & handling a while back. Have a look at http://freespace.virgin.net/shaw.clan/roadholding.htm if you are interested.

 

What size is your front anti-roll bar?

 

Small Boy - with Big Toy!

[StewartG]

Alex, whilst tyre pressures are a quick way to tweak handling I contend that there is only one correct pressure for a given tyre in a given installation. This pressure gives the tyre the optimum temperature and profile and probably load of other parameters for max grip. Ideally handling tweaks should not include compromising tyre performance.

[R500 CYA]

Thanks for all your comments, the bottom line does seem to be there is no simple answer.

 

Alex: I did reduce the front tyre pressures by 3 psi, which did make a small difference, however by that time I think the fronts had well and truly gone off (4 hard track days on ACB's is about it I reckon!)

 

Mike: I was understeering badly into Lavant, and I'm interested in your trail braking comment. What is that?

 

I was also suffering lots of understeer in the faster corners. Madgwick was partly solved by taking a different line, entering the corner much later and getting on the power very early into the bend. This appeared to create sufficient oversteer (well as much as you can get with 140 hp) to compensate for the understeer.

 

Into no name, the secret appeared to be to take a slightly slower approach to the corner, giving a small brake after Fordwater rather than just a lift, brought the nose in tighter and made a tidier line for the quick brake and downshift into St. Marys.

 

This was pointed out by the instructor, though I'm unconvinced it was any quicker.

 

The instructor was not much of a heavy braker, and to be honest I find Goodwood quite a light circuit on the brakes (which probably means I'm not trying hard enough).

 

I'm wondering if it's a simple case of more power required to compensate for the understeer, or whether that would just accentuate the problem.

 

Eugene: I started looking through your site (it's gonna take a while) thanks 4 the heads up, I'm sure it will hlp with my conclusions. I'm afraid I have no idea what size my front ARB is, it's a standard SLR item as far as I know (Arrowstar fitted it for me)

 

I'm learning but it's taking a while!

 

Thanks again

 

Nick

[Mike Bees]

Trail-braking is the art of staying on the brakes as you turn into the corner - not *hard* on the brakes (you'll spin) but just a *little bit*, and gradually bleeding off the braking as you approach the apex. Under braking you get weight transfer to the front wheels, so braking into the corner gives you more front end grip and less rear-end grip. It's more useful in tighter slower corners, the nature of the corner will determine whether it works and how quickly you need to bleed off the brakes.

 

Adding power isn't the *correct* way to fix an inherently understeering chassis. If you've got a big (19mm?) front anti-rollbar and no rear anti-rollbar then you have a big imbalance in roll stiffness. Front anti-rollbars are quite cheap (especially if you can find a secondhand one), try changing to the 0.5".

 

Mike