Running No Arb.....?

[BlueBolt 156]

Not wanting to hijack this thread:

http://forum.205gtidrivers.com/index.php?showtopic=140006&pid=1262502&st=0entry1262502

I thought I would start a new one...

 

I bought a set of coilovers and eccentric top mounts off Sam on here a few weeks back, going to get round to cleaning them up and fitting them at some point soon, but wanted some thoughts and advise about the use of the ARB...

I always thought them to be critical?? But having read the above thread, and spoken to Sandy briefly, I am learning that (again) I am mistaken...!!

 

What's people's opinions on this?? What are the pro's and cons to this?? And those of you who don't use them, what's the main use of your cars??

 

My car, as per this thread:: http://forum.205gtidrivers.com/index.php?showtopic=132506&view=&hl=&fromsearch=1 is being set up as a fast road / track toy... I do use it daily, but my "driving style" (if you want to call it that) is somewhat aggressive and I do like to enjoy my car and engine!!

 

As always, your knowledge, advise, and experience is appreciated

 

Chris

[Baz 421]

Not critical at all, some cars simply never had them. You really need to educate yourself a little or just think about the basics of a car's suspension. It's pretty self explanitory in this case, removing the 'anti-roll bar' allows the front of the car to 'roll' in cornering, giving some degree of compliance, in turn aiding in front end grip, where possible of course, but sacrificing bodyroll which in turn doesn't help weight-transfer.

 

If you don't need it, you don't need it, many competition cars running stiffer suspension set-ups don't. It's simple enough to try it, remove a drop link, body-roll tastic on anything near standard though. Adding a fatter rear-ARB in turn gives a similar effect, without the downside of the added bodyroll.

 

2 of my cars don't run a front ARB, one is a rally car the other is purely a tarmac/track car, both have coilovers with uprated spring rates etc. I've been known to disconnect it on lesser cars when needed too.

Edited June 26, 2012 by Baz

[EdCherry 34 1 Cars]

Primarily a tuning tool and the only reason its there competition/track car wise.

 

Manufacturers seem to use it to give confidence to the driver, lots of body roll doesn't inspire a lot of people!

[parry 23 1 Cars]

I posted in the other thread as well. This is for a dedicated track car on slicks.

 

I was running an ARB with 250lb springs on Gaz coilovers. I then wanted to get achieve 2.5deg neg camber on the front as I was only able to get 1.5 with eccentric topmounts. I moved to cx driveshafts with 306 steering rods (shortned to fit) and compbrake adjustable wishbones.

 

Removing the ARB I was turning much nicer but on full corner load I was on the bumpstops and it unsettled the car and the max I could achieve was 1.1g. I then upgraded my front springs to 375lb and raised the height by 10mm and the car was transformed. 1.4g through the turns with no hitting bump stop. Our little pug keeps up to the fastest cars we race with, check the video out. Remember this is only a stock 8v with TBs and a Haltech ECU.

 

Qulified on the front row, behind me is a field of 27 cars, the were 5 evos around me on the start. Was very scary having such powerfull cars around me off the start, I only have 106hp atw.

 

http://youtu.be/wFx-Zn3Ku9c

 

Edited June 26, 2012 by parry

[Cameron 16]

ARB's are a tuning tool, used to adjust the handling balance front-rear by decreasing grip at the axle they're fitted to. Road cars like to use them as they mean you can run softer ride rates (good for ride comfort) without having boat-like body roll; race cars in general will avoid relying on ARB's so much as it's always better to add grip than remove it - they're a last resort really.

 

I'll stick my neck out and explain.. and will try to do so as simply as I can.

 

Hopefully everyone will know that when you go round a corner load is transferred from the inside wheels to the outside. This amount of load transfer is a constant and cannot be changed with springs or ARB's, only by lowering CoG or reducing weight, so you have to distribute it around the car in the best possible way.

 

Tyres are awkward things, as they behave in a non-linear fashion when it comes to the amount of grip they can produce. If you imagine a graph that shows the amount of grip you have against the vertical load on a tyre, the amount of grip doesn't increase as a nice straight line the whole way up, there comes a point where it tails off - much like an engine power graph - and you start getting smaller and smaller increases in grip as the load applied goes up.

 

Why is that even relevant? Because it means that tyres work much more efficiently the lighter they are loaded - i.e. you ideally want to have equal load on all 4 wheels at all times for maximum possible grip.

 

Of course this is never ever possible, as cornering will always produce some load transfer! So as I said you have to make the most of the cards you're dealt and try to distribute it front-rear in a way that A - makes the car handle well and B - gives you the maximum possible grip; you do this by adjusting the "roll resistance" of each axle by changing springs and / or ARB's. Incidentally, the body roll angle has absolutely no influence on the amount of load transferred at the wheels.

 

This is the point where it gets difficult to explain in simple terms, or without chucking some numbers in and showing you a practical example, but I'll try my best.

 

Since your front and rear axles are connected by the chassis, what happens at one end will directly affect the other; this means that if you increase the load transfer at one end you decrease it at the other and vice-versa. Say you make the front end really stiff in roll, it now takes up most of the load transfer and the rear takes up very little.. your outside front tyre is very heavily loaded, your inside front is very lightly loaded, and the rears are pretty much even. You might think this is exactly what you want as more load on tyre = more grip, but you'd be wrong, because of the way tyres respond to load you'd end up with much less front grip in this situation. This is effectively what happens if you fit a massive front ARB - you get tragic understeer!

 

So think about a 205 now.. it has a >60% front weight distribution so you're disadvantaged from the start as your front tyres will be closer to the point where the amount of grip they produce tails off, and you have to run higher front spring rates which will increase front roll resistance and therefore front load transfer. Say you end up with a 60% (number plucked from the air btw) front distribution of load transfer, as a result of this you will have a car that understeers - acceptable for a road car as understeer is nice and easy to control, but crap for a FWD race car!

 

You can counter this in 2 ways: 1 - decrease front roll stiffness, 2 - increase rear roll stiffness. If you go with option 1 then you end up with more body roll which could be totally unacceptable due to boat-like handling or excessive camber change in corners, which may well reduce front grip rather than increase it. Option 2 is the option that pretty much every FWD racer goes for as it gives far better results, so you fit a fat rear ARB and stiffer torsion bars. If you have the rear end taking up most of the load transfer then you have a tendency to oversteer, but in a FWD car this really doesn't matter so much! All your power goes through the front wheels so you can steer the car on the throttle. There are limits to this, obviously, go too far and the car will be uncontrollable.

 

So.. umm.. back to the original question: can I remove my front ARB?

 

Yes you can, and it could work very well for you but there are factors to consider in order to make it work - the most significant of which being body roll and it's affect on your geometry. If you have a standard GTI and take the front ARB off you will end up with a horrendous barge that wallows about and corners on the sidewalls. If you've fitted some thick rear bars then you may be able to make it work.. it's simple enough to try it out, as Baz said just disconnect a drop link and see what happens. With 24mm rear TB's, standard rear ARB and 350lb front springs I found that removing the front ARB made body roll unacceptable and my tyre wear pattern also showed this. When I re-fitted it the handling was much improved and the car was definitely quicker, so it's important to understand that it's a balancing act between many many variables. You need to discover what works for you and your car's setup.

Edited June 26, 2012 by Cameron

[parry 23 1 Cars]

Good explanation Cameron, it also depends on tyre choice as well. The slicks I have found give you no warning of reaching their limit of adhesion, so an oversteering car is dificult to control with slicks. I have on ocassions run slicks on the fron and r spec on the rear, this is only in very cold weather as it allows me to get more heat in the rears by sliding them around.

 

In my previous post I forgot to mention I am running 24mm rear ARB with 23mm torsion. so very stiff in the rear.

[johnnyboy666 195 1 Cars]

interesting read, thanks Cameron

[BlueBolt 156]

Cameron

Very useful answer and thank you very much!!

 

Parry

Awesome clip that!!

[kyepan 291]

excellent video!! good post cameron. That 205 handles!

[engine killer 6]

what a coincident i found this in the same day.

 

http://autospeed.com/cms/A_112694/article.html

 

.....Sway bar stiffness increases as the fourth power of the diameter. For example, a sway bar might have a diameter of 22mm and you are considering changing it for one which is 26mm in diameter. 22⁴ (22 x 22 x 22 x 22) give a stiffness factor of 234,256 units. The second bar’s stiffness is 26⁴ which is 456,976. Divide one by the other and you can see that the second bar’s stiffness is almost twice (1.95 times) as high, even though it’s only 4mm thicker!.....

 

another interesting read, but can anyone confirm the above-mentioned stiffness calculation?

[Rippthrough 98]

Yep, it does vary like that, it's why even 1mm on the rear bars makes a notable difference.

[Henry 1.9GTi 36]

MV^2/R

 

take it per axel. More mass = more force required. and as cameron points out tyres are not linear so if the car is front heavy you need to compensate by having a larger proportion of the weight transfer at the rear. Then compensate a bit more as the front wheels are driven! With a floppy 205 shell it would be hard to get enough rear roll resistance as the spring change required is greatly increased in terms of balancing the car with a flimsy chassis. fun fun

[Cameron 16]

Yes, chassis torsionall stiffness is a massive factor in all of this, so is definitely worth pointing out! You'll most likely find that a non-caged 205 shell would need a thicker rear ARB to get the same rear weight transfer as a full caged shell.