FeralComprehension

Working atm so can't write a detailed reply- consider that Porsche went thru a series of snap oversteer issues with the 930 and decided to "add understeer" to the cars to lower product liability.

Personally I prefer oversteer any day.

alexjc4

Yeah, you can totally trade off stiffer coil springs for softer roll bars vs softer coil springs for stiffer roll bars. How you strike a balance is taste/fashion/conditions, there are ups and downs to either way. Similarly, how you use the roll bars to balance under/oversteer isn't written in stone.

Probably for absolute track performance you could afford to add significantly to the overall spring rate of the KWv3 springs, with beefy ARBs front and rear or just stiffer springs all round. But you'd loose a lot of real world livability.

The difference between the 18mm and 21mm rear ARB is an 85% increase in stiffness which sounds radical but is moderated by the fact that the ARBs make up a fairly small % of the overall spring rate, most of which come from the coil springs.

Most adjustable bars give a fairly small range of settings. The effect of lengthening the lever, by moving the drop link, on stiffness is linear whereas the the effect of a change in radius is ^4 so going from 18mm to 21mm is like almost halving the distance from the drop link to the pivot point. I think the RS give more range than most though.

FeralComprehension

I learned about the function of anti-roll bars from this thread on the Miata forum; in particular, see post 2: Springs vs. swaybars

Generally, ARBs are used to combat roll (duh) and to achieve the handling balance that the chassis engineers are trying to obtain. Our cars, given their low centers of gravity, are not terribly roll-prone (I come close to getting in deep sometimes, driving the CR-V after logging a lot of miles in the C4...) and as can be seen from examining the historical record 911 suspensions were increasingly calibrated for a bias towards understeer as that's what the 'average driver' copes best with. It does stand to reason- if you go into a corner too hot your first impulse is likely to let off the gas. This is the wrong move in a rear-engined car (though of course none of us would do that). Having that front bar on there decreased the likelihood of snap-oversteer, thereby protecting Mr. Poser 1990 and/or his trophy wife, not to mention the good Doctor's reputation.

Now, in 2012, talking about our present company , all of whom know damn well not to lift in a corner, many of whom have uprated to springs which are stiffer than the factory fitted, we don't need bars to control roll (if indeed we ever did). If you read why people fit bigger rear bars, it's always to eliminate push. Bigger rear bars reduce rear lateral grip, thereby restoring a more pleasant balance but at the cost of lower ultimate rear grip. It's cool if you want to slide more easily (if that's the case, pull the front bar *and* add the big rear bar ) but if your main goal is to reduce understeer I submit it may work as well if not better to run with no front. It is cheap to try, isn't it?

Disclaimers:
1. While this is working for me, you try it at your own risk. Approach the limits gradually or suffer a fool's fate.

2. My experience is limited to my C4, which has some (relatively) high-tech wizardry that looks out for me in my youthful exuberance. Try it on your C2, but.. reread 1, above, again.

3. I'm no suspension genius and cannot comment on the effect of removing the front bar on weight jacking, the 911's roll-couple, or the change in the camber curve that the stock bars moderate. I can say I've had my STREET car running KW V3s and no front bar for ~7,000 miles and have found NO downside: no loss in stability at speed, no overt unexpected body roll, no snap oversteer (generally driver error anyway). I HAVE had joyful, beautiful, mild, predictable oversteer leaving onramps WFO near the top of third. I have NOT seen the understeer that I used to get going into a turn too hamfistedly hot. Maybe I'm just a better driver now, who knows...

peterC2S

Hey FC - appreciate you taking the time to post. had a few laughs as well... lift... who me?! And given your experience is with a C4 - that's cool because that's what I have and about to update the suspension. ARBs are part of that equation - or maybe not. The adjustability angle intrigues me - though honestly I've a bit of work to do as a driver first before truly being able to exploit the benefit there.

And tks for the link - interesting reading

Vandit

Probably gotta dial in a bit more negative camber in the front for those no front swaybar setups.

kos11-12

Feral,

You may well be right .... Probably for a road / track car,
I will try that , with proper rear bushes ,drop links and maybe more front camber, I am always thinking less is better, it will also save some weight ....

jack.pe

Why would that be Vandit? I thought negative camber increased grip... but taking out the sway bar should already do that, so why increase it further?

Johnny G Pipe

^^maybe removing the bar loses a little camber as the suspension arms arent propped apart as much??

I was planning to finally swap my rear bar this winter, might just try the Feral approach instead. Hey, you started a craze!

Maybe doing this would finally convince me I need a strut brace too..

Main issue is that I heard that front Bar is a PITA to remove (and reinstall after the first spin, LOL)..can someone help us with a how-to with some pain-saving tips? (A search only came up with 996 install tips..)

boxsey911

I can't believe so many people are thinking about removing their front sway bar! While, detaching the rear bar at one end to soften the rear for very wet conditions and therefore reduce oversteer, is a well known practice for guys racing, I've never heard of them taking the front bar off! There could be some big oversteer accidents on the horizon for those that try it.

jack.pe

I also share that fear but bear in mind that this is being done (at least in my case) with stiffer springs and car lowered, so technically the effect of removing the sway bar will not be as extreme as just removing it on a standard car.
By the way, as asked previously, how hard is it to remove? can anyone give me a hand? Alex? you've got a good reputation as an engineer...

Vandit

Negative camber increases grip because it compensates for body roll, giving the tire a better contact patch in the corner. One would assume that no front bar = more roll, so adding more negative camber would help better maintain that contact patch.

Johnny G Pipe

I am buying in to the theory that it is more grip at the front not less at the back. (Or maybe that just means the final impact happens at a higher speed ) I would be still be happy to fit a 21/22mm bar, but that quote that all it is doing is reducing rear grip suggests that everyone who does that mod is backwards ditch visit waiting to happen, surely. Regardless I'm still in the market for a rear bar if anyone has one FS.

Whatever, since I put on my Ruf wheels the car understeers noticeably more and the rear is pretty much unshiftable unless I do wild lift-offs, getting the ***-end to move a little would be a treat!

alexjc4

lol a undeserved reputation sadly

How hard to remove the front bar? Remove the end links x2, remove the U clamp bolts x2, try to wiggle it out, swear, repeat. Installation is reverse of removal as they say. You might need to remove the front under tray so you can see what you're doing.

The "wiggling out" is the tricky bit, its like one of those xmas cracker puzzles where you have to unhook two seemingly inseparable convoluted loops of wire. In fact I can't remember if you need the front sub frame lowered to get it out. I think my sub-frame was lowered already (doing the front diff seals) when I had my front ARB out a couple of years back. If so then its another six or eight big bolts and you would need the front alignment doing afterwards.

Still, nothing very hard, should be able to do it with the front up on axles stands, just make sure you have a 1/2 torque wrench to tighten everything back up correctly.

BTW the rear bar is much easier you just need to remove the under trays and you can get at the U clamp bolts and end links nice and easy.

When you're putting the U clamp bolts back in it can be very easy to cross thread them because they will want to go in at an angle.

Always happy lend a hand, just shout

boxsey911

Jonny, I don't pretend to be an expert on this stuff (and hopefully an expert might chime in) but here's my take on it:

You will indeed get more grip at the front by removing the bar. However my concern is that there will now be too much grip. This could provoke the rear to lose its grip quicker and subsequent oversteer. Furthermore, in corners where there is a lot of loading, you could have a situation where almost all grip is put on the front loaded tyre (because there is no sway bar to pass some of the force to the unloaded front). At the limit of grip the car could suddenly pivot round the front loaded tyre like a massive pendulum, with disastrous consequences. I think the car would also feel very unstable in high speed corners.

As an anecdote to this, Porsche originally put a 20 mm front bar on the C2 but then upped it to a 21 mm bar for later years (from MY91 I think). That suggests to me that they decided that there was too much potential for oversteer and wanted to calm down the handling. I guess they stuck with the 18 mm bar on the rear of the C4, because it was always meant to be the 'safest' 911 they had ever produced.

alexjc4

I find it all a bit counter intuitive and I need to go and top my brain up whenever I think about this stuff and I found a good bit of brain food here: http://www.neohio-scca.org/comp_clin...educed%202.pdf

But, as far as I understand it the total load transferred laterally in a corner is a function of cornering force, track width and CofG height - springs and ARBs don't have any effect. The basic grip that is available is a function of the transferred load and the friction coefficient of the tyres, again not the springs or ARBs.

However what we do effect with ARBs is how the total load is spread between the front and the rear. This is because the body of the car is stiff so it wants to roll as one piece but different roll stiffness in the front and rear suspension means, front and rear want to roll different amounts. The body wins the argument and the front and rear ends split the difference; the body will roll more than the harder end "wants" and less than the softer end "wants". This means more load is transferred to the harder end of the car > its leaning harder on the outside tyre on the rear because the the front end isn't doing its bit to support the rolling body of the car. Again you get the same total forces BUT while when you increase load on a tyre you do increase grip, you increase it by diminishing amounts as the load increase, so two evenly loaded tyres grip more for a given total load than two unevenly loaded tyres (obvious when you think about it)

So, you can't really say reducing the front ARB stiffness adds grip to the front without reducing grip at the rear - in fact it adds grip to the front BY reducing grip at the rear.

All the above assumes "steady state" ie once the cars "set" in the corner, and longitudinal accel and decel or dynamic changes in the cornering force make this more complex.

Once you've found the % balance between front and rear roll stiffness the choice of how you do that; be it springs or ARBs, depends on all sorts of other "real world" things like kinematics of the suspension (dynamic camber and toe changes etc), uneven road surfaces, priority of traction/braking vs cornering etc etc. And there are too many variables to safely theorize so you have to simulate or experiment. BUT a good Colin Chapman quote goes something like; "any suspension design can be made to work so long as you can stop it moving"