custom 24mm rear anti roll bar

[sambb]

Whiteline put me onto Signature Swaybars (formally Selby's Springs- same family running it) when I inquired about getting them to bend up a custom rear bar. I spoke to Todd Selby there who said that if I sent down my whiteline BWR19Z 20mm rear bar, they could use it to set up a jig and bend up a bigger reproduction of it. We had a good chat and he thought that given our bar is basically a torsion bar designed to stiffen a torsion bar (our rear axle) rather than a chassis anchored anti roll bar in the traditional sense, that a 24mm would be the go as a next step up from the whiteline 20mm bar.
He thought $250 bucks would be the raw cost of the bar but obviously 24mm urethane bushes and freight to Nowra would have to be factored in.

There are H&R 25mm rear bars for our car but I can only see them sold as a kit with their 22 mm front bar and I believe it is non adjustable. If I'm to be going so much stiffer on the rear I'd like to retain the whiteline 3 position adjustability so thought that in terms of cost and function this would be the way to go. After my next event which is April 2 I'm going to send them my rear bar so that I can get it back on the car in time for the next event which is a month after that.
I haven't broached it with them yet but in case they can do a run of a few bars it may end up cheaper, so if anyone else is interested let me know. They'll be happy to do a few I'm sure but it may represent a cost saving or we might be able to dave on freight.
so if anyoe is interested let me know.
sam

[seangti]

Sam, why would you run more bar as opposed to stiffening the rear springs?

Everything I've read and the guys I speak to recommend increasing spring rate via springs and only refine with bars, as opposed to compensating with the bar. Rear springs should cost about $400 from whiteline, but there are others. That's the approach I'll be taking in order to run less bar.

Are you in Nowra are you? I'm down there every few weeks for work, next week included if you wanna meet for a beer.

[sambb]

As is I have square spring rates 160lb/in all round which probably puts the wheel rates from springs alone somewhere around slightly front stiff. I've run out of rear roll stiffness at the back because I like the existing whiteline bar on hard, but can still go stiffer at the front (1 hole extra on the whiteline front bar) as I run it on the soft setting. To keep the existing balance but make the car overall a notch stiffer I need to add some rear roll stiffness if I'm to go to the stiffer front setting.
If I add rear roll stiffness with springs, that will make it harder to get the inside rear in the air ie less roll angle due stiffer springs yet the unstiffened rear beam will allow the inside rear to droop just as far before it lifts. I'll be going backwards re the inside rear wheel lift thing and it just won't work. If I'm to continue to be able to lift the inside rear with a car that is rolling less then I have to do it with a stiffer beam. Stiffer rear springs will do nothing to help the inside rear lift but a stiffer beam will add rear roll stiffness + help the inside rear into the air when the car is running flatter.

[sambb]

basically what you say is true but I think people underestimate how pathetically soft our rear beam is. My mates Clio RS W172 will sit on his driveway that has a couple of inches of fall and his inside rear will be up in the air. With our car if you have the rear of the car up on stands and put a jack under one side of the beam and jack up until both sides of the beam move, the sag from left to right is massive and that's with the bar attached. I don't think our rear beam can be compared to say what the factory did with the fiesta ST, meganes, clios etc.
I only have the single spinner and in the corners where I can feel the inside rear coming off the deck it drives like it has a limi, everything else is just power down understeer on exit. It might be different for you as you have the limi but my car is hopeless unless that inside rear has lifted, just no ability to get the power down. In the faster corners though the inside rear is still on the deck if you do it right and also you're not pitching it onto its nose on turn in like you would in tighter stuff - might still be action packed in the wet but then you can just soften the rear bar in the wet to compensate which is what I do.

[sambb]

sorry just saw the last bit. No I'm in northern syd - haven't been down there since holidays as a kid.

[teejaypee]

New polo owner I may be in for this need to do some more research...

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[sambb]

no worries. PM me if you want any info/details.

[teejaypee]

can you guys simplify the discussion into pro's and con's of adding this mod!?

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[sambb]

There are 2 main ways of adding roll stiffness to a car. You can do it with geometry (eg linkage angles) and you can do it elastically (springs and anti roll bars). Broadly, stiffening the car with springs only will make the car stiffer in ride and roll, stiffening with anti roll bars only will make it stiffer in roll but it should keep its ride compliance. The more stiffness you add to the rear of a FWD car the less it will tend to understeer, so if you add stiffer rear springs or a stiffer rear bar and do nothing else, then you'll achieve this. Its all relative though - if the car is standard at the front and you stiffen the rear its easy to go over board eg you may get it to point well but it may introduce some lift off oversteer into the car. You wouldn't put the 24mm rear bar (or really stiff rear springs) we were discussing into an otherwise stock car. that'd be going to far. The 20mm whiteline bar would do the trick there. However if you've already substantially stiffened the front with springs and a bar then stepping to a 24mm rear bar or stiff rear springs might get you the rear stiffness you need to get the car more neutral through the corners.
What we were talking about though is more to do with track work. There's a debate that's always raged with FWD track cars about whether the car should be set up to lift its inside rear in fully loaded corners or not. The argument for that setup is that when the inside rear is off the deck it places greater % onto the two front wheels which is needed to get good drive in a platform that will tend to spin the inside front wheel and push wide on corner exit. It can also be used to get the car to rotate more - basically overpower the outside rear and slide the car more which can help in tight courses like hillclimbs or rallysprints. The argument against it is that you can go too far with it. If you want your car set up that way then you want the inside rear just skimming clear of the ground in the corners that are important for a good time. Going further than that may mean the car is hairy on other parts of the track, very taily in the wet or overloading the front geometry unless something is done there to cope with it. A lot of fast circuits cars aren't set up to do it at all because stability is seen as more important for a quick time which is where Sean is coming from I think.
Springs alone will do nothing to help the inside rear lift unless there is some sort of anti droop built into a rear coilover or droop limiters used. A really stiff bar will however get the inside rear lifting. So both ways are adding rear stiffness but the effects on the way the car handles are quite different at the limit. Hopefully that'll help you choose whether lots of rear bar or lots of rear spring will get you what you want. If its just for the street though, a custom 24mm bar would be excessive.

[seangti]

Yeah, it's what Sam has said.

I like to think of the sway bar as a tool to refine and tweak a set-up, not so much to compensate. (I'm not there yet, it's being used to compensate until I get new rear springs sorted)

Part of my focus on rear ride height and stiffer springs is also to improve corner exit grip where I get wheel spin. My car is nice on entry, but not getting power down how i want on exit, even with the LSD. It's also got a stiffer front sway bar, which is what Sam refers to about the balance. Run stiffer front bar, need stiffer rear.

For the most part, go with whichever suspension you want, add a sway bar if you feel it needs it, but start on a soft setting, test it in various conditions and adjust accordingly.