The SwayBar Thread (Nasioc)

by **ildylan** June 29th 2012, 8:45 pm

http://forums.nasioc.com/forums/showthread.php?t=1152714

A lot of good info in the thread, but I will quote the Turn In Concepts part regarding what size bar:

As for what size bars to get, and this is my opinion based on experience, and is in consideration of solid bars (that's what I have the most experience with, and it makes for an easier comparison to stock).

For the rear bar - 22mm is good. You can pull off 24mm but the inside tire gets too light, and you lose traction in hard turns if you are on the stock springs. If you are considering going to 24mm or larger then you really really need to consider upgrading your springs first. See, the springs will stiffen not only the ride, but will also increase roll resistance. Now, stiffer springs does not have to mean a crappy ride. If you do your homework, and get a spring that a) doesn't have a stupidly low drop and b) are good for the operating range of your struts then the ride will feel just fine.

For the front - traditional thinking has held that if you want to fix understeer you want the rear to step out more. While this does work to some extent, I feel this is the wrong way to approach it. Sure CONTROLLABLE oversteer with the back stepping out is fun, and a good thing, but the front is still going wide. As part of this traditional thinking folks scream get a bigger rear bar, and leave the front alone or go smaller. I have to disagree on this. Here's why -

First, let's look at the technical reason. The dynamic camber curve for the mcpherson strut setup sucks. It just does. That's a tradeoff of running this type of setup, and all setups have their good and bad points. What happens is this - you enter a turn at speed. Your ourside front corner gets loaded with weight. That weight compresses the suspension. When the suspension compresses the camber of that wheel, where that tire is loaded, rolls toward positive camber. If you're running very little static negative camber this will actually start to make the inside edge of the tire light, reducing the width of your effective contact patch that resists lateral acceleration. This lose of traction results in that "push" or understeer condition. This is why folks who are more into performance run a decent amount of negative front camber. Sure, they give up some straight line accel and decel grip doing this, but that's more than offset by the fact that they can maximize the width of the contact patch in turns to help resist higher slip angles due to lateral acceleration. If you lower the car any with springs or coilovers that camber curve gets worse. Oh, and the added bumpsteer sucks too. Fortunately the fine fellows at 6Gun have figured out a way to help that, but that's for a different long post I'll most like use to answer somebodies questions in the next few days.

So, what they heck the the point in my saying all that? Well, let's get back to the front swaybar. The front swaybar will increase the effective spring rate of the wheel without effecting the ride spring rate. In other words, it will help keep the suspension from compressing so much at the loaded corner. Less compression means less loss of camber. Less loss of camber means that you can tune to, and maximize the contact patch of the tire to resist that push. Now, one of the things you need to consider - just like you can't make something from nothing, you can't make a good contact patch if you have nothing to give it to begin. Because the suspension will still compress some you need some negative camber in the front to start with. See the bajillion threads on alignment specs for where to start.

Now, for the second item I'd like to bring up something I've thought long and hard about for a long time. For ease I'll call it the philosphical side of the front suspension. Here's what we've got - a car that understeers or pushes quite a bit. Sure, you could throw a big bar in the rear and get the rear end to step out to help eliminate that understeer, but I feel that this is the wrong approach. The front of the car is still pushing, but the rear just happens to be stepping out at a faster rate than the front. The net result is a wider than what I feel is necessary lateral travel of the car. In other words, the rear is whipping around to point the front of the car where you want it to go, but the front of the car is still sliding sideways and taking the whole thing sideways making for a wider path than really is needed.

See, this stems from my philosophy that move oversteer does not necessarily mean less understeer. The front is still pushing. I feel the fix for this is to setup the front end of the car to truly reduce understeer as much as possible. This will make the front tuck in more, and while your tires will be resisting more lateral acceleration taking more grip from straight line acceleration (think traction circle), you'll be able to unwind from the turn faster thus getting you back toward the acceleration portion sooner than your competition. In other words, you'll be able to drive a tighter, and more controlled line.

Additionally, by reducing understeer as much as possible you won't have to set up the car for so much oversteer. This will also lead to more control, a tighter line, and the ability to accelerate sooner.

Now, that's great an all, but if you're looking for a simple answer as to what size bar to get then here it is (I'm giving these in terms of whiteline bars as I am most familiar with them):

Rear - 22mm to 24mm, but if you go to 24mm then you really want to think hard about upgrading your springs. If you go higher than 24mm then you are taking the wrong approach and trying to fix shortcomings of your springs with swaybars, and this is not the right way to do it. Get a proper spring for what you do, and then fine tune with a swaybar.

Front - for the street and mild autocross, and mild track work look at 24mm up front. If you start to get into it more then 26mm is good (WL makes a 24-26 adjustable front). These are also very good sizes if you are not a smooth driver as they won't make things too "darty" with super quick tuck of the front end into the apex. For autocross junkies or track whores who are smooth overall and can anticipate the "dartiness" then look at the 27 to 29mm front bar.

Now, two last thing on these considerations: You need a brand and size, and you need a vendor.

For the brand and size please do some research in the car parts review area. After receiving the parts you choose, and installing them please leave your feedback on them in the car parts review area so you can help others in the future.

The vendor part works the same way. Please research the vendors you are considering in the vendor review area. After the completion of the transaction please leave your feedback for that vendor in the vendor review area so that you can again help others in the future.

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