Help me understand! FWD content

I forget the original post, but it was a while back and it was about FWD suspension setup for autocross.

I believe it was Per, or maybe it was Mr. Suddard... but they chimed in and stated that most fwd autocrossers like a large front sway bar. On the other hand, on a track, a larger rear sway is often chosen.

of course this isnt word for word... and it was quite a while back so who knows? Maybe i remember it incorrectly?

But i was under the impression that with fwd, a larger rear sway bar would be better for rotation while autocrossing. Could this just be a driver preferance situation? OR is a larger rear sway just better in fwd when you are at higher speeds with larger radius turns ?

Just got me thinking... Add in what you would like.

generally you'd prefer a looser car for autoX and a tighter car on a track. whether a bigger front or bigger rear bar loosens the car depends on the car. my protege loosened up considerably when i installed a larger rear bar from a mazdaspeed protege...adding the bar reduced rear grip, which is one way to balance the handling. other fwd cars can improve balance by increasing front grip with a larger bar, which reduces roll and the associated camber gain in strut-based cars. but on other cars a bigger bar reduces grip. every car has its own suspension geometry, so results vary.

in short, it's not as simple as "FWD = add big rear bar".

I know with my older excel.. once I broke the front the front bar.. the car went from terminal understeer at anything faster than parking speeds to a decent handling car.

the larger bar in my saab helped it's understeer a lot too

Larger rear bar helps a FWD car for auto-x'ing. Loosens up the rear and gives the car a more neutral feel (compared to the "OMG it won't TURN!" understeer).

It depends on the car, though. Some Saturn autocrossers (yes, there are some :) ) prefer to "downgrade" their twin-cam cars to the softer from sway bar that came on the single-cam models. This allows more compliance in the front suspension, keeps the front tires planted on the ground better, and reduces wheelspin. On many FWD cars, which are already prone to understeer, a larger front bar just makes the situation worse. I suppose it depends on how a particular car was originally equipped whether a bigger bar helps or hurts.

but they chimed in and stated that most fwd autocrossers like a large front sway bar. said:

Don't ever recall reading this. I've removed the front bar in every FWD auto-xer I've owned.

Large rear bar, no front bar and 3" of ice.

i too removed the front bar on the swift and it made a wonderful difference.

poopshovel wrote:

but they chimed in and stated that most fwd autocrossers like a large front sway bar. said:

Don't ever recall reading this. I've removed the front bar in every FWD auto-xer I've owned.

yeah, E36M3... I mean I might be wrong. I just remember being totally stumped when I read it. Personally i have a 24mm EX front bar and a triple adjustable 24mm Rear on my civic. If I remember correctly, I do think that my understeer may have become a little more prevalent once i put it on (the front bar). But on a somewhat long sweeper of a turn, it is of course more stable and with some left foot braking it feels like it rotates just right...

nice input. i may try without a front sway bar this year.

WITH the 24mm front bar ion the swift it would pull the inside tire on the front, smoking the tire on corner exit and made it plow like a Farmall. Took the bar off, corner exit was managable and could finally get some rear end step out.

All else being equal, increasing the size of a swaybar will give you the equivalent of a higher spring rate. Smaller swaybar = lower spring rate. Depending on the car, a larger front bar can help, assuming you have tires that can take advantage of the increased front end grip.

Again a huge generalization, but auto-x folks usually dial-in more oversteer than you would for a track day. Understeer is safer at track speeds than oversteer.

That was me. I like big front bars on stock-class FWD autocross cars (and even some SP and ST cars) The caveat is that this is for a MacStrut car where you need enough wheel rate to keep the camber (and thus contact patch) more consistent mid-corner. Most nationally competitive MacStrut FWD cars will have larger front bars on them, or at least stock (we keep the MINI 24mm one on there, it's about right)

Wishbone cars or cars that can change springs are a different matter. Although, I've found that even with unlimited rates, I still like to keep a fair amount of wheel rate via bar.

One interesting fact is that large rear bars only help to a point. As soon as it lifts that inside wheel, it's not doing you any good--just slowing you down with its extra weight.

think outside the box.

In general : Stiffer front bar or springs = understeer Stiffer rear bar or springs = oversteer/less understeer.

Sure, in general. But with stock springs on a MacStrut, you're so far under 'optimal' that more front rate will actually equal more front grip.

Then again, I love racing against people who don't realize that :-)

I used to put a Chevy Blazer bar (huge !!) on the front of my GTI, and to Per's point, it still lifted the inside rear wheel when autocrossing. When I converted the car to an ITB road racer, the front bar was removed and I added a Shine racing bar to the rear. Along with the rear bar I'd also run some pretty high spring rates at both ends. Something like 600/700 Fr/Rr. On the race track I wouldn't get the rear wheel off the ground anything near what it would do autocrossing, but I could lock it up pretty easily. In stock form it could lift a wheel a foot on a tight slalom course, that's why the really large front bar helped.

HA! knew I wasn't crazy and seeing things when i read that... I see now... A-arm, Strut... different designs require dissimilar sway bars rates. interesting. Thanks Per.

This is a bit of a thread hijack, but ,,,,,,for anyone running a VW Golf/GTI and needing rear swaybars, a Chevy Caprice front bar can be put on a VW rear axle by drilling 4 holes. One near each shock mount to attach the end links and 2 on the main beam to bolt plates to. Then you use the stock bushing retainers to bolt the bar to the plates.Caprice front bars come in 1/8 increments from 7/8 to 1 1/4 and are peanuts at the local wrecking yard. You need an assortment of bushings, but they're not all that expensive from your local hot rod emporium. Real "grassroots" !!

mad_machine wrote: I know with my older excel.. once I broke the front the front bar..

Did you break the bar or an end link?

Per, funny thing you mention pullking the rear tires.... with the stock 24mm bar on the Swift I could not pull the inside rear wheel, ever. Once the front bar was removed, I can consistently pull inside wheel and have a fair amount of looseness (oversteer) that the car was severely lacking. but then again it's only half macstrut(front), so I have a whole different can of worms to open up there.

Geesh... I am already tired of bench racing. Lets get this party started already!

Per's point is directed to a narrow field. Stock autocross. No increased rear bar allowed. No camber change. So anything to decrease roll and loss of tire contact is an improvement. Improving handling on any car is a trial and error thing until you come up with the point where you are happy with it. Even things like tire pressure, as shown on the GRM tire test.

dj06482 wrote: Depending on the car, a larger front bar can help, assuming you have tires that can take advantage of the increased front end grip.

I made the same assumption at one point, but this statement is misleading. Per explained a part of the situation very well - when the options are limited and the springs are too soft to maintain proper alignment (stock class mac strut cars are perfect example of this), then a larger bar will actually increase grip by keeping the suspension geometry in it's sweet spot. However, sway bars, by their function, transfer weight to the outside tire where you don't want it actually reducing mechanical grip on that end of the car. All else being equal, roll rate produced completely by springs will have more grip than that of a sway bar/spring combo. All else isn't usually equal though. Uneven surfaces and imperfect tracks require softer rates to maintain traction not to mention the obvious need to have bearable ride frequencies on street cars.

Thread necro. 

I was pretty set on upgrading the rear bar on my HS 8th generation Civic Si, but after some more thought, I'm really considering upgrading the front instead. It makes sense, within the limitations of Street: the car has MacPherson front suspension, which as mentioned, gains camber under compression, which would reduce the size of the front contact patch in a corner. A front bar would reduce the amount of roll, thus reducing the amount of camber gain and maintaining as large of a tire contact patch as possible. Even with four crash bolts, one for each strut mounting hole, you can only achieve very little negative camber. A larger front bar should also help the car in slaloms.

In reply to ApexEight :

Just remember, there is a difference between "feels better" and "is faster". The point with the big front bar is to maximize contact patch and grip. You may do that at the cost of making the car feel terrible initially because it won't rotate at all. Generally you compensate with either high or low pressure to reduce rear grip and bring the car closer to neutral. It takes a special driver to say "I don't care how it feels as long as I'm faster" and usually a lot of testing to get there. 

In reply to mazdeuce - Seth :

For sure. I think I'll appreciate the slalom stability and responsiveness, but hopefully I'm also satisfied with the higher (theoretically) cornering grip, despite the lack of rotation. I'm sure I'll have to cater my driving style to the setup as well.

In reply to ApexEight :

Try it and see.

If your front suspension is on a bumpstop, or a rear tire is lifting, then making the front stiffer will only do good things.  A suspension at the end of its travel has infinite stiffness  so a bigger bar will actually make that end "softer". 

And once you are on three wheels, suspension tuning is irrelevant.  Making the lifted end stiffer does nothing since it is already at 100% load transfer.  Making the other end softer just changes how high up you are lifting the other end, and losing camber at both ends.