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nilfinite
nilfinite New Reader
11/17/14 4:20 p.m.

I saw a thread on this on GRM from a couple of years ago. Now that most modern FWD cars are macstruts in the front, I think it's about time to debate the age-old "fact": Never get a front sway bar on a FWD car, it increases understeer.

I'm currently trying to find the magic setup for my Fiat 500 Abarth. No matter what I do, the front tires on the car are not happy. With -3 camber and maxed out caster (via bushing), all of the wear on the tires is on the outside edge of the tire (confirmed on worn tires and confirmed by checking tire temps). Lots of rolling over onto the tire shoulder as well (not because of noob understeer, at least not anymore).

I'm convinced that modern FWD cars, unless they are super slammed and super lightweight, need a front sway. High center of gravity, crappy camber curve, macstruts, nose-heavy, soft springs all contribute to the need for a front sway.

Anyone else feel the same? I feel like I don't understand enough about spring rates and pre-load to be certain enough to splurge on a bar that I potentially might not use.

Swank Force One
Swank Force One MegaDork
11/17/14 4:23 p.m.

Really depends on the car.

I have two(three) Macstrut FWD cars that really hate big rear bars, and work much better with a huge front bar.

nilfinite
nilfinite New Reader
11/17/14 4:33 p.m.

Awesome, glad to know that there are FWD cars out there that prefer a front bar.

Paul_VR6
Paul_VR6 HalfDork
11/17/14 4:41 p.m.

Depends a lot on the spring rates used and how you want to get to the right wheel rate. I have setup cars with a big front bar and big rear spring rates, and no front bar, a big rear bar and light rear spring rates. I like the former, but tons of people like the latter.

FSP_ZX2
FSP_ZX2 Dork
11/17/14 4:42 p.m.

BFSB can make it transition like a mo-fo, but there may be some additional corner-off understeer and associated wheelspin (both of which you can learn to drive around). I had a BFSB on a H-stock MKV Jetta 2.5, and it was a worthwhile addition (along with Konis), IMO. Was like a bag of water without it.

Are you trying to stay within a rule set? Otherwise BFSB + BRSB might help.

nilfinite
nilfinite New Reader
11/17/14 5:08 p.m.
FSP_ZX2 wrote: BFSB can make it transition like a mo-fo, but there may be some additional corner-off understeer and associated wheelspin (both of which you can learn to drive around). I had a BFSB on a H-stock MKV Jetta 2.5, and it was a worthwhile addition (along with Konis), IMO. Was like a bag of water without it. Are you trying to stay within a rule set? Otherwise BFSB + BRSB might help.

I'm trying to stay within ST rules so I can do both bars. The only limit to my setup is the spring rates, I have Bilstein coilovers and would like the car still be drivable on San Francisco's broken roads.

The Bilsteins are 285 lb/in in the front and 217 lb/in in the rear.

Corner-off wheelspin doesn't sound super fun though, already having trouble getting power to the ground with an open diff.

Here are pictures of my ZII Star Specs after 20 or so runs. https://drive.google.com/file/d/0B_wLjhzp36DrbVp2RWZZekZrbk0/view

nilfinite
nilfinite New Reader
11/17/14 5:16 p.m.
Paul_VR6 wrote: Depends a lot on the spring rates used and how you want to get to the right wheel rate. I have setup cars with a big front bar and big rear spring rates, and no front bar, a big rear bar and light rear spring rates. I like the former, but tons of people like the latter.

Huh, I do have a big rear bar and light rear spring rates. Should I should test what happens if I disconnect the front sway? It seems like that latter applies to cars that already have all the right dynamics double a arm, lightweight, etc.

FSP_ZX2
FSP_ZX2 Dork
11/17/14 5:20 p.m.

Those are light spring rates...very much towards the 'street' side of street-touring. Try big(er) bars on both ends, with a slight nod to increasing the rear over the front. The BRSB should help with forward bite and help in rotation.

rcutclif
rcutclif Reader
11/17/14 5:25 p.m.

did you remove the front sway from your fiat? (I'm assuming it has one stock of course, but would be floored if it doesn't).

in general (FWD/RWD/AWD included), a bigger sway bar reduces the grip to the end of the car it goes on (relatively). I visualize this by seeing the sway bar un-equally distribute weight between the two wheels on a axle, and theoretically maximum grip comes when both tires are doing equal work.

unfortunately, if you take sway bars off completely, you will need really stiff springs to keep the tires from doing all sorts of nasty things (like rolling over onto the corners and therefore not using the whole contact patch).

So therefore (assuming you are only changing sway bars), there will be a balance, and swaybars are a good balance tuning tool. You want a soft swaybar for grip in the front, but not so soft that the tires roll all the way over and get into wacky alignment settings at the edge of suspension travel.

What to do then?

  1. Spring rate up or sway bar up at both ends until the tires stay in semi-correct alignment zones while at maximum cornering.
  2. Adjust oversteer/understeer balance by the relative strenght of the swaybar. Going softer at one end will give that end relatively more grip (as long as your tires stay in their alignment zones). Going stiffer at one end will give that end relatively less grip (and is less likely to move the tires out of their poor alignment zones).
rcutclif
rcutclif Reader
11/17/14 5:35 p.m.

I don't know if this is your situation, but it seems you are absolutely right that the 'fact' is wrong if your car is under sprung/barred on the front to begin with.

So now the 'fact' seems almost silly: never put a bigger swaybar on the front of an FWD car, unless the one it currently has is too small.

mad_machine
mad_machine MegaDork
11/17/14 5:44 p.m.

I can only go from my own experiences. I had a 1988 Hyundai Excel. It was an understeering pig in stock form.. to the point where I put it up onto a kerb in light rain, going slow, because it refused to make a hard left going downhill. (no damage, was going slow)

Then the day came that one of the swaybar mounts broke and I removed it. Car was almost neutral after that, it had a hint of oversteer, but otherwise was just as tossable as a friends Mk1 Rabbit GTI

iceracer
iceracer PowerDork
11/17/14 5:52 p.m.

The whole point is to reduce roll.

Stiffer springs, slight lowering of the CG. Changing the bias of front to rear springs is a help.

Bigger front bar will increase under steer, a bigger will reduce it.

mndsm
mndsm MegaDork
11/17/14 5:53 p.m.

I'm running 27/32 f/r with -2.5 static camber on my ms3. It sticks hard. It needed the front to mitigate the rear. I don't remember the spring rates on my coilovers, but its stiff as hell. I think it really depends on the car. I haven't driven a 500 to know what the magic setup is.

turboswede
turboswede UltimaDork
11/17/14 7:05 p.m.

The other thing to think of is that the sway bar not only raises your effective spring rate during roll, it also tries to lift the opposite tire as it tries to keep the car upright. This is generally why FWD cars in stock class have been dropping the front bars to reduce inside wheel spin, reducing understeer at the expense of body roll and transitional speed.

Its all about how much of a compromise the typical strut based suspension is, especially when used in FWD and on the street. So you can either ditch the bars and increase the spring and shock rates until it works well enough for your dual sport needs, which won't be cheap (though Bilsteins are typically able to be revalved to suit your needs for a reasonable price) and may make the car less enjoyable to drive on the street.

Some have found that properly valved shocks will cure a lot of the typical harshness some complained about with lots of spring rate, blown shocks and spring rates way outside of the capability of the shocks to control will contribute hugely to bad drivability/harshness.

mazdeuce
mazdeuce UberDork
11/17/14 7:26 p.m.

First and foremost you need to get the tires to work properly. If you get the car 'balanced' by reducing rear grip to match crappy front grip, it might feel good, but will it be faster? There are four little patches of rubber that need to work well in order to go fast. Get the front to stick as well as you possibly can, then balance the car.

ncjay
ncjay Dork
11/17/14 7:33 p.m.

What exactly is meant by "maxed out caster"? Every suspension design has its own quirks and problems, but normally lots of caster is not friendly. You want just enough, and not any more.

chili_head
chili_head New Reader
11/17/14 8:20 p.m.

Have you tried a rear bar? It seemed to really help my MINI rotate on entry. Next up for me is more camber in the front.

Kenny_McCormic
Kenny_McCormic PowerDork
11/17/14 8:33 p.m.

In the words of Colin Chapman "Any suspension will work if you don't let it".

nilfinite
nilfinite New Reader
11/17/14 11:04 p.m.

So this car does have a larger rear bar. The largest that's available for the Fiat. There is a guy making custom torsion bars so I have the option to increase rigidity back there if needed. Caster was increased to about 3.9 degrees from 2.8 degrees stock via whiteline bushings.

I've tried -2 and -3 static camber, either way the wear is concentrated on the outside edge of the tire.

With the soft spring rates on this car and high amount of roll, I think the car is going far into positive camber in the turns, it's certainly showing up in the tire wear.

These are the potential ideas I'm kicking around to try to improve grip in the front. 1. Front Sway Bar 2. Spacers / Wider track in the front 3. Sway bar end-links. I'm still using the stock front bar and the fixed length end-links. Did lowering the car affect the pre-load and could that be the cause of my weird camber problems?

Not really ready to make the car undrivable on San Francisco's crappy streets. I think at that point, I might as well jump into SMF and turn the car into a track/autocross car with LSD, roll cage, etc.

A potentially interesting point for the suspension guys, there was a time where I was using mixed size tires and wheels on the Abarth for autocross. 17" wheels and 215/40/17 tires in the front, 16" wheels and 205/45/16 tires in the back. The front tires were higher than the rear tires. When I did that, I actually saw the opposite: more tire wear on the inside edge of the front tires. Ironically, the car felt pretty good with that setup. The wear & tire temps was overall more even as well. What does that tell you about what the suspension is doing?

mad_machine
mad_machine MegaDork
11/18/14 3:27 a.m.

If you are already understeering, I do not see how increasing the size of the front bar is going to help.. but you may be onto something with the soft springs

Fr3AkAzOiD
Fr3AkAzOiD Reader
11/18/14 6:39 a.m.

I am in the same situation with my Malibu and keeping it legal for NASA TTF.

Would like to hear what solution finally works for you as more camber, spacers, and bigger sway bars and end links are the only options I know of that will keep me in class.

mazdeuce
mazdeuce UberDork
11/18/14 6:41 a.m.

Per went over this in reference to Mk1 VW's. Stock class allowed one bar. On paper that meant that you wanted to put the bar in back to balance the car. In reality this was the wrong answer. The correct answer was to run a massive front bar to correct contact patch issues resulting from crappy camber gain. THEN balance the car. I think they did that with tire pressure.
I think that's what's going on here. Once you push the car hard enough you lose camber and your contact patch goes away. Normally it would make sense to up spring rates in front until you can get things under control. Because you don't want to up spring rates option 2 is a big bar. This brings other issues with it (more wheelpin out of the corners maybe) so it's not ideal, but it's probably better than just not trying to get more front grip.
1. Maximize front grip.
2. Balance the car.
You're not done with step 1 yet.

GameboyRMH
GameboyRMH MegaDork
11/18/14 6:48 a.m.

I used to have a stock (16mm IIRC?) rear bar only on my AE92. I had good even wear on the front with -2.5deg front camber. When I added a stock front bar (21mm IIRC?), it reduced body roll by about 1/3 (mind you I only had about 3deg thanks to rock-hard springs) and the handling balance was unaffected. It made the steering feel sharper too.

Many people who race these say that the front bar helps in autocross but isn't worth the loss in corner-exit traction around a track. I'm planning to get a quick disconnect for the front bar to test this out.

This car is a good bit lighter and far shorter in height than a modern FWD car though.

Gearheadotaku
Gearheadotaku PowerDork
11/18/14 7:24 a.m.

If a smaller or deleted front bar is better for handling, why do most cars get a larger front bar from the factory when equipped with uprated suspension?

gearheadE30
gearheadE30 New Reader
11/18/14 7:33 a.m.

Well, factory I think is a different bag of worms. There is a lot of understeer and built-in safety there that most of us really aren't looking for in an autox setup. For example, the tendency to oversteer increases with speed regardless of suspension. Set a car up to be pretty neutral on an autox and it will usually be pretty twitchy at high speed on the highway or a road course.

Some of it is the type of suspension, too. Macstruts don't have a particularly favorable dynamic camber curve, and increased roll stiffness can really help maintain decent camber angles through a corner. That's why, for example, BMWs often like a larger front bar and a small or no rear bar. Multilink and A arms generally don't have the same issue. I think there is a lot more to it than just "a big front sway bar is always better" or vice versa.

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