FWD & Front Sway Bar

nilfinite wrote: 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?

That one's easy. By lowering the rear, you increased the effective caster angle of the front suspension. While the built-in caster angle of your front suspension hasn't changed, by lowering the rear, you changed the plane of reference i.e. the ground.

Now in your situation, caster at 3.9 is actually pretty good for a FWD mac strut car. And if you add anymore camber, you're likely to encounter traction issues. Your car obviously doesn't have enough camber gain in bump.

Like Mazdadeuce said, you have to fix the front before balancing the car. So in your case, I would say you have three choices:

1- The best solution would be to lower the car's CG has much as possible. Remove as much weight from the top of the car as possible. But since this is to remain a street car, it's not pratical.

2- Increase the camber gain built into the front suspension. You acheive this by increasing the effective lenght of the control arm. No idea if this is pratical or legal in your situation.

3- Install a BFSB to reduce roll as much as possible to keep what camber you have. This is the easy answer, but realise that it brings other problems with it. Reduced inside wheel traction is one, and I wouldn't be surprise if you'd see air under the inside tire in quick transitions.

Since body roll is the culprit on strut cars. Reducing roll is the target.

Lowering CG, stiffer springs, shocks and roll bars is needed.

Since a FWD car is hindered not only by the drive but weight distribution which produces under steer, increasing the rear roll couple will help reduce under steer. this can be done by increasing the rear spring rate, see "B Spec. cars" or a stiffer rear roll bar.

The bigger front bar thing is only effective when a rear bar is not allowed due to an archaic rule.

mazdeuce wrote: 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.

This is what I tried to say, but mazdeuce said it better.

front/rear balance < maintaining correct contact patch

for the OP, if you cannot change anything in the front but the swaybar, I would try a bigger one and see if that keeps your contact patches more correct.

In reference to my previous comment about a high rear spring rate, I mean HIGH. 2x the front rate (wheel) is a good place to start in my experience. This ended up around 350fr/700rr rates with mac front and torsion beam rear, and a 25mm front sway, no additional rear sway (other than what's already in a VW beam). Of course YMMV.

Definitely agreed about the consensus on this thread about fixing the front contact patch. Maximizing grip is the most important. If only half of the tire is working in the corners (less when it's riding on the shoulder), I definitely need to fix it.

Although now I wonder if I should stick with the mixed size tire setup as the best middle-ground route. It results in more caster and maybe if I dial down camber, I might be able to get even wear across the tire. And less worries about the front bar increasing corner exit wheel spin to boot.

Also another question for the suspension gurus, how important is sway bar pre-load? My car is lowered, I'm assuming I've increased the pre-load on the front sway bar because I'm using the factory fixed-length end links. Visually in my mind, I'm assuming that the front sway bar isn't happy when the car is lowered and in a turn, it's being bent more than it was designed to do, resulting in the massive positive camber change?

Ride height doesn't affect pre-load, don't forget the bar rotates up and down freely on the car's frame. If you have uneven L/R ride heights or unequal length sway bar links you'd have preload. Corner balancing might create some slight preload.

Interesting thread, been noticing the same thing on my MK6 GTI with a 22mm solid H&R Rear bar and stock front bar. I can get the necessary rotation, but I am definitely rolling over my front tire during tight turn arounds in autox. I think in my case a lot of my rolling over the front tires was transitioning between my double a-arm integra and into my GTI, I'll have to try it at another autox, but last month, I was trying to adjust my approach to doing the turn arounds in my GTI by entering slower and it seemed to help a bit more, where as on the Integra with front and itr bars I can just throw it around the turn around without rolling over the tire.

I do like the mild rear bar upgrade in most situations, just the turn arounds at the airport run way seem upset the front.

Most likely you are still getting excess roll due to soft stock springs. Lower and stiffer is the next step.

Next question, how would a LSD affect this equation?

For example, would a LSD counteract the corner-exit understeer with the front sway?

You can try to do that, but I for one think it's better not to try to fix suspension problems with drivetrain solutions - it makes the car's handling a lot less predictable.

I think it has been stated many times to get a front sway bar going on your Fiat.

The other factor that will next come into play with the additional sway bar is tire pressure adjustments. You can change the front sway bar then have to chase the pressures for the optimal grip.

My friend built a front sway bar based on a circle track racer quick change setup. So we were able to try 4-5 front sway bars on his Neon at a single test and tune. There is an optimal front roll stiffness delivered by the sway bar/tire pressure combination given that all the rest of the suspension is fixed. No sway bar was unacceptable. We ended up with the 4th largest bar being optimal for the Comp TA R1s. When we moved to Kuhmos I think that we needed to go down to the 3rd largest bar. As the tire construction needed more motion in the suspension. We noted a 6psi difference between the different bars optimal tire pressures in the same tire.

Be careful though with your assumption of elimination of driver induced understeer. Buy/borrow a go pro and point it at the wheel if you can for a session.

Sub'd for interest.

Advan046 wrote: I think it has been stated many times to get a front sway bar going on your Fiat. The other factor that will next come into play with the additional sway bar is tire pressure adjustments. You can change the front sway bar then have to chase the pressures for the optimal grip. My friend built a front sway bar based on a circle track racer quick change setup. So we were able to try 4-5 front sway bars on his Neon at a single test and tune. There is an optimal front roll stiffness delivered by the sway bar/tire pressure combination given that all the rest of the suspension is fixed. No sway bar was unacceptable. We ended up with the 4th largest bar being optimal for the Comp TA R1s. When we moved to Kuhmos I think that we needed to go down to the 3rd largest bar. As the tire construction needed more motion in the suspension. We noted a 6psi difference between the different bars optimal tire pressures in the same tire. Be careful though with your assumption of elimination of driver induced understeer. Buy/borrow a go pro and point it at the wheel if you can for a session.

Thanks. At the point I'm definitely going to get a front sway bar. I was just wondering of a LSD would somehow mess up the setup. However unlikely that is, thought I would ask.

The driver induced understeer comment is based on the experience of other Abarth AXers far more experienced than me, it's a just common to ride the sidewalls on this car.

So on the docket for the Fiat is a front sway bar, front sway endlinks, LSD and possibly a stiffer rear torsion bar.

Any tips on weight distribution vs stiffness? The only time I tweaked the rear suspension height, I made the car incredibly loose by upping the rear height about 5 turns of the adjuster. My understanding is that upping the rear height means I put more weight on the rear and less weight in the front. I feel like if I did 3 turns instead of 5, the rear would probably be just where I like it.

Only issue is, I want as much weight in the front of the car because it's a FWD car. So in my mind there are two options:

1. Up the rear height to dial in oversteer but give up on weight distribution (currently 64/36) or
2. Get a stiffer bar in the rear and maximize weight in the front.

Thanks in advance

Actually rake has very little effect on weight distribution - if you take a car and compare the weight distribution in a "hooptie" vs. "ghetto wedge" vs "normal" rake configuration, the weight would only move around maybe 2%, about the same as a battery relocation. Might sound strange but it's true.

Changing rake makes a difference in suspension geometry, especially roll axis inclination, and that's where most of the handling differences come from. The aero effects will also make more difference than weight distribution.

Typically leaning the car forward shifts the handling balance toward oversteer and leaning it back shifts it toward understeer due to the RAI changes. And typically, a car with soft-ish springs will have some extra forward rake from the factory so that the ass won't drag when you load up the trunk, so typically you run less forward rake than stock when you go to harder springs.

nilfinite wrote: Any tips on weight distribution vs stiffness?

I'd guess in an ideal world you'd want your bars to have about the same (wheel) ratio as your weight distribution for a 'balanced' setup during steady state cornering.

Problem there is you will likely have difficulties measuring or calculating the wheel ratio of many different bars, especially when you may not know the bar to wheel leverage ratios front and back, and the fact that sways all seem to be sold as "35% stiffer than stock", or other such uselessness.

Gameboy is right that changing the ride height in the front or the rear should not be considered as having any effect on weight distribution.

Thanks guys, really interesting stuff.

So if I'm understanding correctly, I should not worry about weight distribution and instead feel free to tune the rear ride height to dial in understeer vs oversteer. If I can get the car the oversteer without upping the height too much, then my semi-custom rear bar is probably stiff enough.

So the battle plan is this: 1. Get front sway in the car 2. Tweak rear ride height to get controlled oversteer 3. Alignment 4. Install LSD

Going to get the whole shebang installed on the car soon. LSD, Front Sway, Adjustable Endlinks. Installing everything at once means I'm probably going to have to start from scratch on alignment. Made sense to install everything at once though considering so much stuff has to come out for the LSD to get installed.

Any suggestions on the alignment for a FWD car with a front sway & LSD? My current plan is to max out camber (camber bolts) and 0 toe in the front. Can't do much in the rear until I find a decent shop to make rear shims.

How did you add camber to the front? Camber plates add static camber but they also increase king pin inclination which fights caster in the turn. I dont think this will fix much but its something to keep in mind.