Treating excessive roll - SCCA RallyCross Beetle

[helowrench]

if you are keeping the rear track the same, you will want 944 steel (or 924) diagonal arms.
The inboard bushing will need to be changed to the bug unit.
One of the bolts where those two parts mate, has an eccentric to allow for camber/ride height adjustments/corner weighting

[Piledriver]

The steel 924/944 arms are ~identical to single plate T1 arms.

The spring plate and some of the attaching hardware differ and allows some adjustment.

Not as adjustable as aftermarket adjustable spring plates, but probably stronger.
Also has the mounting points for the 944 rear sway bar, you will still have to fab the pivot mounts on the torsion tube.

I have heard of some aftermarket inner pivot setups that allow significant camber change.

[Piledriver]

The tire used has a lot to do with turn in, esp on dirt.
You may need a skinny front tire with sharp corners.

Also: These are still out there: (or could be fabbed)
They are mounted with the springs at rest, the springs are locked top and bottom.

The BJ front compatible units are even easier to find, they used that design for most of the HD return to center steering dampers.

4way1.JPG

See http://www.shoptalkforums.com/viewtopic ... 1&t=136942 for full thread.

[TouringBubble]

I've read through your thread on the 4-way setup. Its interesting, but I don't think that's the way I want to go. Thanks for the tip on the sway bar mounts. I need to look at my plates and figure that out. I can fab the other mounts I think.

[helowrench]

I've read through your thread on the 4-way setup. Its interesting, but I don't think that's the way I want to go. Thanks for the tip on the sway bar mounts. I need to look at my plates and figure that out. I can fab the other mounts I think.

IIRC the rear swaybar uses a drop link to connect to a double ended bolt.
The double ended bolt is also the eccentric bolt used for the camber adjustment.

[Steve Arndt]

The camber bolt eccentric is separate from the sway bar bolt and not the same location.

[TouringBubble]

I want to say there is an oddly offset hole near the three that bolt the "arm" at the end. That's probably it.

[Steve Arndt]

I have the whole Porsche rear end. I can mock it up.
There are already lots of pics on google. Search 944 rear sway bar.

[petew]

One of my big issues is that I have almost no front grip on turn in. This is a big issue as I can't get the rear around and end up with terminal understeer. I need more weight up front, period. Be it static or dynamic with spring rates ... something has to give. I think it will need to be a mixture of both. I have similar issues mid corner, and I think the stiffer rate up front and a sway will help with that.

I've (aka Pete Wood) mentioned this to you on Facebook before but the issue is your front tyres. The rounded edge means they just slide. Are they dirt tyres? Coz they don't look like any rally tyre I've ever seen. Import some of these. They'll last you a season or two and change the steering completely.
http://www.dunloptyres.com.au/dotCMS/Ty ... m=nPerPage
These are the best tyres I ever used.

An 18-19mm rear swaybar will also help you to transfer some weight to the front end in corners. Re torsion bars; get a sway bar on it first, then see if it still needs stiffer springs.

[rayjay]

After years [ early 80s through mid 90s ] of driving and building SCCA Solo 1, 2 and club racing cars I got a chance [ 1989 ] to drive a dirt midget a few times in a track day sort of setting. It was such an amazingly fun car to drive that I set out to build my own midget. I was doing race car fab at the time so I had the equipment and skills, just absolutely no idea about the suspension geometry requirements. I bought a book and a tape from Steve Smith and did a bunch of research. It was a mind expanding journey

Dirt midgets have straight front axles, torque tube rear suspension, torsion bars or coil overs [ or a mix ], no anti sway bars, relatively high CG, big tires, etc. They also only turn left. They are highly refined inspite of the low tech parts.

One of the first requirements is very fast steering. About 3/4 of a turn lock to lock and these cars have a ton of lock available. There is NO time to have to be hand over hand with slow steering. You have to be able to give the car the steering input required instantly. You never move your hands on the wheel. If you watch a vid of a dirt midget or sprint car you will see the drivers going through the turns turning the wheels almost full lock left and right reacting to the signals from the tires. I think dramatically quickening up the steering on your car would be a big help. You could make or have made and extension for the pitman arm on the steering box.

Ackerman geometry. On the midgets you wanted 3 degrees [ iirc ] of steering angle gain on the inside tire. If you turned the right tire 5 degrees to the left you wanted the left tire to move 8 degrees. If you don't have adequate gain you 'pin' the front end [ that's the description from the book ] and have no control. Basically the front end is plowing.

Bump steer can really mess with you on a dirt car. Your frontend design is about as bad as it gets. It would be worth the effort to fab up a system of tie rod links to try to improve this.

Caster. Having a good bit of positive caster in the front end helps everywhere. When turning in it gives you negative camber on the outside wheel. When counter steering on exit, the caster combined with wheel offset effectively drives the outside wheel down into the track. Since weight is always transfered diagonally this increases the load on the inside rear wheel helping your drive off the turn.

Wheel offset. Lots of offset on the front is bad for pavement cars. It's good for dirt cars. It interacts with the caster and camber to help with the diagonal loading of the rear tires. Scrub radius is a term to learn more about. Offset at the rear increases track so the weight transfer isn't so dramatic. It does effectively soften the roll rate of the suspension so this has to be accounted for.

Shocks. Most street oriented shocks have little compression damping. Racing cars need racing shocks with compression damping. Carrera shocks used to be the go to brand. I think they are kaput.

At the track tunability is great on midgets. I think swapping your car to coilovers would be better for this aspect.

The IFS means that you can't easily mess with roll centers [ example, moving the panhard bar up or down on a solid axle car, anti squat, etc. The only way you could gain some anti-squat is to raise the forward pivots of the trailing arms. Extremely difficult while retaining the stock layout. Swapping to coilovers would open up this possibility but still difficult.

Tires are very important. I don't know the rules but if the tires are open I would buy some dedicated dirt race tires from Hoosier, etc.

A lot of the above is probably beyond what you can affordably accomplish but it does give you things to think about to help your understanding of the dynamics of counter steering on dirt.

Good luck

[Jadewombat]

This isn't quite like dirt track racing at all where you're dealing with the same flat surface. Rallycross surfaces are very uneven. You can have a nice sweeping turn with hard packed flat surface smooth as can be, which then instantly becomes a turn of loose gravel and ruts and each wheel is working overtime to compensate the bumps. You need to have enough suspension travel to be able to deal with this, more like a off-road car in some cases with light spring rate out at the corners.

Snow tires are a great low-buck option I used on my bug for tires. Nice footprint and low enough profile for cornering.

[rayjay]

You are probably right that the cg is so high and the car's track is so narrow and the racing surface so rough that sliding through the turns would be a recipe for a tip over.

[TouringBubble]

I've (aka Pete Wood) mentioned this to you on Facebook before but the issue is your front tyres. The rounded edge means they just slide. Are they dirt tyres? Coz they don't look like any rally tyre I've ever seen. Import some of these. They'll last you a season or two and change the steering completely.

An 18-19mm rear swaybar will also help you to transfer some weight to the front end in corners. Re torsion bars; get a sway bar on it first, then see if it still needs stiffer springs.

Pete, they are "winter" tires, which are very common for RallyCross here. They aren't rally tires at all, but have similar properties ... lots of sharp biting edges, voids for clearing mud and a soft compound to wrap around uneven surfaces.

I'm looking in to sway bar options, but I'm trying to first replace the tired old OEM bars/leaves.

[TouringBubble]

This isn't quite like dirt track racing at all where you're dealing with the same flat surface. Rallycross surfaces are very uneven. You can have a nice sweeping turn with hard packed flat surface smooth as can be, which then instantly becomes a turn of loose gravel and ruts and each wheel is working overtime to compensate the bumps. You need to have enough suspension travel to be able to deal with this, more like a off-road car in some cases with light spring rate out at the corners.

Snow tires are a great low-buck option I used on my bug for tires. Nice footprint and low enough profile for cornering.

Exactly. At the event in question we had lots of rain the night before the event. So, the first course was just slick mud, with many cars getting completely stuck on course. That afternoon it dried up some, so we were just digging through the wet top layer to the harder stuff below, leaving sizable ruts to deal with.

I actually found afterward that one of my main problems was braking. My front brake pressure sensor had exploded, leaving me with no fluid and only rear brakes. Without front brakes, it's kinda hard to toss the weight around properly. This made turn in very difficult.

[TouringBubble]

I'm trying to finally get this sorted out and am planning to order some parts today.

I got some info from Mark Huebbe, who has a very well set up stage rally Beetle. He said he's running a 25mm long bar in the rear. I assume he wanted the extra travel, and that makes sense for me too. I assume the mid-length bar would be fine. I don't think I need the really long one. I don't know if the 25mm bar is right for me, but it's a good place to start I guess. Trying to get Sway-a-way on the phone to get their opinion on what rates to go with.

All-in-all I'm looking to do the larger and longer rear bars, 944 spring plates, stiffer front leaves, front adjusters, more front camber and some general refreshing of everything. We'll see how it works out. I'm looking at sway bars too, but with the rear being obviously too soft, I'm going to get the rates where I want them and then work on the single wheel rates with sways. I know the front needs a sway now, but I don't know how much of one till I test with the new leaves.