LSD = Limited Slip Differential, or Positraction
Phil:
I'm assuming that #1 above should read "Speedster", unless you're running two Spyders.
Also, the center of gravity difference in an Audi or Honda upright 4-cyl engine back there and a flat four should be almost negligible and the weight difference should be around 30 pounds - That, in a IRS, will almost be undetectable while driving.
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All good info from everyone, but I want to take a minute to make some points:
First, I don't want anyone to get the impression that Swingarm = Bad, and IRS = good. That is not the case. Both have distinct characteristics that, once learned can be used to the advantage or disadvantage of the driver.
A Swingarm without a camber compensator will typically oversteer into a corner such that the rear of the car will swing wide (some say abruptly, but I would question that) into "oversteer" and then any application of power (more throttle OR more brake) will cause it to suddenly convert to understeer as the rear swings back around and then over-compensates. Think of this as a giant fishtail, sometimes a single oscillation, sometimes several (depending on how the driver reacts).
When you add the camber compensator, it works to keep the wheels about mid-swing of the swing-arm arc, thereby pushing up or pulling down on the center of the car to keep it "level" and the wheels straight. Because of the geometry of the suspension it can't really keep the wheels straight, but it tries. Because of this action, the suspension can tolerate more stress before the rear end breaks loose to swing around and join the front at the head of the class. Camber compensated Speedsters can enter a turn at higher speeds, begin accelerating sooner and exit the turn at a higher speed. They were first used exclusively for racing, and now you can see why - overall lap times came down when using camber compensators. Essentially, the camber compensator increased the speed at which the rear end would break loose and swing around, but it made it a bit more predictable as to when it would happen (the driver could feel the tires roll under and react and (sometimes) save it, but it still had a propensity to cause roll-overs, just at higher g-forces in turns.
But they still have two things going against them: the geometry still allows one or both wheels to tuck in under the car in very hard cornering making them less stable than other geometry configurations, and the camber compensator was an added expense to the manufacturer.
Enter the "Independent Rear Suspension" or IRS, which, on a VW, was a dual-trailing-arm configuration. Not the best, but a HUGE step up because it kept the wheel essentially straight when traveling up and down, as opposed to the circular arc of a swing arm. It was also cheaper to manufacture (especially since the same parts were used on VW sedans and Porsche 924-944), didn't need a camber compensator and had a far less propensity to cause the car to roll over. (You could still do that, but you had to really work at it and do stupid things.) Adding an anti-roll bar (camber compensators, by design, don't work on an IRS rear) worked just like a camber compensator in lap times - they went down. Now, the suspension had far more tire tread to work with, since the tire patch was flat on the ground and didn't get peeled up by changing wheel angle or tuck under when things went overboard.
The VW IRS also exhibited far less of a propensity for oversteer into hard corners - it would enter starting with understeer (where the front plows ahead in spite of you turning the wheels) until you reach the limits of the tire sidewall reach, then the rear tires start to skid sideways a bit (the driver can sense this point) and then they let go and the rear starts to swing out, but either more power (preferably, for racing) or a touch of the brake will bring the rear back in line, much more predictably, or as most racers do, applying just the right amount of power can steer you through the drift.
This meant that "drifting" through corners could now be far more controlled with the right foot only, by applying the right amount of power. This was also true with a Swing arm rear, but there was always this tipping point when the speed exceeded tire adhesion (because the rear wheels were tucking under) and you abruptly lost it, never to be recovered (spin-out).
THAT is the big difference between Swingarm and IRS. Normal driving on the street, and even spirited driving once you get used to what's going on, can be equally fun, but in slightly different ways. I love cornering a swing-arm car reasonably hard right on the brink of the rear-end letting go, but I LOVE doing the same with an IRS, simply because it'll go through faster with more lateral force and exits with authority. It's when you're on a track really pushing the car when you notice the big difference.
BTW: For those of you feeling smug about having an IRS Speedster that's "better", remember that the Suby-based SAS mid-engined cars take it to a whole other level because they have BOTH a better IRS system (unequal "A" arms and MacPherson struts at all four corners) and a center-mounted engine, making the car extremely neutral and predictable in hard cornering, much like a well-set-up race car with softer, street suspension.
So that's it. I've autocrossed both swing arm and IRS Beetle suspensions (both dune buggies) and they're both fun, once you know their distinctive limits and how to take advantage of either.
The Speedstah Guy from Grafton
) did the trailing arms on his car 30mm and made the shorter axles work (I believe he bought brand new type 3 shorter auto axles from an Empi dealer). I think (with a little bit of mucking around) you'd get a 7 or 8" rim and a 215 or 225 wide tire inside a stock body. Well maybe not totally stock- if my earlier Intermeccanica is like the rest of them, there's an inch or more difference in width from the front to the back of the rear wheelwell, so a little pushing and glass work may be in order. Hot VW's covered the procedure in the June '94 issue.
