"overly creative or tortured interpretation"

Street Mod. A1 Rabbit. How would rules-oriented type people feel about building an IRS for the Rabbit?

'Suspension components are unrestricted as long as they use the original attachment points.'

My idea is to build some sort of frame or beam that would attach to the body by the studs for the torsion beam bushings. Trailing arms would then attach to that via bushings. Think of it as removing the torsion beam from the stock suspension. Then there would be links from the ends of the trailing arms back to the beam. I could build the beam so that it didn't quite touch the body, but the mounts might need a little extra pad area. Would this constitute a subframe? I don't know from subframes.

'For the purposes of this rule, “suspension” is defined as any item that is designed to move when a wheel is deflected vertically. This includes blah, etc., but not blah, and subframes.'

If I could get away with this, I have an idea for a double-wishbone front...

Reading this makes me think of the Cobra IRS that was used between '99 and '04. Bolts up in place of the 4-link SRA using the SRA's attachment points.

when i thought about doing this in a toyota truck with a FC rx7 irs, the issue seemed to be the mounting of a subframe to hold the rx7 subframe to the toyota mounting points. that technically changes the mounting points.

I get your idea, but what's the point? Sounds heavier and overly complex considering those wheels are only along for the ride. Plus, you could lose the 3-wheel charm.

Use a TT's rear suspension minus the differential.

cost:benefit ratio approaches infinity. my dad would call it "fly-screwing" which is very much effort for very little reward.

use the stock design front and rear, with as much front tire as you need to make it pull out of corners, and only as much rear tire as is required to keep it from being uncontrollably oversteerish.

In reply to Gimp:

In a straight line, yes, they're just there to keep the rear bumper off the ground. But in a corner, the rear end has a roll to play on any car. The stock suspension has no camber gain. When you lift the inside tire, you're riding on the outside edge of one tire, giving the rest of them more to do, which leads to compromises in the front end. An IRS goes some way towards addressing those things. More grip is more faster if you figure out how to use it. Ask a Honda.

Depending how it's done, I'm not sure how much heavier it would be. The stock setup has those huge steel trailing arms and the torsion beam between them. It's actually pretty damned heavy. If you add a rear sway bar, it's even worse. I bet it's possible to keep the weight the same, maybe lighter.

But the rules probably don't allow it anyway. Another thought is to reduce the rate of the torsion bar to make it more indepentent. Or completely cut it in half and then connect them again with a bar or tube on the same axis as the attachment bushings. That should be legal, and each side would then be independent, but it wouldn't do anything for the camber curve. shrug I can't think of any way to fix that without adding new pickup points. All I have to work with is the two bushing mounts and the upper shock mounts.

The rule that defines suspension specifies subframes as something that cannot be replaced. My interpretation is that anything that bolts to the suspension hols is legal - your subframe included.

That said, I agree with Angry. The rear of an SMF car is doing VERY little. I wouldn't bother with anything outside of saving weight where practical. There is so little suspension movement that dynamic geometry isn't important, and the rules are open enough to get the static geometry wherever you want it. FWIW, I've considered replacing my trailing arm rear suspension with a beam just to save weight.

You could build a subframe that mounts to the stock torsion beam studs and the top of the shock mounts. That way you might be able to build a light ,tubular structure that becomes the mounting points for a fully independent, double A-arm suspension. Still a lot of work for a questionable gain. I would think that it could be made to work if you can somehow, change the front/rear wieght distribution at the same time.Do the rules allow that?

Very true that it probably isn't worth the effort after you lower the car enough and put heavy springs on it. The leeway in SM lets the mind wander, though.

IRS would help a lot more in Stock class where you can't do much with the suspension. The reason people have to run giant front bars is because the ratio of roll-resistance front to rear is so out of whack. Once that rear wheel is off the ground, the rear is contributing zero to roll resistance. Sorry, front tires.

if you can somehow, change the front/rear wieght distribution at the same time.Do the rules allow that?

There's a lot you can do. You can relocate the battery, lighten the front more than the rear, and if you manage to get underweight, you could add ballast to the rear. And drive from the back seat if your arms and legs are long enough. But perversely, the more static weight you add to the back, the less this matters, because the rear beam has a harder time lifting the inside rear of the car off the ground and rolling the tires onto their sides.

A friend of mine (Angry, you might know him as Dr. Corvairkian) sent me this:

AngryCorvair wrote: my dad would call it "fly-screwing" which is very much effort for very little reward.

You dad is a genius. I think that term is "say what" worthy.

In the interest of taking this discussion somewhere people would feel is more relevant to actually going faster, here's my idea for the front. Make a frame that connects the stock A-arm mounts to the strut tower, hugging the inner fender well as much as possible. The A1 strut bearings attach to a flat surface with two studs. The top of the frame could be a circular plate that sits up in there. This frame would give a place to attach an upper link, and the strut tower becomes just a good ol' shock tower. Add a ball joint extender to get the lower arm level. Bingo. Real camber (and caster?) adjustments, and the ability to build in some sort of camber curve.

I've spent plenty of time autocrossing modded A1 VWs, and a lack of grip or balance has never been a problem.

I'll be honest, it's been a few years since I looked, but I don't recall anyone running a tire wider than a 235. If you're running something really wide, maybe you will find the limitations of the stock suspension design though.

I'll agree with everyone else though - spend your cash on some really good shocks, and your time on dialing them in properly. That + good tires + power will be a damn fun ride. Let me know if you need a tire-warmer.

DrBoost wrote:

AngryCorvair wrote: my dad would call it "fly-screwing" which is very much effort for very little reward.

You dad is a genius. I think that term is "say what" worthy.

+a solid 10,000

petegossett wrote: I've spent plenty of time autocrossing modded A1 VWs, and a lack of grip or balance has never been a problem.

No doubt. But consider this: If 400 hp Corvettes turn faster times than A1 VWs, why don't we autocross 400 hp VWs? To quote myself, more grip is more better.

Don't get me wrong, I would never do any of this except perhaps as a total wet-dream back-of-the-garage waste of time project. This is a thought excercise in how much you can bend the rules and limitations of a car. That's how we get fast cars.

I'm still struggling for a way to explain why I think this is important. I need to re-read some of the handling/suspension books in my library. Maybe I'm wrong, but I think there are two things at work here

1. Understeer doesn't mean the rear has too much grip. It means you're asking the front to do too much. (Neutrality is an illusion. Lunchtime doubly so.)

2. I have a hunch that something bad happens to the roll center when the rear end is sitting on one wheel.

I have nothing worthwhile to add, just a +1 for the grim fandango avatar.

angusmf wrote: In the interest of taking this discussion somewhere people would feel is more relevant to actually going faster, here's my idea for the front. Make a frame that connects the stock A-arm mounts to the strut tower, hugging the inner fender well as much as possible. The A1 strut bearings attach to a flat surface with two studs. The top of the frame could be a circular plate that sits up in there. This frame would give a place to attach an upper link, and the strut tower becomes just a good ol' shock tower. Add a ball joint extender to get the lower arm level. Bingo. Real camber (and caster?) adjustments, and the ability to build in some sort of camber curve.

Wouldn't you gain 99.999999999999905143% as much with some drop spindles that allow you to keep idea LCA geometry? Possibly a knuckle/spindle off something else with a custom longer control arm to help control camber gain?

For the rear, if you really feel camber limited why not 'bend' the torsion bar a little in the center. They've been building bent rear axles for decades to get some camber in the back.

angusmf wrote: No doubt. But consider this: If 400 hp Corvettes turn faster times than A1 VWs, why don't we autocross 400 hp VWs? To quote myself, more grip is more better. Don't get me wrong, I would never do any of this except perhaps as a total wet-dream back-of-the-garage waste of time project. This is a thought excercise in how much you can bend the rules and limitations of a car. That's how we get fast cars.

No, but your average Wabbit will only need 250-300hp to have the same power to weight ratio as said 400hp Corvette. I know there are 250hp+Vdub's out there. The biggest issue you'll have is putting that much power to the ground exiting a corner. Traction is not being limited by your twist beam rear.

Adrian_Thompson wrote: Wouldn't you gain 99.999999999999905143% as much with some drop spindles that allow you to keep idea LCA geometry?

That's essentially what the ball joint extenders are. They are used on the normal VW suspension. If they're legal in your class (usually not) they are a must-have for a lowered car.

It's no problem changing static camber (or toe) in the rear if your rules allow shims between the axles and the mounting pads.

Adrian_Thompson wrote: The biggest issue you'll have is putting that much power to the ground exiting a corner. Traction is not being limited by your twist beam rear.

Preaching to the choir. But the rear end does have an effect if it allows more body roll. Once the rear wheel is off the ground, the anti-roll effect goes out the window.

Golf-4 swap????

Anybody want to make some Ball joint extenders for me? Aren't these also called RCAs?

As far as the rear suspension goes seriously look at an Audi TT AWD rear suspension without the guts, the crossmember bolts in place and the rear suspension looks like this: