Best Mod on your Swing....

[Paul Illick]

HoHoHo indeed. That works in theory on a glassine road without a ripple or pebble. One bump and that swingarm will begin flapping its wings like a flightless Dodo and you'll be on your your head in the ditch.

From the site (http://www.rqriley.com/suspensn.htm) where that diagram origionally came from they summarize (you could have mentioned) swing axle performance as, and I quote:

Swing-axles produce large changes in camber and tread during bounce, and the design can become unstable in turns due to the "jacking" effect. Setting the wheels at a negative camber can reduce the tendency to jack. However, too much negative camber can also produce a vehicle with a vague, mushy feel of directional instability. Slings under the axles or zee brackets can be designed to limit downward travel and thereby avoid wheel tuck-under. A correctly designed swing axle suspension works reasonably well, but its undesirable characteristics can never be fully overcome.

unquote

Repeat, no matter how much tweaking is done "..it's undesirable characteristics can never be fully overcome"

And in the real world, if swing axles were so efficient at proper handling then wouldn't you see tham on all kinds of modified class money-is-no-object autocross cars? Count them yourself, you see them on exactly none. Zero, zilch, nada. So it appears the field is wide open for you to go build one, show all those losers what optimum rear suspension geometry is all about. Please don't forget to come back and tell us how it all works out, though I can tell you it's been tried, more than a few times, and the score still stands at zero, zilch, nada.

[Guest]

And in the real world, if swing axles were so efficient at proper handling then wouldn't you see tham on all kinds of modified class money-is-no-object autocross cars? Count them yourself, you see them on exactly none. Zero, zilch, nada. So it appears the field is wide open for you to go build one, show all those losers what optimum rear suspension geometry is all about. Please don't forget to come back and tell us how it all works out, though I can tell you it's been tried, more than a few times, and the score still stands at zero, zilch, nada.

Swing axle equiped cars were doing very well for themselves in World Rally Championships up till the mid 1970s (Alpine A110) against 'superior handling' Porsche 911s. Those roads were not glassline smooth either. It was for the simple reason that the swingalxe car can generate more GRIP than any trailing or semi-trailing car.

One reason being wheel camber not being affected by body roll (as I mentioned already), the other reason is that the newer semi-trailing 1303 type rear axles put more stress on the rear tyres. Because:-
the more the body rolls, the more it tries to generate rear toe-in on the outside tyre. In other words for a given cornering force, the rear tyres are at a higher slip-angle, and will break away sooner.. So the swingaxle has more grip on the same corner because it doesn't stress the tyres as much

The only advantage to the semi-trailing axle is it's more predictable because those rear toe-in changes act like negative feedback to the steering. They make the car easier/safer to drive. Unfortunately it also robs the car of rear-end grip.......

Check the data from Road & Track tests carried out on the 1960's & 1970's Beetles. Swingaxle Bugs got .7G on a 100ft skidpad. 1303's could only generate .6G on the same test. Big difference if you ask me.

But as I already said, a swingaxle car IS more unpridictable & harder to drive. But all the same, it didn't seem to hinder swingaxle cars like the Alpine A110 from seeing off all the Porsche 911s in the 1970's.
http://www.renaultsport.co.uk/heritage/ ... nea110.htm

ps. there are indeed autocross bugs that have been converted to the 1303 type rear axles, and they don't corner as well as did before.
Lap times are now slower. I bet they feel safer to drive though.

cheers, BigGreen

[55superbeetle]

I had first hand experience in this subject at last weekends autocross. I have autocrossed many irs bugs but this was my first try at a swing axle car. The car is a 68 ghia being built for street mod 2. It has 265 victoracers all the way around and a 2332. I learned alot last weekend about how a swing works. I will admit it does look like it should work perfectly in the picture posted above but that is now how it ends up working. As weight tranfers to the outside wheel it starts gaining traction. This load is transfered back to the center of the car and it begins to "weight jack" the car up, in turn creating posative camber wich we all know is bad and unsafe. There are ways to overcome this but none seem to improve traction but only take it away. This effect can be stopped by limiting the downward travel of the axle to stop before posative camber takes place and/or running a very high spring rate. Either method is solving the problem by reducing the lateral traction being produced by the rear tires. U can make a car slide around the course fairly quickly but it is normally not the fastest way nor is it the easiest on the driver or tires! Like Paul I am not saying a swing cant be made to work but it's just not worth it when converting to irs is so easy.

[Guest]

Yeah, that's exactly the same experience I had. I autocrossed a swing axle beetle in northern California in the late 60's, early 70's. We tried a lot of things, ended up basically decambering it to the max and stiffening up all the rebound we could in the rear shocks so they'd resist the "snap". We also ended up using narrower tires than the other cars in our class so it would slide rather than stick. It's basically how the 356 vintage racers are set up, and if you go to any vintage race and talk with them you'll find very wise men, hear the pain in their voices as they describe 40 years of trying to find that elusive "balance". No matter what the fixes are the problem is still in transitions, either from working the suspension over an uneven road surface in onr corner, or in the chicanes, loading one side and then unloading it quickly while transitioning. The rear camber changes so much in a swing car that it upsets everything else you want to have happen, so the only solution is to keep the supsension from working, so you don't get those huge camber changes. Unfortunately if you look at that combination of "fixes" you see that they aren't what you'd ideally want to help the car's overall performance. And we ended up getting killed when the [then] new IRS cars started showing up. I gave up, switched from the beetle to a dunebuggy. It was was also swing, but so much lighter that we could get more traction on wider tires before the car started jacking.

By the way, I've rolled a swing axle car at about 70 mph when it snapped back instead of sliding. Not a nice experience, believe me, and that's one of the reasons I have some strong feelings about them. And that wasn't an uncommon experience back then, either. There was a whole industry of dune buggy and other fiverglass bodies that sprung up to use the chassis' of those rolled swing-axle VW's that you could find in any junk yard. I finally understood what was happening when I saw a video of the rear of a Baja car as it went through some whoop-dee-do's, flapping the rear. You could see the suspension jacking until the rear started steering the front, and the car got so squirrely that it finally went over. And over, and over, and over. Cool for the spectators to see, I guess, but not so much for the driver.

[Paul Illick]

Sorry, that was me, I forgot to sign in. Also I have to admit we never saw any Alpine 110's in NorCal back then. Maybe they had it figured out, I don't know, but nobody else I know did.

[Paul Illick]

One other thing I mentioned but should explain, which is the swing axle suspension "steering" the car. The reason is that in addition the radical camber changes in a swing arm rear it also changes the toe-in as the axle flaps. Imagine the swing arm pivoting up and down from a fixed point in the transaxle, which are those camber changes. Consider that the spring plates are also pivoting up and down, also from a fixed point at the torsion bar mounts. So what happens at the point where those two arcs are connected? It doesn't go staight up and down, but travels in another arc, 45 degrees between those two, and that changes the toe-in, the angle that the tire meets the road. So when cornering and you have all the weight on one side of the car, the right rear for example, that right rear wheel actually begins pointing at the left front of the car as force increases and the toe changes. So the rear wheels actually participate in "steering" the car. That direction they're pointing changes as the suspension compresses and uncompresses, like when you hit a bump in mid-corner, or apply the brakes, or change direction.

That's the reason swing axle cars are described as being "a handful" to drive, because the car changes direction in mid-corner, without driver participation. Not a good thing when you're trying to go fast. This wasn't such a big deal on street cars with big tall tires, but gets REAL interesting on hard suspensions with low, hard sidewall tires. The only solution is to basically make everything in the back as hard as possible, locking it all up solid if you can. But that's not a "suspension". You can have a VERy exciting time going fast in a swing-axle car, and if you're just trying to have fun that's all fine. But you'll never be as fast as the equivalent car and driver with a more modern suspension. Maybe Alpine 110's excepted.

[seahag]

There is a great article on Aircooled.net about improving the handling on both s/a cars and IRS cars. The camber and caster both front and rear play a huge part in your cars handling. Don't overlook the toe angle in the rear either.

[bigGreen]

About the "swing axle is steering the car" statement, "with added toe-in on the outside wheel during cornering"...

Sorry, and I'm not saying this just for the sake of argument here, but facts are facts, and that statement simply isn't true. In fact the swing axle rear end gives as much as half a degree of toe-out during cornering. This is one of the main differences between the swing axle and the 1303 rear geometries.

Like I already said it's the 1303 design of suspension that gets added toe-in on hard cornering. That toe-in is good for stability and bad for tyre grip, due to the increase in slip angle.

About the jacking, well that's what a z-bar is for (or camber compensator, same thing really).

1303 geometry also gets some jacking by the way. Due to the fact that its roll centre is quite high at about 4 inches above ground level. So some jacking is there, but only about one third of what you suffer on a swing axle car.

And as already stated, the factory fresh swing axle Beetle generated more g-force on a skid pad than a 1302 when tested by Road & Track magazine in 1971.
The stock 1302 only got 0.6G. Swing axle cars got 0.7G

The 1303 type geometry certainly wasn't fitted to improve cornering ability. In fact it almost certainly diminishes the cornering power. The 1303 geometry is there to improve stability, and that's all.

Cheers, bigGreen

[Tate]

I have a problem with your comparisons from R&T, you are comparing a sinwg axle standard Beetle to a strut front end and IRS equipped equipped SuperBeetle, the 1302. And you are constantly talking about the 1303, also a Super. I am sorry, but if you are going to compare skidpad numbers and base the results on the rear axle setup alone, you need comparisons between a swing axle Beetle and and IRS equipped Standard Beetle, not a Super. The Super is heavier, the front end is higher, and about the only thing they share suspension-wise is the rear torsion housing. Basically what I am saying is this, if you want to compare skidpad numbers, get some for a IRS equipped standard Beetle, not the Super.

I actually think it would be really cool to have skidpad tests done on Beetles now, using the same modern radial tires on all cars, have all cars stock, and all cars done on the same day by the same driver. If this were to happen I think there should be an early 60's Beetle, SA(Swing Axle) and LP(Link Pin), then the SA with BJ(Ball Joint) and the stock Zbar (67/68?), a standard Beetle with IRS and BJ, and a SuperBeetle. I think it would be interesting to see how they all compared on the same tires under the same conditions.

I am not trying to ruffle feathers, I am just saying that I believe the comaprison you give is flawed for this argument, like comparing oranges to grapefruit.

[bigGreen]

I don't have a figure for the American spec chassis with torsionbar front and semi-trailing rear, but R&T later tested a 1303S Sports Bug fitted with wider 5.5" wheels and 185/70x15 radials. It scored the same as a stock swing axle beetle on crossplies. ie 0.7g

I quoted these figures simply because they're all we have to go on. The closest we have to a purely scientific comparison not based on subjective opinions or heresay.

If you don't like R&Ts findings from the 1970's (which don't show the 1302/3 in a very good light), then by all means find some other source and quote that. If somebody can find more scientific or fairer test for the poor old 1303 chassis, I'm all for that. I'm just as interested as anybody-else is here in making my bug go around corners faster and faster. To be honest though, I'd be surprised if anyone could find test results showing the semi-trailng chassis generating better cornering power than a swingaxle. But I do think there's a lot of misinformed negative opinions regarding the cornering abilities of the swing axle cars. ...

And I agree, it would indeed be interesting to test for ourselves, but I don't think that's ever likely to happen, do you ? Not unless we all buy G-meters for our stock or modified bugs, and then post our results up here.

[Tate]

I actually have a SportsBug, but it is nowhere near stock anymore. What we are really talking about here is modified suspensions anyway, what has more potential, etc. The IRS is more predictable, feels more predictable and can be raced closer to the ragged edge with more confidence.

As far as a test goes, I don't think it would be too hard to get a stock SA beetle next to an IRS Standard Beetle, just need a big empty parking lot and a G-meter. Unfortunately my VW's are in Florida and I am in Seattle now, otherwise I would volunteer my 73 standard.

What I do want to really understand is the SA toe out in a turn, how is that possible? I am running the geometry through in my head and can't see how it is possible? Am I missing something? I am not trying to be a smart ass, I really want to know.

[bigGreen]

Yup, we all admit that the swing axle car is harder to drive.

But I'm the only person on here prepared to stick my neck out and suggest that it corners at least as well as (if not better than) the semi trailing arm cars.

I got that "up to 1/2 a degree of toe out when cornering" figure from my suspension geometry software that I have here on my computer. It has a model of the Beetle swing axle that I made myself.

You're right in thinking the wheel movement always causes extra toe-in as the axles move away from being parallel to the road surface. But body roll always adds some toe-out. Why that is exactly, I'm not sure to be honest. If I work out why & what's happening there, I'll let you know. It seems that all swing axle cars do it.

If you factor in the jacking effect, that adds some toe-in as you would expect. And the 1/2 degree of toe-out is reduced. Another thing, as far as I can tell, lowering a S/A Beetle by around 2 inches makes the toe vary remarkably similar to the semi-trailing arm (1303) Beetle, and the toe-out effect doesn't show up at all.
Sorry I can't explain why, it's just what this SusProg3D software says.

Interesting that the S/A beetle looks smarter than most people give it credit for. It suggests to me that when the geometry was designed back in the 1930's with Prof Porsche & his engineers spending hours with just log tables and slide-rules, the Beetle's swing axle seems to have been optimised for cornering rather than for straight line stability... Probably it was lifted directly from the Auto Union car..

[Paul Illick]

But I'm the only person on here prepared to stick my neck out and suggest that it corners at least as well as (if not better than) the semi trailing arm cars.

Actually it's not just here, I think you may be the only person ANYWHERE to make that suggestion. And that is likely not what anyone who's actually raced the cars has found either, or you'd see more of the S/A suspension configuration outside of just FV and vintage racing.

I got that "up to 1/2 a degree of toe out when cornering" figure from my suspension geometry software that I have here on my computer. It has a model of the Beetle swing axle that I made myself.

The model you made yourself? Hmmm....

You're right in thinking the wheel movement always causes extra toe-in as the axles move away from being parallel to the road surface. But body roll always adds some toe-out. Why that is exactly, I'm not sure to be honest. If I work out why & what's happening there, I'll let you know. It seems that all swing axle cars do it.

If you factor in the jacking effect, that adds some toe-in as you would expect. And the 1/2 degree of toe-out is reduced. Another thing, as far as I can tell, lowering a S/A Beetle by around 2 inches makes the toe vary remarkably similar to the semi-trailing arm (1303) Beetle, and the toe-out effect doesn't show up at all.
Sorry I can't explain why, it's just what this SusProg3D software says.

With all that going on at the same time how exactly is the tire patch on the asphalt being affected? And how does it change when there is any imperfection in the road surface that goes into the suspension in the middle of a corner, or change in direction, braking, or anything else? Everyone agrees that swing axles are a "handful" to drive, meaning unpredictable and inconsistent. Do you think all those coincidental variables might be the reason?

Interesting that the S/A beetle looks smarter than most people give it credit for. It suggests to me that when the geometry was designed back in the 1930's with Prof Porsche & his engineers spending hours with just log tables and slide-rules, the Beetle's swing axle seems to have been optimised for cornering rather than for straight line stability... Probably it was lifted directly from the Auto Union car..

Those swingaxle Autounion F1 cars had super power, but were also said to be killers, the most evil-handling F1 winners ever. Notice any common thread there? Again I ask, if the S/A beetle looks "smarter" than most people give it credit for then why don't any current car manufacturers take up the S/A torch? It's a cheaper design than any of the supposedly "modern" suspensions, so if it performed so well you'd think they'd be interested. And if it creates such better g-forces in cornering why don't you see it in some racing applications outside of vintage and FV, where it's required by the rules? The S/A beetle was never much of a race car, obviously, but the semi-trailing arm configuration of the IRS beetle was nearly identical in configuratioin and geometry to a lot of later BMW's that were famous for their sweet handling. Just another coincidence?

Look, I've actually raced both designs, and it may be because I'm just stupid, but I could never get the damned swing axle cars to handle well. I got them to be O.K., acceptable to the point where on flat asphalt they didn't scare the crap out of me from time to time, but they were never as fast as a mildly modified IRS car almost straight out of the box. So if you have the magic formula, throw it out. But please give it more than theory, get your software to let me know exactly what the hot S/A setup would be. Heck, there's even the chance that I've already tried it and can tell you how it worked out in the real world. Hey, I've been wrong before and certainly will be wrong again, and I've been frustrated for years about not getting those cars to go as fast as I wanted and thought they should, so I'd love to know what I was doing wrong. I even have a swing axle car out in the drive right now, and a lot of old suspension parts in the garage I could play with, try it all out. So what's the hot siwng axle setup?

[bigGreen]

OK, I just worked out why the swing axle gets 1/2 a degree of extra toe-out during hard cornering. It's simply because the two rear axles are pulled closer together as the body rolls. - End result is some extra toe out.

I can't explain it any better than that. You'd have to play with some software like SusProg3D for some time to convince yourselves that toe change simply doesn't behave the same way during body roll as it does during the straight up and down (bump and droop) conditions.

But whatever the reasons behind the original design of the Beetles swingaxle geometry, I've realised the swingaxle controls the toe on the rear axle better during cornering than it does when following a straight line - In other words the swing axle car is (ironically) more stable in a corner than it is in a straight line...

cheers, bigGreen

[Paul Illick]

Does your software say what happens when the suspension has to work in the corner at speed, from braking, a bump, change of direction, or any other of the common everyday mundane things that upset a suspension? The toe changes, right? Swings may do fine in a theoretical perfect corner, they have real problems in the real world. So back to reality. If you're basing your comments about the superiority of swing axle suspension on results from your software program what does it tell you the optimum swing axle suspension setup is going to be? In the real world where real roads have real bumps and variable radius corners, what's the hot setup?