swing axle vs IRS

gaijinda · 11-26-2002, 08:29 AM

If you guys were into older air cooled cars of most excellent German engineering - and you were looking to build up a car to handle (somewhat) better - would the IRS version of said car be better than the swing axle one??

Yes, I am talking about an older VW. I really enjoy the pre - '65 Bug with the smaller windows... But the IRS came out in '68

Much like the P-Car, all kind of adjustable shocks, fatter torsion bars, sway bars and the like are available for old VWs..

Thanks.

tryan · 11-26-2002, 08:50 AM

without question. irs. ralph nader is watching you.

Early_S_Man · 11-26-2002, 09:57 AM

Well, the easy ... ie, safe answer, is IRS, but the emperical data is contrary! There were lots of swing-axle 356's built that handle very, very capably with good tires, KONI shocks set on full stiff, and a suitable static negative camber setting! Likewise with Beetles ... negative camber, fat, sticky tires, and good, stiff shocks are the key to great handling!

gaijinda · 11-26-2002, 10:39 AM

Thanks Early_S_Man...

What in the wide, wide, world of sports is a "camber compensator" ?

I have seen them sold for 356s and old VWs. Looks to be some kind of flat spring mounted transversly across rear. An anti-sway bar for swing axles??

jluetjen · jluetjen's Garage

First off -- Swing Axles are a sub-set of Indepenant Rear Suspensions. I believe that you are comparing Swing Axles to Semi-Trailing Arms.

Swing Axles are simplier. There are two issues with Swing Axles:
1) They have a lot of camber change in bump and droop. This is not a big deal if you have skinny tires, but it is a very big deal if you have modern wide tires.
2) Swing Axles have a fairly high Roll Center. It is usually at the intersection of a line drawn through each axle. Most IRS systems have the roll center much lower, maybe 3 or 4 inches above the ground. This can be a very big deal when cornering hard since it causes the rear end to Jack-up which increases positive camber.

What's jacking? This happens because as suspension's geometry has the roll center above the point where the tire is pushing against the road. For example: In a swing axle VW, let's say the roll center is 6 inches above the road as I mentioned at the intersection of a line drawn through each axle. Assume that each axle perfectly horizontal. See Figure 1 below...

The important point is that the roll center is 6 inches off the ground. Once you start to generate cornering forces, (as in Fig 2) the car's chassis is pushing against a point (the roll center) which is 6 inches higher then the point where the tire traction is pushing against the road. The result is that the chassis tries to ride up and over the point where the rubber meets the road. This is jacking. Note that as the chassis "jacks up", that it increases the hight of the roll center off of the road which makes it even worse, not to mention that the tires is at an awful camber angle.

A late model bugs (as well as a 911's) semi trailing arm rear suspension moves the pivot points around so that the roll center is lower and the tires don't pick up so much positive camber. Double A-Arm suspension get even more sophisticated about it.

I believe that a camber compensator is just what you described, a spring the ties together the swing axles to provide resistance to a lot of change in the angle. FV racers also use a Z-bar which is like C-shaped roll bar, but it is shaped like a Z. The result is that it stiffens the car in bump and droop, but has little affect in roll.

Pillow · 11-26-2002, 12:30 PM

Tough question really. As Warren said in theory the IRS would blow it away, but in practice I think there are many road racers who get better times with the swing-axle setup. I cannot explain why though.

For a street car go IRS as it will be better than the swing axle for performance and ride. Real roads have bumps and holes that is better for the IRS.

If you do run swing get the camber compensator. Easy and cheap insurance. Also kind of acts as a swaybar in a way to tighten the suspension a bit.

Now if you really want to have fun here is the ticket

Early car on a later IRS pan. Porsche brakes all around and specifically in the rear a 944 torsion bar and 18mm swaybar. Put some late offset 52.3mm 16" phones on there and have some fun! Or if you want to stay wide 5, 356 drums in the rear with a custom wide 5 braking system ($800ish). Then put some 6" chromies on there with two tone paint, glue on fat whitewalls and go for the bobber look. Sweeet!

Check out www.germanlook.com for some fun entertainment.

gaijinda · 11-26-2002, 12:55 PM

Thanks guys. The later "IRS" pan cant be that different. There was also a change in the front (pre-super beetle) from link-pin something to ball joint.. Lots to research.

I am thinking total sleeper - maybe wider wheels, but stock moon hubcaps, not too much tire, dual tip exhaust and original color paint.. It is amazing the cc's and horsepower they are getting out of the dual-port motors these days.

I can see it now: "But Officer - that would be impossible, this is 1964 Volkswagon!"

Pillow · 11-26-2002, 01:38 PM

The IRS pan is an easy switch, the body drops right on basically. The front is the newer ball joint style over the king link pin design. Cheap and easy

You should have no problem getting 100-120HP on the street as a daily driver. With a light car this makes for one fast car that can eat Mustangs at will... Of course embarass a lot of rice. At that HP expect 14-15 in the quarter, which is hell-a-fast.

Push it to 150HP and you have an expensive motor and a car that will scare you to death!