The air cooled volkswagen came with two major rear suspensions in its long production run.IRS or Independent Rear Suspension(even though the swinaxle is also independent) and the swingaxle. The swingaxle came first.The IRS took over in 1968.The only major difference between the two is the differential and axle design.
SWINGAXLE the swingaxle has direct drive axles,meaning the axles are one solid, straight peice. they axles get movement from their inner end.the end that goes into the trans mission looks like its been squished in a huge vice. it allows the axle to mve around and up and down.the swing axles advantages and disadvantages come from this feature.the biggest disadvantage is the camber the wheel take on at the extremes of the suspensions movement.because the tire is always perpendicular to the axle,if the axl isnt sticking straight out ,the tire isnt flat on the ground, causing faster tire wear and chronic over steer.over steer is when the car tries to spin around.this is not as bad as it seems,if you drive the car right and never let of the gas around corners it wont affect you.but if you push the brakes or slow down around a corner the weight shifts in the car and the wheels want to jackup and loose contact with the road.Always drive one of these car on this principle"slow in(to corners),fast out". The biggest advantage to swing axle is price.they are readily available ,very strong,and cheap to beef up.almost all drag racers(even the professional pro stocks)use swingaxle,because its disadvantages are inimportant when youre going in a straight line.
IRS The IRS suspension was standard on post 68 beetles.It uses the same basic trans as a swingaxle,but hasa very different way of getting the power into the ground. Instead of one solid axle, it has two stub axles and one solid axle.they are connected with two Constant Velocity joints.the joints allow the wheel to remain perpendicular with the road at all times.This is the best feature of the IRS.It gives the car much better handling with almost neutral handling and gets rid of the fear off spinning of the road if you put the brakes on in a corner.The biggest drawback to the IRS is cost,the IRS is very expensive to make bulletproof.The people who use IRS the most are track racer who have to corner at high speeds.