Whats the difference between an IRS and Swingaxle transaxle? Is one better than another for certain reasons? How can you tell what you have? Thanks for any comments.
Eric
IRS Vs. Swingaxle Trans?
-
Marc
- Moderator
- Posts: 23741
- Joined: Thu May 23, 2002 12:01 am
"IRS" is actually a misnomer since technically the swingaxle setup is also independent (unlike the "solid" axle found in older Detroit iron that doesn't allow either rear wheel to move up & down without affecting the camber of its mate) - but it's a useful shorthand universally recognized in VW circles to describe the later 4-joint system.
Swingaxle has ~2" diameter tubes surrounding the drive shafts (no moving parts visible until you get out to the brake drums) and "IRS" has open drive shafts (~3/4" in diameter) connected to the transmission and outer "stub" axles by four constant-velocity universal joints. In the US market, all 4-speed Bugs through 1968 had swingaxle rear suspension (the `68 AutoStick was IRS). Buses went IRS in `68, and Type IIIs (4-speed or auto) in `69.
The swingaxle design is vulnerable to a phenomenon called "tuck" - when the suspension unweights, the wheels go into dramatic positive camber. Porsche's racing team lost at least a couple of drivers back in the day when their cars left the pavement at speed over humps in the track and didn't settle back down evenly when they landed, resulting in nasty barrel-rolls. In a stock street-driven bug most people won't be pushing the limits that much, but the problem still exists - as the body rolls in a corner, the outside wheel goes into positive camber and the rear end of the car "jacks" (raises) increasing the rear roll center. Only an experienced swingaxle jockey has much chance of keeping the car from rolling over when this happens, and even the best of drivers is still screwed if he misreads the turn and goes in too hot.
In contrast, the 4-joint system experiences far less camber change with suspension travel and is much more forgiving - overcook a corner and you're more likely to simply push off the pavement or spin around than you are to go inverted.
Swingaxles can be modified to handle remarkably well - some have made into very successful autocross racers - by lowering the ride height (which induces negative camber) and limiting the suspension travel to preclude tucking (using a transverse spring affair known as a "camber compensator" or by straps/short shocks/etc.) - but as a rule the resultant ride isn't too pleasant to live with on the street.
Swingaxles's strong suit is its simple and sturdy construction. In places like Mexico, Brazil & South Africa where there are many more "unimproved" roads, the switch to IRS never happened.
Swingaxle has ~2" diameter tubes surrounding the drive shafts (no moving parts visible until you get out to the brake drums) and "IRS" has open drive shafts (~3/4" in diameter) connected to the transmission and outer "stub" axles by four constant-velocity universal joints. In the US market, all 4-speed Bugs through 1968 had swingaxle rear suspension (the `68 AutoStick was IRS). Buses went IRS in `68, and Type IIIs (4-speed or auto) in `69.
The swingaxle design is vulnerable to a phenomenon called "tuck" - when the suspension unweights, the wheels go into dramatic positive camber. Porsche's racing team lost at least a couple of drivers back in the day when their cars left the pavement at speed over humps in the track and didn't settle back down evenly when they landed, resulting in nasty barrel-rolls. In a stock street-driven bug most people won't be pushing the limits that much, but the problem still exists - as the body rolls in a corner, the outside wheel goes into positive camber and the rear end of the car "jacks" (raises) increasing the rear roll center. Only an experienced swingaxle jockey has much chance of keeping the car from rolling over when this happens, and even the best of drivers is still screwed if he misreads the turn and goes in too hot.
In contrast, the 4-joint system experiences far less camber change with suspension travel and is much more forgiving - overcook a corner and you're more likely to simply push off the pavement or spin around than you are to go inverted.
Swingaxles can be modified to handle remarkably well - some have made into very successful autocross racers - by lowering the ride height (which induces negative camber) and limiting the suspension travel to preclude tucking (using a transverse spring affair known as a "camber compensator" or by straps/short shocks/etc.) - but as a rule the resultant ride isn't too pleasant to live with on the street.
Swingaxles's strong suit is its simple and sturdy construction. In places like Mexico, Brazil & South Africa where there are many more "unimproved" roads, the switch to IRS never happened.
-
riverrat13
- Posts: 7
- Joined: Tue Feb 13, 2007 4:30 pm
If you were to go for 350rwhp in either a bug or type 3 and planning to take the car to its limits on the street/race track. Which would you choose? example A Notchback with suby 2.5T+ porsche g50 with lsd and big rwhp.
Ive got to the early stage where fitting the g50 to the late notch irs has thrown up some interesting challenges.
thanks
Rich
Ive got to the early stage where fitting the g50 to the late notch irs has thrown up some interesting challenges.
thanks
Rich
-
Bruce2
- Posts: 7100
- Joined: Sat Oct 13, 2001 1:01 am
With 350 hp, a Type 1 gearbox is not going to survive. If you wanted to use swing axle, you would have to use a Bus IRS trans with the Folts swing axle conversion. Since you are with a G50 already, I see no point in downgrading to swing axle. Continue with the G50 swap and use IRS. The big CV joints that the stock G50 use are plenty strong enough.