Rear IRS Suspension Question

[Steve C]

Hi

An over wide rear track will make the car handle like a tricycle, it will want to fall over towards the front of the car, think of how a tricycle acted if you went around a corner in your driveway to fast, you would get tipped out of the seat.

So you need to the track wider on the front than the back or at the worst the same.

Stick with what you have, but heavier bars for now.

Steve

[Clatter]

Ooohhh, those wide-track alloy arms just LOOK so tasty, don't they..

Couldn't bigger, stiffer torsions in the rear upset the handling if the fronts are not stiffened to match?
My experience with motorcycles is that stiffening up one end really makes the opposite end go much more soft.

[fastbacker]

Originally Posted by Steve C

Hi

An over wide rear track will make the car handle like a tricycle, it will want to fall over towards the front of the car, think of how a tricycle acted if you went around a corner in your driveway to fast, you would get tipped out of the seat.

So you need to the track wider on the front than the back or at the worst the same.

Stick with what you have, but heavier bars for now.

Steve

My 911 track car's rear tires are 2.5" wider than the fronts making the rear track about 5" wider. The bug starts out with a 1" wider front track so with the proposed 6" added to the rear both cars would have the same stance. This is a great set up for the 911 so I can't see why it wouldn't be for the bug. But hey, I don't know.

[wrenchnride247]

The rear on a 911 weighs a bit more than a T1.

[Humble]

Fastbacker, here's a little inside knowledge from someone who's been there...

There's a saying about D-modified cars: that when d-mod cars are built the builder didn't read the rule book. So D-mod is usually a catch-all class for cars that don't fit in any other class. I know this because I made a d-mod super beetle. If you build it the way you are saying, the car will end up in d-mod just because of a type 4 swap and while you'll have a lot of fun at the autox you won't be competitive in the class unless you've got about 400hp/ton (just basing this off of the local d-mod cars)

That being said you will have a kickass street car, and if you take it to an autox you will get a lot of attention just because it's a beetle. But if you want to race competitively you'll be better off stripping the bug, going through the stock suspension, hopping up a type 1 motor, beefing up a bug tranny and racing it in FSP.

What I tell people who are building or planning to build cars is to start at the end of the project and work backwards. Figure out if you want a race car or a street car and then work your way backwards to the start from there.

[fastbacker]

Thanks Humble. Good reading.

What I'm actually looking for is more of a street car that I can autoX non competitively - maybe a couple of times a year.

I actually took the route you recommended with my 911. Built it (w alot of help) for a specific class before I even knew how to drive on the track.

[evilC]

Originally Posted by fastbacker

My 911 track car's rear tires are 2.5" wider than the fronts making the rear track about 5" wider. The bug starts out with a 1" wider front track so with the proposed 6" added to the rear both cars would have the same stance. This is a great set up for the 911 so I can't see why it wouldn't be for the bug. But hey, I don't know.

Agreed. The 911 is in very simplistic terms a more powerful bug. The racing 911s all had IIRC wider rear than front tracks that stablised the straight line running.
If Steve C read my reply fully he will have noticed that I commented on the front suspension that was in addition to the subject of the thread. The WHOLE suspension design is important not just one end and I would have expected the front track to be increased in additon to the rear.

evilC

[fastbacker]

OK. So I think I'm going to look for some wide track aluminum 944 rear arms and brakes (along with t-bars, spring plates and axles). The information out there is a little confusing as it seems there are different versions of the same width arms (?). I did come up with this info on aluminum arms via some searching:

U.S. Models:
==========
86-89 944 S
==========
86-89 944 Turbo
89-91 944 S2
==========
89 944 Turbo S
90-91 944 Turbo
==========

Will all these options work to widen the track by 3" per side. Are all the brakes used the same? All things being equal (if so), are some more easily obtainable?
Any pros and cons in comparisons?

Thanks-
Craig

[wrenchnride247]

ALL 87 and later arms are the same. Four pot brembo's fit.

[evilC]

And besides the rear bearings are so beefy that Porsche racers can regularly use up to 50mm spacers to further increase the track. don't worry get some alloy arms and then fine tune the track with the available spacers.

evilC

[fastbacker]

I just sourced a complete 86 narrow track, aluminum arm, 4 piston caliper rear suspension for $400 usd. It comes with brand new bearings and, as luck has it, the pivot bushings removed. Everything's included - even the torsion bar housing and bare axles.

This seams to be a good deal. Right?