choosing IRS or swingarm rear for performance

VW underneath a classic Italian body design.

Moderator: FJCamper

Post Reply
jazzpur2k
Posts: 1
Joined: Thu Aug 11, 2016 12:32 pm

choosing IRS or swingarm rear for performance

Post by jazzpur2k » Thu Aug 11, 2016 12:55 pm

planning a ghia build in the near future

im coming from the watercooled turbo crowd, ive built a couple 400whp 1.8t setups in the past few years

always had a thing for ghias but this aircooled world is still new to me

basically, if i ultimately intend to do a subaru ej20t swap into a karmann ghia and build for +300whp
does the IRS suspension make for a better performance platform? consider this to be an all around performer (road race, not drag)

caveat is i want it to be lowered and i need the room for a wide rear tire assuming the power, does the camber on IRS setup offer enough room to squeeze a wide tire without fender modification?

basically a want a setup that looks very similar to this....https://www.youtube.com/watch?v=q3a-a6Y13pA
with a slightly higher ride height, less negitive camber, wider rear tire and much more power

is this possible? and would it be best to start with an IRS ghia or an older swing arm setup for my fondation??

just looking for advice from those have been down these roads before

thanks guys!

User avatar
FJCamper
Moderator
Posts: 2690
Joined: Wed Nov 14, 2007 5:19 pm
Location: Birmingham AL

Re: choosing IRS or swingarm rear for performance

Post by FJCamper » Thu Aug 11, 2016 11:12 pm

Hi Jazzpur2k ,

With 300 HP and tires wide enough to put that power to the ground, the cheapest and best mechanical choice is swing axle.

With a swing axle, you don't have to worry about breaking CV joints, and because so much development has been done on drag-race swing axle cars, you can get short rear axles that allow wide tires.

Lowering the car really helps mitigate swing axle jacking.

FJC

Ian Godfrey
Posts: 113
Joined: Thu May 27, 2010 4:52 am

Re: choosing IRS or swingarm rear for performance

Post by Ian Godfrey » Fri Aug 12, 2016 5:47 am

I have got 205/15 on 7" wheels under the back of my stock body '69 IRS Ghia. I had custom offset wheels made so it would work. I don't think you can go any wider on an IRS ghia without body work and/or a narrowed torsion housing.

User avatar
dlamyle
Posts: 109
Joined: Tue Jul 09, 2013 1:27 pm
Location: Northern Virgina

Re: choosing IRS or swingarm rear for performance

Post by dlamyle » Fri Oct 07, 2016 7:01 am

I had to beat my inner fenders a bit but I'm running 235 40 17 in the back on an IRS conversion. Don't ask what I had to do to the front fenders...Also that car in the video is SLAMMED. My inner fenders would need more "work" for that height.
1968 Karmann Ghia , 'JDM EJ205, 5spd Subarugears w/OBX LSD, Blouch 16g XTR, Killer B Headers, DW 750cc, Meth Inj, Cobb AP w/Mach V 22psi Dyno tune (332whp)
http://www.shoptalkforums.com/viewtopic.php?t=143547
https://www.youtube.com/user/dlamyle1/videos

User avatar
Marc
Moderator
Posts: 23732
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: choosing IRS or swingarm rear for performance

Post by Marc » Fri Oct 07, 2016 7:48 am

dlamyle wrote:...Also that car in the video is SLAMMED. My inner fenders would need more "work" for that height.
Plus the beam has been narrowed significantly (looks like at least 4" if not 6" - doubt that it even has front shock towers). Definitely not the thing to do if you want the car to handle - or even steer well. Narrowing the beam pulls the tires in with no change in clearance to the beam, but the turning circle increases due to the inner sidewalls rubbing the pan/body at full lock. Bump steer is exacerbated when the tierods are shortened, and it should be obvious that the narrow track width isn't going to be your friend in the corners.
Unless you plan to alter the front fenderwells it's not likely that you'll be able to fit much wider than a ~5½" rim at the front with a stock-width beam, but I'd choose that over narrowing the beam to fit a wider tire.

User avatar
FJCamper
Moderator
Posts: 2690
Joined: Wed Nov 14, 2007 5:19 pm
Location: Birmingham AL

Re: choosing IRS or swingarm rear for performance

Post by FJCamper » Fri Oct 07, 2016 9:55 am

Hey!

What Marc said. Do not mess with the front suspension.

And, get front tires with good round shoulders.

FJC

madmike
Posts: 1162
Joined: Mon Jul 24, 2006 5:11 pm
Location: Atlanta,Michigan

Re: choosing IRS or swingarm rear for performance

Post by madmike » Sat Oct 08, 2016 5:56 am

You can alway upgrade to 181 axles & flanges :wink:

User avatar
Marc
Moderator
Posts: 23732
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: choosing IRS or swingarm rear for performance

Post by Marc » Sat Oct 08, 2016 6:18 am

madmike wrote:You can alway upgrade to 181 axles & flanges :wink:
IRS wins hands-down for handling. You can set up swingaxle to get around a course pretty well by limiting the travel, but it still takes skills that few possess to save it when you step past its limits. The rear roll center height is at the middle of the diff, and nothing can change that. 'Ghia wheelwells aren't sized to take a very wide tire regardless of the suspension type; you may be able to squeeze a little more rubber in with swingaxle but not enough to make much difference in handling. I think you should resolve to have a set of "track tires" with stickier compound for racing and a set with halfway-decent tread life for the street.
Stock Beetle CVs will handle a surprising amount of power if they're in good condition, and there's a school of thought that it's better to have one break than to have the differential be the weak link, but for the kind of power you're contemplating I think larger/stronger ones are in order.
For pavement duty you don't really need the angularity offered by the 181 CV joints; Bus CVs are a little cheaper and fit the same flanges as the 181s. Ideally get the 181 driveshafts too (they have a longer splined area to accommodate the thicker CV) but it's possible to machine the inner races so they'll fit on standard Beetle shafts. Don't machine the shaft to let the CVs slide on further, though - that creates a weak point where they'll snap right apart.

LouieJ99
Posts: 12
Joined: Tue Mar 18, 2014 11:24 pm

Re: choosing IRS or swingarm rear for performance

Post by LouieJ99 » Sat Oct 08, 2016 8:18 pm

Took me a few tries on my '64 Bug but I got the swing axle to handle pretty well. Hope this explanation doesn't lose anyone.
I found the jacking to be caused by a "ripple effect". The "static" high roll center is a given, but softly sprung rear end is the real problem. (1) Throw the car into a turn, the body rolls and weight shifts to the outside rear wheel. The outside suspension collapses because of low spring weight. (2) The inside suspension expands, body roll raises CG even higher, wheel drops, and travel arc causes inside wheel tuck. (3) "Tuck and roll" causes weight transfer to take a slightly upward vector and now starts to uncompress outside suspension. (4) The now expanding outboard suspension causes the outside wheel to tuck.
The now high weight center and narrow track (due to extreme camber change) cause instability and it all goes to poop at this point.
The simple solution? Coil over rear shocks to increase spring rate but not cause a change in ride height. The car had minimal body roll with the extra spring force. I could throw the car into a turn and drift it and not worry about flipping.

User avatar
Marc
Moderator
Posts: 23732
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: choosing IRS or swingarm rear for performance

Post by Marc » Sat Oct 08, 2016 8:51 pm

You still have the "tuck-under" problem at the outboard tire once the body rolls far enough - as the wheel goes into positive camber the tire's contact patch lifts off the pavement and you start running on the sidewall - at that point rollover is imminent and all-but-impossible to drive out of.
An add-on "camber compensator" works by transferring springrate from the inner wheel to the outer, but so as to reduce the latter rather than increase it as a conventional anti-roll bar, or added coil springs/airshocks do. As a result of softening the outer springrate the suspension compresses/collapses more easily, heightening body roll but avoiding positive camber by so doing...up to a point, anyway. The factory-installed "Z-bar used on `67-up swingaxles is there to do exactly the same thing - the size of the rear torsion bars was reduced at the same time, for the same reason.

The addition of limiting straps to prevent exceeding more than a couple of degrees of positive camber is IMO the single most effective way of making a swingaxle "recoverable" when driven at the limit. A very similar result comes from using shorter shock absorbers (at least until they pull apart).

User avatar
Piledriver
Moderator
Posts: 21790
Joined: Sat Feb 16, 2002 3:01 am
Location: Van Alstyne, Texas

Re: choosing IRS or swingarm rear for performance

Post by Piledriver » Sun Oct 09, 2016 12:53 am

If you are really going to be laying down that sort of power, a Subarugears setup will probably be the most cost effective transmission that will live, take the cost of the suby to t1 trans adapter etc off the kit cost and its not bad, esp as it can be done DIY.
Requires: IRS.
930 CVs are an option. Don't worry much about breaking those.
T4 cvs should be sufficient though.

An early 924 or 944 thru 85 will provide correct axles and cvs for a T1 trans at least, you'll need the trans output flanges from a thing or aftermarket, and stubs, might as well grab the 944 trailing arms/spring plates and disc brakes too.

When pulling the axles. always mark how the axles are installed, L or right and which way is "out", you don't want to reverse load them.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

User avatar
Fiatdude
Posts: 945
Joined: Mon Oct 12, 2009 8:58 pm

Re: choosing IRS or swingarm rear for performance

Post by Fiatdude » Sun Oct 09, 2016 4:30 pm

OK, I'll weigh in here since I've gone thru all these teething issues with my Ghia -- -- These are things I've had to do with my turbo 2963 (350HP) and things that I'd recommend (what I think I need to do)-----

1. Since you're building from scratch, The first thing I'd do is a 3" narrowing of the rear torsion OR custom narrowed swing arms and coilovers. You also should plan a doing a small tub on the inside, Mike Lawless did a real nice install, it is on a drag car, but it translates over real well (( http://lawlessdesigns.com/wkrswingtoirs.html )).... This is something I really need to do and the main reason is to get some serious tire onto the ground. I'm running 225's on the rear and they rub(cut) inside and out with the torsions stock location and they just spin when on the gas leaving a turn, looks cool drifting out of turn, but it is the slowest way around the track.....

2. I've been thru a few trans now, type 1 and a Porsche 901 were my latest victims. I've now got a bus 091 in there now and it seems to be living.... With a 091 you have to be IRS with your suspension.... I've stepped up to 930 CV's and have had no issues there....I haven't been convienced that the Subie trans is the way to go,,, ((talk to the Subie guys on how they break transmissions when they start stepping up the power)) -- (P.S. Mike Lawless has gotten a Rancho 002 bus to live in his drag car) --

The bad thing with using a bus trans is you just can't find a 'good' Ring and pinion set for high speed... I've got a 4.57 in mine and with a .77 fourth,,, it just isn't tall enough.... They do make a .70 fourth, but you have to start looking now to find one.....

3. I did not narrow the front beam with 205 tires on there, I'm slightly lowered and have slight rubs at full lock or when hitting a driveway at an angle...... but out on the course I'm quite happy with the way the front sticks, (you always want more tire though)

4. "Cefolar" did a nice road race Ghia build on the samba a while back -- but this was for about a 150HP car -- http://www.thesamba.com/vw/forum/viewto ... highlight=

and of course FJCamper knows more about road racing Ghia's than any other person in history --- listen to his advice (except about the T1 trans LOL)

My Build and pics-- -- http://www.thesamba.com/vw/forum/viewto ... highlight=

User avatar
Piledriver
Moderator
Posts: 21790
Joined: Sat Feb 16, 2002 3:01 am
Location: Van Alstyne, Texas

Re: choosing IRS or swingarm rear for performance

Post by Piledriver » Sun Oct 09, 2016 5:44 pm

Probably sacrilege to mention it, but the 003 or 010 (true) VW automatic would handle the power just fine.
There are a couple very tall aftermarket R&Ps sets available (for the later 010 anyway)
(have looked at going there but the price puts me off)

Would require ditching the framehorns and making up a rear subframe, but adapting the car to a bolt-in T3 late rear torsion might be a good way to get a narrowed torsion in there.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

User avatar
FJCamper
Moderator
Posts: 2690
Joined: Wed Nov 14, 2007 5:19 pm
Location: Birmingham AL

Re: choosing IRS or swingarm rear for performance

Post by FJCamper » Sun Oct 09, 2016 10:33 pm

Hi Fiatdude,

My experience covers 150hp air cooled swing and IRS axle Sedans and Ghia road racers. When we get into serious engine swaps and chassis reenginering such as you've been doing I'm out of my league.

There is a clarification here I'd like to make about shortening the VW front beam axle. Most beam axle cuts do no more than create some handling and ride quality quirks for street cars.

But in the extremes of road racing, where one deflection of the suspension at the wrong moment because of bump steer can throw you into a violent spin, you weigh such modifications carefully. And I don't mean getting by for a few minutes on the track, but lap after lap after lap, where the odds are physics will eventually get you.

https://www.youtube.com/watch?v=Tng5ReSc2wY

Here's a quick 58-second clip at Road Atlanta last spring with the camera on our Ghia's front bumper. At 27 seconds you'll hear our driver stab the brakes for 1 second and the tires squeal, apexing the turn.

Any upset in the steering at the moment of that quick squeal and we'd have been off the road in excess of 100 mph.

We're on comparatively small 185-60 series street radials.

My point here is we keep it simple for survival.

FJC

Post Reply