V2Rocket

Hi,
I am putting this thread out there to gather ideas regarding the 944 stock rear suspension setup, the torsion bars borrowed from the SuperBeetle.

I know tires and shocks can make a big difference on ride, and I use the Boge/Sachs shocks with Falken 912 tires on 15" wheels. My wheels are about 14lbs each and the wheel/tire combo is about 35-40lbs (in that range) per corner. I am concerned with modifying the suspension components here.

Torsion bars are a very simple, very durable suspension system that require almost no maintenance over their lifetime. They take up very little room (meaning more cargo room inside the car) and aren't all that heavy relative to other IRS systems, not to mention make swapping axles and shocks a breeze.

That said, we are now passing the anticipated lifetime of these components with our cars and so the performance of the suspension is degrading due to age and mileage.

I daily-drive my 944 and am getting to the point where I am more concerned about ride quality than street-racing weight-stripping. With a fantastically functioning AC system I am no longer in such a hurry on daily trips

The first obvious step would be to replace the hardened worn out rubber bushings with new pieces to get some flexibility back. But what can be done on top of that?

One of the areas of my interest regards unsprung weight, which has a dramatic effect on ride quality (due to how the wheel/hub/unsprung weight can react to road bumps etc). Ideally we could have a multilink with inboard brakes with pushrod-actuated coilovers to get as much weight to the sprung side of the equation as possible but that isn't so practical to accomplish on the 944 platform without some major mods/fabrication.

Regarding unsprung weight I do have one easier idea to consider - my car has the early style steel trailing arms and the cast-iron 944 brake calipers.

I am thinking about switching the rear suspension to the 86 turbo setup, with aluminum trailing arms and aluminum monoblock calipers. The aluminum arms are about 9lbs lighter per side than the steel arms (about 33% lighter), and the iron calipers weigh about 10lbs each...I don't know the weight of the 951 calipers but they are lighter for sure based on feel.

If you have any thoughts or comments, please share!

MAGK944

Your reasoning is good but I doubt you will notice much of a change on a road car just by reducing unsprung weight. Another thing is that I'm almost sure those 951 calipers won't fit under 15in wheels, so you'll need bigger wheels and your unsprung weight is back up again.

Btw those aluminum trailing arms were fitted to all 85.5+ cars not just the turbo, so there are lots about.

Absolute best way to improve an NA is to remove as much sprung weight as possible though that might be impractical on a road car due to noise.

V2Rocket

not a whole lot of weight left that can be removed to keep the car nice to drive...need the sound deadening and carpets etc. really need more of the sound deadening to enjoy it more.

seems like a general rule of good rideyness is a high ratio of sprung weight to unsprung. low unsprung can react faster to a bump and the suspension absorbs it and the mass of the car dampens it more so you feel it less.

some rough math here but...
wheel + tire = 40lbs
brake disc/caliper = 25lbs
half a steel trailing arm/hub/bearing = 16 lb
half a torsion bar = 3lbs
half a shock = 3 lbs
half an axle = 8 lbs
= about 95lbs unsprung weight per rear wheel

wheel/tire weight should be about the same in an upsized wheel since the tire would be smaller and the tire is a lot heavier than the wheel.

if a 944 caliper is 10lbs and a 951 caliper is conservatively 7 lbs (-3lbs) (probably less, its a big difference when you feel them together!)...and the aluminum arms are about 10lbs less than the steel (so half that is -5lbs) that change alone is -8lbs unsprung weight which is 1/12 of the total or about 8%.
but then the axle is a little longer on the aluminum arms so add another lb for -7lbs per side, about 7.5%.

not a whole lot but it's a start!

another thing for consideration is friction - i see a lot of discussion of friction and torsion bars on the 911 side of things so the concept can be carried over here. the weight of the rear of the car really rides on the spring plate bushing in the t-bar housing. so when the wheel travels up or down the pivot point is the bushing which is carrying the weight of the car so there is a lot of friction which turns into ride harshness.
they talk about the coilover conversion being beneficial since the car's weight is now sitting right at the shock/almost at the wheel so the spring plate bushing just becomes a mostly unweighted pivot point, so less friction = less harshness...what do you think?

Van

I think you'll find the biggest improvement is replacing ALL of the bushings with new. And getting new shocks.

What's the diameter of Beetle torsion bars you're using? A smaller diameter (softer spring) will be more compliant and a more comfortable ride.

JJR512

Are you saying that the torsion bars on your car came from a Super Beetle, or are you saying that the design of the torsion bar portion of the 944 rear suspension is based on that of the Super Beetle? At first, I thought you were saying the latter, which I would believe, but Van's interpretation makes me wonder if I misunderstood you.

H.F.B.

Basically a good idea. I'm currently working on a similar thing. Another thing to consider according to Joe Paluch when swapping early vs late suspension are the 1/2 shafts and spring plates. But so far I haven't checked that out.

"Rear Suspensions
Early Offset Cars can update/backdate by swapping complete semi-trailing arm assemblies
These assemblies include rear hubs and brakes. Aluminum arm cars can bolt on steel arms, but
steel arms cars need to change the spring plate to use aluminum arms. Any swap also require a
change to the 1/2 shafts as these are longer on Aluminum arm cars. Shocks are different as
well, but I believe can be easily modified to function correctly."

Volhv_944

He meant the design is borrowed from the Super Beetle.

Just weight my back wheels, 15x8 Fuchs with 215/60/15 Falken 912, they are 31.8 pounds. But yes, we could not fit the turbo calipers under them..... a shame, since the NA one are so painfully heavy in comparison. But the Turbo rotors are bigger, so hopefully what you gain on the caliper you don't loose on the rotor.

Another thing about the aluminum trailing arms, is you wouldn't need to run that spacer.

Volhv_944

Aha, 3rd picture in post 42 shows the difference.
https://rennlist.com/forums/924-931-...ml#post9351187

H.F.B.

Hey, quick response. Thank you.

ok, I overlooked SuperBeetle.

SpeedyC2

I replaced the worn-out rear suspension bushings on my S2 with new "Sport" bushings from a company called Powerflex. The results, to me, where nothing short of amazing, with a dramatic improvement in both handling and ride quality. It's a LOT of work to replace all these bushings, but worth it, IMHO.


I have a set of stock 24 mm torsion bars and a 16 mm rear sway bar with drop links from my S2 (same as Turbo) if you'd like them. The price will be very reasonable...

V2Rocket

i've got the stock 23.5mm t-bars in my 944 so can't go softer than that, although someone found that a VW torsion bar (i think from the superbeetle) fits right into our suspension housings and the bars are like $134 a pair.

my issue is that the roads around here (Los angeles) are terrible. expansion joints, concrete slabs, potholes, uneven broken pavement...driving here is like saigon in 68. the front suspension soaks the bumps very well but the jarring comes when the back wheels hit the bumps, you can easily feel this on concrete freeways around here.

my bushings are original so they definitely need to be replaced, but i am seeing if there's anything worth doing while i've got the suspension out of the car.

konakat

Softer shocks might help since you can't really do much about the spring rate. Also, in regards to "wheel/tire weight should be about the same in an upsized wheel since the tire would be smaller and the tire is a lot heavier than the wheel." That is not accurate, you end up adding pounds of wheel weight in exchange for ounces of tire weight. If you think about it, they heaviest part of the wheel, the rim, gets larger when you go up in the size. The lightest part of the tire, the sidewall, shrinks.

944Ross

What profile tires are you running? A tire with more sidewall and air inside might make more difference than $1000's in suspension mods... NM is the Land of Many Pavement Cracks, I find 70-series tires make a big difference over 45 or 55-series.

V2Rocket

The Sachs/Boge are probably the softest OEM-offered shock offering, not sporty like Bilstein/Koni. The only really softer shock would be a generic like a Monroe lol.

My tires F/R are 60-profile sidewalls, 215 wide in the front and 225 in back. 32psi in front and about 30-32 in back. These are Falken 912s which are more sporty sedan tires so they are designed for ride comfort as well as good traction.

mel_t_vin

Spencer, what is your f/r ride height, ground-to-fender? For your goals, I suspect you should probably be 26"+ in the front and 25.5"+ in the rear.

How old are your dampers? If they're worn, you could be bouncing off the bump stops on full compression...which would not make for a very comfortable or compliant ride.

Have you considered KYB dampers? They can probably be had for <$40 a corner.


Anyone care to comment on longevity and ride quality of KYB dampers?