22/28 vs. 22/30

[dd74]

Okay - I was speaking with a well-respected Porsche race driver/car builder who was in the Petite Le Mans in Atlanta last week. He asked me about my torsion bar set up, which is 22/28 with Bilstein Sport Shocks all around. After hearing this, he told me 22/30 is a far more an optimal setup, mostly because torsion bars smaller than 30mm don't adequately compensate for the engine's weight.

I haven't considered torsion bars for a while, but this guy peaked my interest. So my question is does anyone have experience with 28 and 30mm rear torsion bars? Can there be that much difference between the two?

Thanks.

[450knotOffice]

Interesting question. I'd like to know myself since I also run 22/28 torsion bars.

[Jack Olsen]

Bruce Anderson acknowledges in his book that there are a lot of track drivers who use much stiffer rear bars with success. I used to run 21/30 on my 73, and now I run 23-torsions/600#-coils on my 72, which is actually probably too stiff in the back. I keep meaning to drop down to 500# springs.

But even as mismatched as I am, the car corners pretty well.

[island911]

Originally Posted by dd74

....mostly because torsion bars smaller than 30mm don't adequately compensate for the engine's weight.

what does that mean?

I suppose that if you are on a perfectly smooth track or driving very slowly that no suspension is needed.

for what it's worth torsion bars increase in stiffness withthe 4th power, relative to the diameter. 30 mm bars are stiff -if you think that you don't need suspension, think again. Even the Ruf yellow bird had I has stock T. bars ( though much bigger anti -sways).... but it was fast and had a heavier engine.

[island911]

What I meant to say is bigger is always better. ...Always!

If your bars are not bigger than the next guys, then you are not as smart, fast or good-looking.

Seriously, you need to consider much more than the simple # that someone else is using. You should consider your unsprung weight, the car (sprung) weight, the condition of the road, how fast.....

[dd74]

Island - I realize all of what you mention. I've been around these cars for a few years now, and much, if not all of the conditions you propose has been considered in my suspension set up. My question leans more toward any and all real world road and track experiences anyone has had between the two setups I outlined (22/28 vs. 22/30), in particular whether or not the 30mm rears are in comparison to the 28s, much stiffer, mildly stiffer, unnoticeable, etc.

If you have experiences with these or similar setups,, I'd like to read about them.

[Peter Bull]

I used to run 21/30, which was a very good combination. The car had little or no pitching motion when going over bumpy tarmac, or across bridge joints. Pitching motion is otherwise quite common in 911's, and it is governed mainly by the spring stiffness distribution between front and rear. It had stock ARB's but quite a lot of negative camber, and it was quite neutral in its behavior. Unless it was provoked that is.

The reason I'm not running this combination anymore is that I use coilovers, but they have more or less the same spring stiffness distribution front to rear.

/Peter

[rfuerst911sc]

I'm running 30's with Bilstein Sports in the rear and my car handles great and feels firm but not too stiff on the road. Keep in mind the roads in FL. are pretty smooth. But just as important in my opinion is the rear Elephant Racing poly bronze bushings/bearings. These allow the suspension to go thru it's movement ( up + down ) very freely. If I had good 28mm bars I don't believe I would change to 30 just because this guy says so, but if your going in there to change bushings then I would.

[burgermeister]

The 30mm bars should provide a 30% higher spring rate than the 28mm bars. For all that's worth.

A 30% change in spring rate should be noticeable....

[IROC]

I have 22s/29s (right in the middle in the rear) and I would say that after a few track events with the 3.2 in the car, I would like to try some 30s. When the 2.7 was back there, I felt the 22/29 combo was fine, but the 3.2 seems just that much heavier that 30s might be nice.

In the end, though, torsion bar size is just one part of the whole suspension equation. Stiffer isn't necessarily better unless all of the components are matched and work well together.

[jaydubya]

Is this for street or track?

What car? What is the weight of the car?

[Tinker]

What Jay said. What's the intended use of the car, its year, weight and motor?

I'm using a 23/30 with small 18mm bars on each end and about a 2500 - 2600 curb weight. Car has a bit too much push at lower speed corners (22mm fronts would be more ideal) but is relatively neutral at higher speeds (80mph+) I'm leaning towards a bigger rear (sway/anti roll) bar to get a bit more rear grip.

Tinker

[}{arlequin]

i run 22/30's and have no complaints. one thing that helps is having custom valved shocks for the 30's b/c i don't think off the shelf 'sports' have enough in them to control the 30's really well.

[don911]

What Dave said about valving.

I recently changed from 22/28 with sports shocks to 22/30 with valved shocks. I also added #27 anti sway bars. On paper it sounds significantely stiffer but in reality, it doesn't feel that way. The custom valving works with the springs a ton better than the off the shelf sports. Especially in the front. The benefit is in rotation. I think the 22/28 keeps the factory balance (understeer). The 22/30 combo reduces the understeer and the car rotates tons better. Though you should be able to get the same rotation by reducing the front tbar.

My car is set up for the track but it handles great on the street.

[RWebb]

you are going to have to try different combos on the _particular_ tracks _you_ run on

i.e. - the car wt & hp are the constants, and you are going to assess the stiffness (the variable), while holding the parameters (1. you; 2. the track(s)) constant.

I don't see any other way to do it, since you are asking different drivers from you about different cars from yours...

Chuck M. now has the quick change torsion bars for sale. You can probably get around different shock valving for now, reserving that as a fine tuning issue/"keep it in your head" as you compare. If not, then you are going to need to switch shocks for testing as well.

I assume that this HAS to be for the track - nobody would run real stiff on the street for long -- unless they have a LOT better streets than the ones I ever see.

[sbrown.nw]

After a recent upgrade on my 72 Targa and a past upgrade on a 78 Targa, I found out the following on top what was mentioned in this thread that:

- Targas should probably not go stiffer than 21/27
- type and condition of bushings makes a big difference

Scott

[safe]

Originally Posted by white78911

- Targas should probably not go stiffer than 21/27

Scott

+1, at least not without a roll cage.

The upgrade from stock to 21/27 stiffened up the car, but it wasn't a night and day difference. It still a little to soft, if I had your choice I would rather go 22/30 than 22/28.

[dd74]

Nothing on my car will change. It'll stay at its current weight with its current horsepower. Gearing might change, but I'm still debating that with myself.

There is a feeling that the rear might be too soft, though at turn nine at Willow, it does hop around a little. My city streets are so terrible that I could have fat women as torsion bars and my car would still ride like crap, so the street isn't my true concern.

As to the front - I don't know - the car has lost so much weight there - from the spare to a 15lb battery, windshield washer reservoir, etc., that I'm wondering if 21mm as opposed to 22mm wouldn't be the way to go.

Any more thoughts?

[don911]

If you feel like changing anything, you might try having your shocks valved to match the springs. I thought the valving made a huge difference over the bumps. I think you feel the bumps more in the front and mine felt pounding in front with sport shocks. With the valved shocks, the front takes rough roads much better.

[chrisp]

It's really hard to have too much roll stiffness in the back of a 911. I run 31's as do many other club racers. If anything, people are going bigger. I know some swear by 34's.

As mentioned by others, matching the damping to the t-bar is super important.

I used 22/27 on my SC for a while. When I switched to 23/31 that car felt much better. A set of matched shocks went along with the change so the entire system got a lot better. It was very noticeable.

For a race SC I would run a 7-8mm front to rear difference. For a race Carrera I've heard that 8-9mm difference is best due to the heavier engine.