Understanding Spring Perches

[R. Pare]

If I were designing a new car, I would most certainly look at torsion bars, and also flexures. Yes, packaging could be a hassle, especially in the lengths we would need to get long-lived bars (the F1 bars are good for a race, and then they are totally shot), and the extra expense may not be percieved by some as worth it, but if you truely wanted a car with as few compromises as possible, they are the way to go.

[jgaither]

OK, not race cars. Forewarned. I sold Kenworth trucks in 1970 with torsion bar suspensions! Worked really well and was the lightest thing going for the intended job. Very good ride and long life as long as you knew how to grease the bushings. Unique in the industry. Nobody else had the balls to try it.

JAG

[R. Pare]

All Chryslers had front torsion bars up at least thru the early '70s, with adjustable mounts. Can't understand why they changed.

[John Robinson II]

Hell, the old beetles had torsion bars.

Richard, what is the main advantage of the torsion bar suspension?

John

[RussMcB]

I'm not Richard, but I stayed at an EconoLodge this past summer. It was awful.

From a Google search:

[font=Arial][size=2]They have the advantage of working where a traditional coil spring or MacPherson strut may not fit, and also can be used to adjust a vehicle's height. They're cheap to manufacture, and maintenance-free. On the downside, torsion bars do not produce the smoothest ride. [/size][/font]

[R. Pare]

The bid advantage in using torsion bars in race cars is that they do not produce a side load on the shock like a coil spring does, thereby reducing the friction.

Torsion bars by themselves have zero effect on ride smoothness, What does matter is the friction in the suspension arms pivots. The Chrysler bars all acted as the inboard anchor and pivot for the lower a-arm, but I do not remember what the bearing style was either side of the a-arm (been 30 years since I last saw that setup!). If the bearings are cheap(common), there may end up being enough pivot friction to make a car ride harsher.

The F1 cars generally employ the bar down thru the center of the hollow stub that the bellcrank runs on, and it attaches to the bellcrank thru a boss that is rotationally adjustable via a simple cap screw for making ride height adjustments. The torsion bar set up like this adds no extra bearings to the suspension system that could raise frictions levels. Slick and simple.

Russ: What's the connection between me and an EconoLodge? Are you calling me cheap?

[RussMcB]

Russ: What's the connection between me and an EconoLodge? Are you calling me cheap?

No, not at all, Richard. Just trying to be funny - a play on the "slept at a Holiday Inn Express" commercial.

I wondered about that harsh ride statement. I figured a spring is a spring and that it was probably something else that made the ride harsh. The friction reason sounds plausible.

[Steve Demeter]

If it may help, a coil spring is simply a torsion bar wound into a round shape.

The calculations for spring rate for a given size and stiffness of material are identical once you get rid of the allowences for the different geometry (straight bar versus a straight bar that is wound into a coil). Both work on the principle of twisting a shaft.

[Purple Frog]

Hum... reminds me of a Tatuus I used to own. It used very small diameter springs on Ohlins. I thought it was to save weight. It seems to reason, that the smaller the diameter the spring the less it can put side loads on the shock... Was Tatuus onto somthing?

If you had the space. Why not two rods coming off the bellcrank? One to the spring, and one to the shock. Thus no shock side loads from the spring.

[R. Pare]

The 36 mm spring arrangement has been around for a long time on many different cars. Some designers like it because it is a smaller package and a bit lighter.

The smaller dia spring should produce a bit less side load at any given load just because of the greater diameter to length ratio. I doubt that anyone was thinking about the side load issue, though, as very few people are/were even aware that it existed!

Bob Riley has a neat rocker system on some of his cars that puts the shock and spring side by side. He did it for fast spring change reasons.

[Rick Iverson]

Fellas;

As my chassis will be back in the garage within the week with fresh powder coat or paint (jury is still out on this one), my dilemma is: what items should I spend wisely on that will provide the greatest impact on both car and driving performance. Now, unlike all the rest of you, I'm on a steady diet of wiener water soup to support this illness that no doctor can cure. Consequently, I need to prioritize.

So to put it simply, will a $1440 investment have a profound and noticeable impact, or might I go with a Pennon diffuser, ICP calipers, TRE blue printed GB, etc. I recognize in the hands of a genius such as Weitzenhof, it's a done deal. But I'm not Dave. Candid suggestions, please. After all, among friends here.

Iverson

[carnut169]

My .02

1. Depending on what diffuser you are using it can make a huge difference... Gyro makes a sweet one for $450+/-.
2. Is your GB shotty? If so, thats a big deal as well. The guys at Taylor make a sweet shifting box.
3. The spring perches might be next... (4) or the calipers if I was overweight.

[DaveW]

Who set up your dampers? What kind are they?

Since the object of the spring perches is to get rid of friction (kills grip), you may want to have your dampers rebuilt to the latest specs so that they don't have excessive low speed damping (which acts like friction). The best setups use stiff springs to control chassis attitude while letting the suspension move freely in very small motions (low friction).

If your dampers and setup aren't optimized, I think I'd attack that first. Also check any suspension pivots to make sure they move with as little friction as possible. When you've got that set, then go for the perches as the final step.

EDIT:
Of course, using the perches will somewhat affect the spring rates and damper setup, but I think work on the basic setup should come first.

For an overview of all this, check out my handling article at http://www.neohio-scca.org/comp_clin...ut%202005a.pdf

[Rick Iverson]

Dave;

I will make provisions for either Anita Milican or Joe Stimola to rebuild my Penske 8100s. Just seems quite expensive for what I perceive a small gain in performance as opposed to, lets say, a blueprinted GB or a "highspeed - low drag" diffuser.

Although I would be remiss were I not to take advantage from the superb counsel offered off the net by Rick Kirchner. Thanks, Bud.

Iverson

[Charles Warner]

Rick,

Correct shocks/shock valving can provide a great deal more than a "small gain in performance." The combination of proper damping options and a knowledgeable guide to their adjusment can make for seconds of time, depending on the track - more than a blueprinted gearbox. Case in pioint: I picked up almost 1.5 seconds at Road America with two rebound adjustments on the Shadow that predominantly affected the way the car handled in the Carousel which provided about 10 mph increase in exit speed and, consequently all the way down into Canada corner.

[Rick Iverson]

Charlie;

Cripes sake, my first born male child for 1.5 seconds. Well then I guess that settles it, as I am intimately familiar with RA.

Iverson

[Bob Coury]

Reguarding the needle thrust bearings talked about here. Should they be used on the top and bottom of the spring? My first thought is that using them on one side only is almost pointless as that end of the shock would want to rotate instead of the whole spring.


It is a rocker car if it makes a difference.

[R. Pare]

The needle roller bearings will work exactly alike regardless of which end you put it on - you only need to "release" one end of the spring to get the benefits.

Back to my comment (4 years ago??? That long already??) regarding 36mm springs when they are mounted in-line with the shock body - that is the worst setup for producing side loads on the shocks. Simply a matter of leverage - ie - where the side forces are applied vs. where the piston band and shaft bushing are located. This setup created all sorts of problems for a well-known IRL team last year, and I'm not sure that the shock designers fully believe it yet, even though they were destroying shafts every weekend.

[Bob Coury]

Thanks Richard. I can't believe that the post was 4 years old either! Have a Happy & Safe New Year.