Torsion bars for narrowed torsion housing

[hotstreetvw]

At launch, my car is squatting severely.  The current setup is

Narrowed torsion housing, 3" per side
28mm saw torsion springs
Saw thick adjustable spring plates
Jaycee spring plate retainers
Qa1 doubles, at 16 on the compression, didn't help enough.
6w slicks,16psi
Weights 1865 w driver

Updated with clutch info, Kennedy stage 2, stock disk.

By my estimations, the narrowed torsion housing requires more spring to control the wheels than a standard torsion setup.  Any thoughts?

Do you think 30mm bars will cure the squats?

[Erlend / bug66]

Too much clutch?

Wonder how much stiffer 28mm shortened bars are in comparison to "normal" lengths..

[hotstreetvw]

Sorry. I left out that important bit of info.  Its a stage 2 with stock disk.

The bars are 21-3/4 long, standard beetle lengths.  My thoughts are around the placement of the spring plate on the axle, where the spring force is placed.  Consider the axle pivoting about the transaxle, the wheel in stock location (assumption based on wheel offsets etc).  I've reduced the moment arm provided by the spring plate by three inches, but haven't reduced the moment at the wheel.

Too much clutch?

Wonder how much stiffer 28mm shortened bars are in comparison to "normal" lengths..

[hotstreetvw]

How about another way of looking at it.

Since the spring rate of the torsion bar is linear, to reach a given spring force, a angular deflection of the bar is required.  By moving the spring plates inward, the same deflection of the spring plate results in a larger rotation of the axle during squat.  So the tire moves more into the fender on compression.  A higher spring rate, that reaches the same spring force with lower deflection should resolve it?

[richie]

This might sound weird, but your launch rpm is to low and you don't have enough hp, I usually have QA1s at about 5 clicks and 26 or 27mm 21 3/4 bars for N/A cars

I see what you are saying but its more related to launch rpm/hp/clutch than anything else in my opinion



PS cool to see the car run so well at Vegas   Didn't even notice your red light in final and thought you won


cheers Richie

[hotstreetvw]

I agree completely.  I need more power and to get the two step sorted out to get the launch rpms up.  They are big tires and not enough giddy up.  Any suggestions on the clutch setup?

This might sound weird, but your launch rpm is to low and you don't have enough hp, I usually have QA1s at about 5 clicks and 26 or 27mm 21 3/4 bars for N/A cars

I see what you are saying but its more related to launch rpm/hp/clutch than anything else in my opinion



PS cool to see the car run so well at Vegas   Didn't even notice your red light in final and thought you won


cheers Richie

[richie]

I agree completely.  I need more power and to get the two step sorted out to get the launch rpms up.  They are big tires and not enough giddy up.  Any suggestions on the clutch setup?

Which engine set up?

[hotstreetvw]

Considering how long it's taking for my case, let's assume this 2275 through the spring time.

I did go back and do some measurements and calculations.  These measurements are close and good enough to get a warm and fuzzy.  By no means perfect.

Axle pivot to center of the tire, 21.5"
Axle pivot to stock spring plate mounting point on the axle, 17.5"
Axle pivot to narrowed spring plate mounting point, 14.5"

Spring plate length from torsion bar to center of the axle, 17.5"

With the stock suspension setup, let's estimate the torsion bar deflects 1 degree.  Let's us my 28mm bars, that's 1651lbs loaded on the bar.  With a 17.5 arm, the axle at the spring plate mounting point moves upward, sin(1)*17.5 = .305".  Using similar triangles  the tire moves, .305"*21.5/17.5= .375".

Using the narrowed torsion housing, same force applied, 1 degree of rotation, sin(1)*17.5=.305".  Again with the similar triangles, the tire moves .305"*21.5/14.5= .453".  A 20% increase in tire movement.  More squat.

So basically with a narrowed torsion housing, it requires a 20% more spring rate to be equivalent to a standard torsion.  My 28mm bars at 1651lb/degree in narrowed torsion are approx the same as a 27mm bar at 1333lb/degree in std torsion position.  A 30mm bar is 2031lb/degree in a narrowed torsion would be equivalent to a 28mm in standard position.  (2031-1651)/1651*100= 23%

Calculation checker, assuming same force, 1651lbs but on a 30mm bar, the deflection is 1651/2031 = .813 degrees.  Sin(.813)*14.5= .248" at the spring plate axle point, using similar triangles tire movement is .248*21.5/14.5= .368"

.375" with 28s in standard position vs .368" with 30s in narrowed position.  All this will be linear, so as the suspension compresses more or less it will have the same 20% effect across the board.

My car is pretty heavy in the rear, I went a little crazy beefing up the frame horns and tying into the cage.  Might add too it.

None of this takes away from the fact the car needs more power

[Jon]

Interesting problem, I never thought about it before. Good to see you solved it!