torsion bars, what to do.....

[Chuck Miller]

Before I made my ‘one step up’ decision from 19 x 23 stock T-Bars I put on 19mm front and rear sway bars because I started time trialing my car the 5th month I owned it back in ’89.
The car did handle ‘flatter’ so for better or worse I used those sway bars as base line for my subsequent up-grades. I realized I needed more spring (at least in the back) when I started going faster and burying (collapsing) my too soft outside rear suspension coming out of slow tight turns.

So keeping the 19 x19 sways I went up to 21 x 26 T-bars dropped my lap times and picked up speed in those slow exit turns.
Then I started going faster (are you picking up the trend here Max? ) Staying with this set-up for the next 17 years or so I learned to carrying more speed now and found I was burying my rear suspension (not quite as bad) again…..

So about 2 years ago I stepped up to the 22 x 29 T-Bars (while still keeping the 19 x 19 sways) and did some other suspension stuff and found the I not only came out of the slow turns flatter but the car generally gave me more confidence to step up my game and go faster……

With this last change I dropped my time a whole 1 ½ seconds, where for the last few years I was fighting to gain 10ths of seconds……………


I guess with all this I’m feeling it’s a good thing to start with a conservative set-up and get a base line. Then, only when you start out-driving that set-up’s potential, or feel terribly uncomfortable at speed, do you progressively start to go forward with more development….

My buck and a half’s worth..

Hope any of this makes sense….

[RSTarga]

+1 on Flieger's analisis, start with Torsion bars and tune with anti rolls.

The stiff sway bars and soft torsion bars will be a compromise for both realms. The soft ride will only happen if you take a speed bump head on. If you hit a pot hole with one wheel lets say or the bump is not hitting both wheels at the same time then the anti-sway bar will come into play and the ride will be stiffer than the torsion bars themselves would be.

Furthermore, you will either be way overdamped in pitch and heave or way underdamped in roll, or a little of both. This means that if you want to be underdamped for a nice highway ride then when you take a quick chicane the car may become unsettled if you get near the natural frequency. Luckily the stiffer bars will mean that frequency is higher but still more damping would be nice to have in case you need to make a quick correction like from a slide/spin.

Torsion bars should be the ones resisting the roll for the most part (say 90%). Keep the wheel rates in balance with the weight distribution for nicer heave behavior. Valve the dampers for those torsion bars. Then add an anti-sway bar to balance the under/oversteer.

[Mr9146]

The stiff sway bars and soft torsion bars will be a compromise for both realms. The soft ride will only happen if you take a speed bump head on. If you hit a pot hole with one wheel lets say or the bump is not hitting both wheels at the same time then the anti-sway bar will come into play and the ride will be stiffer than the torsion bars themselves would be.

Furthermore, you will either be way overdamped in pitch and heave or way underdamped in roll, or a little of both. This means that if you want to be underdamped for a nice highway ride then when you take a quick chicane the car may become unsettled if you get near the natural frequency. Luckily the stiffer bars will mean that frequency is higher but still more damping would be nice to have in case you need to make a quick correction like from a slide/spin.

Torsion bars should be the ones resisting the roll for the most part (say 90%). Keep the wheel rates in balance with the weight distribution for nicer heave behavior. Valve the dampers for those torsion bars. Then add an anti-sway bar to balance the under/oversteer.

Sounds good on paper, but feel from the driver's seat is what matters most to me.

[edmayo]

I won't get into the whys and wherefores of stiffening through either stronger springing (i.e.torsion bars) or through the use of stiffer sway bars to achieve the desired roll stiffness, but just realize that especially on our cars really stiff sway bars will require reinforcing the sway bar mounting areas, especially the rear as I 'm sure most are aware of.

[jpbadonk]

Really depends on what you want and how much time you will spend at the track. 30mm torsion bars, IMO, are too stiff if you are doing any significant driving on the street. I have a set of hollow 30mm bars that I took off my '72.

Here are two pictures. One is how my car looked at rest. The other is how my car looked while at the track with 26mm rear bars and 22mm fronts. That is running street rubber with a 2.4L motor. I believe that was with stock sway bars. I later upgraded to SRP sways with 23mm front and 30mm rear. That was a more dedicated track machine and it wasn't pleasant on the street.

I am in the process of swapping in a 3.6L and will run 21mm front, 28mm rear with Tarrett RSR bars. Going for 100% street friendly.

[Jens]

For what it's worth, I'm running 20mm front and 18mm rear sway bars and soft springs- 225lb front and 325lb rear. I've been able to reduce my run to the Post Office by 3 minutes, traffic permitting.

Hope this helps.

[a911s]

I am in the process of swapping in a 3.6L and will run 21mm front, 28mm rear with Tarrett RSR bars. Going for 100% street friendly.

Josh, everyone I talked with (pretty much every well known shop and vendor on the west coast), told me 28 would be too soft for a 3.6L. I went with hollow 21/29 mm Sanders bars from Elephant Racing on my '72 T/ST with 3.6L Varioram. Very street friendly, but 22/30 mm would have probably been better for track work (disclaimer: I do drive it pretty hard).