Three Days and Two Sways -- Tarett Sway(bar)s, With pictures! Options

[eeyore]

I got two more weekends in on the Tarett prototype rear swaybar with an AX April 30, a DE May 1 and another AX May 15.

The 200 lbs rear springs plus swaybar setup was too stiff for the street and AX, so I changed to 175 lbs rear springs. I set the rear swaybar to 50/50. The ride quality wasn't all that bad with 200s. But I would occasionally get hung up on very irregular pavement, like the deepish rain gutter that crosses my street.

April 30:
The AX course was very technical. There was discussion afterward where everybody expected to drop 4 seconds between the first and the final, timed sessions. Most managed to drop only one second by the end of the day. I'd rather not say how I did. Fortunately, I can't remember now, and results have not been posted on the PCASDR site yet.

May 1:
The DE course was quite fast for a parking lot course. The first session ranged from 3rd to 5th. After a course change to account for potholes, it ranged from high 2nd to 5th. The very first layout had the course tester getting into the neighborhood of 130 with his GT3. The course was adjusted to slow things down.

Over the 2 days I gradually moved the rear bar softer, and added a bit of stiffness in the front. This allowed me to dial out throttle-on tail sliding from corner exits.

For the last DE session I disconnected the rear swaybar and ran the front at full soft. I fearfully entered the course expecting suspension setup disaster to strike. Alas, the car was still well balanced but there was more body roll. Not huge, but noticeable. Later inspection of the tires showed the tire was rolling almost another 1/4 inch onto the outer sidewall. NOTE: This additional rolling may have been caused by stock rear bushing failure.

May 15:
Looking for additional data, I nearly shot myself in the foot. I spent Friday in a moderate thrash to replace the driver's side rear bushings and a Saturday of twiddling to get the car re-aligned and finished up.

I set the rear bar to full soft and the front to 1/4 firm. Bad move. Way too much oversteer in the 1st practice. I went to nearly 1/2 firm on the front for the second practice and did much better. I added another 1/4 inch of firmness on the front for the time laps. The car was still a little loose, but managebly so.

[eeyore]

Thoughts?

I was bedeviled most of the DE day by a 2nd gear left-hand hairpin. I just couldn't get the braking, turn-in and apex points correct. Then on the last session of the day, without the rear bar, and softer front, everything seemed to come together. There was more feel to the dynamics of the car. After braking and turn-in, the car leaned to the outside and pivoted around the inside front wheel. I clipped the apex much better than any other time and had a very nice track out.

My first thought was that I had finally 'gotten it' and done better than all previous attempts. Then I realized that softer suspension may have had a hand in this breakthrough.

Then I got to thinking about my DE instructor and his '74 911 3.0 on
205/50-something Victoracers. Those 911 guys drive their cars fairly
violently. They use weight transfer square off the corners, swing the car around and accelerate away. In some cases, I think weight transfer is a desireable thing.

As for running two swaybars, I figure that I may need to put in more static negative camber since body roll is minimized and dynamic camber changes are lessened.

[eeyore]

Here's the rear suspension at full droop. The shock runs out of travel before the swaybar arms / droplinks do.

However, when the bar is set to half, the arms / droplinks limit out before the shock.

[eeyore]

Here's the swaybar mounted up underneath the car. It rides forward of the tranny crossmember and above the transmission.

Although it looks close to the trunk floor, the forward end of the arms has 2 inches of clearance from the floor.

Even an unintended off-road excursion didn't cause the arms to hit the trunk floor.

I also managed to hang the car up on opposite corners by pulling into a driveway at an angle, and dealing with the drainage gutter / swale at the end of my street. Still no issue with arm / trunk contact.

[eeyore]

The shock bolt without the droplink in the way.

[eeyore]

Ahh, prototype backing plate model A. It leave a little to be desired.

[eeyore]

Backing plate prototype B

[sean_v8_914]

thanks for sharing your data. does Fernando post here? he had some valuble info about his rear bar experiment

[Brad Roberts]

Good stuff Mark. Cant wait to help you out. It is VERY nice hearing good driver feedback on what he/she is feeling. Just from your description, it appears you are probably pretty quick in your car (and maybe others)

Sean,

How did you do ?


B

[Oracle]

Hello guys,

I had a blast this Sunday at the AX.

There was a total of 3 runs. The second run was without the sway bar and the car was very loose on the back. I decided it was too loose and put it back on on the 3rd and last run. By the time it was all said and done, I felt the run without the sway bar was the fastest and I just have to learn to drive it that way. Besides Herb and Jess suggested running without it and they do very well. (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

[eeyore]

What surprised me was my consistency -- 101.92, 101.81 and 103.86 (101.86 + 1 cone)

Sean did 104.69, 103.43 & 102.5. Herb did 101.07. Both drove Herbs car with Sean's new Azenis.

I have a 2.0, so I'll have to put up with smack-talk about my comparative slowness.

I figure the next AX I won't fiddle with the swaybars so drastically and only do a bit of tuning if necessary. I'll spend the time learing the track and getting more familiar with the car instead.

Now I understand why, when tuning suspension, it is recommended to start out with understeer. Starting out with too much oversteer on two occasions has given be a healthy distrust the back end of the car will come about abruptly.