Birkin - Suspension Setup

My initial suspension set up is as follows:

Front shock length (between mounting point centers): 294mm

Camber: -0.9 degrees

Front Toe: 1/16" toe in

Front ride height: 6.25"

Rear Ride height: 6.75"

To set the suspension I built two castor/camber/toe brackets that are held to the wheels by springs. With these I can directly measure the toe, by turning the wheels 20 degrees in each direction I can measure the castor and and using my digital level I can measure the camber.(Pictures to follow).

To adjust the camber, I choose not to remove the upper ball joint from the upright. I was afraid that I would destroy the rubber boot. So I removed the bottom shock/spring bolt then removed the upper A-arm bolts. The top of the wheel than tips outward and the upper A-arm can be turned in or out. I discovered that on my Super-7, one turn of the A-arm equals approximately 0.3 degrees of camber. Somewhat of a course change, but better than nothing I guess.

Centering the Steering Rack

For some reason, until yesterday I have never taken the time to really look over the steering system. Yesterday while looking over various nuts, bolts, etc., I spun the steering wheel all the way to the left. I noted that the bottom rear of the fender was about 2" from the body. After checking everything on that side, I spun the wheel all the way to the right. This time I noted that the bottom of the fender was very close to the body - something like 3/8". I got out my trusty protractor and measured how far each wheel deviated from straight at the maximum steering angle: approximately 19 degrees when turning to the left and 28 degrees when turning to the right.

After speaking with Woody at Birkin Sports, I set out to center the steering rack. I measured the length of the right tie link at full right and full left turns. I then set the rack so that the tie link was exactly in the middle of this distance.
At this point, the Steering wheel was turned about 120 degrees from straight. I marked the steering hub with a straight line, then removed the steering wheel and reinstalled it the way it should be with the car going straight.

Next, I set up my laser lines (I now use a pair of smart line laser units from Home Depot when I align my cars) and adjusted each front tire for a slight amount of toe in (about 1/32" but it's hard to be exact). I then attached my alignment tools to each from wheel and measured the exact toe setting. I then adjusted each side to get exactly 1/16" of total toe-in.

All that remained was a short check ride. The car drives much nicer now. It is obvious that I have been suffering from a bit of bump steer - bump steer causes steering changes when the front wheels move vertically from bumps (duh!) or transitions from acceleration to braking, etc. This bump steer was pretty pronounced, but I has simply assumed that due to the short wheel base that the cars steering was going to be 'nervous'. Well, it's no longer nervous. It's solid and sweet, just like all automotive designs from the 1950's are (just kidding).


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