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Toe-in Adjustment   1st Oct '95
 
I have always found that measuring Toe-in was a difficult and inaccurate business but I believe that I have now found some improved techniques which may be of interest to others.

 Several problems need to be overcome to make an accurate measurement:

 1. There should be no play in the wheel bearings, king-pins etc and the wheel spinners must be tight.

 2. The wheels must be pointing straight ahead otherwise the Ackerman angles will generate a false impression of toe-out.

 3. Any run-out of the wheels must be removed from the measurement.

 4. A suitable measuring gauge needs to available.

 Checking the first problem is easy and rectification is outwith the scope of this letter. The second requires considerable care. I believe the best answer is to drive the car along a straight road having little camber and accurately note the position of the steering wheel.

 Other descriptions of toe-in measurement eliminate problem 3.  by moving the car backwards or forwards so that measurements in front and behind the wheels can use the same point on the circumference of the tyres, but I found that the iterative process of adjusting and measuring required a lot of movements of the car with the risk of displacing the steering from the straight-ahead position.

My technique for eliminating run-out was to hold a biro pen or other marker against the tyre tread and to spin each front wheel until a mark extends around the full circumference. (Whilst it is necessary to jack up the front for marking, the car should be back on the ground for the measurement)

The final problem can be dealt with by using a measuring tape and an assistant, but if working alone then an adjustable roof bar makes an excellent gauge.

 With steering wheel straight-ahead place the roof bar to the rear of the front wheels and adjust its outer support brackets to correspond with the lines drawn on the tyre treads. Now carefully withdraw the roof bar and position it in front of the wheels comparing the same points on the brackets with the lines at the front of the tyres and check that the roof bar brackets are that magic eighth of an inch wider than the distance between the lines on the tyres.

On SS and "Mark IV" cars the track rod ends are left and right threaded so adjustment is easily achieved by slackening the clamp bolts and rotating the track rod. I haven't looked at the thread pitch of the track-rod ends but a half a turn represents a fairly gross change in toe-in.

Whilst all this may seem rather trivial and obvious, the issues of single-handed gauging with a floppy tape measure, and eliminating run-out, have caused me much frustration in the past, so I hope this letter may be helpful to others.