What my car should look like when finished - Stoneleigh 2015

Monday, 14 March 2016

Rear Suspension Geometry

Apologies for not updating the blog as I go.  I have been steadily working away.

I was trying to get the geometry setup for the suspension as close to what it should be.  Once the car is on it's wheels and bedded in, I will take it to a garage and put in on laser alignment system.  I put in place some steel bars to simulate mid travel of the suspension.

I started off using my brother in-law's Bosch GLL-280 laser level.  I marked centre lines on the chassis, and drew a line on the floor using the laser as a guide.  I then drew two more lines perpendicular (front & rear) exactly 4m apart.  This would then allow me to use trigonometry to calculate the toe angle.  I then strapped the level onto the rear hub which I believed would be the best option to show the toe and camber.

After playing around a bit with moving the rose joints in and out, and the turnbuckle, I have worked out the following:

1 turn of the Upper Rod End (Rose Joint) alters the camber by 0.25 degrees.  It has no effect on the toe.
1 turn of the Lower Rod End alters the camber by 0.16 degrees.  Note: The turnbuckle needs to be rotated by 1/2 turn to maintain the toe angle.

I used the following specification for the rear setup:

Rear toe: 10min
Rear camber: 0.5 to 1.0 deg (to suit track)

I screwed the upper rod end fully in, and then out 2 complete turns which will allow for an alteration of 1 degree without having to alter the toe angle.  To alter the lower joint, the shock absorber has to be unbolted and is a little fiddly with washers etc.  I have seen a GD rear wishbone that had a separate shock mount, so I could maybe upgrade in the future if I regulary track the car and require frequent adjustment.  

I altered the lower rod end and turnbuckle to suit the specifications.  I used a digital camber gauge to measure the camber.  I also checked using the laser and trigonometry.

Once I was happy and within a nearness, I moved all the equipment to the other side.

I then transferred some of the measurements of wishbone length and turnbuckle length to mirror the setup.  When I switched on the laser I discovered that the setup was miles off!  I couldn't understand it.  I double checked measurements and almost came to the conclusion that the chassis was wrong.

I then carefully looked at the laser level.  Although the side is nice and flat and appears to be parallel to the laser, it is not.  The laser sits at a slight angle and over a 4 metre length was off quite a bit!  Also, the laser had to be mounted the opposite way around on the other side, so it was even further off.

Back to the drawing board.  I then used some string and a spirit level and re-adjusted the setup.  This took a bit of time since I had to do the adjustment, then plumb the level against the string at the rear of the car and measure from the centre line.  I then had to move to the front of the car to do the same.  I input the figures into an excel spreadsheet which automatically did the trigonometry calculation for me.

I finished both sides and then moved to the front.......

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