I had a month out from blogging, but that didn’t mean I was idle. Everything I had done on the rear suspension had been removed, re-done, then tweaked, then modified and finally mocked up before I went ahead and fully welded everything.
The first problem I had was I wanted to reduce the amount of anti-squat I had. Previously, I had set everything up for about 95% anti-squat. My theory, at the time, was I had read about several low slung racers that had 100% anti-squat and the Haynes Roadster is a light, low slung kit car with 50/50% weight distribution. The standard Haynes Roadster had 0% anti-squat and my decision was playing on my mind. So, I kept reading, in particular Herb Adam’s ‘Chassis Engineering’, this book basically confirmed my fears. Although many racers have 100% anti-squat, they are driven on perfectly smooth, grippy tarmac and not every car has a double A Arm. According to Herb, the limit for a road car with an IRS is about 25%. Any more and under hard acceleration, the back wheels will hop and try to walk. This action places enormous forces on the Arms and mounts.
Bring out the disc cutter!
Unfortunately it bit into the metal, jumped out of my hands and took a sizable chunk of my hand with it. DOH!
With all the mounts removed I cranked up Kangaloosh and recalculated my mounts. Luckily, the whilst removing the mounts I found I had made the upper arms wrong. Somehow, between looking at the co-ordinates on my laptop screen, writing them down and making the arms, I had managed to loose exactly the width of a tube somewhere.
The uprights’ rear attachment points, join to A Arm that have 2 attachment points. This gives these points great strength in the forward aft direction. However, having these two points alone would not stop the toe in/out angle moving around freely. Therefore, there are 2 additional mounting points. The top A Arms have a turn-buckle links. These links have opposite handed threads at each end, so to adjust the length, you simply loosen the lock nuts, give a few turns and re-tighten the nuts. Due to the Anti-Squat angle of the top arm being different to that of the bottom arm, the caster angle of the rear upright changes as the wheel rises and fall. This mean the front turn-buckle link needs to be able to move up and down very slightly. This is why I have used a rose-joint rear the turn-buckle joins the Arm and not a Clevis joint.
The lower rear suspension A Arm also need to be pretty strong. The urethane mounts that link to the chassis have Clevis type arrangements that allow adjustment yet can be bolted up solid, to provide a strong, inflexible link. The A Arm also has a Clevis joint. This allows the lower rear mount to be move back and forth.