Daily Archives: September 17, 2021

Still thinking, remain in cover until the all clear has been given

I’m still reading my new book about suspension geometry and contemplating the information, but it hasn’t resulted in any changes to the Sprint-T. The front is still a tube with fore and aft location by parallel 4-bar and laterally by a bent Panhard rod to clear frame members, rear is still fore and aft by dual trailing links and laterally by a Watt’s link and a torque arm for control of reaction torque from the engine. And torque reaction links for the brakes. All rotational reaction forces are isolated from the suspension to prevent locking up the suspension from either engine torque or brake torque, allowing the suspension to move freely at all times. The front springs are mounted as close to the ends of the axle as will clear moving parts, and the rear springs are mounted to the trailing links originally designed for swingarm suspensions of much heavier vehicles on rough tracks. This allows easier tuning of suspension stiffness by changing the motion ratio for the springs as there is quite a bit of motion ratio to play with.

To clarify that, the bottom of the spring mount moves less than the wheel in both single wheel and double wheel bumps. This means I can get smaller changes in wheel rate than steps in spring rate which gives me finer control over wheel rate. Also the total travel of the shock is less than the travel of the wheel which reduces the amount of force per inch of wheel travel. There is a formula that gives us the effective wheel rate when the spring rate is known (mr2*Spring Rate) or the square of the motion ratio times the spring rate. On the rear suspension for the Sprint-T there are two motion ratios, the motion ratio for a single-wheel bump or body roll and the motion ratio for a two-wheel bump which is just the motion ratio of the swingarm. The single wheel bump is the swingarm ratio times (the distance from the far wheel to where the swing arm attaches to the axle housing divided by the track).