Steering Geometry and Suspension Compliance

1. What are the two types of tierod errors with respect to ride steer? And what is the effect of these errors on the toe curve?

- The two types of tierod errors with respect to ride steer are:

a. Tierod Length Error = If the tierod is shorter than the expected length i.e. the steering arc remains behind the suspension arc, the vehicle is in Toe-Out condition during both jounce and rebound. And if the tierod is longer than the expected length i.e. the steering arc remains ahead of the suspension arc, the vehicle is in Toe-In condition during both jounce and rebound.

b. Tierod Angle Error = The steering arc remains behind the suspension arc, so the vehicle is in Toe-Out condition during jounce and the steering arc remains behind the suspension arc, so the vehicle is in Toe-In condition during rebound. This could be completely reversed depending on the angle of the tierod.

2. If we have toe out in rebound (due to bump steer) in the rear suspension, is this an understeer effect or an oversteer effect?

- There is an understeer effect toe out in rebound (due to bump steer) in the rear suspension as the turning radius increases with respect to the turn center.

3. If there were no bushings at all in the suspension (all components are hard mounted), would you still have compliance in the system? If yes, where is this coming from?

- Yes, you would still have compliance in the system. This is due to structural compliance where the links in the suspension are having high stiffness but they are flexible under load.

4. In a front-mounted rack setup, if the suspension links are more compliant than the steering, would you have an understeer effect or an oversteer effect?

- We will get and understeer effect if the suspension links are more compliant than the steering in a front-mounted rack setup. This is because the relative stiffness of the suspension with respect to steering is less and the wheel tends to go away from the center.

5. Why does the outer wheel almost always gain positive camber when subjected to a lateral force?

- When the outer wheel is subjected to a lateral force the aligning torque tends to oppose the centrifugal force on the wheels and this tends them to move outward resulting in a positive camber always.

6. Can you get an oversteer effect out of aligning torque compliance steer? Why or why not? If yes, how ? (just a basic explanation)

- Yes, we can get an oversteer effect in the rear axle and an understeer effect in the front axle out of aligning torque compliance steer. The net effect is not purely oversteer. This is because the aligning torque tends to balance the centrifugal force on the wheels.

7. Why does the rear ride frequency have to be greater than the front ride frequency?

- Due to the time delay between front and rear wheel while encountering a bump, front reaches maximum (crest) while the rear reaches maximum (trough) and vice versa. This causes the amplitudes to be out of phase and results in a pitching motion. So if we increase the rear ride frequency, the crest and trough for both the sides coincides and they are in phase with each other.

Usually, Rear Ride Frequency = 1.2 x Front Ride Frequency

8. Can you use the same damping force for: (why or why not)

I. Low frequency and high frequency

- The damping force should be less for low frequency to avoid the size of dampers and it should be more for high frequency so as to absorb the shock efficiently.

II. Compression and rebound

- No, we cannot use the same damping force during compression and rebound because the spring gains energy during compression and release it during rebound. So we need different damping force accordingly.

9. In a passenger vehicle, assume the front suspension has 30% anti-lift and the rear suspension has 25% anti-squat. By what percentage does the total longitudinal load transfer change?

- The total longitudinal load transfer does not change as it is purely a function of weight, CG height, wheelbase and acceleration.

10. Let us say, theoretically you change the brake bias so that all the braking happens only in the front

I. What is the maximum possible anti-lift that you can get in the rear suspension?

- Zero, as there is no compressive effect in the rear suspension.

II. Is 100% pitch compensation possible with this setup?

- Yes, 100% pitch compensation is possible.