Suspension Design - Fundamentals
1. Can you change the total lateral load transfer that occurs during cornering? If yes, how?
- Yes, it is possible to change the total lateral load transfer that occurs during cornering. By altering the height of CG (Center of Gravity) by changing the ride height and track width dimensions using wheel spacers.
2. Does the spring contribute to roll stiffness or is it responsible only for vertical stiffness?
- Yes, the spring contribute to roll stiffness along with the anti-roll bars.
3. Why do we want the load transfer on the front axle to be higher than the load transfer on the rear axle?
- We want the load transfer on the front axle to be higher than the load transfer on the rear axle to maintain the understeer condition.
4. Assume you have a solid anti-roll bar (ID=0). If you want to double the torsional stiffness, by what factor do you have to increase the OD? What can you conclude from this?
- `k_(phi arb) prop D_o^4 - D_i^4`
When `D_i = 0`,
`k_(phi arb 1) prop D_(o1)^4` ... (1)
For double torsional stiffness,
`2 k_(phi arb 1) prop D_(o2)^4` ... (2)
Dividing equation (2) by (1);
`frac(2 k_(phi arb))(k_(phi arb)) = (frac(D_(o2))(D_(o1)))^4`
`2 = (frac(D_(o2))(D_(o1)))^4`
`frac(D_(o2))(D_(o1)) = root(4)(2) = 1.189`
`D_(o2) = 1.189 D_(o1)`
Thus, the diameter changes by a factor of 1.189 if the torsional stiffness is doubled.
5. With reference to an anti-roll bar, if the ID is half the OD, how much torsional stiffness do you lose when compared to a solid bar? What can you conclude from this?
- `k_(phi arb) prop D_o^4 - D_i^4`
When `D_i = frac(D_o)(2)`
`k_(phi arb) prop D_(o)^4 - (frac(D_o)(2))^4`
`k_(phi arb) prop D_o^4 - 0.0625 D_o^4`
Thus, the torsional stiffness reduces by a factor of 0.0625 i.e. 6.25%.
6. What are the disadvantages of a solid rear axle over an independent suspension?
- Since both the wheels are connected in a solid rear axle, a bump on one side will affect the wheel on the other side leading to loss of grip. Also, the unsprung mass of axle and differential leads to a compromise in reflexive response of the car.
7. Why does the Mustang have a split lower control arm with two lower ball joints? Why won’t one ball joint serve the purpose?
- Due to the thick brake rotor and wheel, it is not possible to shift the lower ball joint outwards. By introducing split lower control arm (two lower ball joints), their intersection would fall far outward than it would be in a single ball joint. This reduces the scrub radius without having any handling issue.