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hari00968

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**'Fundamentals of Vehicle Dynamics' by Gillespie**. In the chapter 'Steady State Cornering', it explains how under-steer and over-steer works, using a formula, which is also derived. I can understand the derivation of the formula reasonably well. The formula is:

**Steer Angle = 57.3 L/R + K*(lateral acceleration)**

where:

L = wheelbase

R = radius of curvature of curve

**K = understeer gradient (+ve if the car has understeer, -ve if oversteer, 0 if neutral)**

There's a formula for K as well, depending on the front and rear curb weights of the car, in addition to tire properties, which is easy, no problems with that.

This is what the book says (page number 203):

"

**In the understeer case the lateral acceleration at the CG causes the front wheels to slip sideways to a greater extent than the rear wheels**. Thus to develop the lateral force at the front wheels necessary to maintain the radius of turn, the front wheels must be steered to a greater angle."

"

**In the oversteer case, the lateral acceleration at the CG causes the slip angle on the rear wheels to increase more than at the front, thus diminishing the radius of the turn.**The increase in lateral acceleration that follows causes the rear to drift out even further and the process continues unless the steer angle is reduced."

**It's obvious from the formula**that you would need to increase the steering angle with increase in speed, in the case of understeer, and vice versa.

**But I don't understand what's happening physically**, with respect to the force due to the tire slip angles. I'm very confused with their explanations. Please help.