The Anti-Ackermann Steering Angle

The Anti-Ackermann Steering Angle


Let’s take a look into steering geometry that is Ackermann and Anti Ackermann. The Ackermann steering that connects the two front wheels was invented by Lanskensperger then added geometry by a Jeantand, Charles Jeantand. We will get into four-wheel steering in another series. Let’s start off with the Ackermman Jeantand angle where the front suspension tie rod arm is trailing towards the center of the rear axle so that the car will rotate or yaw around the axis of the rear axle since it is only the front wheels that are turning. Let’s use this as an example two motorcycles one taking a small radius turn and the other a larger radius turn. Notice the difference in wheel angle? So let’s pretend we connect these two motorcycles to create a car Here we can see why it is necessary to create a different angle for the two steered wheels Where the inner wheel is steeper than the outer wheel. So as a single unit a car the outer part has to be faster than the inner to compensate for the longer radius distance. So this is the Jeantand geometry ironically known as the Ackermann steering Now let’s move towards something more exciting, this is opposite to the Ackermann the Anti-Ackermann. This geometry is preferred by racing cars and we will get as to why Let’s take a look at the radius versus geometry, Anti-Ackermann to the left versus Ackermann on the right. What the Anti-Ackermman clearly is here is that it does not conform to what is merely mechanical that the Wheels would turn towards each other and cause friction. This is because it conforms to dynamics instead. One fundamental on the Anti-Ackermann is that it is done around principles of sliding the front wheels, but not quite understeer hence why the illustration has front wheel angle on the Anti-Ackermann steeper than the Ackerman yet still it holds radius. So the reason why Anti-Ackermann defers to Ackermman eventually comes down to tire slip angle. Tire slip angle basically is how much sideways or offset a tire is to its direction of travel until it reaches maximum grip in this case on a corner. As a car corners center of gravity will transfer more load towards the outer wheels Apparently the high weight or load on a tire the higher or more slip angle for the tire before it was this maximum traction so this would also mean the outer tire will have higher slip angle than the inside wheel. So what the Anti-Ackermann does is it caters this, giving more steering angle to the outer tire and less to the inner tire making it a design to get maximum traction without compromise for maximum driving Let’s look at some of the examples of Load to one side of a car and Anti-Ackermann on Formula one cars. Here is also where it gets quite interesting, rear wheel toe. Since tires behave differently to different loads and in this case slip angle requiring different steering angle we can establish the fact that on rear wheel slip angles the different toe in or out is required for the outer inner wheel to get maximum lateral grip What also draws curiosity on tyre behavior and slip angles under heavy load is that those who engineered the Nissan GT-R did claim that being heavy does have its advantages in handling. The same claim also was done by developers of the Bugatti Veyron. So do these claims have anything to do with being heavy relating to these tire attributes? Certainly puts ideas on our heads and also ideas on lightweight cars here

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