Motorsport Wheel Alignment: Ackerman Steering
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Ackerman Steering
02.45
| 00:00 | - Ackermann steering is another one of those aspects of the suspension system that is not typically adjustable and therefore isn't given too much thought by the majority of enthusiasts. |
| 00:10 | It's usually not until we're considering bespoke suspension components or purpose built racecars that adjustability of Ackermann steering may become a possibility. |
| 00:20 | However for the sake of completeness we'll introduce the concept in this module. |
| 00:25 | To understand what Ackermann steering is and why it's used, we need to consider what happens when the car turns a corner. |
| 00:32 | If we look at the car from above and we turn left, we'll find that each wheel on the car turns through a different arc. |
| 00:40 | This is because the car will be turning about a common point and each wheel is a different distance from that point and hence the arc that the wheel will travel through will be different. |
| 00:50 | Now if our steering caused each front wheel to turn the same angle as we turned the steering wheel, this would result in one of the front wheels needing to slip across the road surface as the angle of the wheel would not match the arc that the wheel needs to travel through. |
| 01:06 | If instead we plot a line from the point the car is turning through, we can see that the front wheels need to turn different amounts in order to track the correct arc and this is the principle behind Ackermann steering. |
| 01:19 | Car designers achieve this effect by angling the steering arms inwards towards the rear of the car. |
| 01:26 | A theoretically perfect Ackermann steering design, where the front wheel angles match perfectly to the arc they need to travel through, can be achieved by arranging the steering arms so that the lines plotted through both arms intersect at the centre of the rear axle line. |
| 01:41 | This should theoretically result in no slip being produced in the tyre as we turn a corner and it's often referred to as 100% Ackermann or perfect Ackermann. |
| 01:51 | While perfect Ackermann steering may be ideal when you're negotiating a supermarket carpark at low speed, when the car is at high speed on a racetrack, there's a lot more going on that affects the ideal steering angles. |
| 02:03 | This all comes down to the optimal slip angle that we need the tyre to work at, in order to generate maximum grip and the optimal slip angle is affected by the load placed on the tyre. |
| 02:15 | While the topic is beyond our scope here, what we will find is that often the steering of a racecar is in fact designed with what's referred to as anti Ackermann steering where the outside wheel will turn further than the inside wheel. |
| 02:29 | What works well at high speed in terms of Ackermann steering however, will not work so well at lower speeds so as with almost every aspect of our car's design, Ackermann steering is a compromise. |
