Suspension kinematics and its effect on performance

Posted at September 5, 2012 | By : | Categories : Uncategorized | Comments Off

To make a car go faster around a track, there are a couple of things we can do that generally will improve lap times. We can, lower weight, increase engine power, increase downforce, reduce drag, increase tire grip. Unfortunately all these changes typically come with downsides, for example:

  • Lower weight – decreased durability, more expensive materials/processes
  • Increased engine power – increased energy consumption, more difficult to drive
  • More downforce – usually comes at the cost of more drag
  • Less drag – usually comes at the cost of less downforce
  • Better tires – stickier tires usually wear out faster

To improve performance we will always have to do some trade-off. In endurance racing for example, having more engine power would reduce lap time but increase fuel consumption – which in turn would require more frequent pit stops (our free lap time simulation software OptimumLap could for example be used to determine these relationships).

Another area which is filled with trade-offs is suspension kinematics. Whether it’s about designing a new suspension or setting up an existing design, virtually every decision will be a trade-off. Should my roll center be low to slow down the chassis response, or high to speed up the chassis response? Should I have lots of camber gain in roll or none? Will having a non-linear motion ratio help me control the ride height or will it change the balance of the car too much when the car is rolling?

It’s apparent that suspension design and setup is a minefield of comprises, but what about the performance gains? How much can be gained by optimizing a suspension design?

In this example we are going to look at a front suspension for a generic race car. The car has two possible configurations for the front suspension. A baseline setting and an option setting, the latter lowers the inboard pickup points for the upper control arms about 20 mm (3/4 in).

The baseline and option design are shown in this animation. In the option design, the upper control arms inboard points have been moved down 20 mm.

Using OptimumKinematics, these two kinematics settings are simulated for typical low speed corner. In the middle of the corner, the car will be rolling and steering. The animation below shows the two designs in the mid-corner state. The observant reader will notice how the camber angle of the tires is slightly different between the two designs. The Option design results in slightly more negative camber for the outside tire (about 0.25 degree more negative camber on the outside tire and 0.25 degree more positive camber on the inside).

The two designs shown at the mid-corner state. The small change in camber angle between the baseline and option can be seen.

By using tire data and tire models, the effect this change in camber will have on grip can be calculated. Without going into details, the more favorable camber angles result in a 2.1% increase of lateral grip in the middle of the corner. This effectively means that for the low-speed corner we looked at in this example, the car can go about 1 km/h (0.6 mph) faster (94 km/h instead of 93 km/h). The only difference between these two designs was moving two pickup points down about 20 mm.

This is just one example of how kinematics can be used improve performance; but what we haven’t covered is what other effects moving the pickup points will have. There are a number of trade-offs we have to consider. Perhaps we don’t have valid tire data and still need to make a decision on a kinematics design or setup. All of these aspects are covered in our webinar on suspension kinematics design and setup. It will cover the important aspects and difficult trade-offs you will encounter when designing and setting up suspensions. Filled with examples like this one, it serves as a great introduction to anyone wanting to learn more about kinematics but also provides new perspectives for anyone with past experience in kinematics design and setup.

The kinematics webinar is the first part in the four part webinar series we will be running during the fall of 2012. Other topics that will be covered are Springs and Dampers, Data Acquisition and Simulation. For these webinars gather your colleagues, team members and friends in front of a big screen and together take part of this unique learning experience. If you can’t attend one of the webinars, online videos will be available after each webinar. Sign up now for all four parts and get a discounted price!

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