K&C Case Study – Goals and Objectives
This is the first of a multi-part series which will act as a case study of how kinematics and compliance testing can be applied to a race car. Since we’re careful to keep client information confidential, this study uses in-house engineer Mike Keena-Levin’s vehicle. In this first part a few of the goals of the testing will be outlined. Part 2 will cover the results of the test itself, and part 3 will follow up with changes to the vehicle and the on-track results. The vehicle to be used is a Honda CRX Si racing in NASA’s Honda Challenge H2 class. The specific goals will focus on this vehicle, but the fundamental concepts can be applied to any production-based race car and will illustrate how K&C testing can be used with any type of vehicle.
The overall objective is to use kinematics and compliance data to improve the vehicle from a suspension and handling perspective. The first goal will be to see what information about the car can be learned through a baseline characterization of standard K&C tests, and what correlations we can make between the data and the behavior of the car on track. Working with this baseline data, what changes can be made to improve the vehicle? Based on Mike’s experience on track with the car, there are no major problems with the car that need to be specifically addressed. The balance of the car is good in both low and high speed corners, and the overall grip level is high. Under braking the car runs straight and is stable, and there are no problems with wheel-spin or putting power down on corner exit. The vehicle is fundamentally ok, but that doesn’t mean there are no more changes that can be made to improve the handling of the car, whether in overall grip or drivability.
One popular addition to a production-based race, and street cars for that matter, are bolt-on chassis braces. They come in a variety of shapes to suit various locations on the car, and a variety of price tags as well. The manufacturers claim improved turn-in response as well as stiffening the suspension pickup points that the brace bolts to, improving overall grip. With so many people swearing by dramatic increases in vehicle handling due to the addition of these braces, a back to back test on the K&C rig seems like the perfect way to put some concrete numbers on the effectiveness of such braces. Mike’s car has a front upper brace spanning between the upper shock mounts, and a rear lower brace that bolts on to the lower control arm inner mounting points. By simply running tests with and without the braces connected, their effect can be measured and objectively evaluated.In addition to the baseline data, there are a few items of specific interest. As a front wheel drive production-based race car, the rear has a higher roll stiffness than the front to help with traction while cornering and to mitigate understeer. This can cause the inside rear to lift during hard cornering, which can result in excessive body roll if it lifts too far. With a few different tests on the K&C machine the effects of this can be measured not only in terms of vertical wheel loads, but the effect of the body motion on the wheel positions as the car moves. Mike’s CRX was set up for racing without any anti-roll bars. The overall balance of the car is very good and he hasn’t added any bars for fear of disrupting that balance and causing too much understeer or oversteer. Mike has a few options as far as springs and anti-roll bars available on hand, and a few combinations of those will be tested to see what will give the chassis the most body control, as well as the right balance, in cornering.
There is no shortage of things to improve on a race car, and these are just a few of the things that can be studied on the K&C rig. Some are specific to production-based race cars, while others apply to all types of vehicles. Like any baseline test, just getting to see the data will reveal many things about the car that were previously unknown. Some questions will get answered and others will be raised, but something new is always in store. Part 2 will feature the results of the test and some of the changes that Mike will make to the car.Finally, like many race cars that started life as street cars, the CRX has had the OEM rubber bushings replaced with polyurethane to help with bushing compliance. They incorporate a metal sleeve that slides inside the polyurethane bushing; the sleeve lubricated with silicone. The bushings can have high friction as the sleeve must rotate inside the bushing, and any misalignment of the suspension joints will cause the friction between the sleeve and the bushing to be even higher. The sensitivity of the K&C machine allows it to measure the friction in the suspension as it travels, as well as uncover any increase in friction as load is applied to the suspension in cornering. Honda Challenge rules allow replacement of the suspension joints with spherical bearings, and this would likely decrease both the friction and compliance of the suspension.