Very few consumers will be aware of the intricate craftsmanship that goes into each vehicle to achieve the defined attribute targets. Chris Tandy, wheel and tire technical specialist system engineer at CEVT, discusses the sophistication of vehicle attributes target testing and when to call it a day
What are vehicle development and attribute targets? Basically, someone sets the targets for a vehicle via competitor benchmarking. It sounds ultra-sophisticated, and to a degree it is, with objective measurements and vehicle strip-downs. However, the amusing cost generator is the subjective testing. This requires highly skilled, highly focused testers – elites in attributes testing. They can stop or progress a vehicle’s development cycle, and yet the general public will be totally unaware of some of the issues the attribute owners (the delivery team that works on that specific attribute) identified and the elements that have been developed to achieve perceived key attribute performances.
If we rewind a bit, once the basic form and function of the new model is decided, a significant amount of work goes into defining what the vehicle should achieve, which involves determining a comprehensive competitor set. Sometimes the competitors are existing and sometimes they are yet-to-be-launched cars. Tear-down data on existing competitors is used to determine key elements of the new vehicle and chassis layout. If possible, subjective and/or objective measurements are taken during driving. Core competencies or OEM DNA will also impact the end product, and are unique selling points.
It’s from this that attribute targets are set – and this is when it gets challenging.
Vehicle testers are highly skilled, trained to determine attribute qualities and collect relevant data to analyze in development. OEMs will categorize customer groups – who would notice what – and the percentages of customers that would notice an attribute (to calculate the risk factors, I expect).
But we all have our individual criteria of importance and it’s those that will determine whether the driver is happy with the attribute performance of the vehicle.
In addition, some attributes are at odds with one another. Some are limited by costs. Sometimes physical geometry impacts or compromises performance. For example, an SUV with sporting intent is never going to be as dynamic and sporty as a saloon or a sports car. What vehicle developers must accept is that to achieve some performance attributes, you may lose performance in other areas. For example, building a car with 225km/h (140mph) cornering speed stability is wonderful, but it could mean poor ride comfort at speeds under 80km/h (50mph).
The developer (often the vehicle line director) needs to think rationally and pragmatically. What will be the main use conditions of the target user group? The answer to this should govern the attribute performance of the vehicle.
I’m a tire specialist, and in my role my prime objective is to make sure the performance targets are in scope. By this I mean that they meet future legislation and that any directional changes to the car are taken into account.
At the concept stage, I am interested in competitor usage. I cross-reference with dynamics feedback, and now, more importantly, the energy team’s results. Somewhat surprisingly, the tire impacts a great number of vehicle attributes, and when selecting a size we have to be mindful of this.
To attain dynamic performance is pretty straightforward, but various inputs will dictate the attribute performances and may amplify or degrade them, so we need the capacity to deliver the required attributes. NVH is a little harder, because geometry affects the levels or harmonics generated.
In the tire world, recently we have seen emissions and energy usage come to the forefront of attribute requirements. For the tire, aerodynamics and rolling resistance are the two major influencers, with rolling resistance being in the order of 85%+ of the calculated effect. Prior to this, most of the attributes were second to dynamics, whereas nowadays we are seeing a compromise on dynamics. To put that into context, as long as a vehicle is safe, it can handle all conditions and provide communication that enables a driver to maintain control, the tire maker has fulfilled its duty of care.
As a tire and wheel developer, the minor changes in my realm are attribute requirements. I believe the tire is simple – provided that you understand the demands, which are usually defined by scrutinizing the competitor set and the customer profile. My ambition is to be better across all areas. I use tire modeling to further my developments and to justify my sizing. I boil it down as simply as possible and try to understand how this will influence how the driver perceives the vehicle.
My point is that differences between models can be very small and most purchasers will be unaware of them. This pretty much sums up the role of vehicle and tire developers. Of course we don’t want to do a bad job, but the reality is, some of the things we spend time on are pointless and in the end, pragmatism must win – it’s a job, not a hobby.