I'm assuming that the ray uses a combination of accelerometers, etc to calculate whether you're accelerating/braking too excessively. These deal with two main aspects of driving efficiently: brakes and fuel. The third big one i think is tyres which aren't tracked yet in terms of a 'rating' per se.
My suggestion would be to use the same accelerometers (or new sensors in future products) that can sense lateral G forces as well to gauge turning efficiency. If I were doing it and I had the hardware to track it, I'd take a common 'slipping' point for a common tyre compound, on a common road, at different speeds. Set that point as 100% and going straight as 0. The percentage of lateral acceleration towards the slip mark would be a strong indicator of how much you're unnecessarily wearing your tyres out alongside braking/accelerating too hard.
10 months ago
EDIT: Also, if you're not already using some sort of accelerometer, then you really probably should be. This might also help with things like sensing inclines and thus increasing/decreasing the rating thresholds as required to even things out (e.g if you're going downhill, you shouldn't need to accelerate as much hence you'd reach a red Ray light sooner than if you were on flat ground or going uphill).