Just to follow up some musings on the NVH and tyre sizes, as we have found some issues, that affect all of our cars and many normal cars:
1. we have different front and rear tyre/wheel sizes, even on 4wheel drive vehicles, so need tyre size by axle
2. Our tyre sizes rarely mathematically follow the formulae "(width x profile%)+(Diameter(in mm)/2) * 2 * π", and the size will need manual correction (for both axles), the difference between manufacture spec and the formulae is often large.
3. Correction for a stationary, or very slow moving car, is very different than a moving one, there is a "rule of thumb" that the contact patch created with the tyre on the vehicle, on the floor, changes the circumference by a factor of 0.96, clearly type of vehicle (weight) and profile of tyre and wheel diameter all will affect this ... there may be some more accurate data to be had ...
4. a Fast moving car (yes, that's ours!) will have a different circumference correction than a slow moving car, so the formulae is needing a speed based adjustment from very slow to normal city (25-40mph) to normal roads (55-60mph) and motorway/fast (lets not forget track use or Germany, just to save any "speeding" allegations get discussed)
) of say 75-80mph or even higher, much higher ... thankfully we already have a speed input from the OBD
... but a dynamic adjustment option (for vibrations under acceleration conditions or braking) verse steady speed is something I think needs to be planned for future releases, as these issue become more complex,this sort of correct will be critical ... best start the process/thinking/planning now? Yes, I've had F40 owners complaining of vibrations at specific speeds in the 150mph + range, and did try dyno testing, but was track testing that found the issue.
5. The GM study you have used for your 1.03 adjustment/correction is for American 4x4 which somewhat different from average cars,let alone ours. So this one size fits all is a poor compromise, maybe a good start, but time to allow a more complex correction. In fact using this alone, could lead to over 15% error, just letting you know
6. Tyre pressure (increasing it above normal operating settings) might be a way of reducing some some of these factors, but may in itself cause other problems including masking the fault or creating more unrelated noise hiding/,asking the real problem, let alone potentially causing issues with TPMS etc, but I think it would be good to start to understand how tyre pressure might be used to help the NVH process ... I guess user feedback and back to back runs is the only way, trial and error?
7. Logging other OBD data? While RPM and Road speed are already a key element, what about steering angle? YAW (Lateral and transverse) from the cars sensors, Even ABS parameters (ok, harder due to ABS module ceasing comms at circa 40mph) ... Pump etc might have a direct and very hard to trace relationship? Ok, the last is a bit blue sky, I'll admit that!
Anyway, I think that covers what we've discussed about tyres etc, and some too