Like most people, I use RLM 66 as my starting point for tyres, dry-brushing the sides and treads with progressively less dark shades of grey. The Tamiya NATO black idea sounds good, too. I'll give it a try, sometime.
A couple of points worth bearing in mind. In WW2, Germany used artificial rubber for tyres. This was significantly lighter than tyres made from 'real' rubber. I use Humbrol 27 Matt Dark Sea Grey, mainly because its easily available here in the UK, and is noticeably lighter than RLM 66.
Second, the colour of vehicle and aircraft tyres varies according to the environment in which they are used. The tyres on a F-18 aboard the USS Ronald Reagan today are a very different colour compared to those of a Sturmovik operating out of a muddy field in south-west Russia in spring 1944.
Chris.
Cute and cuddly, boys, cute and cuddly!