Hey Fritz,
In ref to your roadwheel question, from personel experiences from driving track vehicles back early in my career, that the rubber on the roadwheel would come from the factory, green as green could be. But after an exercise or an overseas tour, the constant compression of the rubber would crack the paint and the wear and tear, enviroment, rocks, etc., would quickly remove all traces of the paint. Just off black and chewed up rubber.
With my Tiger 1, I have the Asiatam metal roadwheels with the removable rubber. First I dipped them in AK Interactive Metal Burnishing Fluid, this allows the metal to obtain that dark metal look. Then I give them a coat of automotive Red Oxide primer. Follow up with the over all tank color, in my case Dark Yellow. As i'm doing an early mid Prod Befhels, that had survived numerous months of battle, I painted my roadwheel a lighter color than the overall tanks base color. My reasoning was, being a soldier, we would change camo colors on the hull to reflect our enviroment but very rarely the running gear and I would suspect the German army may have done the same. Only during the annual inspections would we go hog wild with the paint. Once the base coat is on, add a camo pattern if required, do some color modulation and then I clear coat a gloss finish on the items IOT(In Order To) start weathering.
Next I weather, commencing with my favorite part, the chipping.

I simulate chipping and scratches by first starting with a lighter color of the roadwheel, idler, etc. With a fine tip brush, I just go around adding a scratch here and chips there, mainly on the raised surfaces, the outter rim, bolts, etc. Then into the meat dehydrator for 30-45 mins. Next I mix up some Tamiya Red and Brown to represent the Red Oxide Primer. Place some more scratches, add some to your base color scratches in all the same areas as before. Let it dry and with some Tamiya Nato Black and Brown, mix the paint to a darkened metal color and start the chipping and scratching process all over again.
Once the chipping is done and dry, I follow up with some AK Interative Rust, tipping the brush into some of the chipped up areas, scratches, bolt heads, etc. As most heavy armored vehicles will and always do blow a seal, you can simulate the spider webbing effect with either some thinned paint mix or a store boughten product. I use AK products quite a bit. Finally, I'll lay down a light oil based black wash and the follow up with a burnt umber. With oils, let them dry fully before handling them as you may leave finger prints, I let my stuff sit for a week. Once your happy, spray a Flat lacquer over them and they will be sealed from the enviroment. When the tank is complete and your spraying a light mist of a dusty color, just don't forget the running gear.
Also, one other thing you can do, is have a roadwheel or sprocket just painted Red Oxide to represent a change piece due to battle damage, etc.
Here are some pics of my sprocket wheel.
Base color with some color modulation and Tamiya Clear coat.

Chipping, weathering and Oil wash complete.
On my sprockets, I don't paint the silver effect of where the guide teeth would be roughed up. I don't believe paint would represent it properly, I'll let wear and tear take care of that.
I'll post some pics of my complete set for you, just need to get the collection together and flash some pics.
I hope this helps...
Derek