Simulating Rubber.

I use the MM flat balck with a little grey mixed in....

I read somewhere that a good way is to add blue to the black. I did it once on a set of small tires an it look pretty good. When I did that it also made it easy to do a wash and drybrush.

What about using the plastic sheath from copper electrical wire, after having used a wire stripper to remove the copper? I've used it once or twice for general scratchbuilding for rubber hoses, etc. Hope this helps. :)

Not just Bikes but rubber in general, the reason why I used bike parts as an example is because I am very familiar with them and love them.

Thanks, for the tips will try them on the next model.

Front fork seals & handgrips?, we must be talking bikes here!
Try doing a coat in black and then dry brush over it with a slightly lighter shade.
Rubber, especially on tyres (tires) doesn't stay black too long, due to sunlight, dust etc, the lighter shade (black with a touch of light grey) will add depth to it, especially on convoluted fork seals.
All the best
Pete