Cut the wheel out and then stretch and rotate it to make it more of a circle. Highlight or select (so you get the dotted line round the edge of it) the wheel, then apply your radial blur. Resize it back to how it was and repeat for the other wheel.
It helps if you keep a mental note of how much you stretch and rotate the wheel, that way you can get it exactly back to how it was.
To add to that aswell, keep your right foot over the back brake too, especially while filtering and at slow speeds (you should know that already though). Left foot down first when you stop, so i've been told.
I got told this one some time back, very useful. Always keep an eye on the vehicle infront of the one thats infront of you.
You can get away with it more on a bike than you can in a car. But for your own safety you should actually look in your mirrors instead of just moving your head left and right so it looks like you've looked.
I'd imagine he's taking the day off from skinning. At the bottom of the main forum page it says it's his birthday.
So happy birthday Disposable!
Edit: Got bored yesterday and rendered all the DD2 skins. Unfortunately it was using the old XRT model as you can tell with some of the skins. Also sorry the wheels didn't have white text. I'll get a group shot done at some point too.