Auto Tourism Visa....
I've just used Realrussia for my Visa. When explaining to them that I was entering Russia on a bike they said I should go for the auto-tourism visa. It DOESN'T cost any more, but what they do is supply details of your bike (make, model, colour and numberplate) to the Russian embassy with your visa request. That way the Russians record that you'll be entering their country on a bike, and have a record of what bike you bring in.
Where it says "PURPOSE OF ENTRY" you get "ABTOТуризм" (which reads "Auto-tourism") instead of "туризм" (which reads "tourism").
NO details of the bike appear on the VISA, just the word changing above.
Hope this helps!
p.s. the £120 is for the LOI, Visa, Embassy submission and a very, very helpful service. I'd recommend them (they are the ONLY company I've used to get a Visa - so no comparisons with others, but went out of their way to double check details and help me understand the entire process.... very helpful).