I love the graphic showing the distribution of bikes vs. fuel consumption. However I've noticed that not all bikes are equal - some have 39 fuel-up's, while others have only one. How about making the vertical axis the number of fuel-up's instead of the number of bikes? I suspect that will yield more useful information.
The number of bikes on the vertical axis is the number of bikes that have a particular fuel economy number on the graph. I'm not sure how we could plot number of fuel-ups and fuel economy—there doesn't seem to be a relationship there. Maybe I'm just missing the connection. Can you describe it a bit more?
Let's take a hypothetical (worst) case where you have only two riders. Rider A recorded 1 tank at 30 MPG, and rider B recorded 30 tanks at 50 MPG. Ignoring the rider your graph would show an average MPG of 40 MPG, and your viewer would only know that their fuel economy was as likely to be 30-50mpg, and anywhere in between. The problem with your site's data seems to be that you have two main categories of reporters: those that report 1-3 tanks, and those that report them all (yeah!). The problem here is that the underachievers with few tanks outweigh the overachievers which have more data.
Let's use the data from one of your bikes: Tiger 800XC.
That model has 17 registered bikes, but of those only 13 have recorded one or more tanks. So your distribution plot shows those 13 tanks (see http://cmumford.com/vstrom/BikeDistribution.png). Looking at the graph I think that I'm most likely to get 40 MPG.
But in reality you have 118 tank fillups and in actuality the most common fuel economy is closer to 42 mpg (see http://cmumford.com/vstrom/TankDistribution.png). I think that plotting per bike or better yet per mile will yield a smoother distribution and better results for the user.
It's probably time to treat the motorcycle section of the site like we do the car section where we only show vehicles with three or more fuel-ups in public browsing.
You're right that vehicles with only one or two fuel-ups are frequently either way too high or too low. But once a vehicle has three recorded fuel-ups things start to even out.
Our motorcycle section has typically had much fewer users, so taking things down to just bikes with three or more fuel-ups would have killed public browsing. But we're probably to the point where it makes sense to do that.