Should be perfectly safe.  I actually did a similar thing on my road bike to allow a little more cushion in the rear, for my rear.  The only hassle I can see is if you have to carry two different tubes.  Can't remember off the top of my head if you can get some that span those two sizes.

Different tyre width (front and back)
On a 2003 Saab 9-5 Aero, only the left rear fog light lights up.  The right side has a bulb but when I switch the bulbs, the left still is the only side that lights up.

I thought it might be a wiring issue, however a friend mentioned that his Porsche only has wiring and bulbs on the left side for the reverse fog light.

Is the left side really the only side that should light up for a pair of rear fog lights?

(The fact that the right side has a bulb in the Saab seems strange to me, but maybe it was easier to make them symmetric during manufacturing).
