In no way do i want to discourage you, but the most likely outcome is that your wife will ride it once and then decide that the time could have been better spent at a coffee shop with her girlfriends discussing reality TV, fashion, and singing competitions like X-factor, America's got talent etc.
I've seen this happen before.
At the end of the day the result will be that you'll feel unwanted and neglected and sidelined because your wife (after one ride) will show no interest in a hobby that gives you so much enjoyment.
From my experience in life i've found that women want 4 things
1) A mirror, for self adoration of her own image and to reinforce delusional concepts of her personal self worth.
2) A multitude of clothing apparel and accessory options like shoes and jewelry.
3) A never ending amount of of massively overvalued cosmetics to boost her feeling of self worth, which feeds back into No 1
4) A best "g.a.y male" friend to discuss everything that is wrong with her relationship and everything that is wrong with you and options to finding a better man.
A motorized bicycle is the furthest thing on her mind - a bit like living in the North Pole with out a television and a mirror and cosmetics.