Bike Anti-Porn - When Things Go Wrong

Changing one wheel size wouldn't affect the wheel base materially, by nothing if you kept the wheels the same size (i.e. changed both).

Eh?

Wheel base is measured at the point where the wheels contact the ground ie 100% straight down from the axles - on a bike with the same size of front and rear wheels and tyres (and this size is actually irrelevant, they could both be 12"wheels or they could both be 700c wheels) the axles will sit equidistant from the ground. We will call the horizontal measurement between tyre contact points with the ground 'X'

Imagine that there's a strip of tape or a piece of string stretched between the axles, on the forementioned bike with same size wheels and tyres this tape or string would be parallel to the ground - dead flat - horizontal. We will call the this measurement or line 'Y'

At this point, in the plane of X (in the horizontal direction it was measured), X=Y

Now change the size of either wheel. The tape/string will now be at an angle as the height of the two axles from the ground is no longer the same. We will call the angled line 'Z'

It is simple geometry that while X,Y and Z are all lines of equal length - because we haven't changed and frame or fork components which dictate where the axles are placed - in the plane of X, Y reaches further than Z.

Thus changing the size of wheels from 700 to 26" would have no effect on wheelbase and changing the size of only one wheel would actually shorten the wheelbase making the bike - presumably - better for polo.