i put 700c wheels on my '97 gary fisher MTB, and it seemed to make little difference WRT handling, but when i put 26" (MTB) wheels on my '85 trek, made for old school 27" wheels, hands free riding was not only impossible, but dangerous to even try. 'death wobble", "speed wobble", "speed shimmy", type wobble occurred instantly.

but, interestingly, when i put a coaster brake on the Gary Fisher and restored the 26" wheels, and because i had no cables to worry about and could spin the front wheel, i experimented during a ride, by first turning the front wheel 180 degrees and rode like that for a while. mounting the bike was difficult with the handlbars in the way, so i loosened the stem and moved it 180 degrees, so that the handle bars were, in effect, normal when the fork was turned backwards. surprisingly, there was little difference in the ride, excepting the shorter wheelbase, even hands-free riding was easy.

what's all that about trail, again?