D606's - front and rear; X conversion

90/90-21 front, 130/90-17 rear. Put 'em on about a week before Xmas as part of a simple Warp9 21" front wheel and tire conversion.

Warp9 wheel and tire did not take much lead to balance and it is running smooth.

I have never tried a 17" wheel on a bike, but I do know that the larger the diameter the wheel, the easier it rolls over stuff. The 606s pretty tall and would only add to that factor. Kinda like a big ol' wagon wheel.
With mountain bikes a 26" wheel would be standard, but since their popularity has exploded, you can now get a 29" wheel set. I think for those who consider full suspension mt bikes being a little over kill, a 29" wheel seems to roll over rough terrain easier, making full suspension less necessary, so to speak. Even though the wheels are potentialy heavier, in comparison, some people seem to enjoy the trade off in dynamics. They may not be better everywhere, but have their advantage in the right place or with the right style of riding.
Because larger diameter wheels are heavier, especially rotating, the need to be skinnier/lighter is necessary for comparably accepted performance.
If some hypothetically, ultra lite materials, were used...I could only assume that a 21" front tire would be better if as wide as the 17"....only because of weight/performance is it more slender.
Anywho, just sayin that you are probably noticing the diameter, rather than the skinnyness.

thx for input.