Originally Posted by
garage sale GT
Diametrally speaking you can easily put 29er wheels into a 27" frame because the 29ers are 622mm and the 27s are 630mm.
However, the rim width may present a problem. It would likely fit in the frame but if it is a wider rim, it is possible it would be unsafe to use with a tire which was narrow enough to fit the frame. You don't want to put too narrow of a tire on a wide rim. I know a recommended limit for my 27mm wide Rhynolites is around 1.4.
You could probably fit hybrid tires into a 27" frame no problem, because the 27" bikes I have seen usually come with plenty of clearance around a 32mm tire and can run 35 or 37mm cyclocross knobbies (27x1-3/8) no problem. However, it would be wise to check how much clearance you had in the frame, fork, and under the brakes.
It's also possible that the 29er tire is so much bigger than the 27 inch tire that the overall diameter of the 29er is significantly more than the 27 inch. It that case radial fork and brake bridge clearance is an issue, especially with fenders.