There's 25.4mm in one inch. You half that to get the change in angle of attack. So there's .5" difference between 27.5 and 26 when talking about rollover. While you only get .5" difference in rollover, you reduce seat tube clearance at bottom out by the full 1". THis is why you have to be careful with 27" in 26" frames.4 days ago · By switching to 650B from 700C, you suddenly gave clearance enough for medium-width tires, say 35-38 mm width, and for fenders, so you don't need to be a "fair-weather" cyclist. The wider tires will be more durable, more "sure-footed", and give a more comfortable ride on rough pavement or under moderate off-road conditions.
About 5 to 6% lower drive ratios in the same gear combinations. Slightly increased rolling resistance. A better option is to find a 26 inch frame that fit's 650b, and most 26 forks clear, and it would raise the BB and pedals 1/2 inch over the true radius of 26'er wheels (really very near 26.5 inches). Gearing is raised a little over 4%.
A 29er wheel is a 700c, and a hair smaller than a 27" wheel. 27.5 is a 650b wheel. Ah, yes! More obfuscation! 584mm, the same as 26x1-1/2, placing it in the 26" forest of sizes. (And, of course, while a "27.5" wheel is 584mm, the regular 27-inch wheel is 630mm.) Bottom brackets that are too low to the ground cause clearance issues. By reducing the diameter of your 29er wheels to 27.5 inches (650b), you lower the bottom bracket by about 3/4 of an inch, from about 12.5 to 11.75 inches, where you will most certainly bang the pedals on every big rock on the trail. . 242 286 63 170 403 180 209 451