mikesee 18972 posts · Joined 2003. #2 · Nov 22, 2019. If you're going to ride deep, soft, dry, unconsolidated snow, then 26 x 5.2" tires float and dig better than anything in 27.5". If you're riding groomed, or ice, or a mix of those two, and want to use it in non-snow months, then 27.5 x 4.5" for sure. I have one of each.

Ithought 27.5" was 650b. @JoshuaF The OP is not talking about 27.5/650b. 27x1 1/4 is rim diameter 630 which is close enough to 700/29" (622 rim diameter) that the tubes are compatible. Tires are not compatible, but tubes are. Tubes have a bit of freedom in both directions: both the bead seat diameter of the tire/rim, and also the width of the
Mostlyavailable in 27.5 x 3.8″, the new crop of fat bike tires measure close to the overall diameter of a 26 x 4.6″ tire but without the width. If we’re talking about a bike that used to run 26 x 4.0″ tires, upsizing to 27.5 x 3.8″ will be similar to going from a 27.5 to a 29″ wheel on a mountain bike. Better roll over, momentum, etc.
Sotry both and see if there's a significant difference in comfort. Even just inside the shop or its car park can be instructive. At 155cm you’ll probably need the smallest frame size for a bike with 622mm (28"/29") wheels. The smallest frame size often has to make some compromises to allow 622mm wheels to fit.

Arough height and age range for 24-inch bikes for kids is 4’1″ to 4’9″ and 7 to 11 years. Adults must refer to a bike size chart and choose the frame size that best matches their body dimensions (height, inseam). For adult bikes, bike wheel size is relevant to ride characteristics and is chosen based on the style of the bike.

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26 vs 27.5 vs 29 inch wheels