NinerBikes | Pedal Damn It! | Mountain & Gravel Bikes
23945posts ยท Joined 2004. #3 ยท Jan 19, 2018. As Hece said, all depends on the tyre as one manufacturers 2.8" can be very different to another's size/volume wise. As a sort of general rule of thumb, as such, a true 2.8 B tyre is roughly 28.25" tall, a true 3.0" is about 28.75 tall, a regular 29x2.25" is about 29" tall, so you get the picture. Firstup in the comparison of 27.5 vs 29er is cornering and traction. This one is a no brainer because, with more surface area, 29ers are better than 27.5 tires. You can conveniently find the surface area of the tires of your MTB by having a look at the mountain bike tire size chart or mountain bike wheel size chart.