Acceleration plays a large factor in deciding on a wheel size. Typically, a larger wheel size will accelerate at a slower rate, as having a larger diameter and rotating mass requires more energy and time to get up to speed. In this case, a 29” wheel will accelerate at a slower rate than a 27.5”. What does this mean? If you are riding technical terrain that requires brief bursts of punchy speed, then a 27.5” wheel size would be more ideal for you. If your local track has loads of sections where you can carry momentum and flow, you might want to test out a 29” wheel size.
Increased wheel size decreases the angle of attack. That means bigger wheels make obstacles seem smaller. If you ride very technical trails that have very rocky and rooty sections, you have a couple of options. Either you are a rider that likes to plow through these sections, in which case a 29er would be perfect, or you’re the type of rider that likes to get more playful, bunny hopping above, around or off obstacles, in which case a 27.5” ride would be optimal.
A larger wheel rolls over objects with greater ease due to its increased diameter. The wheel literally spans a greater distance without being impeded. So a bigger wheel in general will keep you rolling over the rough stuff and will help to maintain your speed through the corners. There is a trade-off to be made here. Would you rather bash through obstacles? Or would you prefer to use said obstacles to your advantage? If the former, a 29er might be best, if the latter, check out a 27.5” ride.
Wheels with larger diameters tend to have a larger contact patch. The larger the contact patch, the better the wheel connects the rider to the trail through improved traction. Of course there are other factors that affect this such as air pressure and choice of tire, but in general, a smaller wheel standard will have slightly less traction than a larger wheel standard. Do you usually ride in wet and muddy conditions? If so, going for a 29er is a sure fire way to gain more traction.
Bigger wheels, bigger momentum- it is as simple as that. More momentum will allow you to roll through technical sections with a smaller chance of getting hung up on obstacles.
In general, there are more and longer travel options available for a 27.5” wheel standard than for a 29” wheel base standard. 29ers in general are still limited to designs that offer less than 130mm of travel in order to keep the cockpit at the correct height to maintain the intended geometry. If you want something with more travel, then you’re better off looking into a 27.5” wheel standard.