The Open Upper is built around compatibility for both 700c and 650b wheel sizes. Such a change can arguably be done with any disc brake endurance bike, but the key difference here is in the clearance for the 650b tyre – where the stays and fork are adapted to fit a 2.1in mountain bike tyre. For a 700c road wheel, or a 29er mountain bike wheel, the Open can fit a 40mm tyre (left) easily, giving more clearance than on most cross and gravel bikes. For those keen on wide tyres, Vroomen says the 650b option matches the handling characteristics perfectly to a road set-up. A 650b wheel with 2.1in (53mm) tyres comes out with a radius of 342mm, only 1mm more than a road wheel and 28mm tyre. Maintaining this size of wheel and tyre is important to ensure the quality of the bike’s handling, according to Vroomen.