Originally Posted by
flargle
Sounds snarky but yeah, this.
You can measure how much clearance you have with the 32 and extrapolate from there. It would be a pretty unique CX bike that could fit 42. The chainstays are typically the limiter. That said, the actual width of the tire depends on variables including manufacturer, tire pressure, and rim width, for example. It helps if you can borrow a tire from friend or shop to make sure.
Yeah, I did something along those lines, then decided to contact the manufacturer. Pleasantly surprised to find that his answer wasn't too far off from the guesstimate I ended up taking.