Originally Posted by
Dick Chainey
Anyway, I was questioning how stable my road bike will be on trails
Depends on you and the trails.
Some well-regarded gravel bikes, like the Open UP, have what's basically a traditional road geometry. It can be just fine as long as things aren't too technical.
Best way to find out is to try it and see what happens.
and how wide a tire I can get on my road clinchers.
The road clinchers aren't the problem. While there
are reasons to use wider rims when using wider tires, going a bit outside of what a rim is designed for isn't something to fuss over when you're starving for tire width.
The big question is how wide your frame and/or brakes can fit. Since you have the frame in hand, you're going to be the most capable of figuring this out. Look at how much clearance there is around your current tires at places where they're close to the frame or brakes, check how wide they are, and estimate from there. Every 2mm of additional tire width will make the tire about 1mm wider on each side, and a bit taller as well. It's good to leave a few millimeters of clearance for safety.
Unfortunately, from what I can find through googling, most Zurich frames won't take much wider than a 28mm tire, if that. 28mm can be fine on smooth hardpack, but will likely become troublesome as the surfaces get more interesting than that.
I don't want to make it too damn hard to clear the tires through the brakes either.
Just partially deflate the tire whenever you have to remove a wheel. And whenever you fix a flat, just don't pump the tire back to stiff until the wheel is on the bike.