I've run bigger tyres than recommended for offroad rims on the mtb for years without any problems. Any reason why there should be problems for 700c wheels?
Have had 35c 'cross tyres on Rigida Chrina rims (18-28mm tyre recommendation) for the past couple of weeks without any problems and they appear well seated etc. Would 42c be too much, given that clearance is not an issue?
What's the worst that can happen? I've run 29er tyres on similar rims and i'm still here
I run bonty 2.2 29er tyres on open pro rims no problems
Its a pressure/force thing, if you run big tyres at the same pressure as the max recomended for a small tyre it will potentialy rip the rim appart depending how worn the rim is and how big a safety margin the designer applied.
So running a 2" tyre at anything over about 40psi on a rim designed for 25mm at 100psi is probably not the best idea etc.
I stand to be corrected as I'm no engineer but wouldn't the pressure on the rim be the same regardless of the size of the tyre? The contact area ie. bead on rim is the same size, it's the additional size/width outside the rim which changes, therefore the pressure would be the same......or am I being thick?
edit - obviously, larger tyres would be run at lower pressure for an increase in comfort/grip, what I was more concerned about was the increase in the possibilty of the tyre rolling off the rim at lower pressure due to the increase in lateral forces
I stand to be corrected as I'm no engineer but wouldn't the pressure on the rim be the same regardless of the size of the tyre?
You need to think of the tension in the tyre's casing.
At a given pressure, the force per unit area is a constant, but the surface area of the tyre carcass increases (just about) linearly with width. So a broader tyre has a larger casing tension, and exerts a larger force on the rim bead. The angle of application of that force changes as well. Narrow tyres apply more radial force. Broad tyres apply more lateral force, tending to splay the rim walls apart.
Of course most people run their fat tyres at far lower pressures than their thin tyres.