My nephew has a Gravity Liberty flat bar with disc brakes Save up to 60% off new Flat Bar Road Bikes - Gravity Liberty FB | Save up to 60% off new road bikes. The outside width of the rims is 19mm so I am assuming the inside width is 14mm or 15mm. (I have not measured). He wants wider tires- e.g 40mm. According to Sheldon Brown's chart 40mm tires would be too wide. In searching these forums, I get all kind of conflicting information. If run at pressure not exceeding 50psi, e.g., could I safely mount 40mm tires for him or are they too wide. Thank you in advance.