If you look up the US site, you'll see that 305 and even 315 width is common. Depends on the offset of the rim as well, as you might get rubbing/conflict with the UCA at those sizes with standard rims.
Wider tyres will give you lousy handling, less grip, more wear (on tyres and steering/suspension components) and a lot more torque steer and climbing on grooves in the road.
255 or 265 are much better widths for the 100. 275 is standard for the 100 on all 3 standard rim sizes, 16, 17 and 18". The rims are all 8" wide. The 100 was delivered in africa and some places in asia with an option of 16x6,5" rims, with 235 tyres, which handles very well.
What is the purpose of increasing the width for you?