I went from 5.9kg 6"x15" stockies to 5.3kkg 6.5"x15" Rims and barely noticed any difference. Although I swapped the tyres across without increasing tyre width, I could probably stick the next width up on when I replace my tyres.
edit*
Trackphotos wrote:
There is a limit, as there is with everything. People think wider means a bigger contact patch, but it doesn't. Same weight on the tyres, the patch is wider side to side but narrower front to back (assuming same tyre pressures).
While you're correct in saying that the patch is wider side to side but narrower front to back, the patch IS larger overall. The best way to describe it is in chemistry terms.. The system will attempt to oppose the change, and will to an extent (Le Chatelier's principle) but cannot completely oppose the change.
The further apart the sidewalls are, the more maleable the rubber at the center of the tire is. For example, a 2 inch wide tire will have a very stiff rolling circumference, and will have little to no give in the patch touching the ground. A 15 inch wide tire will have a very large patch of unsupported rubber about the center line of the tire, along the circumference, and will have a lot more "give" in the middle of the patch.
That means that a wider tire is theoretically going to give you more grip and less inclination for the tire to have 'give' in a sidewards direction (the wider the tire, the more closely it resembles an extremely low profile tire in terms of aspect ratios.
The negatives should theoretically be increased rolling resistance, and increased force required to turn the wheels using the steering wheel (feels like weaker power steering, debatable whether this is a pro or a con), and increased price of each tire!
Imagine if tires had a third bead about the center line circumferentially, in essence creating another central "sidewall" to increase stiffness? That would be weird as hell
"Don't go crashing into Vulvas. *Volvos"