Replacing tires on an '04

I have an '04 ZQ8 that has to have the worst tires I have ever driven on! When the least amount of dampness gets on the roads my truck is terrible starting AND stopping! I have been told that the Continental Contact AS tires that were OEM when my truck was built are "inappropriate" for a sport truck! I plan to get rid of these tires soon, and want to use wider tires! What I would like to do is go from the stock 235/50/17s to Kumho ASX 255/45/17s! I realize that there will be a difference in the speedometer, what other effects of this change can I expect? I have also been told that I can't make any tire size changes as I would "screw up" the ABS and something in the transmission! :confused: Is anyone familiar with the Kumho ASX tire and want to voice an opinion! ANY comment on this switch would be appreciated! Any suggestions are welcomed! :smile:

Circumference is everything. Measure one of your tires, then go shopping. Within 2 to 3 percent should be OK. Width doesn't matter.