posted June 19, 2001 01:09 AM    
 
    
      
  
I need to replace the tires on my 1998 GMC Sierra. It's a 1998 model Z71 shortbox, extendedcab, halfton... The current tires are LT245/75R16. 
Any recommendations/opinions on what tires would work well for this vehicle?  I do about half my driving on highway, and half my driving on gravel roads, in a northern climate where winter is a consideration.
Also, this truck had a larger tire option, a P265/75R16 tire. 
Since I've never replaced tires before, what would be my considerations for going to a larger 265 tire? Would I need to get my speedometer/odometer/absbrakes or other crap recalibrated, or can I just put on larger tires and go? Is it a bad idea to replace tires with a different size other than the ones they came from the manufacturer with (despite the fact that people do this all the time)? 
I learnt that the 'P' stands for passenger car tire and has 4 plys while LT is light truck and has 10 plys (someone please correct me if this is wrong) and that P tires are not recommended for my area, so LTs it is (but LT245 or LT265, and what tire?). Also if I upsize the tires, would I need to do the spare as well, or would it be fine to be a different size (for the amount I use it, it came off for the first time in 72,000km of driving, when I wrecked one of the other tires). 
About 50% of my driving is highway, while 50% is on gravel roads. 
Thanking you all in advance for your opinions. 
Mike.