First time to post on forum. I have a 2007/2500, 5.9, 3.73 gear, 4 x 4 currently with 315/70R/17's. I need a new set of tires before my wife and I purchase our 5th. wheel. Want to try and keep the trailer dry weight no more than 10,000 lbs. Is this size tire too large? What would be the ideal size tire for the truck? I know stock is probably 265, but I like the larger tires.

 

I have always kept the stock 265/70r/17 on mine for towing my 5th wheel, 12k lbs, 373 auto, I would try 285 but they dont make them in the Michelin tire I like, with the 315 you will loose some of the take off power but will be fine once you are rolling, its the stopping that is the most important.

 

I've been very happy with my Nitto 285/75's. Good compromise in size between too big or too small. They are E rated and I get good wear with them. Just my .02.

 

I know the saying "big is best, more is better" but the manufacturers choose a tire size for a reason, they might choose a brand for price but size... is for a reason. I have always stayed stock, except once I tried a larger size, same make same tire I had been using for years, the truck was all over the place, went back to the exact same tire stock size and problem gone.

 

The problem that your gonna run into is how fast you can tow and still keep EGT's manageable. Most trailer tires are rated at 65mph, so towing faster than that is asking for trouble (IMHO) I have 285/70R17 tirse on mine now and the trouble that I have is that at 65mph I am only running 1650-1700 RPM, which leads into low boost but high EGT's. I have to drop out of O/D to keep my boost up otherwise EGT's skyrocket. If I run 70MPH my boost raises and my EGT's go down because I am more solid into the RPM band that you want to be in. If I had the 250RPM back that I lost going to larger tire from stock I would be golden. For me right now, anywhere between 60-65MPH is useless, RPM too high in 3rd and too low in O/D. I am going back to stock when these where out. I am towing a 12,000lb 40' 5th wheel.

Also keep in mind that the tires that come stock with these measure 31.4 inches, which is very small for the 265/70R17 category. Most of the tires measure closer to 32", making it not so bad. The manufacturers new what they were doing when they put the stock tires on there, yeah they look puny but they put the engine right where it needs to be at the speed that the trailers are rated to tow at. Funny how it works like that

 

I run 315 on mine and my 5er weighs 8900lbs and running 125hp injectors and yes egt will run high but if you tow lots and run hills I would run a 285 for fuel mileage and pulling power. If you tow heavy a little lower is better but if you are running long flat highway miles a 305 works well!

 

My toy hauler is around 11K all loaded up, I've got the same tires/gears as you and it pulls great.

When we get a significantly larger toy hauler, I will re-gear.
I off-road my truck a lot, so smaller tires aren't an option for me.

 

I ran 285/70/17's for one set. Tow around 10,000 and, with the 265/70/17's, I can feel a difference in power pulling hills. Went to LT tires on the trailer and don't worry about the 65mph speed rating anymore.