OK, like a few others on these boards, I am looking to increase the towing capacoty of my 2008 F150 Limited. From what I have read, it is the tires that are limiting the towing capacity. Standard size tires are 275/45/22...giving the tire a 31 3/4" Diameter with a thickness of 4 7/8"...if I increased tire size to 285/45/22 (32.1" Dia/5.05" thk) would that make much of a difference in the towing capability? Or maybe even go with a 295/45/22 (32.45" Dia, 5.23" thk)?

 

Its not the size of the tire that lowers the tow rating of the truck, it is actually the rim dia, I believe it is because there is more rotating mass because of the extra weight of the bigger rims. If anything putting a larger tire on actually makes it harder for the engine to pull the same load as a smaller dia tire.

IMO, either down size to a smaller rim or just stick with the set-up that you have. Also what are you towing that you are wanting to increase the towing cap.

 

What he said. You could (1) regear to lower ration, (2) smaller wheels, (3) tuner, (4) add a spring (5), air bags or all of the above and help with towing.

 

need to jump down to some 17 or 18" tires

 

how much does the softer (sports) suspension affect the tow rating? I will probably get some special towing wheels/tires for the larger loads and just swap them out as neccessary..thanks for the help.

 

It is the final diameter of the tire that lowers the towing capacity as it raises the final gear ratio. raise the ratio, lower the tow capacity. If you look at an owners manual you will see that the higher the rear, the lower the capacity. If you have a 3.55 and jump up in tire size, you are affectively making that final ratio similar to a 3.31, which has a lower capacity. Just like going from 17 to 18" wheels, the maximum tire size you can order goes from 255/70R17 to 275/65R18, a jump of about 1" in diameter.

That is not to say there are not other reasons why the tow capacity is lower on the Limited, but increasing tire size will not help.