Originally Posted by DeeBee
What size truck tire is best for towing? Is there a rule of thumb?
You're prying open Pandora's box...
There are myriad sized truck tires that are suitable for towing, including the 18 and 20-inch varieties. However, there are many other variables that will determine how well one tire will perform over another. The basic rule of thumb is that the tire is certified and is labelled as being able to handle the load that your travel trailer (TT) will impart on your tow vehicle (TV). Now it gets complicated...
Many light trucks of the half-ton variety come equipped with passenger car rated P-Metric tires. That might include those 18 and 20-ich tires you referred to. There are a number of forum members (bless their hearts) that will insist that you can't safely tow a 7,000 lb TT with P-Metric tires and that these tires can contribute to trailer sway. They will further insist that you won't be safe unless you equip your TV with at least Load Range (LR) D or LR E tires.
Here's the complicated part: We've been towing a 7,000 lb plus TT for four years and 21,000 km, over hill and dale, with a half-ton, equipped with... yep, you guessed it, P-Metric tires. We don't have issues with sway save for the occasional 30+ MPH crosswind but at the end of day, the tires perform very well. At no point in our travels have I felt compelled to seek out a tire with a higher LR.
More complications: You and only you can determine what feels right as regards your impending TVs performance when pulling your TT. You may be quite satisfied with a 18 or 20-inch P-Metric tire equipped TV. Or, you might pressure the dealer to install a suitable LR D or E tire on the TV, just to be safe (Pandora's box). Notwithstanding, you must ensure that you have a good weight distributing hitch (WDH) installed with a good sway control.
The ball is in your court...