315/75R16 tires less than ideal for towing?

[LonestarBronco]

I recently drove from North Texas to Corpus Christi with a GCW of 17,500 lbs. The truck pulled like there was nothing behind it along all the flat sections, but the short and steep ups and downs betwen Austin and San Antonio made me have to think about what I was doing. In order to hold overdrive on the hills I had to hit them over 75 mph, any slower and I would steadily lose speed and have to down shift before my EGT shot through the roof. I just felt like having a few more revs in overdrive would be beneficial when driving 65 or 70.

There is also a good chance the issue lies between the driver's headrest and the windshield, this was my first time towing a trailer heavier then 4,000 lbs.

Also, does anyone else experience much better turbo response when using cruise control?

 

[JLDickmon]

A tire that tall is going to raise (lower number) your effective gear ratio... so you'd be forcing the engine to make power at a lower RPM that it was tuned for.

 

[MikePC]

Ratio Calculator

Here is a ratio calculator that I use.


- Dirt Road Magazine - Gear Ratio Calculator - (dirtroad.com)

 

[BJS]

as the others have said you are likely to have problems due to gears when towing a heavy trailer like that, when you are empty or with a light trailer you don't notice the problem as much. I would also hazard the guess that you are running the factory 3.73 gears that were most common in the SD trucks. The optional 4.10 gears would make it reasonably acceptable but will hurt your mileage if you like to run high speeds on the interstates.

Edit: and another factory is that you've grown your sidewall so you have more capacity for sidewall flex

 

[lone_star_dsl]

I hated towing with my 315's so much that I got rid of them. I didnt notice so much of a power difference but rather a LOT of flex in the D range sidewalls. My truck felt like it had squishy butt syndrome.

17,500 is a lot of weight. If I were towing that much, I would expect my truck to lose speed while pulling hills. It sounds like you are fighting both the heavy weight and the taller tires.

 

[DaveBen]

You need stiffer tires, Load Range E or better. You should never use a lighter tire than Load Range E.

Dave