Another Weight Type Question?

Larryzv7 wrote:
I did not want to tag onto that other thread about weights, but I do have a few questions.

1) Does the rear axle gear ratio of your tow vehicle have anything to do with your vehicles towing capacity?

If you read the tow guides you will see that the lower the gear ratio the more you can tow. Example a 4.10:1 can tow more than a 3.42:1 there are other variable like 4 speed or 6 speed transmission and diesel vs gas. The weight carrying ability of the truck (GVWR) (what you put in bed/cab)will normally remain constant between the different rear axle gear ratios. There is what you can carry and what you can pull.

2) A trucker told me that the towing capacity of their semi-truck, 18-wheels, etc., is determined by the size of the tires on the truck. Have you ever heard this before?

I'm a trucker. My gross or how much I can carry is limited by what I'm plated (registered) to carry and the number of axles and weight on each axle is covered under "bridge laws" so I don't break the road or the bridge as I drive over it. The standard class 8 tractor can pull 80,000# or 140,000# it's more do with the limits on the roads and the tax man. More axles (tires) more load and more taxes. See the 8 axle trailers they pull in MI.

I read somewhere that smaller tires will give you a higher engine rpm but more towing power, and larger tires will decrease the engine rpm and towing power.

I can see it in my odometer if I have new or old tires (might log 2 miles less in the same route between new and old tire) but the effect of gearing makes this a mote change in power. Changing tire/rim size I.E. 17" to 19" can effect the effective gearing of the truck but then you are also changing the bed ride height and other issues with the truck.

Fifth wheel trailers generally have small tires while semi-truck trailers, 18-wheels, etc., usually have the same size tires on both the truck and trailer.

Tire size is not an issue here. All that matters is weight rating of the tire and weight of axle on the pavement. We run drop deck/van trailers with small rear tires. Still limited to 34,000# on a tandem axle. The only real difference is small tires cost more, wear out faster and want to turn corners faster so you have to swing a little wider.

3) Last question; is it wise to use overdrive when towing or is overdrive just necessary when gears seems to be struggling?

Your best fuel mileage will be in overdrive since your transmission gear ration is less than 1:1. If the load on the engine permits you to stay in overdrive great otherwise if the transmission starts shifting in and out or the engine "lugs" you are best to downshift. Normally if you use the tow haul mode it will automatically stop the transmission from doing this.

Thanks for your answers, and the education.
Larry:)