Wheel size on tow vehicle?

[meekermichael]

I'm looking at an '04 Dodge Ram 1500 to pull my 5000# (loaded) 5ver and wondering how much difference wheel size on truck makes. One I'm looking at has 20" wheels but from what research I've done, sounds like smaller wheels (and tires), like stock 17" more efficient for towing. Anyone knowledgeable of the physics of this question or better yet with real world experience? Thanks very much.

[meekermichael]

I'm looking at an '04 Dodge Ram 1500 to pull my 5000# (loaded) 5ver and wondering how much difference wheel size on truck makes. One I'm looking at has 20" wheels but from what research I've done, sounds like smaller wheels (and tires), like stock 17" more efficient for towing. Anyone knowledgeable of the physics of this question or better yet with real world experience? Thanks very much.

[ParTheCourse]

Not sure how tire size affects towing efficiency but there are a couple of other issues you should consider. Larger wheels will raise the trucks height and in turn raise the nose of the trailer when you hook up.

1. When hooked up the trailer should be level or a tad (inch or less) nose low. Larger wheels may have you going down the road with the trailer nose high.

2. Clearance between the sides of the box on your truck and under the nose of the trailer should be 5/6 inches. Larger wheels may close that clearance and cause problems towing over uneven ground.

The owner's manual should address the specifics for your rig.

Flipping the trailer axels and/or putting larger wheels on the trailer to raise its height are fixes that are sometimes used but each introduces more questions. Will there be any warranty problems and if you have dual axels will there be clearance between the tires on larger wheels?

Good luck, Mike

[TXiceman]

Tires of different sizes have different aspect ratio, i.e. a 50 series tire vs a 70 series tire which is the ratio of the tire height to the tire width. Based on a given wheel rim diameter, a 70 seies tire is taller and will have a larger rolling circumference or more inches around the tire than a 50 series.

What I'm saying is you really need to look at the rolling circumference of a given tire to see what is going to happen. The tire with the smaller circumference will have an effective "lower" axle ratio or make a better towing choice than a tire with a larger circumference. The circumference of a tire is Pi x the diameter. Pi is 3.14 and the diameter is the diameter of the thread, not the wheel.

If nothing else, you can jack up a wheel and use a cloth tape to mesure the circumference of the tire thread.

On another note, a 5000# 5er may be a bit much for a 1/2 ton truck. The pin weight of a typical 5er will run close to 20% of the trailer GVWR. In the case of your 5000# trailer, this is about 1000# in the bed of the truck. Do you have 1000# of cargo carrying capacity when loaded?

My company provided vehicle is a 2006 Ram 1500 with the 4.7L engine, 3.55 axle and 5 speed aautomatic. According to the data on the truck, it is rated to pull something like 6500#. I have pulled a utility trailer that was between 3500 and 4000# and the poor truck was suffering on the highway between San Antonio and Houston, Texas. I-10 through here is fairly flat. I managed to get a whopping 8 MPG trying to maintain between 65 and 70 MPH.

My brother had a 1500 with the 5.9L gas engine and he has a 21' TT which it is hard pressed to pull in east Texas. SInce he is looking for a larger trailer, he sold it and got a 3/4 ton Dodge diesel.

In short, you need to weigh the truck loaded fro travel (add 150# for the 5er hitch) and work with the trucks GVWR and GCWR to see what you have left over for towing.

Ken

[Hitchhiker]

Here's a tire size calculator that might help with the math.

[Jeff_in_The_Dalles]

I presume you are talking about the 20" wheels with low profile tires?

If so, be sure to check the load rating of the tires vs the 17" ones. Also, replacement tires for the 20" rims are big $$$ (A buddy of mine has one).

[meekermichael]

Thanks very much to all for the helpful feedback, especially the tire size calculator, Richard- slick!!
Mike