RV Tech Q&A: Tow-Rig Tire Pressure


My “Tire Pressures Being Equal?” question was answered in the November 2017 RV Clinic. I must have written you the wrong info. I wanted to know about tire pressures in my truck’s tires when towing, not in my trailer’s tires. I run trailer tires only at the prescribed air pressures. What I wanted to know is whether I should run more air in the back tires than the front ones or keep the same pressure all the way around.

With equalizer-type hitches, the pressure put on the tires should be the same, all things being equal. The tires I run are E-rated BFGoodrich T/As, rated for 80 psi maximum. I run 55 psi all the way around, and I watch the wear. We used to put extra air in our rear tires for loads.

I have asked lots of folks this question through the years, including tire dealers, RV places, friends and other campers. You folks were kind enough to print my first question about this. Sorry for the mistake between trailer tires and truck tires.

Craig Foxgord | Independence, Oregon

There’s a tire pressure and information tag on your truck’s driver-side doorjamb or the edge of the door that lists the manufacturer’s pressure recommendations. These pressures are based on the vehicle’s weight, tire size and capacity, and so on, as equipped from the factory.

Automatically inflating the tires to their maximum psi as listed on the sidewall, with the truck running mostly empty, may result in the tire displaying too much bulge in the
center, which can raise the tread edges from the road and result in a less-than-optimum tire footprint on the pavement surface. That can cause squirrely steering, faster
and uneven tire wear, and a stiffer ride due to the extra psi.

It never hurts to go by the manufacturer’s pressure recommendation for day-to-day vehicle use. When I add a near-capacity load to my truck, I also pump the tires up to handle the extra load, then reduce it to the recommended pressure for most daily driving. Your information tag will show if the pressure should be the same for the front and back tires, as this varies from vehicle to vehicle. Add more air when towing for a bit more tire-load carrying capacity and drop it back to 55 for solo use, per your manufacturer’s recommendation, and you should be fine.

If you want to be more precise, weigh your loaded vehicle and then refer to the tire manufacturer’s tire-pressure weight chart for your specific tire for the proper pressure. The chart is available from the tire manufacturer’s website or your tire dealer.


Residential Thermostat Use


In regard to Chris Barkoukis’ “Thermostat Replacement” issue in the December 2017 RV Clinic, I have been using a Honeywell RTH111B digital non-programmable thermostat in my trailer for a couple of years. It can be purchased online for less than $18 and is powered by two AAA batteries. I recommend lithium batteries, as alkaline batteries have significant voltage drop if the temperature dips into the 30s Fahrenheit.

It is a simple two-wire installation. Although it can be used for both heat and air conditioning, I use it for heat only (my A/C unit has separate ceiling-mounted controls). It’s also simple to use with an on-off heat switch and up and down buttons for setting the temperature. The readout shows the current ambient temperature; when the up or down buttons are pressed, the display changes to the desired temperature.

It is not lighted, however. If I wish to change the setting during the night without turning on a light, I merely hit the up or down button a couple of clicks.

Kent Thompson | Aptos, California

As you probably learned when shopping for a residential-style thermostat for your RV, it’s important to make sure all the connections will be compatible, to avoid damage and ensure proper operation. Thank you for passing along this information. It’s good to know you found a setup that works.


Plugged in During Storage?


We have finished pouring a concrete pad next to our house for our trailer. Is it OK to store the trailer all winter attached to shorepower from our house?

Larry Lower | Roseville, California

This is one of those questions we seem to answer frequently, Larry, and the short answer is, yes, it’s OK, as long as you check float voltage each month to confirm it’s not overcharging the batteries; a single-stage charger should maintain around 13.5 volts. You must also check water levels in flooded lead-acid batteries. Better yet, use a multistage charger, which won’t overcharge and damage the battery.

Check the owner’s manual for the brand and model of converter; if it’s an old-style single-stage model, you can install a newer model converter with a multistage charger or use one of the many battery-maintainer chargers available for use on RVs, and leave the RV unplugged.


Slideout Wiring Cure


My “Slide Won’t Slide” letter was published in the November 2017 RV Clinic. Clearly, you put much effort, research and time into your response. Your reply was very complete and thoughtful.

I investigated all aspects thoroughly, to the extent of removing the ceiling in my basement and lying on my back with a bright light to watch and listen while a friend moved the slide in and out. I could find no problem, so I went back to square one with the wiring question
I asked you about.

I am happy to report that the slide on my Redwood 36RL now works for the first time. And all by itself! The issue was electrical. I found 12-gauge wire in the old fuse holder and a twisted connector with a wire nut. I replaced the primary-feed cable with 10-gauge wire, replaced the terminals with properly sized and soldered terminals, and replaced the fuse holder with a much heavier unit and a new 30-amp fuse.

It works fine now.

Thanks for your help, and I hope my solution will help others.

Jim Stollm | Searchlight, Nevada

Thank you for the kind words, Jim.
It’s always fun to get feedback on how well some of our technical suggestions work out.


Truck Push-Pull


My wife and I are proud owners of a 24-foot 2012 KZ Spree 240. We purchased it new in 2012 and have a dealer-installed Equal-i-zer hitch. We pull the trailer with a 2006 Ford Expedition, the XL version, with a 5.4-liter V-8 engine.

The Ford seems to have all the power needed to tow the trailer. However, I do have a concern when I am pulling and am passed by a large semitrailer. There’s severe wind push from the truck passing.

It feels as if, when the truck first approaches, that the front end of the tow vehicle is pushed toward the passing truck, and then as the truck passes, we are pushed away. This is disconcerting, especially on some narrower roads and bridges, and it is exacerbated when there is a crosswind.

Is this primarily due to the wheelbase of the Expedition versus an F-150? What can I do, if anything, to fix it?

Glenn Lygrisse | Wichita, Kansas

We know that push-pull feeling well, Glenn. It’s safe to say that most people towing travel trailers, and to a lesser degree, those towing fifth-wheel trailers, experience the same sensation. It’s caused by the “bow wave” of wind that’s pushed by a large commercial truck, and that wind effect also interacts with the same but lower-intensity bow wave produced by your tow-rig-and-trailer combo. It acts to push the trailer away, and pulls the trailer back in as the truck moves past the trailer or vice versa. Strong crosswinds can aggravate the effect because you’re already fighting that wind, and the truck blast just makes things worse.

In general, there’s nothing you can do about that push-pull effect, other than making sure your towing setup is as stable and well-balanced as it can be. A longer-wheelbase tow rig tends to provide more stable towing in general, but as long as your setup is satisfactory the rest of the time, there’s no reason for you to change anything.

When I’ll be passing or passed by a large truck or bus, I tend to ease over to the far side of my lane, to the extent it’s safe to do so. I make sure of my firm grip on the wheel, and, because I know what’s coming, I brace myself and am ready to make whatever modest steering corrections I need to, to remain in safe control. It’s important not to overcorrect when steering, as it can cause trailer sway and possible loss of control. It can also help to reduce your speed a bit, which allows the other traffic to pass and be gone in less time.


Greasable Axles


I had an older 26-foot Fleetwood travel trailer. Every year I would grease the wheel bearings. I now have a new 32-foot Forest River travel trailer. When I removed the wheels to have them balanced, I noticed a zerk fitting on the end of the axles like boat trailers have. After examination, I found the outlet at or near the inboard bearing.

My question is, am I lubricating the axle or lubricating the bearings? It looks like the axle is being lubricated.

Bob Maager | Perryville, Missouri

That zerk fitting and that axle hole are designed to help grease the wheel bearings, Bob. The axle is a piece of steel tubing with no moving parts, and thus requires no lubrication. The hole near the inner bearing allows the grease to enter the hub from the center and move outward toward each bearing.

Note that the presence of the zerk fitting does not mean you need to routinely add grease to the hub as part of your occasional maintenance activities. Inspect and pack the bearings annually, as you did with your previous trailer, and you’ll be good to go.


 

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