RV Clinic FAQ: Top 20 Tech Questions

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A one-stop shop for answers to readers’ most-asked technical questions

Trailer Life’s RV Clinic column receives a wide range of questions from readers looking for help and advice. While we always do our best to provide detailed answers, we noticed that a lot of the same questions kept coming up. After all, new RVers are constantly entering the fray. Like good stewards of the RV lifestyle, we kept answering them over and over.
Then one day we had a brainstorm: Why don’t we compile the most frequently asked questions (FAQ) and put them in one article along with the answers? So we did.


The Tech Team

CHRIS DOUGHERTY: Technical editor for Trailer Life and MotorHome, Chris is an RVDA/RVIA certified technician and lifelong RVer, including 10 years as a full-timer.


CHRIS HEMER: Trailer Life and MotorHome’s previous technical editor, Chris has been an RV journalist for 20 years and is an avid camper and outdoor enthusiast.


JEFF JOHNSTON: Jeff served as technical director of Trailer Life for 20 years and has been an RV enthusiast, mechanic and writer since he could hold a wrench.


BOB LIVINGSTON: An RV/MH Hall of Fame inductee and publisher emeritus of Trailer Life and MotorHome, Bob is a full-time RVer and frequent Trailer Life contributor.


Can I tow this [overweight] trailer with my [underpowered] tow vehicle?

The short answer is no. Sorry. Tow ratings are put there for a reason — to ensure that the vehicle can do a safe job towing the trailer of your choice, at a performance level that pleases the operator, without wearing out prematurely or, worse yet, failing suddenly. We often get readers who ask why this year’s model can tow more than the previous year’s, even though the equipment seems exactly the same, and that can come down to something as small as a decrease in weight or a change in equipment (think bigger brakes or a transmission upgrade) that make this year’s vehicle more capable than last year’s. A manufacturer may also change its testing procedures, resulting in different numbers.

Always think of a tow vehicle and trailer as a team. If you already have a tow vehicle and are looking for a trailer to tow with it, make sure you know the tow rating and seek an appropriately sized trailer. Most such tow ratings are available in the yearly towing guides available on our website (www.trailerlife.com/trailer-towing-guides). Generally speaking, it’s best to choose a trailer that has a gross vehicle weight rating (gvwr) that is the same or less than the maximum tow rating of the vehicle. That way, you leave yourself a good safety (and performance) margin.

If you already have a trailer, it’s a good idea to get it weighed with the freshwater tank and LP-gas cylinders full, and the trailer packed with all the supplies you usually bring on a trip, or use the trailer’s gvwr. Then choose a tow vehicle that can tow at least that amount — preferably more. If you’re buying the tow vehicle and trailer at the same time, consider that most people get more emotionally attached to the trailer when they go shopping, so choose the trailer you want first, then find a tow vehicle that can handle it easily.


Can I increase my tow vehicle’s tow rating?

 

In most cases, the answer is no. While changing the vehicle’s official tow rating is a difficult process that requires extensive and costly testing and certification, you may be able to make some changes that affect its towing ability.

A manufacturer’s tow rating is based on a lot of different criteria, including suspension, brakes, steering components, engine power and engine cooling. What you’re changing or modifying may not be the weak link in the system that improves that towing ability. However, there are some exceptions.

The same make and model tow vehicle may have been available with three different gear ratios, with the lowest one (numerically higher) assigned the highest tow rating. By swapping the ring and pinion to a lower available ratio (for instance, changing from 3.54:1 to 4.10:1 gears), you can effectively tow the amount listed for that specification (all other things being equal, of course).

The difference between a series 2500 and 3500 truck may be something as simple as the rear spring pack and the tire load range, for example. While items that improve performance, such as a tuner or exhaust, may make the tow vehicle run stronger, they won’t increase the tow rating. In any case, always conduct thorough due diligence before making any changes to a tow vehicle. Safety and reliability should always come ahead of performance.


How do I weigh my tow vehicle and trailer?

 

The easiest way to get an accurate picture of what your tow-vehicle-and-trailer combination weighs is with a commercial truck scale (an internet search for “truck scales near me” or “CAT scales near me” should yield multiple results). Make sure the freshwater tank and LP-gas cylinders are full, and load the tow vehicle and trailer with all of the supplies you would normally bring on a trip.

Weighing the rig before an actual trip is a good way to kill two birds with one stone.
When you arrive at the scale, tell the operator what you want to do and ask for instructions. On a typical commercial scale, you drive only the tow vehicle’s front wheels onto the scale, then the rear, then the trailer. A multi-platform scale allows you to do this all at once. This will give you front-axle, rear-axle and total weight. Driving the tow vehicle off the scale, and then disconnecting the trailer while the trailer’s axles and A-frame jack are on the scale will give the trailer weight only. The scale operator can print out and review the numbers with you. Most commercial truck scales have multiple-scale pads that will weigh the front, rear and trailer axles at once.

Keep in mind that this is still just axle weight, and it won’t show if one side of the trailer is heavier than the other, for example. To get a truly accurate picture of what your rig weighs, you’ll need to find a shop with individual wheel scales. Doing this will help you find out if one or more wheel positions are overloaded, or if the tires on that axle require higher inflation pressure to carry that load. A visit to www.rvsafety.com will show where RV weighing events are being held.


What do all those weight ratings mean?

 

The ratings the RV and automotive industries use to specify maximum weights can be confusing, especially if you’re new to RVing. However, you’ll need to understand them because you’re going to see (and read about) them a lot.

GVWR (gross vehicle weight rating): The maximum amount the vehicle is rated to weigh.

GAWR (gross axle weight rating): The maximum amount the axle in question is designed to carry. The gawr includes the weight of the axle.

GCWR (gross combined [or combination] weight rating): The maximum allowable combined weight of the tow vehicle, passengers and cargo, plus the weight of the trailer and its cargo.

UVW (unloaded vehicle weight): The stated unloaded weight of the RV when it left the factory. The uvw does not include water, LP-gas or dealer-installed accessories.

NCC (net cargo capacity): Used up to the year 2000, this is the maximum allowable weight of all personal belongings, freshwater, LP-gas, dealer-installed accessories, etc. Since this is a somewhat ambiguous figure, it was rectified with the introduction of ccc in 2000, which is still used today.

CCC (cargo carrying capacity): The trailer’s gvwr minus its actual weight with full LP-gas cylinder(s).

Wet CCC The trailer’s gvwr minus the trailer’s actual weight with the freshwater system full.

SCWR (sleeping capacity weight rating; motorized RVs only): The number of sleeping positions designated by the manufacturer, multiplied by 154 pounds. The U.S. Department of Transportation uses 154 pounds as the average passenger weight when calculating vehicle payload statistics.

Payload Capacity The tow vehicle’s gvwr minus its road-ready (wet) weight. Payload includes passengers and cargo, not just cargo, as is commonly thought.


Should I get a trailer or a motorhome?

 

The first step to a satisfactory answer is to ask yourself (and your significant other, if you have one) how you want to travel. If you plan on long stints behind the wheel and short overnight stays, a motorhome is usually a better choice because it has more room in the driver’s compartment, and you can use the bathroom or kitchen while traveling. A tow vehicle and trailer may not be as comfortable to drive, but when you get to your destination, some owners believe trailers tend to “live better” for extended stays (comparing apples to apples, of course).

Then, consider how you would like to get around your destination while you’re staying there. Do you want to drive a tow vehicle or a car that you tow behind a motorhome? If the latter, be sure to shop wisely for a car that can be towed on all four wheels (dinghy-towed or flat-towed), make sure the equipment for towing is readily available (base plates, for example), and be prepared to spend extra money on accessories like an auxiliary brake system for the dinghy vehicle and having the car wired so that its brake lights and turn signals mimic those of the motorhome towing it. If you’re lucky, you might be able to find a used car that has already been set up for dinghy towing.

Other considerations have to do with towing and breakdowns. It can be more of a challenge to find a repair shop to service a large motorhome than a dealership or other shop to service a tow vehicle. If your motorhome breaks down or requires service when you’re traveling, you may need to find a motel to stay in until repairs are made, but if you’re towing a dinghy, you’ll at least have transportation. If your tow vehicle breaks down, you can have your trailer towed to a campground and still have a home, and rent a car or “Uber it” to get around until your tow vehicle is fixed.


Why are my trailer’s tires wearing unevenly or blowing out prematurely?

There can be a lot of reasons. If you’ve just purchased a new trailer, it may have been equipped with cheap imported tires. To be fair, some brands are better than others, but keep in mind that tires are one of the most common places RV manufacturers cut material and component costs to keep retail prices down.

To reduce the likelihood of a tire failure, make sure the tires are properly inflated and not overloaded. If they’re blowing out with abnormal regularity, it is likely that you are overloading the trailer and/or subjecting the tires to atypical usage — for instance, frequently backing into a sharp driveway (which puts a lot of load on the sidewalls), clipping curbs as you go around corners or driving over potholes.

Of course, uneven tread wear should be your first clue that something isn’t right, and alignment may be the key. Many readers have asked, “How can trailer tires be out of alignment?” It’s possible that the axles were not installed square with the chassis or parallel to each other, and the tires are “scrubbing” as the trailer travels down the highway. It could also be that the cheap plastic factory leaf-spring bushings have worn out, creating “slop” in the suspension that is allowing misalignment. An overloaded axle may be bowed down in the middle due to excess trailer weight, and that can dramatically change tire camber. Hitting a large pothole or curb can cause an axle spindle to bend, resulting in abnormal tire wear.

Alignment issues are characterized by an inner/outer edge wearing more quickly than the rest of the tire, or “feathering,” where the tread feels smooth in one direction and sharp in the other when you run your hand across the tread (not up and down). A balding center section means the tires are overinflated; balding outer edges mean they’re dangerously underinflated. A good commercial alignment shop or one that specializes in trailers should be able to identify and correct the problem for you. Balancing tires can improve tread life and reliability, to say nothing of reducing wear and tear on the suspension and trailer body. Less tire vibration means a smoother ride for all components.


Can I use Light Truck tires on my trailer?

 

In a word, yes. Many RVers are making the switch to Light Truck (LT) tires because some of the Special Trailer (ST) tires can have quality issues that affect reliability. The main differences between the two types is that ST tires have heavier sidewalls to handle forces common in trailering (such as tire “side scrub” when backing) and may contain more UV-resistant materials to help the tires last while the trailer is in storage. However, LT tires are also designed to carry load, and as long as they are properly inflated and do not exceed the wheel’s rating when inflated to the correct pressure, we see no harm in using them.
You should not, however, use passenger car tires on a trailer. They are not designed for high inflation pressures and heavy loads, and their thinner sidewalls can contribute to increased trailer sway.


Should I upgrade the size of my tow vehicle or trailer tires?

 

That depends. Your tires are part and parcel to the tow vehicle’s and trailer’s load ratings, so just adding a tire with a higher load range doesn’t mean you can carry more weight. However, a tire with a higher load range can typically be run at a lower inflation pressure at the same load, which may smooth out the ride somewhat. Just remember that a higher load range tire will also have a higher maximum inflation pressure, which may exceed the rim’s rating, and that can have catastrophic consequences.

On a dually, tire choices can be even more important, as too wide a tire can cause what’s known as “dual kissing” where the sidewalls of the rear-tire pairs touch — a very bad thing. On a trailer with two or three axles, you also don’t want the tires to be large enough that the adjacent tire treads can contact each other, and you need to make sure there’s enough wheel-well clearance.

Always consult a tire professional when considering an upgrade.


Are nitrogen-filled tires a good idea, and are they worth the money?

It depends. Nitrogen-filled tires run slightly cooler and are less susceptible to natural deflation, which is the air loss most tires experience over time while sitting. That said, tire pressures must be monitored, and many tire shops and service stations don’t have nitrogen filling, so the tires are topped with air anyway. Given that nitrogen-filled tires won’t perform better, last longer or improve fuel economy, and that nitrogen isn’t readily available, we’d have to say probably not. Spend the money on a good tire-pressure monitoring system instead.


Why does my travel trailer sway so much?

 

The most common cause is insufficient hitch weight. Your travel trailer should carry a minimum of 10 percent of its weight on the hitch when it is loaded and ready for travel. To determine hitch weight, drive your tow vehicle and trailer onto a small-size single-platform scale until only the rear wheels of the tow vehicle are on the scale. On a large commercial multi-platform scale, make sure each tow rig wheelset is on a separate scale. Record that weight. Drive off the scale, disconnect the trailer, then drive only the tow vehicle onto the scale until its rear wheels are in the same position. Alternately, tell the scale operator what you are trying to achieve, and let him or her guide you.

If you find there is insufficient hitch weight, locate the freshwater tank first. If it’s in the rear, travel with it empty (or near empty); if it’s up front, fill it up. Shift heavy cargo to the front and load the heaviest cargo in the forward-most compartment(s). In extreme cases, weight may also be added to the front of the trailer in the form of ballast, but this should be done only by a qualified truck or RV center after individual wheel weights have been identified.

Long travel trailers (25 feet or more), especially the “ultralight” variety, have a tendency to sway simply because there is a lot of surface area to catch the wind and insufficient weight in the trailer to keep it in line. Use of a weight-distributing (WD) hitch with an anti-sway component or a stand-alone friction-type sway control in addition to proper loading can help in these situations. Low tire pressure, worn shock absorbers, worn steering and suspension components, and a badly adjusted WD hitch can all contribute to trailer sway. When towing, the trailer should be parallel with the ground. Any tip toward the rear of the trailer will increase sway.


How can I keep my RV’s freshwater from smelling and tasting bad, and how can I fix it if it does?

Freshwater that has been stored awhile can grow all kinds of critters that can adversely affect the taste and smell of your RV’s freshwater and make hot water smell like rotten eggs. The bacteria that creates this smell is offensive but harmless. The first step is to completely drain the system. Locate the low-point drains for the freshwater tank and the water heater. Then turn on every water outlet in the trailer (sinks, shower, exterior shower, etc.) until water stops coming out.

The NFPA 1192 RV standard procedure, which is approved by the U.S. Public Health Service, details the most common way to sanitize the system. 1. Prepare a chlorine solution using 1 gallon of water and ¼ cup of plain household bleach (sodium hypochlorite solution). With the tank empty, pour the chlorine solution into the tank. Use 1 gallon of solution for each 15 gallons of tank capacity. This procedure will result in a residual chlorine concentration of 50 parts per million (ppm) in the water system. If a 100-ppm concentration is required because of growth or contamination, use ½ cup bleach with 1 gallon of water to prepare the chlorine solution. 2. Complete filling up the tank with potable water. Open each faucet and run the water until a distinct odor of chlorine can be detected in the discharged water. Do not forget the hot-water taps, and the water heater must not be in bypass mode. 3. Allow the system to stand for at least four hours when disinfecting with 50-ppm residual chlorine. If a shorter period is desired, a 100-ppm chlorine concentration should be permitted to stand in the system for at least one hour. 4. Drain and flush the whole system with potable water.

If you search the web, you’re likely to find at least half a dozen opinions on how to do this, and most of them require waiting several hours or overnight for the bleach to do its job. Using Thetford’s Fresh Water Tank Sanitizer system takes the guesswork out of the process, and it is effective and environmentally friendly as well. Both bottles in the two-part system provide clear instructions on how to use the products, and there’s no waiting involved.


What can I do to keep my tow vehicle’s aft end from being too low when hitched up to my trailer, or the back of my truck and the front of my fifth-wheel from riding too high?

The most common towing-setup problem, with apologies to our readers, is a sagging rear end. This can be a sign of excessive trailer hitch weight or fifth-wheel pin weight, but not always. The first step should be to weigh the tow vehicle and trailer at a commercial scale and determine if, in fact, there is too much weight being carried by the tow vehicle’s rear axle. “Too much” can mean an excessive amount of trailer hitch weight or fifth-wheel pin weight (more than 10 to 12 percent for a travel trailer or more than 20 percent for a fifth-wheel), or too much weight for the tow vehicle to carry.

If the weight on the rear axle does not exceed the tow vehicle’s gawr, then you’re in good shape and the problem can be easily corrected. For a travel trailer, try tightening the tension on the WD hitch spring bars first (you do have a weight-distributing hitch, right?). As an aid to help support some weight, there are a variety of products to help address suspension sag including aftermarket helper springs, airbag kits and more. For fifth-wheels, the same rules apply, except for the hitch part. Note that adding aftermarket suspension aids such as airbags does not increase the vehicle’s tow rating, gawr, gvwr or any of the manufacturer’s specifications.

A fifth-wheel that is too high in the front not only looks strange, it can create a contact point at the rear of the truck bed, because the cabover section of the trailer is too close to the truck’s bed rails. There are really only two ways to correct this — lower the rear of the truck or raise the ride height of the trailer. Lowering the truck a couple of inches can be accomplished with re-arched or lighter-duty leaf springs, or a suspension adjustment on some trucks, while the trailer can be raised with what is commonly called an axle “flip kit.” Leaf springs on a trailer are typically located underneath the axle; a flip kit locates them on top, thereby raising the trailer several inches. Using lighter springs on the tow vehicle can cause a loss of hauling capability, so consider your options carefully. When flipping the axles on a trailer, be aware of the increased overhead clearance.

As a rule, we recommend maintaining at least 6 inches of clearance between the truck bed rails and the underside of the trailer front section to allow for unhindered, damage-free independent movement between the truck and trailer.


Will adding an axle “flip kit” to raise my trailer’s chassis and body height adversely affect the handling?

Not typically. While raising the trailer does change its center of gravity, it’s usually not enough to affect handling characteristics. Note that this applies to your average axle flip, not extreme lifts done for cosmetic reasons.


Should I put a cover on my RV when it is in storage?

 

Opinions vary greatly on this one. While a good UV-resistant cover will protect the RV’s finish if it’s stored outdoors in sunny weather, an ill-fitting or neglected cover, or the use of an inexpensive plastic tarp can do more harm than good. Flapping material, combined with dirt that can collect underneath, can cause severe abrasion to the finish. Make sure the cover fits properly and is snugly fastened, and that you check on it regularly.

In wetter locales, a waterproof cover can help prevent mold and mildew from forming on the outside of the rig, which would normally require hours to remove come travel season. Again, make sure it fits properly, and leave one or two roof vents plus a few windows slightly open to promote movement of fresh air through the interior.


How do I keep moisture and rodents out of my RV?

If you live in a damp climate, moisture will collect inside, no matter what you do. If the RV is in storage long enough, you could return in the spring to find mold on the seat cushions and warped cabinet doors.

A good way to prevent this problem is with a desiccant product that draws moisture out of the air. A quick internet search will uncover a variety of products, from chemical alternatives that require no power source to battery-operated solutions and plug-in dehumidifiers. If your storage spot has 120-volt AC power available, a plug-in dehumidifier, with a drain that dumps the accumulated water outside the RV, is the best way to keep the RV dry inside.

As for rodents, that’s a tough one. If they really want in, there’s not much you can do to stop them, but you can make your RV less attractive to them. When putting the rig in storage, make sure you clean it completely and remove all traces of food, including crumbs. Carefully examine the underside to make sure there are no areas where the rodents can easily enter, and fill any gaps with expandable foam.

Some readers have suggested that steel wool can discourage entry. We’ve heard dozens of other proposed solutions, from battery-powered ultrasonic devices and botanical products used inside the RV that mice apparently don’t like the smell of, to poison, which we don’t recommend. A product that we hear is effective, albeit expensive, is Mouse-Free (www.mouse-free.com), a peppermint-laced spray-on undercoating for RVs. For RVs that move, it has to be replaced annually, which is quite pricey. We’ve never heard of one solution that works for all RVers in all circumstances.


Is it safe to leave my RV plugged in while in storage?

 

That depends. Some RVs are equipped with a standard converter/charger that can overcharge and damage the battery(ies). A “smart” converter/charger, on the other hand, offers four stages: Bulk, which quickly gets batteries to near 90 percent charge; Absorption, which tapers the amperage down and slowly charges them for the remaining 10 to 20 percent of charge; Float, which keeps them topped off at a lower voltage; and Equalize, which increases battery voltage to remove sulfation on the battery plates.

Check with your dealer or local RV professional to find out which type your RV has. If you have a standard “dumb” converter, the upgrade to a smart model will be worth the investment. If in doubt, leave the converter disconnected and connect the battery(ies) to a maintenance charger to keep it or them topped up for the next use. Keeping them charged also will prevent freezing in most climates.


How can I keep my trailer’s battery(ies) from going dead when I’m not using the RV?

Most RVs have a parasitic electrical drain on the system, such as a carbon-monoxide sensor, LP-gas sensor, electric clock, or a stereo with station presets and built-in clock display, and over time they’ll discharge the battery(ies). If you want to prevent this from happening, make sure to disconnect them using the master switch (usually located in a storage compartment, if equipped) or physically disconnect the cables.

If you want to keep the battery(ies) charged, consider using a smart converter/charger (see above) or connecting them to a maintenance charger. Note that even disconnected batteries can lose up to 3 percent of their charge per month in storage. The new lithium batteries don’t have these issues.


How can I keep items in my trailer from shifting or breaking during travel?

You might be surprised to learn that your trailer has no suspension other than the leaf springs, so the ride can get pretty rough in there. You can work with an RV center to add the appropriate shock absorbers or swap the suspension for a complete system like rubber torsion-sprung axles, Roadmaster’s Comfort Ride (www.roadmasterinc.com), Lippert Components’ Equa-Flex or Center Point suspension (www.lci1.com), or MORryde’s LRE/CRE and SRE suspension systems (www.morryde.com), which incorporates shocks and goes a long way to smooth out the ride. You should also check to see if your trailer tires have been balanced (look for balancing weights on the rims) and, if not, visit a tire shop and have it done. Not only will these steps smooth out the ride, they’ll also improve tire life.



How can I keep my trailer from rocking when we walk around in it?

Depending on the trailer and how it’s built, movement inside can be a problem, especially if you’re a light sleeper. If your trailer doesn’t already have stabilizing jacks, a good RV center can easily install them. If it does, consider adding a jack-stabilizer kit. JT’s Strong Arm (www.lci1.com/jt-strong-arm) makes a popular system that ties the jacks together and to the trailer frame in a diagonal brace fashion. Additionally, stabilizing wheel chocks can prevent fore and aft movement on dual- and triple-axle trailers by locking the wheels/tires together. These additions may not solve the problem completely, but they will definitely make a difference.


Where can I find a wiring or plumbing diagram or owner’s manual for my older RV?

You probably won’t be able to. Believe it or not, many current manufacturers don’t have wiring or plumbing diagrams or schematics available for customers, and the odds of you finding one for an older RV are even slimmer. Like anything rare or hard to come by, your best odds are to search Google, eBay and Craigslist on a regular basis, or find an online RV owners’ club or forum for your particular make and model and see if anyone has had luck finding these materials.

As for an owner’s manual, you can often find them online in a forum or via the manufacturer’s website. Most new RVs come with a folder full of appliance or accessory owner’s manuals for the equipment onboard, from the television(s) to the microwave, which are a good reference and can also be replaced online. If you have a component or appliance question, you’ll have better luck simply contacting the manufacturer of that component.

 


 

4 COMMENTS

  1. I am experiencing excessive “bounce” when my trailer goes over uneven street surfaces and pot holes. I have a small (11 feet), lightweight (2,800 lbs. GVWR) camper. When loaded up, it weighs about 2,600 lbs., and the tongue weight is 315 lbs. My tow vehicle, a 2016 Ford Transit, is rated to handle almost four times that weight and a tongue weight of 750 lbs. The shocks and springs are in excellent shape, yet the sensation is like the trailer is “pulling” or dragging the van when this happens, even at 40 mph and no wind. I don’t think this is a sway issue since it trails smoothly at 70 mph on the highway. The van has great power and can easily accelerate through these events, but I find it suboptimal. What do you think is hapening and how can I fix it?

    • Mike: To submit a question to Trailer Life’s technical experts, email it to [email protected]. Although time does not permit them to respond directly, each month they answer many of the questions received in the RV Clinic section of the magazine.

    • Hey Mike, 70 mph down the highway? What state are you in? In California the law if towing anything behind your vehicle is 55 mph. Big ticket if caught in that state, just a heads-up. As far as bouncing goes, I found the way they make the roads here in California are with runoffs every so many feet. When in a vehicle not towing, you can really feel them when exceeding 65 or 70. When towing a heavy load and doing 55, they are not as noticeable. It always helps stiff suspension when you have a load on it.

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