Tire Selection

Tire Selection



WE BOUGHT A 2Q-FOOT FIFTHwheel trailer new in 2003. On a trip we took I had a tire tread separate, but it didn’t blow out. After getting home I found out there was another one doing the same thing. The trailer came with LT235/85R16 Load Range E Carlisle Tires. I called Carlisle to tell the company what happened, and a representative asked for the trailer’s gross vehicle weight rating (GX-WR). When I said it was 12,000 pounds, I was told Carlisle would send me five new tires.

When I got the tires I saw they had sent me ST235/85R16 Load Range D tires. I had to go ahead and put the tires on because we were going on another trip. I’d like to know if you feel these Load Range D tires will handle the load.


Manhattan, Kansas

* Your original LT235/85R16 ?-range tires are rated at 3,042 pounds per tire, Don, and the replacement ST235/85R16 D-range tires are rated at 3,200-pounds each. It seems unusual to have a D range tire rated higher than an E range tire, but that’s how Carlisle figures it with its Special Trailer (ST) tires compared to its Light Truck (LT) tires. That extra 632 total pounds of tire capacity is a comfortable margin. Take a look at the tire’s sidewall and you’ll find the capacity information molded thereon.

Since the tires aren’t carrying the trailer’s hitch weight – probably at least 15 percent of the trailer’s overall weight (about 1,800 pounds) – you have a bit more load rating to spare. Remember, that doesn’t mean you can add more cargo and exceed your original GWVR, of course, since the higher tire rating doesn’t change the load rating on the springs, bearings, brakes and so on. It just means your tires aren’t being pushed to their limit.

Overloading, underinflation and excessive speed are among the most common causes of tire failure – be it a tread separation or other contributing factors that lead to a blowout. You should take your loaded trailer to a public scale and have it weighed to determine exactly how much the tires are carrying, and you may be surprised at the result; you may also consider checking the owner’s manual in your tow vehicle for general information on tires, speeds and loads. – JEFF JOHNSTON

Cold-Start Knock

IN 2001, I BOUGHT A NEW GMC Yukon XL with the 6.0-liter V-8 engine. At 50,000 miles, I now notice there is a cold-start knock that lasts for 10 to 20 seconds. The knock has all the characteristics of faulty hydraulic lifters or severe pre-ignition knock. I visited the GMC dealer for service and correction of the problem and was told that GM engineering considers this normal. I was also sent a copy of Service Information Bulletin No. 01-06-01-028A (dated March 18, 2003) that applies to the 4.8-liter, 5.3-liter, and 6.0-liter engines. The bulletin concludes with this paragraph: “This noise may be caused by an interaction between carbon that has formed on the piston, the piston motion and the cylinder wall. GM Powertrain Engineering, and an analysis of engines with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine. This noise does not have any effect on the longevity of any of the engine components.”

I read that to say, “We don’t know, but the problem may be caused by…” If GM hasn’t defined the root cause of the problem, it can’t legitimately reach this conclusion. I have been unsuccessful in gaining any definitive information from GM customer assistance and have been denied access to anyone in engineering. Without a better understanding of this problem, I doubt that I will achieve the normal 200,000-plus troublefree miles I expect from my vehicles. My file has been marked “Dissatisfied and Closed” by GM Customer Assistance. Does anyone in our RV community have more definitive information on this problem?


Sun Lakes, Arizona

* There are several causes of the cold knocks. You may be able to narrow down the location with a mechanic s stethoscope. The low-viscosity oil plays a significant role in this. Upon start-up, the crankshaft has very little oil-film cushioning, which is one source of the knocking. The new alloy in the pistons also has a higher rate of thermal expansion. What that means is when cold, the pistons are going to shrink more and fit a little more sloppily in the bore. The new lightweight piston design has shorter skirts than the old cast-iron small block, which can also be noisier.

To make it worse, your aluminum small block doesn’t have acoustic damping like the older cast-iron engines. Aluminum blocks and heads cool off much faster, and condensation can form in the upper cylinders. That can result in corrosion, carbon build-up and even sticking valves when cold.

The carbon deposits come in two types: the hard carbon that is inside the combustion chamber and the softcarbon deposits in the intake runners or on the back of the intake valves. The soft type is problematic for cold starts because the soft carbon acts like a sponge. It will lean out the incoming air-fuel mixture and many of the engine-control programs do not allow the knock sensor to retard spark during warm-up. The end result is too much timing advance for the lean condition until the system goes into closed-loop.

To solve the problem, before you tear into the engines internals, I suggest you try changing gasoline and oil brands and viscosity. Make one change at a time, so you know which one helped. You need to find the combination where the cold knock does not happen all the time.

I do not recommend using extended viscosity index oil such as 5W-40. In California, 10W-30 instead of 5W30 is fine. Just changing oil viscosity may make the problem occur only once in awhile. It is important to use an anti-drainback check-valve type of oil filter such as included in the original equipment.

Premium fuel usually has more detergent than regular fuel, which helps to keep the intake tract clean. If you do not want to use premium fuel, at least use the Chevron Techron (or equivalent) additive once a month. It does help keep the upper cylinders clean. – KEN FREUND

Solar-Panel Planning

I’M SEEING LOTS OF SOLAR-PANEL chargers in RV catalogs, farm and equipment catalogs and at discount tool-supply companies. I have a 27foot, dual-slide fifth-wheel. It has only one battery, and I must have a phantom load somewhere because my battery dies between uses while the fiver is in storage. Please give us some tips and advice on how large the solar panel should be. Wattage choices are all over the map, some require controllers and so on. Also, can it be mounted on the roof with about 1015 feet of wire to the battery or, if it comes with a cigarette-lighter plug, can I put it into the DC plug-in for the TV in the coach bedroom – which theoretically is the closest inside 12-volt connector to the battery compartment under the bedroom floor?


Kettering Ohio

* You’re correct that you probably have a phantom drain someplace in your trailer, Jim. Digital clocks on stereo equipment and the like are prime sources for battery drain in storage. Disconnect a battery terminal when placing the trailer in storage and you’ll eliminate the drain. Just be sure the battery is fully charged to start with and it’ll be in better shape when you rescue the RV for another trip.

The more the merrier when it comes to solar panels. Those little ones with the cigarette-lighter-type plug are too small to charge your batteries after heavy use, and generally produce minimal wattage and fractional amperage. The best they can do is provide a tiny trickle charge that may help maintain the batteries and maybe offset the effects of your phantom drain, but not much more.

You’ll need to invest some cash, but choose a full-size solar charging system rated at 75 watts or more to help keep your battery charged. The charge controller helps avoid overcharging, and the roof is the most convenient place to install the panels. The solar-panel instructions will detail what gauge of hook-up wire to use for each application. You might also want to consider adding another batteiy to help extend your powered dry-camping time. – JJ.

Dodge Diesel Difficulties

WE HAVE A 2004 DODGE 2500 Ram with a Cummins diesel engine and six-speed transmission. In smrimer we use it to tow a 28-foot fifth-wheel.

When we start the truck, especially in cooler weather, it gives off white smoke. It also gets poorer fuel economy than several of our friends report. Our dealer checked it over and determined that nothing was wrong. Do you have any ideas?


Dallas, Texas

* Have your dealer look up Dodge Technical Service Bulletin No. 18037-04 dated September 27,2004, titled “Fuel Economy Improvement, White Smoke On Start Up, Accuracy Of Fuel Mileage In Overhead Console Display.” This bulletin involves reprogramming the Cummins ECM with new software. It applies to 20042005 Ram trucks equipped with a 5.9liter Cummins turbodiesel engine with an engine serial numbers 57130285 through and including 57246361, and an engine date of manufacture of 12/10/2003 through and including 8/17/2004.

The new ECM calibration should provide owners an average fuel-economy improvement of approximately 1 MPG. It also reduces white exhaust smoke on cold-start at temperatures below 50° F, and improves the accuracy of the fuel-economy calculation in the overhead console display. It is free on vehicles within the provisions of the warranty. – K. F.

Towing-Weight Distribution

LAST FEBRUARY, I PURCHASED A 32-foot travel trailer with a weightdistributing hitch. I noticed when I tow my travel trailer I hardly ever experienced the same ride in my truck twice. I’m pulling with a 1998 Dodge Quad Cab four-wheel drive with a Cummins diesel. I have tried different solutions with the same handling results.

The truck drives like all the weight is on the bumper, but it doesn’t pull like this all the time. Does the trailer need to be level when I hook up? Do I need to let all the weight on the ball before I hook up my weight distributing arms? Any help you could give me would be greatly appreciated


Brandenburg, Kentucky

First, T.J., as long as you load the truck and trailer more or less the same each time, and the hitch is adjusted the same, you should not get significantly different handling characteristics from your truck every time you tow. This of course does not account for changing weather conditions such as wind and the like.

The trailer should sit more or less level front to back when in towing mode, or it should tip down slightly in the front. Towing with the trailer in a nose-high tail-dragger attitude may be asking for extra sway. This may call for adjusting your hitch head height to arrive at the proper towing angle.

If you feel there’s too much weight on your trucks aft end – as manifested by the back of the truck sagging when loaded, or the front end feeling light and squirrelly – you probably don’t have the equalizing hitch spring bars adjusted tight enough. The spring bars are designed to transfer some of the trailer-hitch weight toward the tow vehicle’s front end, and if they aren’t tight enough, they can’t do so in an effective way.

Start by measuring the height of your truck at its front and back when sitting solo, then measure the same spots when the trailer is hitched using the equalizing setup. You should see the front of the truck come down as well as the back. Ideally, there should be an almost equal amount of lowering, front and back. If not, take up another link in the spring bar chains, and check again. It may surprise you to see how tight the spring bars get when under full load, and how much the spring bars bend, but that’s how they’re supposed to be.

Connect the trailer coupler to the truck hitch ball, but before you tighten the spring bars, crank the hitch up a bit so in effect, you’re lifting the back of the truck by the ball. This takes some of the load off the spring bars and makes it far easier to snap them into place. When you raise the jack and lower the Aframe, the bars will tighten more as the A-frame drops to travel position.

If you get the bars where you want them, but you don’t have enough chain links left to allow free fore-andaft movement of the spring bars when cornering, you may need to do more head adjustment. This calls for tilting the head down toward the back, using the bolt adjustment plates, shim washers or whatever adjustment system your hitch brand employs. This aims the bars down at the back, and leaves more room for raising them when tightening them up.

Finally, once you’ve determined your proper adjustment, be sure to take up the same number of chain links each time. That way you’ll be sure to have consistent, secure towing every time you head out in search of adventure. – J.J.

A Weighty Question

WE HAVE A 2003 RAM 3500 Dually that I use to pull a Holiday Rambler 33FKT. The GVWK of the truck is 11,500 pounds and that of the trailer is 14,400 pounds. The combined rating is 22,000 pounds. I had the rig weighed by RVSEF and am presently within all limits. I am very close to the gross combination weight rating (GCWR) and would like to increase that rating without changing either of the GVWRS. I noted that changing the differential ratio from 3.73:1 to 4.10:1 is what increased the GCWR from 19,000 to 22,000 pounds.

Is it possible to add an aftermarket system that would also increase the GCWR as long as neither vehicle exceeded GVWR?


San Antonio, Texas

All ratings such as GVWR, GAWR and GCWR are set by the vehicle manufacturer, based on a stock vehicle. Adding aftermarket equipment does not increase ratings beyond those set by the manufacturer. – K.F.

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Copyright T L Enterprises, Inc. Jun 2005

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