Tire Pressure The correct pressure to carry in your tires is probably the most misunderstood topic concerning vehicles. Let's start by stating the correct pressure is NOT the max pressure on the sidewall. Anyone that tells you different is full of it.
The correct pressure is determined by weighing each axle and consulting the tire manufacturer for the pressure for that weight. Search for 'suggested tire brand rv tire pressure'
Weighing the RV You need to know the weight on each wheel, each axle, and the all-up weight. The LD should be weighed with the gas and propane tanks full and the freshwater about 1/2 full and the storage tanks empty. All gear normally carried and all humans should be aboard for the weigh-in. You should seek out a segmented scale, rather than a platform scale. Commercial truck stations have such scales.
If the front axle weight is 4,200 and the weight is equally distributed left to right (and it should be reasonably close) then each tire is supporting about 2100 pounds so the proper pressure should be 60 pounds.
ABOUT YOUR TIRES (UPDATED 2022)
READING A LIGHT TRUCK TIRE SIDEWALL
Rub a piece of chalk over any markings that are difficult to see/read; the chalk makes the letters stand out.
- LT = light truck (Not all “light truck” tires are appropriate for RV use!)
- 225/75R/16E is the tire size on the Ford E-450 chassis. '225' is the tire’s width in millimeters. '75' is the aspect ratio, i.e., the relationship of the sidewall height to the tire width; the sidewall height is 75% of the tire width. 'R' indicates a radial tire. '16' is the diameter – inches – of the wheel (rim).
- Load range relates to the maximum load an individual tire can carry; on LT tires, a letter indicates the load range, e.g., D or E.
- The maximum load capacity for the individual tire (stamped on the sidewall of the tire) is indicated as 'X' pounds when the tire is used as a single.
- The tire’s maximum cold pressure is indicated near the maximum per-tire load ratings.
- Tire markings vary according to the manufacturer, but the tire’s description/specs should include its intended use, e.g., commercial, highway all-season, etc
- The number and composition, i.e., polyester or steel, of belts under the tread and plies in the sidewall are (usually) indicated near the tire size marking. E load range tires should be 10-ply.
- The date of manufacture of the tire is located in one of the 'DOT boxes', small rectangles containing the tire’s identification, serial number, etc. Beginning with the year 2000, the manufacturing date is indicated by a four-digit number; the first two digits represent the week of manufacture, and the last two digits show the year of manufacture. For example, '3519' means that the tire was made during the 35th week of 2019.
TIRE TIPS
Tire Rack offers the most comprehensive, updated listings of available LT225/75R/16E tires. Search tire listing websites by tire size, not by vehicle.
All-steel, i.e., steel mesh belting and sidewall reinforcement can be a good choice, but the selection is (currently) limited to two manufacturers.
Michelin XPS Rib
Goodyear G947 RSS Armor Max, G949 RSA Armor Max
Tire wear patterns indicate over/underinflation, poor wheel alignment and balance, damaged wheels, and/or suspension problems.
Over-Inflation Wear
Tire wear in the center of the tread pattern tells you that the inflation patterns are too high. Too much pressure can cause the contact patch to shrink and the center of the tire to carry all of the load.
Under-Inflation Wear
Tire wear on the edges of a tire will typically indicate inflation pressures are lower than specified. When a tire is under-inflated, the contact patch grows and the load is carried by the outside edges of the patch.
Feathering
The indicator of excessive positive or negative toe angle is a feathering or scuffing that can be detected by stroking your fingertips across the edge of each tread bar or tread block. A feather edge on the inside of the tread bar indicates excess toe-in, while a feather edge on the outside of the tread bar indicates toe-out. Because the angle is affected by changes in camber and caster angles, it’s always the last angle to be adjusted during the wheel alignment process. In addition, any change in camber or caster angles will immediately change the toe angle. Toe angle geometry can also be greatly affected by changes in suspension height.
Scalloped
Cupped or scalloped dips appearing around the surface of the tread could indicate loose, worn, or bent suspension parts. Worn shock absorbers or unbalanced tires can also cause cupping, but the cupping would typically be more indicative of a concentric pattern. Shocks and struts are the most likely culprit because they provide damping force to control tire movement. When the tires move excessively, the scalloped pattern can appear. A lack of rotation can cause this condition.
Outer Edge Wear
Wear on the outer edge of a tire is rare these days, but it does happen. Positive camber, caster, and toe can lead to wear on the outer edge. If you see edge wear on one side, check the thrust and setback.
But, it should be noted, that the leading cause of outer edge wear on modern vehicles is over-enthusiastic cornering.
Inner Edge Wear
Inner edge wear on tires is the most common problem most technicians see. The angles causing this type of wear are typically negative toe and camber. For parts, there are three component sources of the inner edge wear: bushings, springs, and loads.
- Bushings
Ozone, extreme temperatures, and other atmospheric issues tend to destroy rubber bushings and cause the alignment angles to change. Some vehicles have hydraulic bushings on the rear lower control arms. Some bushings will leak when they fail. When a bushing in the rear fails, the extra movement causes the wheels to toe out and the camber to go negative.
- Springs
As a suspension compresses and rebounds, the alignment angles change. Engineers tune alignment angles for a specific ride height to maximize handling and tire wear. If a spring can no longer support the vehicle, the alignment angles will suffer. Most engineers tune the suspension to toe out when the rear suspension compresses. This increases vehicle stability. But, it also causes the inner edge of the tire to wear. Springs are made of metal that is heat-treated but can still fatigue. This includes leaf, coil, and torsion bar springs. If you see a vehicle that needs considerable adjustments for camber on both wheels of the same axle, inspect the springs.
- Loads
Loads in the rear of the vehicle will cause changes to the toe, caster, and camber in the front (and possibly the rear). The camber and caster will become positive in the front, and if the vehicle has an independent rear suspension, the camber will become negative and it will be toed out. This could lead to outside edge wear in the front and inside edge wear in the rear.
Chalk Test - You can visually determine if the tires are over or under-inflated with what is known as a chalk test. There are numerous YouTube and explanatory articles that can be found by searching for ‘chalk test’. All you need is a piece of chalk, an empty parking lot, the rig loaded as it would be going down the road and 15 minutes.
Use the recommended tire application, size, and load rating for your RV
Look for the certification sticker on the door jamb of your LD; it contains information about tire size/type, recommended tire pressures, and tire weight capacities.
Light Truck is the somewhat confusing tire designation used for tires that are the appropriate size and application, i.e., designed for commercial or RV use, for your E-350/450 chassis.
Commercial grade/RV tires are often made of better grades of rubber, contain more UV and ozone protectants, and may have additional plies of polyester (or another material) in the sidewalls, and/or extra belts under the tread; these are usually steel 'mesh'.
Use the appropriately-sized tire for your wheel. Using even a slightly wider tire than the 225/75R/16E, i.e., a 2/5” larger 235/75R/16, reduces the amount of space between the duals. Less space means excess heat build-up and possible blistering (and weakening) of the tires’ sidewalls.
Also, 'non-spec' space between duals leads to possible contact between the duals when the tires flex during normal use; contact can cause the tires to 'scrub' and weaken the sidewall. (And, the wider tire may not form a thorough seal when seated on the rim.) Never install a 16.5” (bead width) tire on a 16” rim, or vice versa.
Load rating E is the appropriate choice for the E-450 Ford chassis.
Currently, Michelin, Goodyear, Bridgestone, Kumho, Toyo, and B.F. Goodrich are among several manufacturers that offer at least one LT/225/75R/16 E-load range tires that are appropriate for use on the E-450 chassis. Check each manufacturer’s website for tire choices of the appropriate size, load rating, and application; the availability of tire models and applications changes frequently!
Note: The 'M+S' tire tread designation means that the tread grooves are wide and begin close to the outside edge of the tire; the wide tread grooves allow mud and snow to be thrown off more easily than from a narrow-grooved highway tire. Sipes, usually hook-shaped or zig zag slits around the outer edge of the tire tread, provide increased traction on wet roads. M+S tires are not true snow tires; they are classified as all-season tires, suitable for a variety of road applications.
The most common causes of tire failures are overloading and underinflation.
Weigh your coach, loaded and ready for the road, on all four 'axle corners'; the weight (of each corner of) your coach determines the inflation pressure(s) of your tires.
All tires on the same axle should be inflated to the same pressure; if there is a weight discrepancy between the right and left side of the RV, air the tires to accommodate the higher weight.
Don’t exceed the maximum cold tire pressure, stamped on the tire sidewall (or the GVWR of your coach!) If your weight indicates a tire pressure over 70 pounds, remove the rocks and scrap steel you are grossly overloaded.
Load Rating Tables
Individual tire manufacturers’ websites offer tire care tips, application, size, load rating information, and inflation tables for their tires; check selections among LT225/75R/16E Examples of load rating tables.
https://www.michelinrvtires.com/reference-materials/load-and-inflation-tables/#/
www.goodyearrvtires.com/tire-inflation-loading.aspx
A closer look at a load range table. Using the Michelin XPS Rib as an example.
If the front axle weight is 4,600 pounds, then the proper inflation would be 65 pounds. (2,300 per tire x 2)
If the rear axle weight is 9,200 pounds, then the proper inflation would be 75 pounds.
(Note 4,600 + 9,200 is 13,800, the typical weight of a 26-foot going down the road with full gas, 2/3 water, and empty storage tanks)
Make sure you are typical and get it weighed.
TIRE MAINTENANCE
Inspect your tires regularly; don’t forget the inside duals! Check the sidewalls for cracking, checking, bulges, tears or (excessively) scuffed areas. (Also check the tire bead area for any gouges or shredded or missing rubber.) Check the tread for tread depth, uneven wear, rocks or other road hazard debris, and any cuts or areas of missing rubber.
Tires deteriorate much more quickly when exposed to UV light and ozone in the air; wash tires with mild soap and water and rinse thoroughly. Keep tires covered while the RV sits in storage or at a campsite.
Do not use tire dressings or vinyl/rubber treatments containing petroleum distillates, e.g., Armor All, on your tires or any vinyl or rubber surface; using these products can actually increase the rate of deterioration. 303 Aerospace Protectant is the good stuff! https://www.goldeagle.com/brands/303-products/
RV tires should usually be replaced when the tires are about 5-6 years old, even if the mileage is low and the tread still appears good. The sidewalls of RV tires are far more vulnerable to the effects of weight and wear than the tread, and time and exposure can deteriorate tires faster than use.
Tire Stores - You should seek one that normally handles larger vehicles.
Install long brass valves; these valves make checking tire pressure and airing the tires much easier! Search for dually tire valves or Borg tire valves.
http://yourtireshopsupply.com/category/796/dually-valve-kits is one source for these valves. These are NOT extensions, which can be dangerous.
Carry a reliable, accurate truck/RV tire pressure gauge that registers tire pressures up to about 100 pounds. The pencil types are less accurate than numbered or digital read-out gauges. Make sure that the gauge head is deep enough to allow a complete seal around the tire valve when you check the tire pressure. Do not rely on the gas station or even tire shop gauges that are attached to the air hose; these are notoriously inaccurate.
Make sure that the gauge selected is for truck/RV use, i.e.; the gauge needs to measure high enough pressures and be of a configuration that allows you to reach the valves to check the air pressure. I use an Accutire MS-4021B Digital Tire Pressure Gauge; see Amazon. Jayco is another quality vendor. A flexible hose is a plus.
Besides the gauge, other handy tire tools are a valve core tool, extra valve caps, an old (dull) screwdriver to pick rocks out of the tread, and a depth gauge measure.
Check your tires’ air pressure before each day’s driving; the tires have to be cold for an accurate reading. 'Eyeballing' does not substitute for using the gauge to verify correct tire pressures!
A laser digital thermometer is useful to quickly check tire pressure/temperature at a rest stop. You just walk around the rig and shoot all six tires noting the temperature. You will quickly learn what a normal temp is. The inside dual will always read a little higher than the outside. 80 to 120 degrees depending on ambient temp are normal.
Use metal valve caps to keep dirt, debris, and moisture out of the tire valves; these can damage the valve core and cause a slow leak. The best 'air-through' valve caps are German-made V2B Alligators:
https://shop.myerstiresupply.com/ERP2Web49/e2wItemMain.aspx?parentId=00083256
https://www.amazon.com/Alligator-V2B-Inflate-Through-Valve/dp/B014VCY3S2
Depending on speed, ambient temperature, and length of driving time, a tire can inflate to several pounds over its cold inflation (even exceeding the maximum) pressure. This is normal; never bleed air from a hot tire.
Carrying a small 120V (or capable 12V) air compressor makes airing the tires much easier!
400P-RV AutomaticPortable Compressor is an example.
https://www.viaircorp.com/portables/400p-rv-auto
If you use wooden or plastic blocks for leveling your coach, make sure that the blocks are wide enough and long enough to support the entire footprint of the tire!
Always block both rear duals when leveling the coach; never block just the outside dual.
Air the spare to the maximum pressure listed on the sidewall.