RV Tire Covers: How to Choose and Fit Them

Why RV tire covers matter

Tire rubber ages when it sits in the sun. Ultraviolet light dries the compounds, and ozone in the air attacks the rubber surface. Federal standards put a name on the result: cracking, which under the rules means any parting within the tread, sidewall, or innerliner that extends to cord material. Small surface checks are the first sign of a tire losing flexibility, and they are the damage a cover is meant to delay.

RVs and trailers sit for long stretches between trips. A daily driver flexes its sidewalls and sheds some of that stress, but a parked RV leaves the same patch of rubber facing the sun for weeks. A good cover shades the tread and sidewall and keeps rain and dew off the rubber, which is one of the simplest parts of tire preservation.

• Blocks direct sun from the sidewall and tread
• Shields the rubber from airborne ozone
• Keeps rain and dew off the tread and sidewall

RV and trailer tires follow their own rules

Motor homes and recreation vehicle trailers have load rules written into federal standards. Standards 571.110 and 571.120 require load carrying capacity information for motor homes and RV trailers, and they tie the tires to the axle ratings. The sidewall size, load range, and inflation pressure are chosen for the rig, not swapped casually. For trailer tires and motorhome tires, the marking tells you exactly what you have to protect.

Most travel trailers use ST tires, which the rules treat as special trailer tires for highway service. Heavier motorhomes use LT sizes or commercial tires designed for a higher gross vehicle weight rating. The construction differs, but the aging process is the same. Covers sized to the marked diameter work for both.

Size a cover to the tire, not the wheel

The cover is sized to the inflated tire, not the rim. The sidewall of every new tire carries a size designation, and federal standards require that the markings include the size. A size like ST225/75R15 or LT235/80R17 states section width, aspect ratio, and rim diameter, and the same markings give you the outside diameter you need for a cover.

Section width is defined as the distance between the exteriors of the sidewalls of an inflated tire, excluding decorative ribs. The overall width, with ribs and protective bands, is a little larger. When a cover lists a range of diameters and widths, match it to the numbers printed on the tire. When in doubt, move to the next size range rather than fight a cover that is too tight. See sidewall markings for how to read them.

Fit the cover over the tread and down the sidewall

A proper fit covers the tread and reaches toward the bead. The bead is the part of the tire made of steel wires, wrapped in ply cords, that is shaped to fit the rim. Cracks often start where the sidewall flexes near the bead, so the cover should come close to it without riding up.

The cover should be snug enough that it does not flap in the wind, since flapping chafes rubber and can loosen the cover. It should not be stretched so tight that it strains the seams or traps moisture. Fit covers only on clean, dry tires and remove them from time to time to let trapped air escape. How to clean and prepare the rig is covered in the tire storage guide.

Set cold pressure before you cover

A cover does not hold air. Before storing the rig, inflate every tire to the cold pressure on the placard, not the maximum pressure molded on the sidewall. Low pressure lets the sidewall flex even at a standstill and stresses the carcass over a long season.

For vehicles with a gross vehicle weight rating of 10,000 pounds or less, federal rules require a tire pressure monitoring system that lights a warning when pressure falls 25 percent below the recommended cold inflation pressure. Many RVs and most trailers park without a monitoring system, so a manual gauge check is the reliable tool. Set the target pressure for each axle, and see tire pressure basics for how to read it.

What a cover cannot fix

Remove the covers for a visual inspection before every trip. The endurance test in Standard 119 allows no visual evidence of tread, sidewall, ply, cord, innerliner, or bead separation, chunking, broken cords, cracking, or open splices. Use that list as a checklist when you check the rubber.

Age is part of it. Every tire carries a DOT date code that gives the week and year of manufacture, and rubber loses strength with age even when it is not driven. If you see deep cracks in the sidewall or at the base of the tread blocks, replace the tire before covering the next one. See the DOT date code guide and the dry rot guide for what to look for.

What to pick for your use

Questions

Do RV tire covers really work?

They work by shading the rubber from UV and reducing ozone exposure, which are the two main causes of sidewall cracking on parked tires. They do not stop aging entirely, but they slow it noticeably for a rig that sits for months.

What size cover fits my trailer tires?

Read the size designation on the sidewall. The markings give section width, aspect ratio, and rim diameter, and most covers list a diameter and width range. Match the cover range to the tire's markings.

Should I put covers on hot tires?

No. Fit covers on clean, dry, cool tires. A hot tire that cools will shrink and the cover will loosen. Always set cold inflation pressure before covering.

Do I need to check pressure while covers are on?

Yes. Covers do not hold air. Check cold pressure before each trip and after long storage, using the placard values, and recheck after the first few miles of a trip.

Do covers prevent dry rot?

They reduce the UV and ozone that cause dry rot, but dry rot also comes from age and heat. Keep tires out of direct sun when possible and inspect the DOT date code.