GETTING THE RIGHT RUBBER

What you need to look for before making that next tyre purchase

WORDS AND PHOTOGRAPHY BY GRANT HANAN, ADDITIONAL PHOTOGRAPHY BY CARAVAN & MOTORHOME

When it comes to tyres, choosing the right ones for your set up requires an understanding of tyre types and markings. In this article, we take a look at what you need to know before making that next RV tyre purchase.

RV WHEELS

You wouldn’t be alone if you thought RV wheels were identical to those found on vehicles. But in fact, a reputable RV manufacturer will use a wheel designed specifically to be used on an RV or trailer.

Compared to a vehicle which distributes its load over four wheels, a single axle RV with only two wheels definitely has its work cut out. Add to that the differing suspension systems, and it becomes apparent why not all vehicle wheels would be suitable for an RV. Before fitting any vehicle wheels to your RV, check with the wheel manufacturer to ensure they’re suitable for an RV and the large load being placed on them.

RV TYRES

There is no specific manufactured tyre for a caravan although there are tyres specifically available for trailers. These come in a range of sizes and configurations, and have been designed to carry heavy loads.

With tyres and trailers, the tyre’s load-carrying capability forms part of the overall suspension system. The tyre type and its inflation rates will be specified by the RV chassis suspension engineer.

WHAT’S DIFFERENT?

It’s important to note that there are significant differences when comparing vehicle and RV tyres.

One major difference is vehicle tyres (the driving wheels in particular) need to apply traction whereas RV wheels are not powered. Vehicle tyres also have higher cornering forces and there is a requirement they are quieter for road noise. They are generally softer due to sophisticated vehicle suspensions and have to meet a specific Noise Vibration Hardness (NVH rating).

Most RV tyres don’t have the luxury of being supported by sophisticated vehicle suspensions. So it’s therefore expected an RV tyre will take out some of the road harshness when the tyre is correctly inflated for its load. Generally speaking, an RV’s tyres aren’t subjected to the excessive kilometres usually travelled by a vehicle’s tyres. This means tread wear rates can be low. But RVs that are stored for long periods leave their tyres holding heavy loads. This applies pressure and straining to sidewalls and tread surfaces, especially the areas in contact with the ground surface.

SIDEWALL MARKINGS

You could easily be mistaken for thinking buying a new RV means that the tyres are the same age. Tyres are manufactured in large supply runs and can therefore be stored for long periods before being used. Provided they have been stored in suitable conditions, i.e. temperature, humidity and sunlight, then they will be ok. Whilst this can be impossible to judge, you can look to see the age of the tyre on its sidewall.

If we take an average sized tyre used throughout the industry, the information found on its sidewall may read something like A/T LT 235/75R15 104R. So what does all this mean? Most tyres will have a great deal more information marked on them. But let’s focus on these key markings to help you make a tyre purchase.

CONSTRUCTION TYPE -

Manufacturers will use abbreviations to describe the characteristics of a tyre and its construction, e.g. H/T (highway terrain) or A/T (all terrain).

There will often be other letters such as LT (Light Truck construction) or XL (this can indicate that the tyre has extra load carrying characteristics). Refer to tyre manufacture charts for further details.

SECTION WIDTH -

The tyre is measured in millimetres from the widest points of the tyre – sidewall to sidewall.

ASPECT RATIO -

This is the dimensional relationship of the section height compared to the section width expressed as a percentage. Basically it’s the height of the tyre sidewall express as: Overall Diameter/Rim Diameter x 100.

CASING CONSTRUCTION –

The R in this case designates the tyre is of a radial casing construction.

RIM DIAMETER –

This is the size of the rim diameter measured in inches.

LOAD INDEX –

The load index is a number indicating the tyre’s maximum load capacity.

SPEED RATING –

Denotes the maximum speed for which the tyre is rated.

TYRE PRESSURE MONITORING SYSTEMS (TPMS)

Having one of these devices installed provides the driver with real-time tyre pressures and their heat rates. Simply put, the system works by sending a signal from the tyre to a monitor display inside the vehicle. Even a slow leaking tyre can be detected by setting alarm values to alert the driver. So being armed with this information means you can observe the changes and take corrective measures. For an RVer they are a great insurance policy and money well worth spent!

SECONDHAND RV AND TYRES 

It’s difficult to know whether a secondhand RV still has its original tyres so always check the tyre manufacture date to determine its age. The RV may appear to be in A1 condition, but UV, lack of tyre rotation and under inflation can cause tyre damage. Ensure to check the spare wheel as it may tell a story if it’s a different make.

Tyres that have not been well cared for are likely to let you down without any prior warning. It pays to check and know their history. Replace them if you’re in doubt, particularly if they’re more than 6-7 years old.

TYRE PRESSURES

Durability and safety will be affected by running incorrect tyre pressures on a loaded RV. Get it wrong and it may affect your RV’s handling and increase unnecessary loading on the suspension, affect braking efficiency and increase fuel usage.

It’s important to know the weight of your RV and the loads on the axles to ascertain what’s expected from your tyres. Chances are you will be at the top end of the scale. Tyres have an optimum pressure range labeled on the sidewall. Further load carrying pressure information can be found in the tyre manufacturer’s reference guide.

FINDING THE SPECS

New model RVs will come with a tyre placard or handbook which details the recommended tyre types and pressures. It’s important to regularly check your RV’s tyre pressures as you can’t see or feel the effects of under-inflated tyres easily until it’s too late. Don’t forget to check spare wheels as well.

WHEN TO REPLACE YOUR RV TYRES

1 It goes without saying, but if they are worn down to the legal minimum levels.

2 Sidewall damaged in the way of a tear or bulge.

3 Badly chipped where the tyre tread pattern has chunks missing.

4 Signs of uneven wear (this also warrants an investigation as to why this is occurring).

5 Inspect condition of valves for marking or slow leaking. 6 Age - 5 to 7 years (as a guide).

SUMMING UP

Your RV’s tyres are what keep you rolling when out touring this magnificent country. They are not something you can just set and forget. By understanding what to look for when selecting and maintaining your tyres puts you in the driver’s seat when it comes to negotiating a new set for your RV. And armed with that information, it’s safe and happy RVing!