Diamond Dave

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Have you checked your motorhome's tyres recently? They are crucial to safe touring and, as our expert Diamond Dave explains, it's not just about tread

Tyres – those simple round rubber things at each corner of our beloved motorhomes – are quite possibly the single most important part of the vehicle as far as driving safety is concerned.

They are the only area of the ’van that should be in contact with the road. Therefore they are required to deal with traction for going forward, steering for following roads, and braking for bringing the whole shooting match to a safe stop.

It’s a big ask, which is why it’s crucial to make sure yours are of the correct type and in fine fettle.

Despite them being so important to the safety of us and others on the road, I frequently see motorhomes sporting some worrying tyres – and the problems are mostly down to significant age.

The power to perform

As some of you may know, I indulge in a little bit of motorsport, and I believe that there is no better arena for discovering the importance of those four (or sometimes six) round, black bits of rubber.

In general we measure the performance of our tyres by four main criteria: wet grip, dry grip, wear rate and noise generation. However, we largely ignore the degradation of these four factors over the passing of time, and that is often because of cost. Cost takes a bit of a back seat to grip performance in the world of motorsport, along with wear rates and noise generation.

I’ve just disposed of a set of tyres that were four years old, but that had only covered a few hundred miles – the problem being that, as tyres get older, they also get harder.

›The make-up of tyres is not entirely dissimilar to that of petrol: both have a wide variety of chemical components. Some of these are referred to as ‘volatiles’, which simply means that they will readily evaporate into the atmosphere.

The issue here is that those volatiles are what make the tyres work in respect of grip, both in the wet and the dry. Th›e loss of volatiles results in harder rubber, which almost always means less grip.

In general a soft tyre will give more grip on the road because it can deform more easily, which allows it to follow the variations of the road surface more accurately. Harder rubber simply scrubs over the surface, giving less grip in the process.

Wet grip is slightly different in that it also depends on the tyre’s ability to displace water, which is largely a function of tread-pattern design – although a softer rubber will also help to displace it. The downside of soft rubber compounds (which is probably obvious to followers of motorsport) is that the tyres wear out more quickly.

The reality is, however, that even the softest compounds that are available as road tyres will generally be good for many more miles than the average motorhome will cover in six years. The average mileage for a motorhome is around 4000 miles a year, so 24,000 in six years is commonplace.

Compounds for your camper?

So what about campervan-specific tyres? Well, in my experience they all tend to be of harder compounds.

When you consider that commercial tyres generally start off with about 2mm more tread than car tyres, this means that they will die of old age long before they wear out. I often see tyres well past six years of age that still have 6mm or more of tread depth left.

And therein lies the problem: it seemingly goes against common sense to dispose of tyres with lots of tread depth left, simply because of their age.

However, look closely at the sidewalls of yours if they’re more than five years old. I recommend using an LED lamp at an angle to the sidewall to highlight cracking.

It is often difficult to see at first (hence the LED light, because it does show up crazing and cracking), but I’ve never known it to heal up and get better!

The harder compounds of many motorhome-specific tyres are also fine for fuel consumption and road noise, but don’t generally give good road grip in either the dry or the wet.

The lack of wet grip is vastly aggravated by wet grass, too. My work van was shod with Goodyear Cargo tyres when I bought it. They were great for long life but awful on wet grass. Last year on flat, level and dry ground I was experiencing loss of traction at idling speeds with only dew on the grass!

I replaced them with Hankook RA 08s which have transformed the roadholding and, most importantly, the grip levels on wet grass.

Softer rubber and a more aggressive tread pattern have led to a slightly noisier tyre on the road, and an increase in fuel consumption (which is fairly insignificant given the low mileage this vehicle covers). These are minor issues, though, compared with the improved traction in both the dry and the wet.

Get a grip!

As far as grip levels go, most of us will hopefully not get anywhere near the limits on public roads – although I suspect that this will be more down to a relaxed driving style when behind the wheel of a motorhome rather than a desire to get to the destination in the shortest possible time.

But every now and again you might encounter a stretch of road with a greater-than-normal level of standing water, and this is where that ‘wet grip’ feature of your tyres should hopefully keep you out of trouble.

When encountering standing water we first need our tyres to disperse as much water as is physically possible. This is largely dealt with by the design pattern of the tread.

The rubber compound itself does play a large part, however: a softer compound can press into the gaps in the road surface better than a hard rubber, and thereby dispel water into the main tread area for total dispersal.

Of course, motorhome tyres also have to cope with standing around for long periods of time without being moved, which requires a harder rubber compound to cope without permanent deformation.

So, as always, there is some compromise to be made.

A keen motorcaravanner, Practical Motorhome's technical expert Diamond Dave runs his own leisure vehicle workshop. Find out more at Dave Newell Leisure Vehicle Services.
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