Time for new tyres

The saying goes there are two things you can’t escape: death and taxes. But there are a few more things that fall into this category.

Your caravan’s tyre need care too

Sooner or later you’ll inevitably go out for dinner with your stingy brother-in-law with the expensive taste and at the end of the meal he’ll suggest you split the bill 50-50 – even though you had the fish and chips while he enjoyed exotic imported mushrooms marinated in the Pope’s tears. It’s also inevitable that a school’s sponsor form will arrive at home asking you to donate R1 per word for some or other reading Olympiad your child has to take part in.

It is as inevitable that you’ll have to replace your caravan’s tyres at some stage. This is never pleasant, and it always feels as if it’s too expensive. And while we understand you’re going to shop around for the best value for money, it isn’t always a good idea to put Honest Ernie’s bargain-of-theweek tyres on your trailer. There are a lot of things to consider.

LOOK AT THE MANUFACTURER

’A good starting point is to look at how the manufacturers decide on the tyres their caravans are fitted with in the factory. Clive Cox, Jurgens Ci’s development manager, says the first thing they consider is the size of the wheel rim. “This can range between 13, 14 or 15 inch, but this is more of an aesthetic thing than anything else,” Clive says. “In fact, we’re moving away from 13-inch rims because they are so difficult to get hold of nowadays. At the moment most of our caravans are on 14-inch and our bush trailers on 15-inch rims.” Once the size of the rim has been established, they look at the tyre itself, Clive says. “One of the most important factors we consider is if the tyre can carry the caravan’s load. And for this we look at the caravan’s gross vehicle mass (GVM). For this purpose we use the weight of the heaviest caravan in our various ranges, for example the Exclusive. We then take its GVM and use the load index for tyres that is internationally recognised to find the appropriate tyre. This then applies to all the caravans in that range. For example, if you have a single-axle caravan with a GVM of 2 000kg, the law states that each of the caravan’s tyres must be able to carry a weight of 1 000kg.”

SPEED FREAK

Clive says the second, and equally important, consideration is the tyres’ speed limit. “In terms of our legislation, where we’re not allowed to go faster than 120km/h, we therefore need tyres with a speed limit of at least 120km/h.

“The tyres that are available in South Africa can go up to a speed of 180km/h or even faster – not that you must tow that fast. But the reason there’s a speed limit on tyres is related to the composition of the rubber the tyre is made from.

“When you drive, heat builds up in your tyres, and they are developed and manufactured to ensure the rubber in your tyre can stay intact at that particular speed and heat. If you therefore drive at 120km/h and your tyre’s speed limit is only 80km/h, you can be sure your tyre is going to burst sooner rather than later. It is extremely important to take note of the tyre’s speed limit, because it can lead to major problem if you make a mistake.”

WIDER WIDEST

Once the carrying capacity and speed limit have been sorted out, they decide on the width of the tire. “We look at 185mm, 195mm, 205mm or whatever the case is. But this is less important than the load index and speed limit of the tyres,” Clive says.

They then find out which tyres that adhere to these specifications are available on the market. “For our caravans we use commercial tyres. These are similar to those used on minibus taxis, specifically because of those tyres’ carrying capacity. We don’t fit ordinary sedan motor vehicle tyres on our caravans.

“We look at what is available on the market from the various suppliers. For understandable reasons we do not buy tyres on the retail market, but rather from people who import them or directly from the factory. So we definitely also consider the price of the tyre and try to establish savings for our clients.”

THE SPECIFICATIONS

All the information you need about your caravan’s tyres, is on the side of the tyre. As an example, let’s use the tyre the Sprite Tourer SW, with a GVM of 1 450 kg, is fitted with in the factory – a 215/80 R 15 110 S tyre.

The 215 is the width of the tyre in millimetre.

The 80 is the tyre’s profile, meaning the relation between the height of the tyre’s side opposed to its width. This is given as a percentage.

The R is for radian, which basically means there’s a low enforcement that runs across the tread.

The 15 means the tyre was developed to fit onto a 15-inch rim.

The 110 is the tyre’s load index.

According to the index a tyre with a

110 index can carry a weight of 1 060 kg.

This means the carrying capacity of the

two tyres on the caravan is 2 120 kg.

The S is the tyre’s speed limit, meaning

it was made to travel up to a speed

of 180 km/h.

NEW TREADS

If it’s time to buy new tyres for your caravan, Clive recommends you stay as close to the specifications of the tyres the caravan originally had.

But when is it time to replace them? According to the Road Traffic Act your tyres are legal if there is at least 1 mm tread left on the tyre. The tread needs to be even across the width and circumference of the tyres, and the pattern must still be clearly visible. But Clive warns that tyres also expire, even if they still have more than enough tread left. “That rubber composition of your tire has an expiry date and this is usually about five years after the manufacturing date,” he says. The date your tyre was manufactured is also on the side. In the case of the Tourer SW’S tyre we used as an example, it’s the number 4313. This means the tyre was manufacture in the 43rd week of 2013, which means it will expire around mid October 2018.

“You often hear about guys with older caravans they haven’t used for a while, who go camping and then a tire bursts after travelling a short distance. This is because the tyre has expired, even though the tread was still good,” Clive says. “The thing you need to remember about caravan tyres is that they never really reach their life expectancy in terms of kilometres travelled. It’s not like with your car where you’ll travel 60 000-80 000 km with your tyres. In the same time frame your caravan might just travel 15 000 km.

But you still need to replace them after five years.”

KEEP A LOW PROFILE

But what to do if you want to soup up your caravan with brand-new 17-inch rims and a set of low-profile tyres?

You can and may, says Clive, if the rim and the tyre have the load index to carry your caravan’s GVM. Remember, this is divided by two – so if you want to put new tyres on your Tourer SW, they must each be able to carry a weight of at least 725 kg. You must also ensure the diameter of the rim and the tyre are the same as the standard tyre the caravan was issued with.

The reason for this is your caravan’s brakes. They are set according to the specifications of the standard rim and tyre, and if you surpass this, you’re asking for trouble. So never fit a larger rim while still using the same profile tyre as the standard. Always consider the overall diameter of the combination.

Clive suggests you chat to your local dealer and tell him about your plans to find out if they will work.

Another thing you need to consider when you want to fit new rims, is the position of

the centre point (where the wheel bolts go through). Clive says it must be the same as the caravan’s original rim.

“If the centre point is further away from the undercarriage than the original, your tyre could be too close to the caravan. And if it is too close to the undercarriage your tyre will stick out beyond the wheel arch. And neither of these situations are good for your caravan or tyres.”

KEEP THE WHEELS TURNING

Clive recommends you rotate your caravan’s wheels at least once a month if it is stationary for long periods at home. Tyres that are stationary for long periods get smooth underneath – this is what causes the knocking sound when you tow for the first time in a long while. In terms of tyre pressure says Clive you must be guided by the recommendation above your caravan’s wheel arch. “For road trailers it’s usually around 2,5 bar, depending on how heavy the load is. The heavier the trailer, the closer to their maximum tyre pressure you need to pump them.”

DID YOU KNOW?

Everyone knows the earth takes 365¼ days to revolve around the sun. But did you know during that year the earth moves through space at 108 000km/h on an orbit of 838 million kilometres?

We didn’t think so. Here are some other equations about your wheels to think about.

Round and round The average caravan tyre Jurgens Ci uses, is a 195/80 R14 tyre. The tyre has a diameter of 66,7cm and circumference of 2,095m. So if you head to a weekend camping site that’s 100 km away, each tyre has completed about 95 000 revolutions by the time you get back home. If someone from Pretoria goes camping at Yzerfontein on the West Coast and takes the shortest route (about 1 500km), the wheels would each have turned about 1,4 million times by the time you see the Union Buildings again!!

Choose the inside track. A 2014 Toyota Fortuner’s wheel track is 1,54m and it uses 265/65 R17 tyres. The tyres have a diameter of 77,6cm and a circumference of 2,44m. If you drove around the block along four straight roads and 90o turns the left-hand tyres have actually turned much more – and therefore travelled a longer distance – than those on the right-hand side. ( We use the front tyres as the example, because the back tyres follow a shortcut behind the front tyres around a turn.) If you theoretically go around the corner with the right-hand tyre a metre from the corner, the right-hand tyre has travelled 1,57m on that corner and the lefthand one 3,99m. So if you therefore go around all four corners the left-hand tyres have travelled 15,96 m on the corners and the others 6,28m. if you consider the distance of all four corners, the Fortuner’s outside front tyre has travelled just more than double the distance once you’ve gone around the block.

Keep up, dude. When you tow a Venter Elite 6 trailer, the wheels complete many more revolutions over a specific distance than those of a towing vehicle such as the 2014 Ford Everest. The Venter has 155/80 R13 tyres (diameter 57,8cm and circumference 1,816m) and the Everest 245/70 R16 tyres (diameter 74,9cm and circumference 2,353m). If you’ve travelled 100 km, the Venter’s wheels have turned 55 000 times as opposed to the Everest’s 42 000 times. For every time the Everest’s wheel makes one revolution the Venter’s wheel had to turn 1,3 times to cover the same distance. Therefore the Venter’s wheels make 30% more revolutions than those of the Everest. So if you travel 100km/h and a distance of 1,67km in a minute, the Everest’s wheels turn at 708 r.p.m. and the Venter’s at 918 r.p.m. If you want to get even more technical: The total movement energy – due to the movement at 100km/h and the wheel rotation – is about 7 700 Joules. Now imagine the tyre gets detached from the wheel hub and runs along a stretch of road straight up into the sky. It will only come to a standstill at a height of 26 m – that is about 7 storeys!