(Originally Published in the January 2020 issue of Ski-Boat)
By Erwin Bursik
THE tyres on one’s ski-boat trailer can become a real problem if shortcuts or lack of knowledge result in the incorrect tyres being fitted.
Consider the inconvenience and potential danger of having a tyre “malfunction” while towing your rig even for a short distance, let alone the more serious consequences if you are travelling a long way from your home base.
Close to home — like when you’re travelling to a club launch site — the inconvenience of a burst tyre or a puncture can usually be overcome by merely fitting the spare tyre you should have attached to the boat trailer. Fifteen minutes of toil and you should be up and running and, more than likely, still able to go fishing.
Revisit this scenario when you’re off on a trip to Moçambique, for example, and this “minor” incident occurs 20km on the Moçambique side of the border post. That happened to me recently. Suddenly the options are much more limited and the challenges bigger.
A simple tyre change to one’s spare can be easy, but this is where the “what if” factor comes into play.
With a substantial distance still to travel to the next city or town, carrying on regardless of now having no spare plays havoc with one’s mind.
I’ve been there and done that and will admit to being extremely concerned about what I would do if I got another flat before I reached the next town. I had visions of leaving my boat and crew on the side of the road while either going back to South Africa or into Moçambique’s next big town to try and find a suitable replacement. I estimated that even if I could find a tyre in Maputo, the delay would result in upwards of four hours being lost.
“It’s simple,” some people say, “just take an extra spare on the boat.” That’s exactly what I now do.
Looking at all the what ifs and maybes, the most sensible option is to fit the best possible tyres available with respect to your craft’s overall weight and ensure they are correctly inflated. This will give you the best odds of getting to and from your destination without any tyre problems.
There are two very definite extra criteria that are of utmost importance when fitting or replacing existing boat trailer tyres. First ensure that you’re not running under-specification tyres with regard to the load index, and second, ensure that your tyres are inflated to the correct pressure for your rig’s weight and your specific application.
In the May 2016 issue of SKI-BOAT, Malcolm Kinsey, our motoring correspondent, outlined in great detail what tyres and tyre pressures should be used for the tow vehicle and trailer when the rig is being used on off-road terrain, especially on the beach. However, I feel that article did not have enough detail with regard to the boat trailer tyres and their use during long distance, fairly high speed travelling.
In an endeavour to better understand the technical aspects of tyres and their use on boat trailers, we approached Glennn Evans of Hi-Q La Lucia to give us some expert advice.
Glenn is also a ski-boater and, having launched off the beaches of the KZN coast and Moçambique, he has had plenty of practical experience regarding the problems that can be experienced by ski-boaters towing big or small rigs over tar, gravel roads and beach sand.
This article will set out some of the basics of what is required to ensure that the tyres you select for your ski-boat trailer provide you with trouble-free towing on all road and beach surfaces.
Glenn’s first piece of advice is simply that one needs to accept that all vehicles, including boat trailers, run on air, not rubber. Think about it and then think back to the last time one of the tyres you were relying on to keep you moving lost air through a puncture or blowout. Now think about the distance you travelled on the deflated rubber tyre before you came to a grinding halt.
The volume and pressure of the air in your tyres is vitally important to keep you moving forward. It is also the volume of air, regulated by pressure, that allows us to regulate the profile of the tyre to optimise the central patch of tyre which is in contact with the surface you’re driving over.
It’s extremely important to remember that underinflated tyres build up heat extremely quickly, and the one thing rubber does not like is heat. Heat and excessive flexing are the primary causes of tyre deterioration and side wall damage.
If you choose to run low profile tyres you are physically reducing the volume of air able to fit in those tyres. This, together with the heavy load you’re expecting the tyre to carry, will increase the likelihood of tyre degeneration and the possibility of a blowout. Note that low profile tyres are not recommended for boat trailers.
One has to be extremely careful when it comes to the load rating or carrying capacity of a tyre, especially with regard to single axle boat trailers and where tyres are generally loaded very close to their maximum load rating and legal parameters.
The boat trailer tyres must be rated for the gross vehicle mass of your trailer weight plus the weight of the boat and the weight of all the additional items you load on the boat when travelling. You also need to adhere to the legal load rating of your tyres as well as the recommended tyre pressures and running speeds.
As a rule of thumb with regard to tyre pressure it’s better to over inflate than under inflate tyres, but you should not exceed 3.4 bar for long distance high speed towing.
As an example, using a GVM of a boat and trailer of 2.7 tons and a single axle trailer:
A) Tyre 245/70R 16” 109R
total allowable load: 2060kg
B) Tyre 225/75R 16” 121R
total allowable load: 2900kg
Despite the fact that the 245/70×16 is a slightly wider tyre (ie: 245 vs 225) the 225 has a better load rating because it is constructed for an intended commercial application. Infact a 225/75 is almost the same diameter as a 245/70 because the 75 and 70 are aspect ratios, ie: a percentage of the width.
225 x 75% = 169mm
245 x 70% = 171mm
Effectively there’s a 2mm difference in the radius of the tyre.
With a double axle trailer one can multiply the tyre loading rate by four which gives you quite a large safety margin. However, as double axle trailers are primarily used for larger craft, one needs to do the maths to ensure the tyres used are adequate for the GVM of the rig.
WORKING ON THE BEACH
For those of us who tow rigs on the beach, the general rule is to drop your tyre pressure to 0.8 bar for both tow vehicle and trailer. Beware: This is a guideline only.
Many factors must be taken into account when determining the tyre pressures on the tow vehicle and trailer. To start with you have to determine the power of the tow vehicle, its tyre specs and the specs of the trailer tyres. Combine this thinking with the approach to the beach, the gradient of the beach and, of course, how churned up the beach sand is thanks to the other boats launching,
The most worrying factor is the road condition to and from the beach. Very sharp turns or lateral gradients in these turns where the entire boat and trailer’s weight is shifted on to one wheel can and does result in an underinflated tyre being pulled off the rim. This also applies to the bigger double axle rigs being turned very sharply on the beach sand. Once again, if the tyres are under inflated it’s easy to pull the tyre off the rim.
Glenn’s advice in this regard is to start with all tyre pressures set at 1 bar. Then, if sufficient sand traction is not achieved, drop the vehicle’s tyre pressure to 0.8 bar but leave the trailer tyres at 1 bar.
Should you still have difficulty towing on the beach then resort to dropping all tyre pressures further, but you must then be extremely careful when it comes to making turns and driving on a sloping beach. Furthermore, reinflate the tyres as soon as you’re off the sand because driving with such low pressure can cause serious damage to tyre walls.
• Carry an extra spare tyre (ie two spares) — preferably on the right sized rim — during a long trip.
• Make sure your jack — rated to a minimum of three tons — can physically fit under the trailer axle in case the entire tyre shreds and the rim is on the ground.
• Have a puncture repair kit available and a 12 volt compressor on hand so that you can deal with a spiked tyre or slow puncture.