“Always Buying, Consigning and Selling Queensland’s Best Used Boats Since 1964”

Disclaimer: This article is written with the intent of bringing to your attention that tyre choice / selection is very complicated, before making any decisions we recommend that you seek advice from your local Tyre Retailer for your needs. John Crawford Marine will not be held liable for misreading, misinterpreting the following information as it has been written in general terms and may not be information that is pertinent to your towing needs and state regulations.

With that aside……

Did you know that one of the biggest costs associated with keeping your trailer road worthy are the tyres under your pride and joy? Tyres are often forgotten about as most of us simply walk past them and if they look inflated we leave them be.

However tyres on boat trailers are subject to many stresses that will significantly shorten their life if not properly looked after. I am going to give you some pointers and information that will help lengthen the life of your tyres and save you some money.
Do you know what the numbers on the side of your tyre wall mean?

Along with the manufacturer's name and the name of the tyre there's always a set of numbers and letters that relate to the size, load, tyre pressure, model and specifications of the tyre. Here's a rundown on what those numbers mean based on the tyre in the photo.


Photo of tyre as used in this article.

Example: Kenda 165 R 13 Light Truck

* Kenda is the brand

* 165 is the width of the tyre in millimeters.

* R means it is radial construction.

* 13 is the diameter of the wheel rim in inches.

* Light Truck means built to a commercial standard exceeding specifications of general passenger cars.

The tyre pictured is fitted to a Redco Sportsman trailer which trailers a Sea Jay 455 runabout. I have chosen this rig as a lot of boats fall into a very popular size category of boat ownership.


One of the biggest issues related to tyre degradation and tyres not compliant with road worthy standards are when cracks occur in the walls of the tyres or valleys of the tread. Generally found near where the tyre meets the rim. Queensland’s Transport does not permit any cracking in the tread valleys nor on the side walls,

If you are unfortunate enough to be involved in an accident when towing, this is one of first things that an insurance claims officer will inspect as they have the right to cancel your insurance due to failure of having a road worthy vehicle. Think of the consequences if someone is hurt and your insurance is revoked?

So what makes cracks appear in the tyres?

Most side wall and tread valley cracking occurs due to under inflation. Most of us assume that a trailer tyre should be inflated like a car pressure, around 30 psi. However 9 times out of 10 this is a misnomer.



Load and tyre presssure indicator found on wall of tyre

Photographed, is the Kenda tyre again, this picture defines the maximum load and tyre pressure that the manufacturer recommends. You may be very surprised to find that recommended tyre pressure could be as high as 65 psi!

These pressures are usually well in excess of the operating pressures required for most conditions as load and speed will also determine pressure. For an answer to this question, we strongly advise talking to your local tyre retailer for expert advice.


The cracking in the side walls occurs as the tyre is made very stiff in the side walls. When underinflated the tyre wall belies causing the outer rubber to stretch to the point that it splits, hence the cracking and then the expense of replacing just because tyre pressure wasn’t adhered to.

Another cause of tyre cracking is lack of use. Tyres are made from rubber and rubber is elastic by nature and needs to be moved and rotated. So even when in winter or at times of little use, it is important to at least tow the rig around the block to remove flat spotting where the tyre has been in contact with the ground and to allow the rubber to bend/mould and form again.

Direct sunlight also fatigues tyres, we have seen this occur on the boat yard over time, tyres that don’t have rims attached perish simply to exposure. So if the side of the tyre is exposed to the sun during the day, I recommend a piece of timber ply that leans up against the tyre keeping the direct sunlight off them. Also after each use I personally spray a tyre shine / Armor Oil on the tyre to help keep the tyre rubber soft (and looking good!)

Another thing to check on your tyres in the tread depth.

Most new tyres have about 8mm of tread pattern when manufactured but as tyres wear their ability to disperse water reduces. Tyres should be replaced before the tread wears down to the level of the Tread Wear Indicators. The Tread Wear Indicators are moulded into all major grooves of tyres in at least four positions around the tyre. These indicators sit at least 1.6mm above the bottom of the grooves.

For most trailer boat owners, wearing a trailer tyre due high kilometres is very rare as the reason has more to do with wheels out of alignment. This can be caused by the trailer frame bending due to overloading, hitting a pot hole and damaging the wheel etc.

Deciding on the right tyre for your trailer.

Purchasing new tyres for your trailer is a complicated issue and is something that John Crawford Marine recommends that you seek professional advice. Many factors have to be considered including, ATM and tare weight of the trailer, Trailer manufacturers recommendations as per the registration of the trailer and the trailers design specifications (found on the trailers VIN Plate), Suspension type, intended use; Load carrying, State Transport regulations etc.

The repercussions for incorrect choice can be as serious as towing a non compliant / non road worthy trailer which has serious ramifications in the event of an accident.

John Crawford Marine regularly replaces tyres as we have a duty to ensure all our trailers meet the strict road worthy standards when being sold registered. Even our workshop staff seeks professional guidance from time to time due to the complexities of ensuring correct tyre choice.

I hope the information provided helps you understand the difficulty of tyre choice for your trailer and some simple things to do at home to maintain the life of your tyres.

Safe towing!

Matthew Hodson

Managing Director
John Crawford Marine

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