How to Choose the Right Trailer Kit

A trailer kit is a matched set of wheels, hub and stub axles and a tow hitch, sold together so the components are guaranteed to fit each other. Choosing the right one comes down to three numbers: the load you need to carry, the size of your chassis box section, and the top speed the trailer will travel at.

Get those three right and the rest follows. This guide walks through each of them, using real specifications from the kits we hold in stock, so you can work out what you need before you order.

What's actually in a trailer kit?

A standard Parnells trailer kit contains two wheels with tyres already fitted, two hub and stub axle units with bearings in place, and one tow hitch. Everything is matched on stud pattern and load rating, so there is no guesswork about which hub fits which rim. Some kits come as four-wheel sets for twin axle builds, and some are supplied without a hitch if you already have one.

The stud pattern across most of our range is 4/100, meaning four studs on a 100mm pitch circle diameter, usually with a 60mm centre hole. Hubs are forged steel with a black paint finish and M12 wheel bolts fitted.

If you need to add a jockey wheel, lights, mudguards or a different coupling, those sit outside the kit and come from our wider trailer parts range.

How much weight does your trailer kit need to carry?

Start with the fully loaded weight of the trailer, not the empty weight. Our kits are rated from 200kg up to 1,800kg, and the rating covers the axle, hubs and tyres as a set. Add the weight of the chassis and body to the heaviest load you expect to carry, then choose a kit above that figure.

The point people most often miss is that tyre pattern affects capacity far more than wheel size does. Two kits can use the same 22x11.00-8 wheel and be rated very differently depending on the tyre fitted:

• 22x11.00-8 with a P334 utility tyre on a 40x40 axle: 900kg
• 22x11.00-8 with a P323 knobby ATV tyre on the same axle: 310kg

Knobby tyres are built for grip on soft, broken ground, not for carrying weight. If you fit an aggressive off-road pattern to a trailer you intend to load heavily, the tyre becomes the limiting factor long before the axle does.

Speed derates capacity too. A kit rated to carry a given load below 25km/h will carry noticeably less at 25 to 90km/h, and that lower figure is the one that matters for anything going on the road.

Which stub axle do you need, 35mm or 40mm?

Measure the box section of your trailer chassis. Our stub axles come in two square sizes, 35x35mm and 40x40mm, and the axle has to match the section it bolts to. The 40x40mm option generally carries the higher load rating of the two, so on kits offered in both sizes, the 40mm version is the heavier duty choice.

The same 18x9.50-8 grass care kit illustrates it neatly: on a 35x35mm axle it is rated at 750kg, and on a 40x40mm axle at 1,000kg. Identical wheels, different axle, 250kg of difference.

One further point on the 40x40mm high speed units. These are available as a sealed waterproof hub and stub assembly, which is the option to specify for boat trailers, slipway use, fishery work or anything else that spends time submerged or washed down. Water ingress into a bearing is the single most common reason a trailer hub fails early.

Hitches come as pressed steel or cast. Our pressed steel 750kg hitch sits over a 50x50mm box section and fixes with two M12x70mm bolts, and is manufactured to the guidelines of Regulation 55 of the United Nations Economic Commission for Europe.

Which trailer kit suits your application?

Our range splits into three groups, and the right one depends less on what you tow with than on the surface you're driving over and the speed you're travelling at.

Grass care kits use wide, low-pressure turf patterns that spread load across the surface rather than cutting into it, which is why they suit golf courses, sports grounds and anywhere the ground has to look the same after you leave. Our ATV trailer kits go the other way, prioritising traction on mud and rough ground.

If you're not sure which wheel size you already have, our tyre size chart explains how to read the markings on the sidewall.

Are Parnells trailer kits road legal?

Kits in our high speed road legal trailer kits range use E-marked tyres with load and speed indexes marked on the sidewall, and hubs designed for sustained road speeds. Utility kits using E-marked tyres such as the P334 are rated for road use up to 50km/h in Ireland, the UK and across the EU.

Anything using an unmarked agricultural or knobby tyre is for off-road use only, regardless of what it is fitted to. Check the E-mark and the speed index before you take a trailer onto a public road, and check the towing rules that apply to you. The RSA covers this for Ireland and gov.uk covers it for the UK.

Every kit page on our site lists the tyre size, load index, speed index and E-mark reference, so the information you need is on the product itself rather than buried in a spec sheet.

Can you supply a custom trailer kit?

Yes. If none of the standard kits matches your build, we can put one together to your axle rating, stub size, stud pattern, wheel size and tyre spec. This is common for trailer manufacturers and fabricators working to a fixed chassis design, and for anyone refurbishing an older trailer where the original components are no longer made.

Send us the chassis box section, the loaded weight and the intended top speed, and we will spec it from there.

Wheels and tyres are assembled into complete units at our Dublin warehouse before dispatch, so kits arrive ready to bolt on rather than as loose components to be built up on site. [CONFIRM WITH JONNY: is this true across the full trailer kit range, or only certain lines?] Orders ship across Ireland, the UK and the EU, with same-day dispatch on stocked lines. Post-Brexit UK orders are covered on our UK delivery information page.