Jockey Wheels are important part of a Trailer or Caravans running gear and there are many options to choose from.

When fitting or replacing the Jockey Wheel assembly there are a few key things you must consider:

1.  The diameter of the shaft of the jockey wheel assembly
2.  The weight capacity of the unit
3.  The closed height of the unit
4.  The open height of the unit
5.  The size of the wheel
6.  Is it a smooth or serrated shaft?
7.  Is it a fixed manual or Auto retractable?

Here are some pointers to help you establish the information:

Trailer Jockey Wheel Shaft Diameter

What is the diameter of my Jockey Wheel? 
This is the overall width of the shaft of the assembly that goes through the clamp.

There are a few sizes available 34mm, 42mm, 48mm and 60mm

These are normally a lightweight jockey wheel with a smaller wheel and used mainly on smaller trailers like Camping, Motorbike, Boat and Dinghy Trailers.  They are usually fitted to the drawbar with a 34mm Jockey Wheel clamp.

These are wider used and as such have more to the range with different wheel sizes and weight capacities. Older Horse, Plant, Goods and Flatbed Trailers are fitted with these, they are sometimes attached using a 42mm Jockey Wheel clamp or fitted directly through the coupling body.

These are now the most popular size of jockey wheel fitted to almost all new trailers and Caravans. They are available in many different heights, weight capacities and styles with various size wheels.  Caravans tend to have a shorter body jockey wheel with a smooth shaft and heavier duty Goods and Plant Trailers have a long body with ribbed shaft.  They are attached to the trailer using a 48mm Jockey Wheel clamp or fitted directly through the coupling body.

These are only used on very heavy duty trailers up to 3500kg.  These are not the most common application so there is a limited range. They are attached to the trailer using a 60mm Jockey Wheel clamp.

What Jockey Wheel weight capacity do I need for my trailer or Caravan?

This mainly depends on the gross weight of the unit it is being fitted to.  The rule of thumb is the heavier the gross weight of the trailer or caravan the higher the capacity the Jockey Wheel would need to be.
Camping trailer with a gross weight of 500kg would have a light duty jockey wheel with only 150kg capacity.
Car Transporter trailer with a Gross weight of 3500kg would have a heavy-duty serrated unit with 300kg capacity.

Closed Trailer Jockey Wheel Height

What is the closed height of a Jockey Wheel?

This is the overall height of the unit from the top of the shaft to the bottom of the shaft, not including the wheel. This can sometimes be crucial depending on the clearance you have above and around the jockey wheel on the A-Frame of the trailer or Caravan.

What is the open height of a Jockey Wheel?

This is the overall height of the unit from the top of the shaft to the bottom of the shaft, not including the wheel when it is fully wound out and extended to its maximum height.  Generally, you need less travel on a single axle caravan and more travel on a twin or triple axle trailer.

Open Trailer Jockey Wheel Height
Wheel only on Trailer Jockey Wheel

What size wheel do I need on my Jockey Wheel?

There are various options for wheel size.  There isn’t a hard and fast rule but generally the heavier duty the overall assembly is, the larger and wider the wheel will be.  It is important to measure these and match them when replacing a damaged wheel like for like.

What type of shaft does my jockey wheel have?

There are 2 types of shafts available.
1.  Smooth / plain
2.  Serrated / ribbed

The smooth shaft is the most common and used on mainly light weight applications.  The ribbed type helps to stop the jockey wheel from slipping when under load and is used on the heavier duty trailers.

Different Jockey Wheel Shaft Types
Auto Retractable Jockey Wheel

What’s the difference between a fixed or Auto-retractable Jockey Wheel?

The standard type of jockey wheel that is mounted on the A-Frame by a clamp or through a clamp on the coupling is known as a manual type.  This is moved up and down by releasing the clamp and then just moving the jockey wheel to the required position.
An auto-retractable type of Jockey Wheel is one that is fixed in one position but as you wind the handle the jockey wheel automatically pivots down in to position and then back up out of the way clear from any obstructions. This is particualarly useful on trailers with very low ground clearance.