Fitting the wrong trailer wheel bearings is one of the most common and costly maintenance mistakes trailer owners make. Get the size wrong and you risk hub failure on the road. This guide explains how trailer bearing codes work, how to measure your existing bearings, and how to find the right replacement for your trailer.
Types of trailer bearing
Most UK trailers use one of two types of trailer bearings:
Sealed ball bearings. The most common type on lighter trailers. These are pre-greased and fully enclosed, so they require no maintenance and no grease seal. They are identified by a suffix of 2RS (rubber seals) or ZZ (metal shields). Most Ifor Williams, AL-KO and Indespension light axles use sealed ball bearings.
Tapered roller bearings. Used on heavier trailers, car transporters and boat trailers. These are open bearings that require a separate grease seal and periodic repacking with grease. They carry higher radial and axial loads than ball bearings and are the type most commonly found on Knott and heavy AL-KO axles.
How to read a bearing code
Every bearing has a reference number stamped on its outer race. Once you can read these codes, finding an exact replacement becomes straightforward. The most common codes you will see on UK trailer bearings are:
|
Prefix/Number |
What it means |
Example |
|
6000 series |
Single-row deep groove ball bearing |
6004 — 20mm bore, light duty |
|
30000 series |
Tapered roller bearing |
30206 — used on medium-duty trailers |
|
First digits after prefix |
Bore diameter (multiply by 5 for mm) |
04 = 20mm bore, 05 = 25mm bore |
|
/22, /28 etc. |
Non-standard bore — exact dimension in mm |
6205/22 = 22mm bore |
|
2RS or ZZ suffix |
Sealed bearing (2RS = rubber, ZZ = metal) |
6004-2RS = 20mm sealed ball bearing |
|
C3 suffix |
Increased internal clearance |
6204-C3 = looser fit, higher speed |
For example, a bearing stamped 6205-2RS is a sealed ball bearing with a 25mm bore diameter. A bearing stamped 30206 is a tapered roller bearing — 30 is the series (tapered), 2 indicates a medium load rating, and 06 means a 30mm bore (6 x 5).
How to measure your existing bearing
If the code on your bearing is worn or unreadable, you can measure it directly. You will need a digital calliper for accuracy. Take the following three measurements:
• Inside diameter (ID). Measure across the bore of the inner ring. This is the dimension that fits onto the spindle.
• Outside diameter (OD). Measure across the outer ring. This is the dimension that fits into the hub.
• Width. Measure the depth of the bearing from face to face.
With these three dimensions you can cross-reference any bearing catalogue or search by size on TrailerTek. Bear in mind that many bearing manufacturers use the same ISO standard dimensions, so a bearing from one brand will be an exact dimensional match for another — only the quality and grade may differ.
Common bearing sizes for popular UK trailer brands
The table below lists the most commonly used bearing specifications for popular UK trailers. Always verify against your hub before ordering, as specifications can vary between axle generations and load ratings.
|
Trailer / Brand |
Inner bearing |
Outer bearing |
Seal |
|
Ifor Williams (light axle) |
6204-2RS |
6204-2RS |
Sealed — no separate seal needed |
|
Ifor Williams (heavy axle) |
30206 |
30204 |
Oil seal — check hub spec |
|
AL-KO (standard) |
6205-2RS |
6204-2RS |
Sealed — no separate seal needed |
|
Indespension (light) |
6004-2RS |
6004-2RS |
Sealed — no separate seal needed |
|
Knott / Avonride |
30206 |
30204 |
Oil seal — check hub spec |
|
General taper hub |
LM67048 |
LM11949 |
Grease seal — ID varies by hub |
For Ifor Williams trailer parts in particular, it is worth noting that Ifor Williams moved from taper bearings to sealed ball bearings on many models in the early 2000s. If you are working on an older trailer, check the hub before assuming sealed bearings are correct.
Ordering your replacement bearings
Once you have the bearing code or dimensions, you can order directly from TrailerTek. We stock individual bearings, matched inner and outer pairs, and complete trailer bearing kits that include the bearing, seal and cap for a full hub service. Kits are the most cost-effective option if you are stripping the hub anyway.
Always replace bearings in pairs — inner and outer together — even if only one appears worn. Mixing a new bearing with an old one accelerates wear on both and increases the risk of premature failure.
When to replace trailer wheel bearings
As a general rule, trailer wheel bearings should be inspected annually or every 12,000 miles, whichever comes first. Boat trailers used in salt water should be checked more frequently, as saline immersion accelerates corrosion inside sealed bearings. Signs that your bearings need replacing include a rumbling or grinding noise from the wheels, heat from the hub after a journey, or play when the wheel is rocked from side to side. If you are replacing bearings, it is also worth checking the condition of your trailer axles and hubs at the same time.
Shop trailer bearings at TrailerTek
TrailerTek stocks a comprehensive range of trailer bearings at TrailerTek, including sealed ball bearings, tapered roller bearings, bearing kits and hub assemblies for all major UK trailer brands. If you are unsure which bearing you need, call us on 01962 774 988 and our team will help you identify the right part.
