Trailer Suspension Units: Brands, Repairs & UK Insights

Ensuring your trailer is roadworthy and safe is paramount, and at the heart of its performance lies a robust suspension system. Whether you're towing for work or leisure, the integrity of your trailer's suspension units directly impacts stability, handling, and ultimately, safety on UK roads. From preventing complete collapse to ensuring your load remains secure, understanding these vital components is essential for any trailer owner.

Trailer suspension units are designed to absorb shocks and vibrations from the road, protecting both the trailer and its contents. They come in various capacities, typically ranging from 150kg up to 1800kg, catering to both braked and unbraked trailer configurations. The choice of suspension unit depends heavily on the trailer's intended use, its maximum gross weight, and the specific application it will serve.

Who Makes Trailer Suspension Units? Top UK Brands

When it comes to sourcing reliable trailer suspension units in the UK, several manufacturers stand out for their quality and durability. Our experience shows that units primarily made by Avonride are among the most dependable. These units are renowned for their robust construction and the smooth, stable ride they provide, making them a preferred choice for many trailer builders and owners. Their commitment to quality ensures that trailers equipped with Avonride suspension handle well under various loads and road conditions.

Beyond Avonride, the market offers a comprehensive range of options to cover diverse requirements. We also frequently supply units from other reputable manufacturers such as Indespension, Meradith & Eyre, and Peak. These brands are particularly useful for those specific weight ratings or dimensions not covered by Avonride’s extensive range, ensuring that a suitable suspension solution is available for virtually any trailer application.

For those requiring bespoke solutions, made-to-order axles are also available. These can be custom-fabricated to suit your precise application, offering different Pitch Circle Diameters (PCD) and varying weight ratings. This customisation ensures perfect compatibility with your wheels and trailer design, optimising performance and safety.

The UK market boasts a vast selection of trailer suspension components, including not just complete units but also individual parts such as brake components, hubs, bearings, and mounting plates. This extensive availability ensures that trailer owners can readily find the necessary parts for both new builds and essential repairs, maintaining their trailers to the highest standards.

Understanding Trailer Suspension Systems

Trailer suspension systems primarily come in a few common types, but rubber bonded suspension units are particularly prevalent for small to medium-sized trailers in the UK. Unlike traditional leaf spring or coil spring systems, rubber bonded units use rubber elements to provide damping and suspension. These units are often compact and require less maintenance than their sprung counterparts, as they don't rely on separate shock absorbers or intricate linkages.

In a rubber bonded unit, the suspension arm rotates within a housing, compressing rubber elements that provide the spring and damping effect. This design is straightforward and effective, offering a good balance of durability and ride quality for many applications. However, their unique construction also presents specific challenges, particularly when it comes to long-term wear and tear, and repair.

The Critical Issue: Corrosion and Suspension Failure

Despite their robust design, trailer suspension units, especially those on smaller car trailers, are highly susceptible to corrosion and mechanical failure. It's a sobering fact that cases of complete trailer collapse whilst being towed, or wheels detaching due to failed suspension components, are not unknown. This is largely attributed to the harsh environment trailers operate in, coupled with design weaknesses in certain units.

A significant concern in the UK is the absence of regular MoT-style testing for small car trailers, unlike some other European countries like Germany and Sweden. As of 2012, the UK Department for Transport had no plans for such regular testing. While new trailers must meet EU directive EC 2007/46 for type approval, this directive does not address potential issues arising from poor design or specification of components that can lead to premature corrosion and failure over time. This lack of rigorous oversight means that many unroadworthy trailers continue to be used, posing a significant risk.

A common failure point, particularly in small trailers, involves hollow box-section suspension drop arms. These are often not hot-dip galvanised, leaving them vulnerable to rust, especially where stress is highest. Once corrosion takes hold in these critical areas, the structural integrity of the suspension is severely compromised. It becomes impossible to weld corroded units back to an acceptable strength, making repair unsafe and impractical. This design flaw essentially creates a built-in obsolescence, forcing owners to consider replacement after a relatively short lifespan unless meticulous preventative maintenance is undertaken.

Furthermore, the dangers on UK roads are exacerbated not just by commercially built trailers with design flaws but also by a multitude of 'DIY' trailers. Many of these are constructed from inadequate materials or with poor welding techniques, making them inherently dangerous. Overloading and poor maintenance of older caravans or converted chassis frames also contribute to the risk. When considering buying a used trailer, particularly online, the phrase "buyer beware" rings especially true due to the prevalence of these dangerously corroded or poorly constructed units.

Repairing Rubber Bonded Suspension Units: A Detailed Guide

Addressing a failed rubber bonded suspension unit is a task that requires precision, the right tools, and an understanding of the specific challenges involved. Given the severe consequences of suspension failure, attempting a repair should only be done if you possess the necessary skills and equipment.

Diagnosis and Initial Assessment

The first step is to accurately diagnose the problem. Signs of suspension failure include an abnormal ride height, the trailer listing to one side, uneven tyre wear, or, most alarmingly, a wheel that visibly splays outwards, particularly under load. The Trelgo T50T trailer example highlighted a common scenario where the offside suspension arm was severely affected by corrosion, leading to the wheel splaying outwards. Such damage is often too extensive for safe welding repairs, especially in high-stress areas where proper access for cleaning and welding is impossible.

The Removal Challenge

Removing corroded rubber bonded suspension units from an axle is notoriously difficult. Unlike some other suspension types, these units cannot simply be pulled out. The most common DIY method involves using an angle grinder to cut off the compromised drop arms. Following this, the remaining rubber within the axle housing must be drilled out, a task made challenging by the need for exceptionally long drills (around 450mm). This mechanical removal process, though laborious (potentially taking several hours), is crucial for safety.

It is absolutely critical to avoid using heat, such as an oxy-acetylene torch, to burn out the rubber. This process not only generates a mass of noxious smoke but also vaporises the galvanising, releasing dangerous fumes that are harmful to breathe. Always opt for mechanical means to separate the components of the original axle, even if it means leaving the cut-off steel tubes in place.

Choosing Replacement Parts

When replacing rubber bonded units, opting for high-quality components is paramount. Knott Avonride units are widely regarded as one of the best makes on the UK market. Most replacement units are designed to accept standard 4-inch PCD trailer wheels, which typically have minimal or zero offset. However, some units feature extended stub axles with 108mm PCD hubs, suitable for certain Ford Fiesta and Peugeot wheels.

Consideration of wheel compatibility is vital. Original continental standard 115mm PCD wheels are often not compatible with UK pattern replacements, as bearing sizes differ. Given the higher cost of new 115mm PCD wheels and tyres, it's often more economical to convert your trailer to a UK specification using UK pattern suspension hubs and either new UK wheels or salvaged car wheels. Using old car wheels from scrapyards can be a cost-effective solution, often providing tyres with a higher load rating.

The Installation Process

The installation of new suspension units typically involves welding new mounting plates to the underside of the existing axle. This process requires precise measurement to ensure the new mounting plates are in the correct position. Careful attention must be paid to tyre clearance, aiming for approximately 40 to 50 mm between the tyre sidewall and the trailer body to prevent stones from becoming trapped and damaging the tyre.

It's important to note that welding undertaken in small workshops using carbon dioxide as a shielding gas may not achieve the same high standard as automated argon-arc welding. While functional, it's a detail to be aware of. High tensile 8mm bolts and nuts (either 8.8 or 10.9 grade) must be used to secure the new units to the mounting plates, ensuring they are extremely strong.

A critical aspect of installation is ensuring the drop arms always face backwards, providing a 'trailing' suspension. This configuration is essential for correct geometry and safe towing. Due to variations in drop arm length between original and replacement units, the centre of the wheels may shift, potentially affecting the ride height and the trailer's neutral (unloaded) nose weight. Mudguards may need to be repositioned to accommodate the new wheel position and maintain adequate clearance. If the nose weight is reduced, relocating a spare wheel to the front of the trailer can help restore balance.

While a complete new axle assembly can be costly (around £220 retail, compared to £440 for a new trailer of similar type), the cost of replacing suspension units and wheels can be significantly less, often around £150 plus labour. This makes repair a viable and economical option, preventing the unnecessary scrapping of otherwise sound trailers.

Re-settling Rubber Cords in Suspension Units (DIY Refurbishment)

For those looking to refurbish existing suspension units, particularly if the main housing and stub axle are sound but the rubber elements have failed, re-settling new rubber cords is a challenging but possible DIY endeavour. This process involves:

• Removal of Old Rubbers: Grinding out the square tube and carefully extracting the old, often 'Dairylee cheese-shaped' rubber segments.
• Preparation: Thoroughly cleaning the square bar, perhaps with an electric brush, and applying a silicone grease to protect it.
• Sourcing New Cord: The key is finding the correct specification rubber cord, typically 15mm, with a 75 shore hardness. This can be difficult to source from general suppliers.
• Component Preparation: Procuring new square tube and mounting plates, cut to size. Filing any internal weld seams and chamfering lead-in edges on internal faces will aid insertion.
• Insertion Mechanism: A hydraulic car trolley jack can be adapted to create a frame or press. The method involves inserting short lengths of cord into the welded-on squares and mounting plates, then slowly jacking the stub up onto the tube, allowing the cords to push through.
• Alignment: Crucially, it is advised to refurbish one side at a time. This allows you to use the uncut side as a reference to ensure the reassembled stub and axle maintain their correct relationship, as they will have aged and stressed to run in a certain direction over the years.
• Securing: Once assembled, adding a bar across the stub square bar at the open end can prevent the stubs from ever coming out, especially for lower-rated units.

This method requires significant mechanical aptitude and access to tools, but it highlights the ingenuity that can be applied to extend the life of trailer components.

Maintenance Tips for Longevity

To maximise the lifespan of your trailer's suspension and ensure ongoing safety, regular maintenance is key:

• Routine Checks: Before each journey, or at least regularly, perform a visual inspection of the suspension units, looking for signs of corrosion, cracks, or distortion. Check the condition of the rubber elements.
• Tyre Pressures: Maintain correct tyre pressures, which can be as low as 20psi for light loads like garden refuse.
• Wheel Stud Tightness: Regularly check the tightness of wheel studs. Hard rubber-based suspension systems, unlike the soft, well-damped systems in cars, can cause studs to work loose. This is a particular concern with alloy wheels, which lack the 'give' of steel wheels and are generally not recommended for trailers. Steel wheels are designed to deflect, acting as a giant spring washer, which helps prevent studs from loosening.
• Storage: Whenever possible, store your trailer in a warm, dry garage. For trailers stored outdoors, consider coating vulnerable suspension arms, especially hollow box sections, with grease to provide an additional layer of protection against corrosion.

Frequently Asked Questions (FAQs)

What are the main causes of trailer suspension failure?

The primary causes are corrosion, particularly in ungalvanised hollow box-section drop arms, and general fatigue from constant road vibrations and loading. Poor design and inadequate maintenance also contribute significantly.

Is it worth repairing an old trailer suspension?

Often, yes. While a complete new trailer or axle can be expensive, replacing just the suspension units and wheels can be a cost-effective repair, extending the life of an otherwise sound trailer. However, severe corrosion on the main axle beam or chassis might make repair uneconomical or unsafe.

Can I use car wheels on my trailer?

Yes, it is often possible and can be more economical than buying dedicated trailer wheels. Old car wheels, especially from scrapyards, can be cheaper and may offer higher load ratings. However, you must ensure the PCD and bearing sizes are compatible with your trailer's hubs, and that there is adequate clearance within the mudguards and chassis.

How often should I check my trailer's suspension?

It's advisable to perform a visual check before every journey. A more thorough inspection, including checking wheel stud tightness and looking for signs of corrosion or damage, should be done at least annually, or more frequently if the trailer is used heavily or stored outdoors.

What does PCD mean for trailer wheels?

PCD stands for Pitch Circle Diameter. It refers to the diameter of the imaginary circle that passes through the centre of the wheel studs or bolt holes. Matching the wheel's PCD to the trailer's hub PCD is crucial for safe and secure wheel fitment. Common UK trailer PCDs are 4 inches, while some continental designs use 115mm or 108mm.

Investing time in understanding and maintaining your trailer's suspension is not just about extending its life; it's about ensuring the safety of your load, your vehicle, and everyone else on the road. By choosing reputable brands, understanding common failure points, and committing to regular checks and timely repairs, you can keep your trailer safe and reliable for many years to come.

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