How To Fit a Bike Rack Onto Your Towbar

Bike Racks, Towbars & Towballs

For cyclists, a towbar mounted bike rack is one of the safest, most stable, and versatile ways to transport bikes around our wonderful country. Compared to roof-mounted systems, they’re easier to load and unload, and they also offer better aerodynamics while driving. But not all bike racks are the same, and regulations do vary.

Here’s a guide to the main types of bike racks and the legal requirements in New Zealand, the UK, Europe, Australia, and the USA.

Types of Bike Carriers for Your Car

There are a number of different ways you can mount your bike to your car. The option that’s best for you will depend on the type of vehicle you have and how many bikes you’re wanting to transport.

Towball/Towbar Bike Racks

Towball/towbar carriers are a convenient option if you already have a towball or towbar on your car. It’s important to remember with any bike carrier mounted on the rear of your vehicle, you need to be sure that your license plate is visible.

Roof Mounted Bike Carriers

Roof mounted carriers are also quite popular as they are easy to install and can have other uses. They also still allow access to all areas of your car when your bikes are mounted. It can be difficult lifting bikes on and off the roof of your car and you may notice some drag on your car when driving.

Hitch Mount Bicycle Carriers

Hitch mount carriers or vertical bike racks are perfect for the avid cyclist who is wanting to transport a number of bikes. They are relatively easy to install and remove when not in use and are generally one of the more sturdy ways of transporting your bike.

Spare Wheel Bike Rack

Spare wheel carriers, as their name suggests, require a spare wheel to be mounted on the back of your car. This makes it a perfect option for an SUV or 4WD bike rack. These racks are super easy to install and are a cost-effective option if you happen to have the right car setup.

Towbars, Bike Racks & Vehicle Chassis Capacity

When fitting a bike rack to a towbar, it’s essential to remember that your towbar and vehicle chassis are designed primarily for towing trailers, not carrying suspended loads. This makes weight limits and leverage forces especially important. Some important considerations before fitting a bike rack to your towbar and venturing out on the open road:

• Towball Sizes: Towball mounted bike racks must match a towball size (50 mm or 1 7/8”).
• Lighting & Plates: If bikes obscure the vehicle’s lights or number plate, a light board with indicators and a supplementary number plate is legally required.

Load Capacity of the Towbar & Vehicle Chassis

Vertical Load Rating (Downforce)

Every towbar has a maximum vertical load rating, often referred to as downforce or ball load. This is the maximum weight that can safely press down on the towball while towing a trailer. Multiple bike carriers and e-bikes can exceed this rating, which can place the towbar and its chassis mounting points under excessive stress.

If the rating is exceeded, the towbar may fail, or its attachment bolts could loosen, creating a safety risk to other road users. If in doubt, check with our team who will be able to help you out.

Leverage & Torque Considerations

Unlike a trailer coupling, where forces on the towball act mostly in line with the vehicle, a bike rack carries its load further rearward and away from the chassis. The further the bikes extend from the back of the vehicle, the greater the torque (rotational force) placed on the towbar.

This leverage effect means that even if the combined bike weight is within the towbar’s stated vertical load limit, the stress on the towbar and chassis can be significantly amplified. Excessive torque can cause the towbar, its mounting points, or even the vehicle chassis itself to fail, posing a safety risk to other road users.

Design Standards & Intended Use

Towbars are built and tested according to standards related to trailer towing, not necessarily for carrying bike racks. This means that the stresses from a bike rack may exceed the intended design loads, particularly if the rack holds multiple e-bikes. Always consult both the towbar and the vehicle manufacturer’s specifications before fitting a bike rack to your towbar.

Practical Safety Check

Before loading bikes, consider:

• The combined weight of the bikes.
• How far they extend from the towball (which increases torque).
• The towbar’s maximum downforce rating.

Consider reducing the number of bikes, repositioning the bikes closer to the vehicle, tethering the bikes and rack to the vehicle, or choosing an alternative mounting system.

Tip: E-bikes in particular can quickly exceed the towbar and vehicle ratings. Consider reducing the number of bikes being carried, and safely tether the bikes to your vehicle as a secondary safety measure.