Some Thule towbar-mounted bike racks require an ISO-compliant 50mm towball to clamp correctly and securely.

Although many towballs are 50mm in diameter, differences in the ball shape, neck profile and available clearance can prevent a Thule bike rack from fitting properly. The towballs below are suitable options for vehicles needing an ISO-compliant setup.

Always check your towbar type, mounting pattern, towball rating and vehicle towball download limit before ordering. Get in touch if you are unsure which option suits your vehicle.

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Already have a Thule bike rack? Check that your towball has the correct shape and clearance before fitting the rack. A towball being 50mm in diameter does not automatically mean it is suitable for Thule’s clamping system.

Need help confirming compatibility? Contact Stoke Equipment Co with a photo of your existing towball and towbar setup.

Why Thule Bike Racks Need the Correct Towball

Thule towball-mounted bike racks clamp around the towball and require enough clearance beneath and behind the ball for the clamping mechanism to seat correctly.

  • Ball diameter: The towball must be 50mm.
  • ISO profile: The ball and neck need the correct shape for the rack clamp.
  • Neck clearance: Some low-profile or short-neck towballs do not leave enough room for the rack.
  • Load rating: The towball and towbar must support the combined weight of the rack and bikes.

50mm ISO-Compliant Towballs

Frequently asked questions

What is an ISO-compliant 50mm towball?

An ISO-compliant towball has a standard 50mm ball profile with a distinct flat section at the bottom of the ball radius, where the ball transitions into the neck.

That flat area is important because it gives the Thule bike rack clamp the correct surface and clearance to seat and lock properly. A towball can still measure 50mm across the ball but be unsuitable if the underside is fully rounded or the neck begins too close to the ball.

Will any 50mm towball work with a Thule bike rack?

No. The 50mm diameter alone is not enough. The towball also needs the correct ISO profile, including the flat section beneath the ball radius and enough neck clearance for the Thule clamp.

Some older or non-ISO towballs are fully rounded underneath or have a neck that begins too close to the ball. These can stop the rack from seating or locking correctly.

How can I identify a suitable towball for a Thule bike rack?

Look closely at the underside of the ball. A suitable ISO-profile towball should have a visible flat section at the bottom of the ball radius before the neck begins.

If the ball curves continuously into the neck with no flat section, the Thule clamping mechanism may not fit or lock correctly, even though the towball is labelled as 50mm.

Which Thule bike racks require an ISO-compliant towball?

Many Thule towball-mounted platform racks require an ISO-compliant 50mm towball, including models from the Epos, EasyFold and VeloSpace ranges. Always check the specific product requirements before fitting the rack.

Do I need to check my towball download rating?

Yes. The vehicle, towbar and towball must be rated for the combined vertical load of the bike rack and all bikes being carried. This is especially important when carrying heavier e-bikes.

Can I replace the towball myself?

This depends on the towbar design and your mechanical experience. Bolt-on towballs are often straightforward to replace, but the correct fasteners, torque settings and mounting orientation must be used. Have the installation completed or checked by a qualified towbar installer if you are unsure.

What else should I check when fitting a towbar bike rack?

Confirm the towball compatibility, towball download rating, electrical plug, rear light visibility and number plate position. If the rack obscures your vehicle's registration plate, you may need an official supplementary plate. Read our NZ supplementary plate guide .

About Stoke Equipment Co

We're a Dedicated Roof Rack Store, based in Nelson, New Zealand.
We are proud stockists of Roof Rack Solutions from Thule and Rhino-Rack. Secure and reliable cargo solutions for carrying skis, snowboards, bikes, kayaks, or extra gear.
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