Tow bar boxes are a great size for a large range of luggage, they are ideal for bulky items that might be awkward to load on the roof. You can find dimensions of all our tow bar boxes and platforms on their individual product pages.
We have a range of tow bar boxes and platforms available. They are all slightly different sizes and will take differing loads. To work out how much weight you can carry in a tow bar box you need to consider (1) the weight that the box/platform will take and (2) the noseweight of your vehicle. You'll need to be guided by the lower amount.
The weight that the tow bar box/platform will take: this varies and will be specified on the product pages for all out tow ball boxes and platforms.
The noseweight of your vehicle: the weight of your gear plus the platform and/or box can't exceed the tow bar noseweight. You should be able to find your tow ball noseweight in your handbook. E.g. if your tow bar noseweight is 75kg and you are using the Thule Arcos L (20kg) plus the Arcos platform (9kg) you'll be able to carry 46kg (75kg - 29kg - 9kg = 46kg).
It's also important to check your handbook for any other restrictions on carrying an unsupported load on the tow bar for your vehicle.