Home Towing weights calculator help

Towing weights calculator help

I don’t understand all these terms!

Yes, it’s unfortunately complex, lots of numbers to go find and enter. Read this.

The results are wrong!

Possibly, but before you comment please read this:

  • TBM counts towards payload, so if you have say a 3000kg GVM, car weighs 2750kg ready to tow, and TBM is 250kg, then you’re up to 3000kg GVM.
  • The heaviest trailer you can tow might be limited by GVM, GCM or max tow…whichever comes first!
  • There will be a maximum TBM; the calculator doesn’t allow for this yet. That will be the lesser of the limit for the vehicle, towbar and tongue.
  • There’s no units marked (kg or lb) as the calculations are the same.

If you do have an improvement suggestion or find an error, please let me know in the comments.

Why can’t I just select my car and trailer and it works it all our for me?

Because every towcar and trailer combination is different. In particular, there’s many different limitations to specific vehicles which one calculator cannot cover without becoming overly complex. For example:

  • Some vehicles like Pajeros reduce TBM limits as trailer mass increases.
  • Nissan have guidance to reduce GVM by more than the TBM.
  • Sometimes the max tow rating changes depending on gearbox and engine.
  • Some vehicles require a weight distribution hitch to tow their maximum, or are speed-limited, or require special towing brackets.

What you’ll need to do is get your vehicle and trailer weighed, figure out your load limits, then plug them in.

It is possible to link to a datasource where I can look up much of the data such as GVM and GCM, but that costs significant $ and there’s only so much I give away for free.

What else do I need to worry about when setting up to tow?

  • Your trailer should be as light as possible relative to the towcar. The heavier the trailer, the more the trailer can boss the towcar around.
  • More towball mass is not necessarily good – it can prevent trailer sway, but too much brings too much straight-line stability and cornering becomes problematic.
  • Trailer sway…a complex subject, explained here.
  • Run tyre pressures commensuate with the load. Usually that means a bit more in the rear tyres as those are heavily loaded. There is actually a reduction in weight on the front tyres.
  • Weight distribution hitches? Watch this.

Comment below with suggestions for this page.


  1. I own a Subaru Outback 2018 2.5i Premium and I’m trying to find out the GCM and when I contacted Subaru, they told me that the GCM for my vehicle is the GVM plus ATM. I didn’t think that was correct. Can you please help?

  2. The rear axle weight increase / front axle weight reduction apparently assumes the towball overhang behind the rear axle is half of the wheelbase (1.5 times towball load added to rear axle, 0.5 times subtracted from front axle). I appreciate that is a conservative approach as i gather few vehicles have a longer overhang than that, but given your brilliant graphic that shows so clearly what is happening, perhaps you could provide an option for those that know wheelbase and towball overhang to enter those distances and get more accurate vehicle axle weight changes. Either way, thanks for a useful tool


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