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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.

Comment(12)

  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

  3. Hi Robert
    Excellent advice, excellent towweights calculator – I just plugged in my numbers which I knew to be near the compliance limits (under Evernew heading) – but was pretty sure they were generally Ok and yr info confirmed. However………yr calculator does not specifically seek to address rear axle ratings compliance – unless I missed something (I know your calculator results did mentioned rear axle load @ +495kg)……& it seems to me (with the numbers I’ve done on a few cars now ) that rear axle rating non compliance is proving to be a very big stumbling block if you want to pull a heavy van.

    eg landcrusier 200 series – rear axle rating 1950….but by my calcs, my rear axle load is 1986 ! – using a rear axle load factor of 150 (1300/2850* 330 tbm……on a van atm of 3300 )) results in a rear axle load of 330 +150= 480. (Yr calculator indicated a rear axle load with my numbers of 495 so it either used a higher tbm or slightly different rear axle to hitch & wheelbase dimensions…but it doesnt matter anyway). Both numbers result in rear axle rating non compliance (ie 3012 total car weight/2 = 1506 + 480 = 1986 or 1506 + yr number of 495 = 2001.
    V interested in yr thoughts. Cheers Ron

    1. I may add rear axle loads to a future version, for the moment if you take the TBM and x 1.5 that’ll be close enough with a little safety margin. You have the correct formula there (WB/overhang) but also allow for hitch length which varies. 4X4 wheelbase is typically 3m or so, overhang around 1.4-1.6 so it works quite well.

  4. Thks- understand now where your rear axle load number comes from. Can I make a final comment. As u know, vastly better than I, there is mass confusion “out there” re car/van weights. In all this confusion, rear axle ratings almost dont rate a mention & the v great majority of non car enthusiasts would not give it a thought! (I fit this category and only stumbled across this issue after hours and hours of reading stuff ……& finally a lot of help from you (yr excellent “Example tow weights” video should be mandatory reading for anyone pulling a van). Anyway my key point is this – the REAR AXLE RATING for the cars most favoured to pull a heavy van (ie one over 3000kgs) becomes perhaps THE MOST CRITICAL FACTOR to evaluate for legal compliance . Two examples (1) Toyota 200 series car with a payload of just 250 kg (eg 2 people = 150kg + 100kg allowance for absolutely everything else ie not that much!) cannot pull a van with an ATM of 3200 or greater without failing toyota’s rear axle rating. (2 ) RAM 1500 Laramie -an even worse example…notwithstanding its longer wheelbase. It has a rear axle rating of only 1770kg (& a kerb mass of 2650) Allowing for a payload of just 150 kg (ie 2 people in the car AND NOTHING ELSE!) it cannot pull a van with an ATM of 2800 kg or heavier without failing its rear axle rating. (My maths for the Laramie is as follows – rear axke load factor 1300/3569 = 0.364 with a tbm of 280 =102 + 280 = rear axle weight due to van download of 382. 382+1400 (2800/2) = 1782kg . Rating 1770).
    I’m just shocked with these outcomes- given the marketing associated with these cars. Am I missing something or over-reacting? Cheers Ron.

    1. no, you’re not missing anything. I was the first journalist to alert people to the 3500kg tow issue, now I’m presently alone on rear axle loads. But I have plans to make a noise…it is a problem!!!

  5. Robert.
    On “% of weight on rear axle”.
    Is there any way to calculate this based just on vehicle specifications? For example, Everest Trend front axle 1480 rear 1750 with a GVM of 3100, can I take an approximate ratio of 1750/GVM or 1750/(1480+1750)?
    How could I determine the ratio without buying the van first?

    1. No accurate way other than a weighbridge or ask owners to record their weights. Usually 4X4s are around 50/50 front/rear. The greater rear axle load doesn’t indicate more weight on the rear axle, it is so the back can be loaded more than the front eg when towing.

  6. I think your Margin to GCM may be incorrect as it calculates using GVM + ATM to get the GCM

    RACQ, Without a Hitch and many others, calculate GCM as:
    GTM = ATM – tow ball mass
    GCM = GTM + GVM

  7. Thank you Robert for the many videos etc that I have viewed. I was led to your calculator and I have questions about the towing legality of a 2015 Colorado 7 (which I have used since new to tow a Traveller Caravan over 40,000 kms).
    Entering details for 1) Colorado 7 with just the driver as payload 2) a much lighter caravan than mine (1500kg) into your calculator flags a rear axle overload of 42kg @ 60% weight on axle. By changing it to 58% it just becomes acceptable. Surely the Colorado 7 is not limited to 1500 kg as my van is much heavier. I am happy to email the document I created from your calculator, so that you can highlight where I am making an data entry error. Much appreciated (happy to speak on the phone too 0422206854)

    1. The rear axle load is a function of the TBM, not the total trailer weight. The Colorado can tow much more than 1500kg, but you may find the rear axle load is exceeded early.

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