GVM vs GCM vs TBM: Which Are You Most Likely To Exceed?

Exceeding your GVM, GCM or rear axle load is easier than you’d think.

Let me break it down.

Your large 20-21-foot van weighs about 2700 – 3000 kg tare, depending on options and build. (Some vans are a bit heavier while some are a bit lighter, but this is a good ballpark)

Before you tow it anywhere, you’ll fill it with:

  • 180-270 kg of water. Now you’re up to 2880 – 3270 kg.
  • 150-250 kg of personal gear. This is typically comprised of furniture, kitchen gear, food, clothes, bikes, laptops, chocks, jockey wheel, tools and other bits. Now you’re up to 3030 – 3520 kg.
  • 20-40 kg additional diesel. In jerry cans. Just in case. Hello, 3050 – 3560 kg.

Your tow ball mass (TBM) at this point is likely to be 250 – 350 kg. This tow ball weight is transmitted to the 4WD which, along with the car’s GCM limitation, makes it the source of your big 3 towing problems.

1. TBM Eats Into Your 4WD’s Payload.

Unfortunately, very few SUVs have enough payload capacity to carry a heavy TBM, two passengers and a decent amount of aftermarket equipment without exceeding GVM – unless they have a GVM upgrade.

For example, LC200’s GVM of 3350 kg and 2740 kg kerb weight leave it with 610kg of payload. Subtract 150kg for two passengers and 15kg for the tow hitch and you’re left with 445 kg. If your TBM is 350kg, you’re left with only 95 kg of payload before you hit GVM. That’s enough payload to fit a bull bar and winch, but not much else.

2. You Will Exceed Your 4WD’s Rear Axle Limit First.

Your TBM, which forms a huge part of your rear axle load, is much heavier than you think.

When you hook up your caravan, a proportion of your SUV’s weight shifts from your car’s front axle to the rear. In practical terms, it means that you need to add about 30% extra weight of the TBM itself when calculating your rear axle load.

A lot of people miss this “rear axle tax” in their calculations. This makes it very easy to exceed your rear axle load limit – before you exceed your GVM.

For example, the LC200 has a rear axle limit of 1950 kg. With a kerb of 2740 kg and assuming a 50/50 weight distribution across axles, it will exert a 1370kg load on the rear axle, empty – leaving you with 580 kg of wiggle room. Now, a 350 kg tow ball weight will place approximately 480 kg of weight on your rear axle, leaving you with just 100 kg. By the time you and your partner sit in the front two seats, almost all of that will be used up.

3. The 3,500 kg Towing Capacity Is Meaningless.

A lot of SUV manufacturers boast about the car’s ability to tow heavy weights.

A 3,500kg BTC, night and day, baby!

In most cases, that is all smoke and mirrors material. A lot of SUVs have a low GCM that will not allow them to carry more than just you alone in the car when towing 3,500 kg.

This occurs because their GCM is less than the sum of their GVM and max BTC.

The real question you need to be asking is – how much will your SUV be able to tow at, or near, GVM? The reason is, you’re very, very likely to be touring Australia near your GVM limit.

For example, Australia’s darling, the Toyota Hilux SR5, has a 3,500kg BTC. It also has a 5850kg GCM, which means that, with a 3,500kg caravan attached, this 4WD can’t weigh more than 2350kg. Yet, the “unbreakable” Hilux has a kerb weight of 2110kg, which means you can only add 240kg to the car before you hit GCM and possibly “break” it.

Flipping the question the other way gives you a much more helpful piece of insight.

How much will the SR5 tow at its GVM? In other words, how much will it tow when you fill it with you, your wife, kids and all the aftermarket gear, as well as the TBM? Well, the car’s GVM is 3050 kg, so we take GCM and deduct GVM to arrive at 2800 kg. For context, that is just above the unladen weight of most 21-foot Jaycos. An unladen 21-foot Kedron is about 3200 kg.

1 comment

Leave a comment

Your email address will not be published.