Does a GVM upgrade affect axle weights?
QUESTION
Dear John,
Your recent articles on overloading vehicles has (unless I missed it) not touched on the unmentionable - maximum axle weights.
We had a 4WD single cab tray truck with a slide on camper. It had, of course, a GVM. The camper was a bit heavy so we had an upgrade for the suspension engineered to increase the GVM.
But, the owner’s manual specified maximum axle loads. The problem was that hitting the GVM, let alone the upgraded figure, put us over the rear axle weight limit.
Part of the problem is that, say, 100kgs added behind the rear axle adds more to the axle than 100kgs. It shifts some front axle weight to the rear.
Try your numbers on a dual cab tray truck with one of those off-road super dooper canopy bodies and rear-mounted spare tyres, and see how adequate the rear axle is. Does it meet the axle limit, even if not being over the GVM?
Sincerely,
Graeme
HOW WEIGHT AFFECTS YOUR VEHICLE
4WD dual-cab utes and the 'bent chassis' problem: The Truth >>
My AutoExpert AFFORDABLE ROADSIDE ASSISTANCE PACKAGE
If you’re sick of paying through the neck for roadside assistance I’ve teamed up with 24/7 to offer AutoExpert readers nationwide roadside assistance from just $69 annually, plus there’s NO JOINING FEE
Full details here >>
ANSWER
Graeme,
Engineer here: You’ve explaining to me, below, how altering the loads on a beam affects the way those loads are resolved by the supports. It’s a little ironic, don’t you think? (Seeing as I kinda studied that, in all of its different flavours, for six years, at university…)
GVM upgrades are a disgraceful joke because the chassis is the weak link, and a GVM upgrade does not strengthen the chassis - it makes the chassis even more susceptible to catastrophic failure.
Obviously increased cantilevered loads significantly increase the burden on the rear axle. (Axle load specifications are there so you don’t break the chassis.)
This whole ’the camper was a bit heavy’ thing is completely unacceptable in my view. What you mean is really that you took the decision to drive the vehicle dangerously overloaded. This cannot be interpreted any other way.
The suspension is not the problem in this situation - therefore changing the suspension does not fix the problem or eliminate the risk to you or the public. It is, however, a great way to risk your life while voiding the warranty and also your insurance.
I know this is not what you want to hear. I blame facts generally, for being so inconvenient.
Sincerely,
JC
MODIFYING YOUR VEHICLE TO CARRY MORE WEIGHT
Should I fit my 4WD with stiffer suspension for towing? >>
Are GVM upgrades a good idea? >>
Modifying 4X4 dual-cab utes for remote adventuring >>
QUICK LINKS FOR TOWING RESOURCES
How to do heavy towing: A dummy’s guide hitching up >>
My Complete Heavy Towing Guide: GVM, ATM, towballs >>
How to bend your ute: Triton chassis-snapping truths >>
Load levelling and weight distribution hitches: Know this >>
LIVESTREAMS
Don't forget to join me for my 'Ask Me Anything' Q&A livestreams on YouTube (Sydney time).
Subscribe to my YouTube channel and hit the bell icon to get an alert you every time I go live.
More reports
Mazda’s CX-70 is a large five-seat SUV with generous legroom, loads of equipment and a supremely comfortable ride. It’s one of four new additions to the brand’s prestige model onslaught, but for a fraction the price of a premium German SUV.