A Swedish automotive magazine suggested the Jeep Grand Cherokee is dangerous to drive and should be taken off the roads. Their statement is based on the Grand Cherokee lifting its wheels and coming close to rolling over at 39.5 MPH while maneuvering through the Moose Test, which is nothing more than a lane change. A video of the test.
For those who have attended our training program the Moose test is the lane change without having to make a decision. As a side note – students have driven through our Lane change at 50 to 55 MPH, make a lane decision, and get through it. Exciting – but get through it.
The Science of Driving
In my opinion what caused the Jeep to lift was a combination of the driver, the load in the vehicle, and tire pressures that could not handle the load. The fact is if you apply sufficient amount of energy to the CG of a vehicle, you can get any vehicle to lift, and roll. It’s the laws of physics. If you’re going to make a profound statement – like “take the vehicle of the road” you should back up it with a computer analysis of what the vehicle is doing. For very little money the producers of the video can purchase a G Meter that will tell them everything they need to know about what the vehicle is doing, including how much energy is placed on the CG, for how long, and where in the scenario was the maximum energy applied to the vehicle. If the magazine is too cheap to buy a G Meter, those characteristics can be computed by data collection and analysis. We do it in every school for every exercise for every run through the exercise.
For all those who use SUV’s as executive vehicles or for that matter all those who have a SUV as a personal vehicle there are some important safety issue that should be taken away from the Jeep Vs. Moose Test.
Just because a vehicle looks like it can carry a lot cargo and people does not mean that it can.
For SUV’s the vehicles payload is an important safety number, know what it is and do not exceed it.
I strongly recommend that the tire pressures are checked often – an overloaded vehicle, with low or even standard tire pressures will (not can – will) produce what you see in the video. Please do not take this lightly.
I am doing a forensic analyst of the “Moose Test” and will make it available to those that are interested (email me). There will be a lot of math involved, so it will come with a warning it can make your brain hurt.
Some definitions
Payload – The combined, maximum allowable weight of cargo, occupants and optional equipment that the vehicle is designed to carry.
Tire Pressure vs. Payload
SUV’S are much more sensitive to loading and tire pressure. Consult the vehicle manual for correct tire pressure and for the payload capacity. You will more than likely find that the tire pressure will vary in accordance to the load being carried. The payload is defined as- the combined, maximum allowable weight of cargo, occupants that the vehicle is designed to carry.
perhaps a cautionary example of ‘what can go wrong will’? the vehcile has an unherantly high cg to begin with, add speed times occupants weight, then throw the wheel?
what does one expect when defying the laws of physics?
Stewart – As you know, apply enough energy you can get any vehicle to lift wheels – if the magazine makes such a profound statement “take the car off the road” they must offer a better explanation than they did.
10-4.
(ps I gotta spell check more often)
Thanks for this article as I’m about to hire a Grand Cherokee when we come to the States at the weekend. I have driven top heavy vehicles in the past, namely semi armoured Range Rovers, which had bad handling characteristics. I agree with regular checking of tyre pressures and prefer a chunkier side wall than some of the low roiled options which look good but dot handle as well.
I wonder if anyone has tried using 100% Nitrogen in the tyres to help with handling, I have had my S197 Mustang converted and it’s really changed the car, the rear doesn’t spin out and the car feels totally planted. The tyre pressures remain constant and are not affected by temperature. It’s one of the best things I have done to any vehicle I have owned.
Keep up the great standard of articles.