Comment 5724

By the_experience03 (anonymous) | Posted March 04, 2007 at 08:26:05

I have mixed feelings about this article. I will agree with the fact that there are WAY too many body on frame based SUVs and trucks on the road today. However, they do have their place.

Nevermind the logistics of who should and shouldn't be driving a truck or SUV. I'd like to address some of the physics.

The frame:
Please do not confuse rigidity with strength. In terms of all out raw handling, a properly braced unibody vehicle will do better in fast corners on a road track. However, even many of these flex. Don't believe me? Just look at all the ads for subframe connectors and strut tower braces. Theys are to help with that torsional rigidity you claimed unibody vehicles inherently have. The ultimate in torsional rigidity actually comes from a tube frame such as that which a race car has. It also offers amazing driver protection.

So then...where does that leave the full frame? Simply put, to bend is better than to break. Watch a semi the next time you are at a stoplight next to one. When they let off the clutch in first gear you will see the whole frame twist. The front left tire will unload tremendously. This is due to the incredible torque. Pickups are no different with amounts of torque not seen in smaller vehicles. The current Duramax diesel makes over 650 ft lbs of torque. Show me a common unibody vehicle that deals with those kinds of forces without ripping apart.

The frame gives a solid mount to mount items such as the suspension and hitches to. Unibodies get scary in the engineering department when it comes to this.

The unibody SUV and truck is nothing new. The Jeep XJ Cherokee, MJ Pickup, ZJ Grand Cherokee, WJ Grand Cherokee, WK Grand Cherokee, and KJ Liberty all are unibody. I am an avid offroader and many of the people in my club have the XJ Cherokees as they are affordable and capable. However, an XJ is the only vehicle I have ever see pop its windshield out on a trail. The reason? All vehicles have some degree of body flex. In a body on frame vehicle, this is taken up by the body mount bushings such that the body is relatively unaffected by frame torsion. This is not the case on the unibody vehicle where the A, B, and C pillars which support the windows also serve a role in preventing vehicle torsion.

The suspension:
Short-Long arm independent suspension is king of the road course. However, it is flawed when it comes to hauling a large load. The same properties of SLA suspensions, that is changing camber with varying load, that makes it reign supreme at speed on sharp corners is what makes it unsafe in a towing or hauling application. As the camber changes, the load is shifted more to the sidewalls of the tires. This will happen when a load squats the rear of the truck. This is where live axles reign supreme. A load will squat the suspension, but save for some sidewall flex (which the SLA IRS will also suffer from), the contact patch remains the same.

Leafsprings will be king of the towing-hauling world as long as air ride is prohibitively expensive in small vehicles. Air ride has its own set of disadvantages which I will not get into in this post. Leafsprings are predictable, simple, inexpensive, and provide one thing your beloved coil springs cannot offer; controlled down travel. What I mean by this is that leafsprings have a neutral point. It will take a certain amount of force to bend them up or down. Coil springs also have this property, but are not mounted such that they can take advantage of it. If you start to get body roll with coils, you're done. If you get body roll with leafsprings, the inside spring will unload and will require a force to continue flexing past its neutral point. This force is exactly opposite of that which is causing the body roll in the first place and as such they will neutralize each other. This is not a bunch of mumbo jumbo, but rather proven offroad physics. I would direct you to search for competition rock crawlers mounting Fox Air Shox. Most often they will have the Air Shox in the rear for the suspension travel will having leaf springs in the front to control body dynamics (i.e. not flopping on the roof).

Live axles also have the advantages of being stupidly simple. They suffer less from parasitic loses when compared to an IRS setup. They are also well suited to large loading with bearing designs being easy, size requirements for flex resistance being easy, etc. Again, the proof can be seen in the fact that semis and trains both use live axles. An IRS designed to take the load of a 10.5 inch AAM 14 bolt full floating rear axle (1973-2000 GM 3/4 and 1-ton trucks) would be incredibly large and heavy. Compare the front end of a 1994-2008 Chevy 1-ton (IFS) to that of a Honda Civic and you'd be amazed. Even more amazing is that the front end GAWR is far FAR less than the GAWR of the rear axle. It is impractical to independently spring these vehicles.

I could go on for a long long time, but what it all boils down to is that you have an issue with the people who own and operate SUVs and trucks that do not belong in one and I can agree with you wholeheartedly. A Ford Windstart will seat 8 comfortable, gets great mileage, can be had with AWD, is incredibly safe etc. These are the reasons soccer moms buy SUVs when their needs could easily and more properly be satisfied with another vehicle.

However, your article attacks the engineering of the trucks and SUVS themselves. They are not flawed. They are built for a purpose. You are mismatching the vehicle and the purpose. Would it be fair of me to write an article about how terrible my Honda Civic is at towing an 18.5 foot boat? Of course not. The designed use of the vehicle must be matched to the actual use of the vehicle.

Basically, I'd just like to recommend that you write a post about the horrors of people buying the wrong vehicle rather than criticizing the vehicle itself for being purchased by these people.

For the record, I own a body-on-frame truck AND a Honda Civic so I feel as though my opinion can be taken at face value. I do not care to be accused of being one of those truck driven' young redneck males, even if I am one.

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