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Death of the body-on-frame SUV?



  • Just commenting on the idea of driving a second car for the daily commute and then having an Expedition (or other) for when it's needed. I tried this for about two years and gave up. Yes, the cost of insurance alone on the second car is more than the extra gas of driving a large SUV every day but the bigger issue for me is that I had to plan my days around what vehicle I had. Finally I just admitted defeat. With two dogs and two kids and bikes and skis and all the rest I'm impressed and jealous of anyone in a similar situation who is efficient enough to survive with a small SUV / sedan.
  • bobw3bobw3 Posts: 2,997
    Since you probably put the skis & bikes on the roof and the dogs behind the 2nd row, you could get something smaller like a Subaru Forester and fit what you're talking about.
  • sddoc07sddoc07 Posts: 19
    I had no idea that so many people would contribute to this topic - thank you for your thoughts!

    Bobw3 - I totally empathize with your points on safety of BOF SUVs. My dad, a Suburban disciple, has driven one since 1988 and has had a number of serious crashes (mostly not his fault =)) that he has walked away from with not so much as a headache. In contrast, the cars that run into Suburbans look devastated. That being said, he doesn't drive the thing like a racecar and when people do, they tend to flip.

    I have a question for everyone - why is GM so ancient with its refusal for rear IRS and thus non-rear folding seats? Is there an advantage to their solid rear axles?
  • boxtrooperboxtrooper Posts: 843
    solid rear axles have been the most efficient drive, independent axles take more gear changes and each change is a loss.
  • bobw3bobw3 Posts: 2,997
    My dad, a Suburban disciple, has driven one since 1988 and has had a number of serious crashes (mostly not his fault =)) that he has walked away from with not so much as a headache. In contrast, the cars that run into Suburbans look devastated.

    No offense, but I wouldn't want to be driving anywhere near your dad on the road, especially after the comment, "mostly not his fault" I wonder how many accidents he could have avoided if he wasn't driving such a big vehicle?
  • dificadifica Posts: 9
    Well, there has obviously been a lot of new unibody crossover SUV's coming lately, and obviously those are the choice who want to use an SUV for just commuting and running errands.

    But for those people who really use BOF SUV's off-road and towing abilities, it's just basically a crew cab pickup with a bit shorter bed and a bed cover as standard, and if they weren't available, they'd be using those, but SUV's are simply more user friendly with their one pull opening rear hatches and various other small things, such as the slightly smaller size (crew cabs are hugely long) and the more luxurious interiors of many SUV's compared to pickups.

    If i were to buy a towing vehicle now, i'd go for a regular cab pickup (live alone, no need for four doors), but as a combined family and recreational towing and off-road vehicle (i doubt too many SUV's are used in only work conditions, companies apparently tend to use pickups), there aren't many options.

    So, the BOF SUV isn't going anywhere in a long time.
  • explorerx4explorerx4 Central CTPosts: 9,614
    rwd. jeep grand cherokees are unibody plus rwd. not sure how many others.
  • I am the exact opposite....I did away with the small car for the SUV because I was run over. My Subaru Legacy was totalled last June because a Dodge 2500 truck ran a red light and nearly T-boned me (hit just in front of the passenger door). I felt like I was on the end of a whip. I still have effects from that wreck. No question about what to buy to replace the Subaru. I'm in an Expedition now.
  • explorerx4explorerx4 Central CTPosts: 9,614
    off road capability and towing capacity.
    for a while bof rwd suv's were better than the alternatives, for many people.
    the circumstances have changed.
  • steverstever YooperlandPosts: 40,013
    SUVs and trucks? BOF ones?

    Isuzu Buying Alabama Land for Plant (Auto Observer)

    Need help navigating? - or send a private message by clicking on my name.

  • paisanpaisan Posts: 21,181
    Interesting. I haven't heard anything from the Isuzu camps on new trucks. We shall see!

  • boxtrooperboxtrooper Posts: 843
    Thank you for that post, I would very much like a diesel Trooper with the increased mpg.
  • sagalibasagaliba Posts: 31
    BOF SUVs are not less saf than unibody. They tend to be heavier though.
  • bammbamm65bammbamm65 Posts: 2
    i think you are misrepresenting a given fact while unibody suv's have more crumple zones this only helps the other veh inwhich you are involved with. as the crumple zones absorbe more energy. however framed suv's survive much better than the rest and i think that is something alot of people are looking at when it comes to safety.
  • paisanpaisan Posts: 21,181
    Well yes the framed vehicles themselves survive better, however I'm pretty sure that the impact is transfered to the occupants more in framed vehicles than non-framed as a general rule of thumb. With large trucks however there are still crumple zones and thus still safe.

    Interesting thing happened over the weekend at a road race my team was involved in. Our car weighs 3100lbs and a competitor driving a 1700lb car tried to knock us off the road course in a turn, unfortunately for him he bounced off our car and spun off the track, we continued on w/o issue. So weight does play a factor.

    I also don't see the frame on SUV going away, they are quite useful in towing and hauling applications.

  • jim314jim314 Posts: 491
    A BOF vehicle is more rigid than a unibody vehicle. In the parlance of the "crash research" community, a BOF vehicle is stiffer. A unibody vehicle has a deeper and more controlled crumple zone and gives more in a crash. If the intergity of the passenger compartment is not compromised, a unibody vehicle protects its occupants better than a BOF because the unibody vehicle spreads out the crash forces in time and reduces the peak crash accelerations experienced by the occupants.

    But here's what is not sometimes understood: the less stiff vehicle protects both its own occupants and the occupants of any vehicle it crashes into.

    In a head-on crash between a BOF and a unibody, the crumple zone in the unibody reduces the peak crash forces experienced by the occupants of both vehicles. This is the case because in a two-vehicle crash the vehicles exert equal but opposite forces on each other. This is one of Newton's laws relating force and motion.

    The forces are always equal in magnitude, but if one of the vehicles is more massive than the other, the effect of the forces on the vehicles will be different. Remember that F = m a, so a = F/m. That is, the crash acceleration of the lighter vehicle will be greater than that of the heavier vehicle because the F is the same for both vehicles, but m is different, and this is in the denominator.

    The injury to the occupants of a vehicle is strongly related to the peak crash acceleration that the vehicle experiences.

    Consider a head-on crash between two Suburbans, identical except that one is red and one blue. Each is travelling at 30 mph relative to the ground. High and identical peak crash forces are transmitted to the occupants of the two vehicles

    Now consider the same crash except that a serious but lightweight engineered crush zone 4 ft in depth has been attached to the front of the red Suburban. That is, the two Sururbans are still the same mass. The result will be lower peak crash accelerations to both vehicles.

    The crumple zone strapped to the red Suburban has protected equal benefit to the occupants of the blue one.

    If both vehicles had had the same 4-ft crumple zone, then the peak crash accelerations would be even less because there would be a total of 8-ft of crumple zone. If each vehicle had had the same design 2-ft crumple zone it would be the same as either one having a 4-ft crumple zone.
  • sagalibasagaliba Posts: 31
    BOF and crumple zone are not mutually exclusive. Framed vehicles can have crumple zone built in them as well. In fact, the concept of the crumple zone is often combined with providing a more rigid structure encompassing the passenger space. Mercedes has been using crumple zone technology since the late '50s.
  • jim314jim314 Posts: 491
    Within the limits of what people can afford, every attempt should be made, and presumably is made by the manufacturers, to make the passenger compartment as rigid as possible. You don't want the passenger compartment to deform, nor do you want anthing to "intrude" into the passenger compartment. Clearly intrusions are potentially extremely injurious. It seems to me that both BOF and unibody designs could have equally rigid and strong passenger compartments.

    But it also seems to me that a unibody would be less stiff than a BOF design outside the passenger compartment and so would protect from the other source of crash injury to vehicle occupants--the high peak g-forces of the passenger compartment due to the sudden change in velocity (the "delta-V") that occurs in a collision.

    I personally am attracted to the idea of a body-on-frame design because I drive conservatively and I "don't think" I'll be in a crash. I am sure that I must underestimate my risk. I value strength and durability in a vehicle. At my age, early 60s, I enjoy imagining that the car I'm driving (2004 base V70) will be the last car I'll buy.

    My ideal vehicle would be a BOF "minivanoid" with relatively high seating position (comfortable leg angle), 3000-lb curb weight, powered by a small gas or diesel engine (120 hp max) and a 6-spd manual. It would be rated to tow up to 2000 lb. It would have a variable height suspension to get best fuel economy on pavement, but be able to go on rough roads when necessary.

    But when I awaken from my dreaming I find that in the real world a unibody design will best protect me from crash injury at a price I can afford.
  • sagalibasagaliba Posts: 31
    >> But it also seems to me that a unibody would be less stiff than a BOF design outside the passenger compartment

    Less stiff does not necessarily translate into better crumple zones. On BOF vehicles, crumple zones are strategically placed in front and rear portion of the frame (often appear as tiny waves), so that when enough force is applied (i.e., when vehicle is hit hard), the frame will bend at certain points, and in certain directions. In other words, the way it "crumples" is controlled, and not by relying on the random way the metal may fold.
  • coldcrankercoldcranker Posts: 877
    I'm hearing a lot of misunderstanding on this forum. Maybe some actual crash pictures of a BOF will help, compared to a unibody crash.

    First, note how in these pictures BOF Example -- click on this..., the frame is low, and is still extending out, and has actually penetrated the barrier, representing another car. This is because the frame, with engine/suspension mounts is very stiff and tough, and will skewer the occupants of other, lower vehicles if the BOF hits on a door. Very dangerous. What Ford has done on the above late-model F-150 is to secure the cab to the very tough frame to keep it from collapsing, although the protruding frame doesn't make a great "crumple" zone at all.

    Now compare that to Unit body crash click here... where the front end is much flatter, with no protruding tough frame to stick out and through the barrier.

    Conclusions: The frames on pickup trucks and SUVs protrude and can enter a unibody structure. The frames are very stiff and don't collapse much when hitting a unibody vehicle.
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