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PostPosted: Fri Mar 07, 2008 8:33 pm 
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AHTOXA wrote:
Really, if the BOF was more prone to twisting, would the offroad community use it as much as they do?

yes. because IF it does flex enough to be permanently deformed (im not talking like bucked over on itself, just a little crooked), its not severely detrimental to the cosmetic appearance, driveabilty, usability, or safety of the vehicle.

now if you offroad in a unibody car and there is enough stress to permanently deform the unibody, then it IS severely detrimental. doors wont line up, body panels will ripple, etc etc. and at that point the car might as well be totaled because the structural integrity will be severely compromised.

BOF gives you a higher margin of error before the car is totally trashed.

and im not saying BOF is like a limp noodle or something. its stiff, but unibody is stiffer.

in other words, a BOF is more durable and has a higher 'margin of error' in terms of flexing. a unibody is stiff, but unforgiving.

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PostPosted: Fri Mar 07, 2008 9:15 pm 
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Spaceframe > all.

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PostPosted: Fri Mar 07, 2008 11:03 pm 
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Steel can be flexed a fair amount and keep 100% of strength, think leaf springs and such.

I think some folks use this property of steel to their advantage with an off-road body-on-frame vehicle. Gives a little more real-world suspension travel, ie keeps as many wheels on the ground as possible.

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PostPosted: Fri Mar 14, 2008 9:44 pm 
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Interesting thread. I'm a little late on this but here is a unibody:

Image

note that some body panels, i.e. front quarter panels, hood, are not stressed members of the chassis, thus, for example, you might see people occasionally driving without a "front clip," and the car does not fall apart. note that the a, b , c etc. pillars are all stressed members of the chassis, different from body on frame. also note the steel box frame cross members integrated into the chassis. It should be apparent modern steel unibody construction is quite advanced, I'd take a modern unibody over body on frame anyday.

I don't see how the fiero in the pic is a true space frame. The fiero chassis is similar to the one above. Below is a true spaceframe:

Image

note the use of tubuar steel in contrast to folded sheetmetal.

In terms of chassis in racing, spaceframes and unibodies are common. Spaceframes are used in NASCAR, sprints and midgets, and until the 70's and 80's, common in formula cars. Since the 70's, unibodies have taken over formula car racing, although not metal unibodies, like most street cars, but composite unibodies, mostly constructed of carbon fiber/kevlar sandwiched over a foam/aluminum honeycomb core. Modern formula car chassis construction is quite interesting, with a composite "tub" comprising the front half of the car where the driver sits, the engine bolted directly behind that and the gearbox behind that, both stressed members of the chassis, and the rear suspension basically bolted on to the gearbox. I think the only place you'll ever see a traditional body on frame racing is pure stock/sportsman class at your local short track.

composite unibodies are expensive and rarely used in street cars besides exotics. Lotus once designed a fiberglass unibody car. Now thats one unibody I'd be scared to drive!

we haven't talked about backbone chassis (a variant of the body on frame I'd say).


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PostPosted: Sat Mar 15, 2008 2:51 pm 
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Standardshifter wrote:
Steel can be flexed a fair amount and keep 100% of strength, think leaf springs and such.

I think some folks use this property of steel to their advantage with an off-road body-on-frame vehicle. Gives a little more real-world suspension travel, ie keeps as many wheels on the ground as possible.


BOF on unibody have little to no affect on how suspension performs.

Suspension for offroad vehicles is a whole different ball game in itself.

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PostPosted: Sat Mar 15, 2008 3:01 pm 
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VTECaddict wrote:
AHTOXA wrote:
Really, if the BOF was more prone to twisting, would the offroad community use it as much as they do?



BOF gives you a higher margin of error before the car is totally trashed.

and im not saying BOF is like a limp noodle or something. its stiff, but unibody is stiffer.

in other words, a BOF is more durable and has a higher 'margin of error' in terms of flexing. a unibody is stiff, but unforgiving.


Not quite. Have you ever ridden in a BOF vehicle? Compare the ride to a unibody. BOF is very unforgiving on bumps. It's got less of a margin for bending and flexing, thus not absorbing the bums as well as a unibody car.

Unibody is more flexible, less stiff and more absorbing. Thus unibody SUVs are more popular than BOF SUVs, simply because unibody rides better.

The stiffer something is, when it comes to a vehicle's suspension or body design, the harsher it will ride.

BOF is very stiff and durable, but it trades off ride comfort on the road. Meanwhile the unibody gives you more comfort but it's by far not as durable as BOF.

My suggestion: google BOF vs unibody and you'll see multiple articles that back up my point of view.


You're saying that BOF gives a greater margin of flex before structural damage occurs, however this is not the case. I've seen people bend unibody SUVs (cherokee) offroad while BOF vehicles never flexed as much and got away unscathed.

So if the BOF twisted less and never deformed while unibody deformed given the same conditions, how come you say that unibody is stiffer? It does not make sense... I see your point that everything flexes, sure, however unibody was simply never designed to flex in a condition such as taking the vehicle offroad, that is all. It's like taking a knife against a machine gun in a fight, you know?

Bottom line: Unibody is for road use with advantages like improved crumple zones, quieter ride, safer with lower center of gravity and so on. BOF is more rugged, more durable, more solid/rigid foundation designed for hard use in pick-ups and offroad vehicles. It trades off conford and some safety for the durability and stiffness needed in extreme cituations.

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PostPosted: Sat Mar 15, 2008 4:56 pm 
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ra64t wrote:
Interesting thread. I'm a little late on this but here is a unibody:

I don't see how the fiero in the pic is a true space frame. The fiero chassis is similar to the one above. Below is a true spaceframe:

Image

note the use of tubuar steel in contrast to folded sheetmetal.

In terms of chassis in racing, spaceframes and unibodies are common. Spaceframes are used in NASCAR, sprints and midgets, and until the 70's and 80's, common in formula cars. Since the 70's, unibodies have taken over formula car racing, although not metal unibodies, like most street cars, but composite unibodies, mostly constructed of carbon fiber/kevlar sandwiched over a foam/aluminum honeycomb core. Modern formula car chassis construction is quite interesting, with a composite "tub" comprising the front half of the car where the driver sits, the engine bolted directly behind that and the gearbox behind that, both stressed members of the chassis, and the rear suspension basically bolted on to the gearbox. I think the only place you'll ever see a traditional body on frame racing is pure stock/sportsman class at your local short track.

composite unibodies are expensive and rarely used in street cars besides exotics. Lotus once designed a fiberglass unibody car. Now thats one unibody I'd be scared to drive!

we haven't talked about backbone chassis (a variant of the body on frame I'd say).


There's a difference between a tubular spaceframe like used in that race car in your picture, and the spaceframe used in the Fiero.

The picture you have of that unibody SUV is not a true unibody. In a true unibody, the entire body is 1 with the frame. If you look there, there are some pieces missing, like fenders and stuff. My Camaro was like that, it was a weird unibody hybrid, so some panels were plastic like my Fiero, but the main part of the body was the steel frame. They've been doing that with cars since the 80's and 90's because the plastic panels don't dent. On my Camaro though, the sides of the car were metal, and dented easily, so I don't see the point in what they did.

In my Fiero though the frame is completely separate from the body. It is a spaceframe, and its one of the only mass-produced cars to have a spaceframe. In any unibody the frame can be seen as the outer sheetmetal, on my car there are like 10-20 different plastic body panels that make up the exterior of the car.

Saturns up until a couple years ago were built with the same technology. The people who designed the Fiero in the early 80's went on to work with Saturn in 1985. They were slightly different though, my Dad has a '96 Saturn SL2 and its a spaceframe with plastic bodypanels like my car. The only difference is they used steel panels for the roof, hood, and top of the trunk.


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PostPosted: Sat Mar 15, 2008 7:26 pm 
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^^it depends on to you intepret things I guess. By strict definitions, a unibody is just a type of spaceframe, and almost no cars are true unibodies, but all hybrids; very few cars, for example have the front quarter panels as stressed members.


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