PacerX

".....maybe we can get someone with an engineering background like PacerX, etc., to give us a pros and cons of body on frame vs unibody construction?"

Welp, I'm a mechanical guy more than a structural guy, but I can give a couple of the advantages.

1) For any given total system stiffness required, a unibody can be made stiffer at any given weight, as long as the load requirements are not localized loads (which would cause buckling) and there is enough room to get a big enough section of material in there. Sectional stiffness goes up with the cube of the size of the section.

(***Engineering Explanation: As material is moved further away from the neutral bending axis, the stiffness of the section goes up as the cube of the distance moved.***)

2) A full frame is better for towing because the hitch itself is a near point load. The thin sections used in unibodies will tend to buckle locally, while the full frame can take the localized load much more easily.

3) Full frames (especially hydroformed sections) can use materials that in most cases cannot be stamped. High Strength, Low Alloy steels (HSLA'S) will be used in unibodies with increasing frequency, but a stamped 50,000 psi HSLA steel section is chump change compared to a 190,000 psi Inland M190 hydroformed steel section of equivalent size and thickness of material.

4) Full frames are generally less sensitive to corrosion (given equivalent protective processes such as galvanizing or e-coating). One bad joint in a unibody can cause a real mess structurally.


The really important point is #1. Unibody cars are inherently lighter than full frame vehicles for a given stiffness because they use thinner material in larger sections.

That being said, in many cases SUBFRAMES are used to take the load of very dense/heavy areas of the car - like the front subframe of the Camaros. The rest of the car is a unibody because it doesn't see the high localized loading due from the weight of the engine, transmission and front suspension.

The best of both worlds?

Possibly a stamped HSLA steel unibody structure with a front subframe manufactured from hydroformed ultra high strength steel. In this type of system plastic body panels such as those used on the Saturn cars can be used, or... even better yet... be integrated into the vehicle structure as additional load bearing members - like a monocoque race car.

Corvette is kind of a special case because it was designed as a convertible first - and couldn't take advantage of the "C" pillar hoop providing a lot of structure like most unibody cars can. Hence - the hydroformed rails.

quick

The problem with truck chassis is WEIGHT; a new Camaro needs less weight for better handling, braking, and, heh-heh, acceleration. Also, better mileage is a bonus, and as gas issues come to the fore, better mileage is a good thing. Less weight is like having your cake and eating it, too, for a performance car. Truck chassis are just too darn heavy! New Camaro--3200 lbs, max.

redzed

PacerX, I agree with your explanation of chassis engineering, but the theory behind it was too conventional. SUBFRAMES are an ideal way of distributing localized loads, but they do not contribute to overall structural rigidity. Subframes carry none of the torsional loads, and as such, and are really just dead weight.
If you compare a unit body, with subframes front and rear, to a body-on-frame setup, the weight penalty of traditional construction is negligable.

The most important aspect of separate chassis construction is manufacturing efficiency. Since the final mating of frame and body don't occur until the body sheel is nearly finished, there is the potential for tremendous savings. If you take the ultra-modern modular manufacturing technique that Chrysler uses in Brazil to the next level, you can dramatically reduce UAW labor input in the final assembly process. (Fewer $70-100/year autoworkers=cheaper cars.) I personally would like to see complete body shells and built-up chassis completely "outsourced" .

I guess I've never been convinced as to the outright superiority of the unitized body. While the material costs are lower, engineer and tooling expenses are far higher. Much like front wheel drive, unit construction makes more sense as you look at smaller, higher production cars.

Should the next Camaro be "based" on the chassis of the Trailblazer, much like the SSR? Perhaps GM should re-examine the engineering of the old full-framed A/G-body. The chassis of the 1978 Malibu wouldn't be a bad inspirational basis for the platform of a new V8 muscle car.

Z284ever

I'd say that the SSr's chassis and the one from the old A-body have more similarities than differences. And I would expect similarities in ride and handling.

Maybe such mechanicals would be an interesting starting point for a future RWD V8 muscle car.

....but not for Camaro.

PacerX

"PacerX, I agree with your explanation of chassis engineering, but the theory behind it was too conventional. SUBFRAMES are an ideal way of distributing localized loads, but they do not contribute to overall structural rigidity. Subframes carry none of the torsional loads, and as such, and are really just dead weight."


Well, structures aren't my thing professionally, I do mechanisms mostly, but I'm going to have to disagree with you in one area.

I think front subframes can be engineered to contribute to torsional resistance. The way to do it is to tie the front subframe to the unibody rails coming down the sills at the bottom, tie it to the front lower radiator support up frotn (that's usually a "hoop" of stamped sections that also support the front bumper), then tie it together across the strut towers AND finally tie it up top to the A pillar at the junction of the A pillar and the firewall.

If you look at the strut tower brace designs (specifically the three point braces that tie into the cowl) this is really what they are doing.

One other example are aftermarket subframes that are available for first generation Novas and Camaros - they both tie into the unibody the way I have described, minus the strut tower brace.

jg95z28

I want a swoopy design that still mantains styling cues carried on from generation to generation.

I want a high performance RWD V8, manual six, and a tougher rear axle. (Here's where they could use a "truck" part.)

I want a Z28 option, however leather, t-tops, and power windows, sound system would be extra.

Above all, make it cheap... no more than $20-25K for a base Z28. And under $30K fully loaded.

Z284ever

Would you really consider a future Camaro with a live rear axle?