Jason

GM was the first company to hydroform an entire side rail in mass production. Was pretty revolutionary stuff, in 1995. Now almost all their trucks (and the few cars with real frames) are made that way.

mgarfias

I think you missed John's point. Namely that while the frame rails are hydroformed, the chassis is still welded together. The rails aren't the entire chassis, they're just part of it.

The hydroformed rails don't give the chassis its stiffness, thats don't to make production costs cheaper. Its the chassis' stamped sheet steel backbone that is welded together and into the frame rails that gives it the stiffness.

davidfarmer

I think the hydroformed rails increase stiffness, NOT because they are hydroformed, but becuase they are enclosed all the way around (unlike many older C-shaped frame rails). Hydroforming gives you the opportunity to have a completely tubular frame-rail and still make it in one piece.

I think the front and rear subframes, the steel tunnel, and b-pillar hoop all add to the overall stiffness.

mgarfias

But David, there is no difference between a hydroformed rail, and a rail that is built from boxed steel that has been cut and welded together (and heat treated afterwards).

I do agree with you re: boxed vs C shaped rails though.

davidfarmer

I don't disagree with you, but I think it would be hard to weld boxed steel that thin, and do as good a job. This is why repairs are always sleeved, not butt-welded. I personally find the frames impressive, although there are plenty of good unibody cars out there too!


Just looking around at several sites, they all state that the advantages are the use of thinner material, less total material, and less corrosion (around weld sites) as advantages of Hydroforming. Also, one site states that the parts are "cold worked" which increases stiffness even more. I don't think they are heat treated......

We are way off topic.... I know the C5/C6 chassis is very stiff, very strong, and a great foundation!

drivinhard

one of the GM pieces I read stated that the C6 tubs (once bonded to the frame) contributed to some of the additional stiffness the C6 has over the C5.

johninar

The Hydroformed rail is stronger because of uniform thickness in the bends. Something that traditional bending could not do.

John Shiels

Lighter frame also.

vettehardt

The hydroformed side rails do make the car stiffer than a car with a welded toghether frame. That is why the C5/C6 do not need a cross member to add stiffnes for convertibles like the C4s did. GM designed the frame rails to be stiff enough to allow the convertible not to flex.

The frame rails are definatly lighter than a C4. In the C4s there were upwards of 27 pieces welded together to form the side rail. Just think how much difference there was between two rails. Now with the hydroforming, there is only one piece with no welds. Now every piece can be exactly like the next. The pictue below shows the process from a straight tube on the right to the final product on the left. First its bent in a general shape to fit in the die. Then it is formed by blowing up the tube with water 7000psi. Lastly the excessis cut off and holes are drilled where needed.



In 2001 I wrote a paper for a class a Purdue. It is titled Hydroforming in the Automobile Frame Market. The class was a machining class in my mechanical engineerign technology studies. I wrote the paper on how the hydroforming specifically affects the build and performance of the car. I have provided a link below if anybody is interested in reading it.

http://www.4shared.com/document/9RDZ...utomobile.html

vettehardt

By the way, My dad and I have been jacking our cars up with one jack for ages. He has a 90ZR1 and I have a 76 and 73. The Z we use the front jacking point to lift both front and rear to change tires. On my cars I can jack on the frame just infont of the tranny crossmember to get an even lift of both tires.

When my dad buys a C5 Z06 this summer, we will be doing the same thing.

Bill Dearborn

I have been jacking Corvettes from one side with one jack for 35+ years. Never had a problem. The 69 Roadster and the 86 Coupe were the most flexible whereas I could get three wheels off the ground on my 71 Coupe, 97 Coupe, 03Z, and 08Z. The C5 and up chassis is the stiffest. Just jacking the car from one side at the front shipping slot will get both front wheels off the ground with little difference in height.

Bill

USA1C5

I jack up one side from the rear puck point all the time on my C5 and my C6Z06. No problems. I also used to jack up my old C3 from the rear jacking point to lift both tires on one side and I don't think it was as stiff a frame as the newer cars. No problems with any of this.