Tell me about this.
Let's say strictly rhetorically speaking, i have a chassis with 300k miles. Everything mechanical has been replaced. Bushings, suspension, motor, blah blah blah.
I'm offered a chassis with 10k miles. Besides the fact that it's likely going to LOOK better, would the advantage of a low miles/low stress "Fresh" chassis be worth the work of tearing down two cars?
What kind of chassis ?
BG.
In this particular case, there's other "end game" advantages, but "chassis freshness" or "chassis fatigue" is what i'm focusing on at the moment.
Metal fatigues. No matter how freshened a 300k chassis is, it's not going to be as stiff as a 10k chassis. Think of it like a spoon. Bend one a dozen times, and put it back. Then don't bend one. Both will certainly shovel cereal into your face, but the bended one is more likely to E36 M3 out when you go for the rocky road.
That's kindof what i'm thinking. And in a class that has pretty stupid bracing rules, a chassis that hasn't been fatigued to hell in back could pay dividends in feel, and potentially speed, yes?
I ask because i seem to remember a similar thread concerning Miatas in which it was almost a 50/50 split of "it matters" vs. "it doesn't matter."
If it were a racecar, I'd definitely suggest doing the work. For a daily driver, I'd think that's quite a bit of work for not much benefit. Anyone that says it doesn't matter knows nothing about metal fatigue. It matters a bunch.
Swank Force One wrote: That's kindof what i'm thinking. And in a class that has pretty stupid bracing rules, a chassis that hasn't been fatigued to hell in back could pay dividends in feel, and potentially speed, yes? I ask because i seem to remember a similar thread concerning Miatas in which it was almost a 50/50 split of "it matters" vs. "it doesn't matter."
That's just it, you want to give yourself every advantage possible. And if you're not allowed chassis bracing, you need as fresh a chassis as possible. Even if you ARE allowed chassis bracing, you want as fresh a chassis as possible.
When is flex not such a bad thing?
Mark Donohue wrote that he preferred to drive a 911 Targa around the track than a coupe, because it had more flex.
Maroon92 wrote: When is flex not such a bad thing? Mark Donohue wrote that he preferred to drive a 911 Targa around the track than a coupe, because it had more flex.
I can see a road course wanting some flex, but not auto-x... which I'm guessing he's after.
What do you mean by BG? I'll assume that's some sort of body code...
But are you sure the older shell going to be more flexible?
Metal breaks from continuous bending because it work hardens and becomes LESS flexible up to the point where it cracks.
So, if the older shell is not showing any signs of cracks, is it really less stiff than the low mile one?
Gearheadotaku wrote: What do you mean by BG? I'll assume that's some sort of body code...
protege, escort, 323 etc
Swank are you switching to the same BG chassis? I assume there will be less difference in stiffness between a new and old chassis vs different designed chassis.
The only way to really find out is rig up a chassis torsion strength tester.
I'm not trying to argue or anything, but I knew a blacksmith that would make knives out of old coil springs and leafs. He said all the flexing over the years made for strong steel. Curious.
A fresh chassis definitely feels a lot better to drive. They respond better.
I've had a few customers with convertibles who replaced the shocks/struts and then brought them to us because the car felt funny. I drive and everything feels okay but you can feel the chassis twisting and shuddering over bumps and heaves. No, it wasn't like that when it was new. No, you probably didn't notice it with the worn out struts, because they weren't loading the chassis as much. No, there's nothing that can reasonably be done about it.
I discovered how noodly my then-300k mile VW was when I had my hand out the window, fingertips between the door and the rain rail, and accelerated/decelerated. WOW! Feels like the whole thing is twisting and flopping like a C3 Corvette. Doesn't feel that bad to drive... until I drove a friend's same-chassis car with a third the mileage. Night and day difference, his felt way way better. Didn't pinch my fingers either 
And then there was my late, lamented Golf, which was so bad near the end that it wouldn't lift its leg anymore around corners, and sometimes the driver's door would pop open all by itself.
In reply to mw:
Same thing. 300k mile chassis is a 93. 10k chassis is a 92.
RoughandReady wrote: I'm not trying to argue or anything, but I knew a blacksmith that would make knives out of old coil springs and leafs. He said all the flexing over the years made for strong steel. Curious.
He's half right. The steel does get work hardened, but this makes it more flexible, not less.
Old Chevy Spring is great for making chisels and punches because spring steel is an excellent material for it. New spring steel works just as well, but old springs can be had for cheap-to-free so why buy new?
Swaybars and torsion bars can be cut up to make EXCELLENT prybars, too. Same for Ford twin I-beam tie rods.
I know that cars can get bad enough that I wouldn't want to make them stiff enough to reasonably autocross. I know of a Corolla that has to have the doors shut to jack it up to change tires. If you try with the doors open the car twists so bad it's scary. That car is so floppy that you could never put stiff springs under it and expect them to do anything. I think the low mileage chassis would be worth it.
Knurled wrote:RoughandReady wrote: I'm not trying to argue or anything, but I knew a blacksmith that would make knives out of old coil springs and leafs. He said all the flexing over the years made for strong steel. Curious.He's half right. The steel does get work hardened, but this makes it more flexible, not less. Old Chevy Spring is great for making chisels and punches because spring steel is an excellent material for it. New spring steel works just as well, but old springs can be had for cheap-to-free so why buy new? Swaybars and torsion bars can be cut up to make EXCELLENT prybars, too. Same for Ford twin I-beam tie rods.
Interesting. I could use some cheap pry bars. Sorry to get OT.
Also a little OT, Doesn't aluminum fatigue faster than steel? Does this mean bad things for the long term future of the new aluminum F-150?
Not sure about faster but it's less friendly about it. Speaking from the bike world, aluminum frames got a reputation for being extremely stiff (some believe it adds to ride harshness, but I could never tell...) but this isn't due to the material so much as it was the frame design. If you built a bike out of the same general dimension tube as a steel bike, it would be a floppy noodly mess and the flexing would cause it to fail more rapidly. So, aluminum bikes were designed with much larger diameter tubing than steel bikes, to cut down on the flexing that would lead to fatigue failure. And then you have Cannondales which were bikes built to be both super light AND inexpensive, which led to them being nicknamed "Crack-n-fail"...
The aluminum-bodied cars I have seen were NOT designed like steel cars. They were built around largish castings/forgings at various bulkhead points, not merely spotwelded origami.
In reply to Rufledt:
There are a lot of things that mean bad things for the aluminum framed f-150s.
Sorry to go ot.
It depends. I'd take a 300K mile chassis that did all highway commuting well before a chassis that did 10K as a cop car, rallycross car, etc. Usage is far more important to steel than age.
It also depends on the chassis itself. Fully boxed perimeter frame? 300K won't make a measurable difference. Fox body? It's trashed in 6 months. The bonded unibody chassis are the most susceptible.
Let's assume that both cars have led a fairly typical life. Equivalent sort of driving throughout their respective miles.
I have noticed that the 300k mile car will twist pretty hard when jacking up with the door open (can't close door after it's in the air), but i always sortof attributed that to being a hatchback.
Work hardening does not change the modulus of elasticity for steel, and only happens when the material is plastically ("permanently") deformed. IE: doesn't apply to un-crashed chassis or (most) springs found in automobiles.
You could certainly argue that the chassis gets floppier as the various joint loosen up,but I believe that typically chassis 'flex' is either a result of rust, or aged bushings and dampers.
Just my .02. I would certainly swap chassis if rust was an issue, but would be much less likely if it was 'only' mileage.
Knurled wrote:RoughandReady wrote: I'm not trying to argue or anything, but I knew a blacksmith that would make knives out of old coil springs and leafs. He said all the flexing over the years made for strong steel. Curious.He's half right. The steel does get work hardened, but this makes it more flexible, not less. Old Chevy Spring is great for making chisels and punches because spring steel is an excellent material for it. New spring steel works just as well, but old springs can be had for cheap-to-free so why buy new? Swaybars and torsion bars can be cut up to make EXCELLENT prybars, too. Same for Ford twin I-beam tie rods.
You'll need to log in to post.
