Last night I was drawing a roadster frame...got out a chassis engineering book to calculate roll centers etc... Just some thought/ideas A stock Model A has the same roll centers as a heavily channeled roadster The only way to lower the roll center is by runnin smaller diameter wheels Leaf springs have maximum friction at zero deflection, coils don't reach max until they are bound That makes good shocks more important on a rod...not just "whatever chrome ones will fit" Old Brit sports cars went for the "very stiff suspension on a flexible frame". Similar to a lot of trad hot rods Also thinking about weight distribution, 650 pound fifties V8 in a sub-2000 pound car? All these thoughts were about steering and handling...hot rods were road raced against imports in the 50s in so cal and new york...I wonder what Gs a well built AV8 would pull on a skid pad, bias plys and all? Stayed up too late I guess.
I can't say how well built they were, but in this month's Rod and Custom, they have cornering figures for some of the particapants' cars. Larry Metz' 32 Ford Cabriolet is listed as cornering at .59g.
I have been talking about that for some time now... I am willing to put my Roadster through those kind of tests, As long as somebody will accurately measure the results, shoot good action photo's, and publish it all in a magazine. So far nobody has taken me up on that...
By the way... It is easy to change the roll centre by adding a Panhard bar, and moving the mounting points up and down. The Panhard bar needs to be as long as possible, and level at rest ( ride height ). By doing this to one or both axles you can dial in the under/over steer of the car, with out having to put sway bars on.
Rod and Custom did a tire test using Dennis Varni's roadster with lots of different tire combinations on it about a thousand years ago (early 70's). As I recall, some of the setups got right around the skid pad, to the point that the motor lost oil pressure and got hurt. Great article. I don't remember any tweaking on the chassis tune at all, just changing tires.
I've wondered about stuff like this too, although for my car, not a light little roadster. Since I need to replace them anyway, what are the best shocks I can get for a 4200lb sedan? Kanter offers the generic one-type-fits-all fluid kind for only a little less than gas-charged ones. All I know is that gas-charged shocks are supposed to be "better", I don't know what that means though. The ride is already kind of harsh (maybe because of the helper coilover shocks on the rear axle...), but there's still more body roll than I'd like when going around corners.
[ QUOTE ] The ride is already kind of harsh [/ QUOTE ] What tire pressures are you running? 35 psi - the usual max rating for passenger car tires - is way too much for a lightweight roadster or coupe. Fwiw, I run 28-30# - most times 30# - in the front of my 32 roadster w/195/70R-14 BFG radials. 20# in the back w/285/70R-15 BFG radials. Works well, helps in the ride dept and the tires don't roll off in hard corners due to the light weight of the car. You can figure the proper inflation pressures for your car by rolling it across a partially damp cement driveway and taking note of the wet pattern left on the dry part of the driveway. Dark in the center, light on the edges = overinflated. Light in the center, dark on the edges = underinflated. Some guys do the same thing with chalk. Swipe a line on the tire, drive it in a straight line, take note of the chalk pattern. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Far as the cornering capabilities go, about 18-20 years ago one of the car mags - done with Joe Kress as the editor and it was a new entry on the market - did a skid pad test with three cars. Porsche - not sure of the exact model, one of the bathtub wonders. 32 Roadster - highboy -with Kugel style independent suspension front and rear and it may have had Jag suspension on the front. Don't remember for sure. It did have Jag suspension on the rear. This roadster had tires similar to what the Porsche had. Lastly, 32 Ford highboy roadster with 4" dropped axle front and 9" in the rear. I think this car had coilovers in the back, front was the usual transverse spring. Both roadsters ran SBC I believe. The Porsche and the independently sprung roadster recorded virtually identical G force figures on the skidpad. The typical roadster - not sure what tires it ran - recorded a G force figure that was about 90-95% of what the other two cars ran. The thinking was, if the trad suspended car was running the same tires as the other two, G force figures would have been virtually identical. My experience on winding mountain roads has been that my 32 does about as well as the modern day sporty cars on the corners. I don't get too crazy though. Once the 32 hits the short straights, that's it for the sporty cars. Granted, I haven't run up against a seriously sprung and tired sporty car with a touch of power and the driver wearing official Momo glasses and gloves so that's not much of a test. Even so, struck surprise and maybe even a bit of fear into more than a few yuppie hearts....
Machinos, I think gas shocks have the fluid and the inert gas in separate bladdrs so that the fluid doesn't aereate. At least that's true on bike shocks. A heavy car can really work shocks. Most big American sedans by the 60s had sway bars, do some measurements out at Windy Hill or French Lake and see what will adapt to your sled. Shocks wont help much with the body roll.
Another factor in getting the suspension to "work" is reducing unsprung weight- even more critical when you're talking about a lightweight roadster (which has less sprung weight).
Actually it is a big American sedan with a front swaybar! I'm sure the suspension isn't supposed to transmit bumps and rough roads so much, but it does for some reason. Could be that there's like 4 body mounts missing, too. It's probably the shocks, though. So is the only advantage to gas shocks that their performance doesn't decrease if they're being compressed on and off a lot?
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