You guys straightend me out recently about sway bars. On my '65 roadster I had a sb front sway bar [7/8] and a bb rear [7/16]. That gave me a ton of oversteer. I now have availabile to me a 15/16 front and a 9/16 rear. What combo should I use for the best cornering? The car is currently a sb but the bb conversion is just around the corner.
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If you want a factory BB sway bar(s) conversion ..
...as would have been found on an original 396, the front should be 7/8" dia. and the rear 9/16". The 15/16" dia. front stabilizer bar was installed only on F40 heavy duty suspensions, and this option was available only on L78 and L84 (396's and fuelie's) for 1965. -
Re: Advise please JohnZ and Duke, C2
You still don't have it straight. Base SB C2s have a 3/4" front bar. Base C2 BBs have a 7/8" front and 9/16" rear bar. Z06/F40 SBs have a 15/16" front bar, and F-41 BBs substitute the 15/16" front bar and have the same 9/16" rear bar as base BBs. Of course Z06/F-40/F-41 also have stiffer springs - about double the wheel rate - as base suspensions, so these stiff springs add considerably to roll stiffness.
Increasing/decreasing front bar size increases/decreases understeer.
Increasing/decreasing rear bar size increases/decreases oversteer.
If a car is set up close to neutral as C2s are then decreasing understeer is the same as increasing oversteer.
Even if you install the 15/16" front bar the car will probably oversteer. You either need to further increase the front bar size or reduce the rear bar size.
Note that the FE7 Gymkana suspension available beginning in '75 included a 1 1/8" front bar and 7/16" rear bar. Of course, only a SB engine was available in '75.
If you want to keep the 9/16" rear bar you are going to need about a 1 1/4" front bar.
Also keep in mind that C2s have a higher rear roll center than C3, so C2s have more inherent rear roll stiffness due to the springs alone. My recommendation is to install the 15/16" front bar, remove the rear bar and run about -1 degrees camber on both ends. If this causes too much understeed you can either increase front negative camber or install the 7/8" front bar.
Before one embarks on re-engineering their suspension, I would recommend the purchase and study of Fred Puhn's "How to Make Your Car Handle". It is old, but the basics haven't changed. I think it's still available from Classic Motorbooks.
DukeComment
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Duke, can you explain.......
Duke,
Can you expand on you statement a bit?
"Also keep in mind that C2s have a higher rear roll center than C3, so C2s have more inherent rear roll stiffness due to the springs alone."
Have not heard this before.
tom...Comment
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Re: Duke, can you explain.......
Both the front and rear suspensions have a "roll center", which is the instant center that the body rolls about in a corner. These roll centers vary in both height and distance from the longitudinal centerline of the vehicle depending on the actual attitude of the suspension members, but roll centers are usually quoted at some distance above the ground at normal ride height and at zero roll they will be on the centerline.
The line connecting the front and real roll centers is called the "roll axis", and in a corner the centrifugal force acting at the CG creates a "roll couple" that causes the body to roll about the roll axis. This roll is resisted by both spring force and anti-roll bars.
On initial inspection it would appear that a high roll axis will minimize body roll and the C2 Corvettes do have a high roll axis by current standards. In fact, is is possible to place the roll center above the CG, which will cause the vehicle to bank into the turn as does a V-hulled speedboat. Rear roll centers are usually higher than the front, and since a higher roll center provides high inherent roll stiffness, C2 SBs do not need a rear anti-roll bar, with a "normal" size front bar. C2 BBs have a rear anti-roll bar to offset the increased inherent understeer with the heavier engine.
The trouble with high roll centers is that they create considerable track and camber change as the suspension moves, and while traveling in a straight line these changes in track and camber will make the car darty. Low roll centers minimize track and camber change, so modern cars generally have low roll centers - at or near ground level. Springs are selected to achieve the desired ride frequency, and desired roll control is achieved with anti-roll bars.
The narrow tires of the early-mid sixties were more tolerant of track and camber change, and Chevrolet decided to reduce the rather high C2 rear roll center a couple of inches with the change to wider F70-15 tires. This was accomplished by redesigning the rear strut rod bracket to lower the pickup points of the rear strut rods. This required the exhaust pipes to be mashed down more at this point to provide adequate ground clearance.
With a lower rear roll center a C3 has more inherent understeer than a C2 with the same spring and bar setup.
If you want to get into it at a lower leve than this you should buy Puhn's book. The old Chevrolet Power Manuals also have a good chapter on vehicle dynanmics.
DukeComment
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Re: Duke, can you explain.......
Thanks Duke and Wayne. Duke, that was a very informative lesson. You've shown me where I need to do some more reading on the subject. A least I now know what to look for. Did you say the rear strut rod bracket is different on a C2-C3 and would a C3 bracket be a worthwhile swap into a C2?Comment
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Re: Duke, can you explain.......
If you're into serious racing and running wide wheels and tires, swapping in the '68-up strut rod bracket could be beneficial, but your mid-year under the car exhaust may interfere with it.
DukeComment
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Re: Duke, can you explain.......
No, I'm not into serious racing but my goal is to bring this car up to date in handling as much as possible [altho I'm amazed at it's cornering as it is] for general use as well as some slalom time. I've just had the car for a while and I love it way more than I thought I was gonna, and I thought I was gonna love it a lot! I've had street rods and muscle cars all my life. I now intend to devote my life to this car . I have changed to a side pipe system of my own design to keep the exhaust out from under the car and out of the way for reasons just like this. Wouldn't you know it, I just thought of an even better idea for side exhaust .Comment
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Re: Duke, can you explain.......
The key to handling is to have the stickiest tires avaiable that will fit on your wheels and within the fenders. Once you have the right tires you tune the suspension to get the most of of the tires. When you start with a car like a Corvette, even a vintage C2, which has a pretty good suspension even by todays's standards, handling is about 80-90 percent tires and the rest is suspension tuning.
DukeComment
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Thanks Duke appreciate it. nm *NM*
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