C2 Handling Question

[67ragtop]

I just had the complete undercarriage professionally rebuilt on my 67 SB (w/manual steering). Thinking it would handle like a new car, I was somewhat disappointed with the results. While driving at a steady speed of around 50mph, the car tracks fairly straight with no hands on the wheel. Under the same conditions, if I accelerate, it pulls to the left or if I let off the accelerator, it will bolt to the right. It’s been back to the shop twice but they can’t find anything wrong and tell me everything is within specification.

It doesn’t seem possible but is this normal for a mid-year?

 

[67HEAVEN]

It doesn’t seem possible but is this normal for a mid-year?

This is a common complaint, however they can be made to handle very well.

A great deal depends on the tires you are using and the alignment settings. Tell us about those things.

 

[Ken Anderson]

67 Heaven is right. Did they rebuild the rear, as well? If the rear settings aren't right, the car can swap ends under hard acceleration & braking. You need to find a new shop.

 

[JohnZ]

What kind/size/brand/type of tires are on it? What were the target (and resulting) rear camber and toe settings from the alignment shop - what does the printout say from the alignment rack?

 

[67ragtop]

The tires are new Dunlop SP40's, P205/75R15. The rear end was completely rebuilt as well. I was never given the settings and was told they were not kept in my file. The only way I could get them would be to re-align the car. This has already been done twice and I was only told that it is to specification.

 

[JohnZ]

Tell them that's not an acceptable answer - you're entitled to the printout the machine generates for every job that shows ALL the settings - "to spec" is garbage, especially when they probably set it for bias tires (the "book" specs) when you have radials on it - it matters! For the rear of a normal street-driven Corvette with touring radials your size, you want zero to 1/2-degree negative camber, and 1/16" total toe-in, split equally across the thrust centerline (1/32" per side, exactly). I've never heard of an alignment shop that wouldn't provide the printout from the rack. The rear toe-in setting is absolutely CRITICAL for proper handling and transient response for an IRS Corvette - if they took short cuts (as many non-Corvette-knowledgeable shops will, especially if you have "hole" shims instead of "slot" shims), you were short-changed, which is probably why they won't give you the printout. For the front, you want zero camber, 2.5 degrees positive caster, and zero-to-1/16" total toe-in.

 

[67HEAVEN]

Tell them that's not an acceptable answer - you're entitled to the printout the machine generates for every job that shows ALL the settings - "to spec" is garbage, especially when they probably set it for bias tires (the "book" specs) when you have radials on it - it matters! For the rear of a normal street-driven Corvette with touring radials your size, you want zero to 1/2-degree negative camber, and 1/16" total toe-in, split equally across the thrust centerline (1/32" per side, exactly). I've never heard of an alignment shop that wouldn't provide the printout from the rack. The rear toe-in setting is absolutely CRITICAL for proper handling and transient response for an IRS Corvette - if they took short cuts (as many non-Corvette-knowledgeable shops will, especially if you have "hole" shims instead of "slot" shims), you were short-changed, which is probably why they won't give you the printout. For the front, you want zero camber, 2.5 degrees positive caster, and zero-to-1/16" total toe-in.

Good info, John.

What difference in settings would P295/50R15 (10" rims) on the rear and P265/50R15 (8" rims) on the front require?

 

[JohnZ]

With your wider tires and larger contact patches, alignment is even more critical, to keep as much of those wide tires on the ground as possible; C2/3 Corvette suspension geometry wasn't designed for wide tires, and has more camber gain with a higher roll center than later cars with wider tires. For normal driving, I'd recommend the same specs I outlined above; if you intend to explore handling closer to the limits, I'd go to 1/2-to-1 degree negative camber at both ends, leaving caster and toe the same.

90% of the handling equation is tires; the rest (assuming proper geometry) is shock and stabilizer bar tuning for chassis balance and rebound damping. My car is a stock tourer on 205/75-15 radials on stock bolt-on aluminum wheels, and in that configuration it will never handle like a current car, and I know that and accept it. Yours has far more potential, and will respond well to tuning.

 

[BacaBill]

Does anyone have the exact alignment specs for a '66? My other computer crashed w/ my links page now gone. I have a '66 coming into my shop on Friday & the aligner machine doesn't go back that far. Thanx a bunch,
Baca

 

[JohnZ]

Original factory specs (bias-ply tires) were (Front) - zero to 1 degree positive camber, 1-2 degrees positive caster, 1/8"-1/4" total toe-in; (Rear) - 1-2 degrees negative camber, 1/8"-1/4" total toe-in. Those are the original assembly specs with flabby 7.75-15 bias-ply tires; experience with more modern radials says the specs I posted above in my first post on June 14th are optimal settings for normal street driving, or crank in a little more negative camber for more "spirited" driving with performance tires as noted in the second post. The positive caster setting (2.5 degrees) improves tracking and returnability and is fine with power steering, but will significantly increase static steering effort with manual steering - 1.5-1.75 degrees is a better setting with manual steering.

Rear toe is the most critical setting on the whole car, particularly getting it evenly split to both sides across the thrust centerline.

 

[67HEAVEN]

John,

Thanks, not only for the specs but, for the description of how the various changes will work with later tires.

Great stuff as usual from you.

 

[Tyler Townsley]

OK a little tougher alignment question. Have a 68 running 95 Corvette 17' 9.5 rim with P275/40ZR17 in front with 2.5 spacers(bolt on Adapters), and P285 and 2.75 spacers(bolt on adapters) rear. It exibits what seems to be a loose condition in the front. I am going to get the VBP Spreader bar for the front to tie the control arm towers togeather for additional stability up front but what should I be using for front and rear alignment spects?

Thanks.

Tyler

 

[JohnZ]

With your setup, that's going to be a trial-and-error process; the '63-'82 Corvette suspension was never designed for wide, low-profile tires, and exhibits a lot of camber gain and a higher roll center compared to '84 and later front geometry.