1966 alignments specs when using bias ply tires

[Gary B.]

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[Gary C.]

Re: 1966 alignments specs when using bias ply tires

Gary,

Frame shop adjustment specs.
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Gary
....

[John F.]

Re: 1966 alignments specs when using bias ply tires

It's in the AIM, under front/rear suspension geometry.

[Duke W.]

Re: 1966 alignments specs when using bias ply tires

The primary difference in alignment specs between radial and bias ply tires is toe. (Typical internet "advice" is you need different settings for radials and bias ply without specifying actual numbers, but the only difference, if any, is toe.) Because radials have a longer contact patch and more self-aligning torque they should run with less toe, but I believe that radial toe specs are okay for bias ply tires, too.

For radials front and rear total toe should nominally be 1/16", and it's critically important to have this equally divided at the rear wheels, which is 1/32" per side.

At the front toe will automatically equalize on both sides on a level road, but if it's not set correctly the steering wheel will be cocked off center.

Note that minimum rear total toe in the OE specs is 1/16" inch, and I also recommend this for the front, even with bias ply tires. This is best especially for those who swap between bias ply tires for judging and radials for driving.

Understand that wheel alignment is a "tuning parameter" just like the spark advance map for the engine, and the OE recommendations may not be the best for various driving styles.

John Hinckley and I always recommended zero front camber and 1.5 deg. positive caster for the front, and -0.5 deg (negative) camber for the rear for "touring" type driving, and up to -1.0 (negative) camber for "sport" driving. Power steering front camber should be up to 2.5 deg., but this may not be available within the range or normal adjustment.

Cross settings, the difference between right and left settings should be as close to zero as possible. Some alignment shops want to bias camber or caster to account for road crown, but modern roads have very little. This advice dates from 100 years ago when most roads were dirt and highly cambered for drainage.

Don't expect the alignment shop to understand ANYTHING about a C2 Corvette even if they claim they do. Their machine may have "specs" but who knows where they come from.

You need to talk to the alignment shop before you commit to schedule an appointment. Bring your own specs and insist that they use them. Emphasize the critical nature of having equal toe on both rear wheels. (Any modern four-wheel alignment machine should measure per wheel toe.)
Ask them if their machine can measure toe is inches or degrees or either. You are giving them toe in inches. Can they convert that to degrees if their machine can't. If not, they or you are going to have to make the conversion. If they don't know how to do it, do you?

Your '66 likely has the "captured" shims. Do they know how to change them and how much toe is changed by swapping a shim of any given thickness from inboard to outboard or vice versa?

There have been too many reports of botched alignments, so owners need to do due diligence to be sure the shop understands how to align a C2 Corvette, and if they don't you need to explain it to them. If they resist (most shops firmly believe that the customer is stupid) find another shop.

Once you find a shop you have faith in and commit make sure you look at the settings upon initial measurement then direct them to make the changes you deem appropriate.

Duke

[Gary B.]

Re: 1966 alignments specs when using bias ply tires

It's in the AIM, under front/rear suspension geometry.

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[Gary B.]

Re: 1966 alignments specs when using bias ply tires

Duke,

Thanks for the alignment numbers that would work for both bias and radial tires.

Regarding the rear shims, at least for the time being the rear shims are and will remain the slotted kind. And I do have faith in the particular shop that will do the alignment. They have done hundreds of C2 Corvettes over the last 40+ years, both by the previous shop owner up thru 1996, and by the current shop owner since 1996. The shop is well known by classic car owners throughout the SF Bay Area.

Gary

[Duke W.]

Re: 1966 alignments specs when using bias ply tires

The slotted shims are certainly easier to swap than the captured type, and I'm convinced that loss of slotted shims is due to improper installation. Proper installation is as follows: Once the shim stack is determined to achieve the desired toe the last one installed, a thick one, should require light tapping with a small hammer to seat. in other words, a slight interference fit. Then with the rear suspension at normal ride height torque the trailing arm nut to spec.

Swapping a 1/32" shim from inside to outside or vice versa will change toe by the ratio of tire radius to trailing are pivot point to axle centerline distance (17 7/16"). OE 775-15 tire diameter is approximately 27" so 13.5/17.4375(.03125)= .0242". So if cross toe is less than this you can't get it any closer to equal, as long as both wheels have at least a slight amount to toe-in. Any rear toe-out will cause these cars to handle like they are possessed by the Devil.

The length of the arc subtended by a small angle is equal to the angle in radians times the radius and this is nearly equal to the secant, a straight line between the two points on the arc, and this is essentially the toe measurement. A complete circle, 360 degrees is 2pi radians, so for 1/32" toe:

Toe angle = .03125(360/6.2832(13.5)) = .1326...call it 0.13 degree and it proportions linearly, so 1/16" toe is 0.26 degrees.

Duke