Alignment Question

[Gary R.]

Re: Alignment Question

I use the same new std arms Bairs does, and they are better then originals.I have never had one problem with any new arm and doubt Bairs has either. Now if you had offsets installed then this is a common problem and has been for years.Some are so bad the poly bushings need to be ground out.

You can read my thread on rebuilding arms to see how to check them. The tolerance is not as tight as some believe. I've found original arms vary up to .100" in some cases. This is not a measurement of the bushing thickness. while .100 is bit more then I like they should work,more then that and I would replace the arm.

[Rob M.]

Re: Alignment Question

I have only put 5 miles on it (driving it home from the shop), but it drove fine and went straight on the flat spots. I did check that out.

[Rob M.]

Re: Alignment Question

If I'm reading the numbers correctly I don't like them. Front camber should be close to zero, with as much caster as possible up to1.5 deg. with manual steering and 2.0 with power steering, and cross camber, cross caster should be as close to zero as possible.

At the rear camber should be nominally -0.5 deg. with as close to zero cross camber as possible.

Toe readings should be about 1/32" per wheel on all four corners.

Toe per wheel in deg. = (toe, in.)(360)/2Pi(tire radius, in.)

Using a tire radius of 13.5", 1/32" toe in per wheel should be about .13 deg.

Alignment has been discussed many times, so before having your car aligned, look at the archives or ask. There are two recommended sets of specs for C2s with radial tires (by John Hinckley and me) - "touring" and "sport". The sport settings are a little more aggressive on negative camber and positive caster (half degree more camber in the neg. direction at both ends with as much positive caster as possible)

Give the shop WRITTEN INSTRUCTIONS with the target values and an instruction to keep cross readings as close to zero as possible.

Duke

Duke,

Thanks for posting. The tires are 205/75 R15 radials - if that helps.

I will check the archives for the specs and evaluate them. Finally, do you have a shop you would recommend in So. Cal.?

[Bill M.]

Re: Alignment Question

Rob:

Your numbers don't address thrust angle. You can check that by driving the car and having an observer follow. Have the observer sight down both sides of the car. The car shouldn't appear to be dog-tracking. If it's OK, then having no shims on one side is what you get, but it's unusual.

To be more clear: If I had a trailing arm with no shims on one side, I would want to do a visual check to make sure the car doesn't dogtrack no matter what the machine reads.

Bill

[Duke W.]

Re: Alignment Question

Duke,

Thanks for posting. The tires are 205/75 R15 radials - if that helps.

I will check the archives for the specs and evaluate them. Finally, do you have a shop you would recommend in So. Cal.?

Typical inflated OD for your tire size is about 27.4", so that would effect the calculation slightly. I used 27" (13.5" radius), which is the spec for 215/70s.

Modern alignment equipment is wonderful, but the guys doing the work usually leave a lot to be desired. I gave up on them 25 years ago and do my own alignment with an inclinometer and tape measure, and I get closer to my target specs than they will even with a six-figure state-of-the-art alignment machine.

The only shop I know of that has a good reputation is Johnson Alignment in Torrance. The do a lot of work for Porsche racers and appear to know what they're doing, but one should always arrive with a set of specs and instructions in writing!

Thrust angle is caused by cross toe at the rear. You have a little but it's not too far off. A 1/32" shim on the inside of the RH arm might bring the difference closer or might throw it off the other direction.

The trailing arm effective length is about double tire radius, so a 1/32" shim will affect toe by about 1/64".

Your rear toe is probably about as good as you can get without shaving shims, so it looks okay. Rear camber is easy to set and easy to get the cross readings close to zero.

At the front the cross readings should be closer to zero, and the "touring" settings are probably best suited to your driving style. If you still have threads showing on the shim nuts, then you can still move the camber in the negative direction. Once the camber is set, moving shims from the front to the rear stud will increase caster in the positive direction with only a slight affect on camber.

Setting Corvette alignment is actually pretty easy except rear toe. You don't have to crawl under the car to set the front camber and caster, which can be a real PIA when you have to deal with cam bolts like on my Cosworth Vega and Mercedes.

Duke

[Rob M.]

Re: Alignment Question

Duke,

Thanks again for the great detail in your response. I can work with this and am confident it's close. I'll get it dialed and then . . . I'm driving it!

[Steven S.]

Re: Alignment Question

If I'm reading the numbers correctly I don't like them. Front camber should be close to zero, with as much caster as possible up to1.5 deg. with manual steering and 2.0 with power steering, and cross camber, cross caster should be as close to zero as possible.

At the rear camber should be nominally -0.5 deg. with as close to zero cross camber as possible.

Toe readings should be about 1/32" per wheel on all four corners.

Toe per wheel in deg. = (toe, in.)(360)/2Pi(tire radius, in.)

Using a tire radius of 13.5", 1/32" toe in per wheel should be about .13 deg.

Alignment has been discussed many times, so before having your car aligned, look at the archives or ask. There are two recommended sets of specs for C2s with radial tires (by John Hinckley and me) - "touring" and "sport". The sport settings are a little more aggressive on negative camber and positive caster (half degree more camber in the neg. direction at both ends with as much positive caster as possible)

Give the shop WRITTEN INSTRUCTIONS with the target values and an instruction to keep cross readings as close to zero as possible.

Duke

Duke, can you point me in the right direction for those alignment specs you and John came up with?

Thanks,
Steve

[Duke W.]

Re: Alignment Question

C2/C3 NOMINAL TARGET ALIGNMENT SETTINGS

Touring w/ radial tires
Front:
0 deg. camber
+1.5 deg caster (+2.0 w/pwr steering)
1/32" toe-in per wheel

Rear
-0.5 deg. rear camber
1/32" toe-in per wheel

Sport w/radial tires
Front:
as much negative camber as can be achieved up to -1.0 deg.
maximum positive caster that can be achieved
1/32" toe-in per wheel

Rear
-1.0 deg. rear camber
1/32" toe-in per wheel

All cross readings should be as close to zero as possible; 1/32" toe-in per wheel is equivalent to 0.133 deg. toe-in per wheel with 27" diameter tires.

These camber/caster and rear toe settings can also be used for bias-ply tires, but the front toe settings should be doubled.

When you go to an alignment shop present the target specs for your specific case in writing and preferably write them on the work order.

The shop should present you with printouts that have the initial alignment settings and the final settings. Make sure they understand that you want these printouts.

Visit the alignment shop before you commit to the job. Find out what kind of equipment they have (make/model) and who the alignment techs are. Observe a car being worked on. Discuss your car and show them the specs. You can later google the make/mfg. of the alignment equipment to find out more about it.

If you're satisfied that they can do the job properly, make an appointment.

Don't leave anything to chance and don't be "afraid" to ask questions. You are the customer who is paying for the job. Demand quality!

There will be cases where the above nominal settings cannot be achieved. For example at zero degrees front camber the maximum postive caster that can be achieved may be 1.0 deg on one side and 1.5 deg on the other. In this example, set the caster on both sides to 1.0 deg.

Front settings may be limited by shim stack thickness on the front upper control arm cross shaft mounting studs. The maximum stack is achieved when only two threads are showing above the nut. Moving camber in the negative direction requires greater shim stack on both studs, and swapping a shim from the front stud to the rear stud increases positive caster with minimum effect on camber, so the shim stack limit usually first appears on a rear stud.

If you leave the shop with one rear stud stacked to the limit, that's probably a good sign.

If I was doing a C2 and wanted to achieve the most aggressive "sport" settings possible, I would load shims on all four studs to achieve two visible threads above the nuts. This would yield maximum negative camber.

I would then take the measurements and remove front shims to achieve maximum positive caster commensurate with negative camber in the target range and equal on both sides, and I would end up with one rear stud stacked to the maximum and less on the other three.

Once front camber and caster are set the final step in the job is setting toe-in.

The rear should allow a wide range of camber settings. Once camber is set the toe should be set and then the camber rechecked.

If you do some searching you should find posts by me in years past about how you can do the whole job yourself in your garage with an inclinometer, string with plumb bobs, and tape measure

Duke

[Steven S.]

Re: Alignment Question

Thank you!!

Steve

[Timothy B.]

Re: Alignment Question

Duke,

What's the reason for the 0 to negitive camber on the front wheels? My 63 shop manual calls for +3/4* +- 1/2*

Also, I set a fishing line running the length of the car parallel to the frame side rails to set toe. The alignment seems to be fine, your thoughts..

[Duke W.]

Re: Alignment Question

First consider that the shop manual specs are based on the OE bias ply tires, and the range is +1/4 to + 1 1/4.

So now we can argue about the quarter degree, which is somewhat akin to arguing whether the intial timing should be 8 or 10 degrees and whether dwell angle should be 30 or 32 degrees.

Radial tires are more senstive to camber than bias ply tires and radial's optimum grip usually occurs at about -1.0 degree camber, so running zero to slightly negative camber will optimize front end grip and minimize any side wear that might occur in normal straight and level driving if camber is very far off from zero.

Maximizing caster maximizes negative camber gain on the outside front tire while cornering, which offsets body roll to some degree and keeps the tire closer to vertical to the pavement. Caster also increases slow speed steering effort and increases wheel return torque, which is why more caster is okay with power steering. My own preference is to run as much positive caster as the adjustment will give mewithin the bounds of the camber I want, which is how all my cars are setup - both those with manual and power steering.

Keep in mind that things like suspension alignment, initial timing, dwell angle, centrifugal advance, and many other specs are established by the manufacturers based on OE equipment, average drivers, and average conditions.

Also, the '63 Shop Manual specs are basically "reset" specs. If you look at a later shop manual, you will find multiple sets of specs.

For example, the following three sets of specifications are given in the 1976 Vega shop manual for front camber. Caster and toe also have similar explanded ranges, but I'm just listing camber to illustrate the point.

State vehicle inspection: -1 1/4 to +1 3/4 deg.
Warranty or customer repair: -3/4 to +1 1/4 deg.
Service reset: +1/4 +/- 1/2 (-1/4 to +3/4)

As you can see there is a much wider allowable allowable range for state inspection than service reset, and I'm sure a similar vintage Corvette CSM will show similar multiple sets of specs. Maybe someone can post them.

For reference I ran my CV's front camber at high as -2.0 deg. when I was doing a lot of track work, but I backed it off to -1.0 degree after I quit running track events.

The specs that John and I developed are based on experience for a vintage Corvette with radial tires and two different driving environments.

The "touring" specs are likely best for 90+ percent of vintage Corvette owners - those who "cruise" or do a lot of highway driving and do not commonly drive their cars aggressively on twisty roads, autocross, or do track events.

The "sport" settings are for those who regularly seek out twisty roads and drive them aggressively, autocross, or run track events.

I have never experienced inside wear of any significance with up to 1 degree negative camber on any of my cars, because I tend to corner aggressively, which wears the outside shoulder and tends to offset any excess wear on the inside of the tread that might occur during straight line driving - at most about 1/32" over the life of the tire.

Duke