Alignment results - Duke and others?

[Timothy B.]

I had my 67 convertible aligned today at a local reputable shop by a tech who has been doing it for many years. I followed Duke's recommendations for alignment settings, and handed the tech a paper with what I wanted on it just as Duke suggested. My previous alignment was only a guess since I had the entire front and rear apart over the last couple of years. The process did not go without problems however, and I am posting the results here to see what Duke and others think.

First off, I had referred to many previous posts on alignment recommendations. One of those posts back from April of this year is this one:

https://www.ncrs.org/forum/archive17.cgi?review=125545

In that thread Duke lays out his recommendations very succinctly for everyone. It was these basic values that I gave to the tech, and also stressed my desire to be equal left to right.

Front camber, -0.5 deg
Front caster, +2.0-2.5 deg
Front toe, 1/32" per wheel

Rear camber, -1.0 deg
Rear toe, 1/32" per wheel

The tech knew right off what to put into his alignment machine in decimal degrees for toe settings, but they didn't match Duke's posting. Duke, you might want to respond here but best I can tell 1/32" toe is about 0.13 degrees, not the 0.015 deg in your posting (see email from me with calculation). The tech for my alignment used 0.13 as the target per side. Unfortunately, as you can see in the results, the tech misread my request for the rear, and used the 1/32" figure as the TOTAL toein not the per side value. We had used up my alloted time on the machine so it wasn't corrected, but he agreed that I could come back and we could tweak it. Also, you can see that I am currently not able to get as much positive caster as I wanted without going more negative on camber. The tech recommended leaving it as-is, but I wanted to get the forums thoughts.

Here are my results:

Front camber left: -0.85 deg right: -0.52 deg
Front caster left: +1.24 deg right: +1.88 deg
Front toein left: 0.16 deg right: 0.16 deg
Total toe front: 0.32 deg

Rear camber left: -1.07 deg right: -1.04 deg
Rear toein left: 0.05 deg right: 0.06 deg
Total toe rear: 0.11 deg
Thrust angle: -0.01 deg

As the results show, I have less toe in the rear than I wanted, but wonder if I should try to increase it or just leave it? The tech insisted on a little more positive caster on the right front, and I wasn't up to objecting too much so I let that go. The reason that the desired amount of positive caster could not be obtained is that on both sides all or most shims were removed from the front bolts and a large stack on the rear bolts. Increasing the caster more would mean increased negative camber. The tech said that he sees this all the time in older Corvettes and Camaros, and suggested using offset upper shafts.

From a driving standpoint I can immediately tell that I have much more centering feel. I think I had just about zero caster to start with and maybe some toeout. My first impression is that the car wants to go straight now without any of the dartiness that was there before.

I would appreciate any comments guys! I will of course spend some time driving it and see how it feels, but what changes might I consider making when I take it back in after a week or so?

[Eugene B.]

Re: Alignment results - Duke and others?

Tim, Duke, et al,
I won't be ready for front and rear alignment until spring, but this seems like a good time to ask the question.

What's wrong with using the GM specs for F&R alignment? I would imagine that the folks who designed and built the car know what's best.

Perhaps modified alignment specs are for folks who choose to run radial tires?

Need enlightenment in addition to an alignment.

Regards,
Gene

[Timothy B.]

Re: Alignment results - Duke and others?

Gene,

Others can chime in here but I believe that these aren't really "modified" specs but rather a zeroing-in on more precise settings basically within original specs. There are many threads on this forum highlighting that the original specs had large +/- margins. Based on the actual type of handling you might want out of your car, you can tweak the settings within GM spec ranges and get more of what you are looking for. Also, todays radial tires respond to alignment settings differently than the old bias ply tires did, justifing some updated targets.

[Duke W.]

Re: Alignment results - Duke and others?

In previous posts I have quoted "touring" and "sport" alignment settings. As with the ignition timing map and fuel flow curve, alignment is a "tuning parameter", but for ride and handling rather than the engine torque curve.

My touring and sport recommendations are the same except the camber settings, with the sport settings having a little more bias in the negative direction. As with the timing map, the OE alignment is an "average" for "average drivers" and "average roads", and improvements in handling can be obtained by biasing the OE camber a bit in the negative direction and running as much caster as possible just as improvements in engine performance can be had with judicious modification of the ignition and fuel maps.

The ONE alignment setting that is specific to radial tires is toe. Radials do not need as much toe as bias ply tires and running excess toe (such as the OE toe settings, which were established for bias ply tires) with radials can cause excess tire wear and handling problems.

The nominal TOTAL rear toe-in should be established at about 1/16" front and rear. But any value between zero and 1/16" should be okay, however, it is critical to get the rear toe split equally between both sides. On the front the wheels align to equal toe on both sides, and if it is not distributed equally the steering wheel will be cocked off center when driving on a straight road. Since you have about 1/64" per side on the rear, they are close to equal and the total of 1/32" should be okay.

Since the nominal OE caster is about 1.5 degrees, I don't know why one side will only go to 1.24. Most C2/3s should be able to achieve 1.5-2.0 if everthing is straight.

If the car drives okay, then I would leave it be, but the 0.6 degrees cross-caster could cause some pull. If it does pull, back the 1.88 on the left downb as close as possible to the 1.24 on the right, however, my preference is to set caster and camber as close to equal on both sides as possible. If the targets cannot be met, I always back the high side back to equal the most I can get on the other side at the limit of adjustment.

Regarding converting between inches toe-in and degrees toe-in, you need to know some basic Euclidian geometry. Namely, a circle subtends and angle of two pi radians, or two pi radians equals 360 degrees. Further, the length of an arc is equal to the radius times the angle in radians.

OE Corvette tires are about 27" in diameter, which is a radius of 13.5".

Arranging the formula to compute the angle in degrees for .031 (1/32) inch toe-in for a 27" diameter tire:

Angle = .031/13.5(360/2pi) = 0.13 degrees, which is the target for each rear wheel, and each front wheel with the steering wheel centered. This is not quite exact because we want to measure the chord length, not the arc length, but for very small angles, the difference is not significant.

If I made a calculation error in a previous posting, I apologize.

Duke

Duke

[Wayne W.]

Re: Alignment results - Duke and others?

Thats funny, I cant imagine there would be any real difference between .13 deg. and .15 deg. especially when the published tolerances are 3/8 of an inch. It just aint going to make any difference. The reason that they want to set the caster figure higher on the RH side is to set in a little pull to the left. This counteracts the effect of the crown in the middle of the road.

[Duke W.]

Re: Alignment results - Duke and others?

The trouble with this "more caster on the right to offset road crown" is that it dates to the 1920's when most roads were gravel and highly crowned for drainage.

Modern roads have little crown and the LH lane of most interstate highways is cambered toward the center, so a car could pull noticeably if it was set up for a high crown two-lane road.

The best way to set up alignment is to achieve as close to ZERO as possible cross camber and cross caster. That's how new Corvettes are set up. A final alignment setting is made on the line to minimize cross camber and caster by adjusting just one side.

Some myths just never die!

Duke

[Wayne W.]

Re: Alignment results - Duke and others?

I agree. I like to set them up equal too, but almost every alignment shop that I know will add a little caster on the right. As for the new Corvettes, with about 6+- degrees of caster, you can hardly make one of those pull anyway.