Alignment Specs ?

[Timothy B.]

Re: Alignment Specs ?

Mark,

With negative camber the tires will give more surface contact while cornering but the tire wear will suffer. The factory settings in the front simply give the best tire wear after weight is put in the car. Same for the rear, the negative camber will straighten the outside tire in a hard corner.

[Duke W.]

Re: Alignment Specs ?

If you do a lot of aggressive driving on twisty roads, up to -1 deg. front camber will reduce understeer and improve ultimate grip with better steering response, but this should only be done in conjunction with replacing the rubber anti-roll bar link bushings with urethane. Otherwise the C2 tendency to snap into oversteer at the limit or on trailing throttle will be exascerbated. If limit oversteer is still an issue, install the 13/16" front bar that was standard on base suspension C3s. beginning sometime in the seventies

More than -1 degree front camber will likely wear the insides of the tires excessively with road driving.

The problem is that the rubber compresses, which transfers roll stiffness to the rear with increasing roll, which is a very bad situation. If anything it would be better to increase front roll stiffness with increasing roll with more rear compliance, but there is no rear bar on C2 small blocks.

For the vast majority of vintage C2 owners, my recommneded "touring" settings are the best compromise.

Alignment, like the engine spark advance map is merely a "tuning parameter". Most engine spark advance maps can be improved for better broad range performance with no adverse effects. This also applies to alignment settings up to what I call "sport" settings.

Of course, as far a handling is concerned - steering response, understeer/oversteer balance, and ultimate grip is ultimately limited by tires, and if one has the typical rock hard S-rated radial tires mounted, just get the alignment in the ballpark of the "touring" settings.

The same applies to "suspension kits". I'm always amazed at the guys who spent hundreds of dollars on stiffer springs and bigger anti-roll bars, but pay no attention to tires. It's like building a house on dirt rather than a solid footing. The purpose of the suspension is optimize the grip characterisitcs of the tires. You can put dump truck springs and anti-roll bars the size of your arms on a car, but if it has low grip tires all you will get is a buckboard ride, while a decent kid driver in a Honda Civic pulls away from you in the twisties. It starts and ends with the tires, period!

If you want a C2/3 to handle on a par with a modern sports car, get some DOT legal racing tires like the Avon CR6ZZ, set the alignment to "sport" settings, install some rebound adjustable Spax or QA-1 shocks, and go hunting.

BTW, CASTER, is not spelled correctly on the chart.

Duke

[Mark E.]

Re: Alignment Specs ?

Duke,

Thanks for your patience with my alignment questions. Looking at the archives I realize you've already posted quite a bit on this topic over the years.

This learning is good timing for me; I just restored the front and rear suspension on my '70 and now need it aligned. It's interesting to compare your recommendations with Gulstrand's and Chevy's.

For "touring", you recommend 0 deg. camber while Chevy says +3/4 deg. (for 1969). As Timothy suggests above, maybe Chevy specs slightly positive camber on the machine because they're targeting zero with a driver in the car?

And why do you recommend less front toe-in? Your spec is 1/32" per wheel (1/16" total) while Chevy says 3/16" to 5/16" total.

As you point out, Gulstrand may be a good racer, but not so much a good speller.

Time for my CASTOR oil and nap!

[Duke W.]

Re: Alignment Specs ?

Positive front camber promotes understeer, and it can also cause excess outside shoulder wear if you like to corner fast. OE alignment specs are a compromise for "average drivers". Even though the rear roll center was lowered beginning in '68, which yielded more understeer bias, C3s can still be twitchy at the limit. Setting the camber at zero will improve steering response and reduce understeer, even though it may lose some limit stability, but a decent driver can handle it. As with most dynamic systems, the more responsive, the less stable they are.

For example, the F-16 is one of the most maneuverable aircraft ever built, but it's dynamically unstable. The flight control computer makes continuous high frequency corrections to keep it doing what the pilot wants. Without the electronics, it could not be controlled by a human being because we cannot react quick enough to the instability.

Another good example is two-wheel vehicles - bicycles and motorcycles. They have three dynamic response modes - capsize, weave, and wobble with frequencies of about 0.5, 1-2, and 4-6 Hz, respectively. The capsize frequency is low enough that we can easily apply countersteer pressure on the bars to keep the bike upright. Most people don't understand "countersteer", but learn it intuitively. Weave (weaving through a turn) is often at a higher frequency than we can handle, so the solution is to slow down. Wobble is when the bars vibrate back and forth, and the worst is referred to as a "tank slapper", and they often cause crashes.

I didn't learn about countersteer until I got some SAE papers about motorcycle dynamics about the time I bought my '83 Honda CB1100F and started doing some serious canyon carving. If you want to turn right, you apply pressure to the right bar. This cocks the front wheel slightly left, which causes the bike to roll right and move in an arc. Once you achieve the correct roll angle to keep the bike on the arc of the turn you neutralize bar pressure. To roll out of a right hand turn you apply left bar pressure and the bike will return upright. The higher the bar pressure, the faster the roll rate. It's analogous to using the ailerons on and airplane. After I understood this concept I became a much better rider - able to control the bike with much more precision, and I never crashed.

When you learn to ride a bike as a kid you think that transfering weight to the right will cause the bike to roll right and vice versa, but what you're really doing, unconsciously, is increasing force on the right bar, which is countersteering.

I had never experienced wobble until a Honda engineer taught me how to induce it, and how to stop it. At about 35-40 MPH on a straight, level, and wide road I took my hands off the bars, then gave the right hand grip a bump with the palm of my hand. The bars immediatedly began to wiggle back and forth at high frequency and increasing amplitude. I damped it out by immediately putting as much force as I could on both bars, and it stopped. (It scared the sh-t out of me.) The F never went into an uninduced wobble, but at least I learned how recognize and stop it.

A lot of vintage bikes are afflicted by wobble. By the 80's enough was understood about the phenomenon that the engineers were able to design wobble resistant front ends, but it can still happen, especially if you strike a small rock slightly off center from the front tire. Some older bikes have steering dampers - either a conventional damper between a fork and the frame or an adjustable knob a the top of the steering head that adds damping (friction) to the steering head. I remember one of those on my Honda CB160 that I rode in the sixties.

Radial tires need less toe than bias ply because they have greater self-aligning torque at any slip angle and operate at lower slip angles than bias ply tires. If you look at later C3 alignment specs after radials became standard, you should see lower toe-in specs.


Duke

[Mark E.]

Re: Alignment Specs ?

Thanks Duke. Learned from the information, and enjoyed the F16 and bicycle examples.