Frank88

Could someone please explain how to do this?

thanks,
Frank

82camaro

With a caster gauge. Turn the wheel 30 degrees out, zero the gauge, turn the wheel 30 degrees in and read the gauge. Thats on the older, not computer type alignment equipment.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

Frank88

Thanks, but I was curious about how to do this without a gauge. I think it has to do with measuring camber at +/- 30 degrees and subtracting one side from the other, but I don't understand the process. This is in case of need to do a "garage floor" type job before getting to an alignment shop.

thanks

AlkyIROC

Caster is the forward or backward tilt. You can't "backyard" check it without some sort of gauge.

82camaro

It's not going to affect tire wear to the alignment shop. Eyeball them both the same and you will be fine. Mine are both pushed all the way back and are almost +5.

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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

ANDYZ28

If you do not disurb the original adjustment. And do not install or remove any obviously bent components. Little will change. Allowing you to get to the alignment shop.
I did a complete front end rebuild, poly bushings, ball joints etc. All of this was done duing my 1LE front brake upgrade, I even replaced the spindles. And I still havn't gone the the alignment rack. And I work there! I have noticed no ill effects at all.

MY87ROC

i also have a ques bout this caster adjustment also, just rebulit front suspention, including upper strut mount (moog) went to alignment shop and they aligned it but he said the camber on the driver side was maxed out and was still .5*
out but that was as far as it will go, why is that, is this how they are made, my car is stock and not lowered or anything like that but it does steer straight and drive fine, he said this will not affect tire wear,i have been watching that and so far he is right.

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TPIS airfoil,relocated MAT,AFPR,TB h2o bypass
March Underdrive Pulleys
otherwise stock 5.0TPI
700r4, 10 bolt 3.23 g92 axle, 4 wh. disc brks.

[This message has been edited by MY87ROC (edited May 28, 2001).]

Eightyninef

you don't need to measure caster or camber. just slide the strut towers all the way in and back. then your done. no alignment shop can do it better than that.

If you want to have the toe set up by machine, then go to an alignment shop, but otherwise forgot it.

82camaro

Larry, both sides probably won't be exactly the same if they are maxed out. Alot of cars will be off quite a bit is you just max it out and set the toe.
MY87roc, +.5 camber shouldn't be much of a tire wear problem if you drive it decent. Toe is what kills tires quickly. The 3rd gens have pretty crappy factory alignment specs. That being said, was the alignment guy trying to get additional camber--higher that .5. Or was he trying to get less camber--lower than .5. What you want is less camber.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

Norm Peterson

You do not need a gauge. All you need is a carpenter's combination square with a bubble level in it. Hold the 12" ruler of the square vertically (make sure that it is plumb looking from the side too) with one end against the wheel rim and measure the gap at the other end of the ruler with a scale that measures to 1/32" or finer (I use one that reads to 0.01" - probably overkill but it's what I happened to have in my toolbox). Then do the math. As a matter of reference, every 1/32" of gap over the 12" length is 0.15 degree.

The formula is:

camber = arctan(gap/12)

where gap is expressed as a decimal


Actually if you have a reasonably flat and level garage/driveway (and a bit of patience) you can set the alignment practically as good as a shop can. It just takes longer, since you have to stop, measure, and calculate. A significant side benefit particularly if you autocross (or just corner hard most of the time) is that you can set whatever alignment spec's you want without having to argue with anybody about setting outside the factory ranges.

Norm

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1979 Malibu w/some cornering tweaks and a few other interesting things

[This message has been edited by Norm Peterson (edited May 29, 2001).]

Stuart Moss

Norm,

A man after my own heart. I too measure caster on my Z28 essentially the same way you do, except that I drop a string with a nut on the end (to keep it straight) from the fender at the mid-point of the wheel. Then I measure the difference from this string (a staight line, perpendicular to the ground) to the upper and lower wheel rim.

If both measurements are equal, then the caster is 0.0°, or the wheel is straight up, or perpendicular to the ground. Your calculations are correct, although I use tan to get the angle or distance by the following formula, which any basic algebra student should know.

Tan = a ÷ b

Where "a" is the leg of a right triangle adjacent to the 90° angle and opposite the angle to be measured and "b" is the other leg of the triangle adjacent to "a" and the 90° angle. (while "c", not used, would be the leg opposite the 90° angle.)

"b" will be 17 because the rim is 17" and this is where I take the two measurements so see how far inward/outward the wheel/tire is.

"a" will be whatever I measured using the technique described above. Let's use -0.089 (the wheel is tilted inward, so I measure 0.089" more on the top of the wheel than I do on the bottom of the rim).

The result will be the angle opposite the "a" measurement.

Filling in the equation, then:

0.089 ÷ 17 = 0.0052353

I then invert 0.0052353 and convert the result to tan, which equals 0.2999575, or -0.3° camber (negative because the wheel is tilted inward - a higher measurement of distance on the top of the rim than on the bottom to the string).

Changing the equation around a little and it's a simple matter to calculate the distance I should see if I know the angle.

While I like your method (straight edge and bubble), mine just uses gravity to get a straight line. And if you don't like the math (I do), then just use your "1/32" for 0.15° trick.

My only problem (as you hinted at) with this method is to find relatively level ground (bubble level is best to determine this).

While I'd like a professional tool to adjust camber/caster (e.g. http://smartcamber.com/ProdCat/AlSuTool/alsutools.htm ~$300), until then I'll have to wait.

[This message has been edited by Stuart Moss (edited May 29, 2001).]

MY87ROC

thanx 82, yes he was trying to get less but said thats it, it won't go back anymore.
so this is how they are made, even when the car was new it was like this? he also said that this was not bad at .5, he has seen other cars as much as 5.* over and that was all it had!!


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TPIS airfoil,relocated MAT,AFPR,TB h2o bypass
March Underdrive Pulleys
otherwise stock 5.0TPI
700r4, 10 bolt 3.23 g92 axle, 4 wh. disc brks.

Frank88

Thanks guys. I think you're describing camber measurement which I agree can be done at home using a level or string (I like the string idea.) Sounds like there's no way to accurately measure caster (fore-and-aft tilt) w/o the special gauge.

I found a site: www.longacreracing.com who sell equipment at a reasonable cost. They also have some interesting info on their site.

thanks again,

Frank

AlkyIROC

Correct. Camber is the inward and outward tilt of the tire and can easily checked with a level but the original question asked about caster and that needs a special gauge.

82camaro

my87roc, Your car might have been in a little fender bender or the wheel/tire hit a curb. Some body/frame shops can tweak the subframe and correct the problem--I know of one near here that has done it before. That is, if you want to fix it. If it's not chewing up tires, I wouldn't worry about it. Setting the toe with a tape measure can be fairly accurate--A couple of months ago I put a tie-rod on my wifes 95 cutlass supreme SL and did a tape measure alignment. The alignment shop said it was off by .01--basicly perfect.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

Stuart Moss

As posted above, I adjusted caster by just moving the struts all the way back, hoping that that'll be ~4.5° and that both sides will be fairly close to oneanother.

I saw the site Frank88 posted. It had some interesting information.

I still like the "Smartcamber" tool that I posted in my post above. At the site Frank88 posted (which uses a magnet for mounting), the other attaches directly to a 12-18" rim (and it too measures caster/camber). It also compensates for un-level ground (important to me) and uses an accurate, digital/electonic gauge which can also be used to deteremine angles on other things (driveshaft angle, etc.).

The "magnetic" tool didn't seem to be able to compensate for unlevel ground (it stated to just park on as level ground as possible...).

Norm Peterson

You are correct, it is a description of camber measurement. But caster cannot conveniently be measured directly (you'd have to remove the front wheels without letting the suspension move and then somehow establish the locations of the balljoint centers), so it's indirectly determined from two camber measurements. With the gauge you zero the gauge with the wheels turned 30 degrees one way, turn the wheels 30 degrees the other way and read. With bubble or string methods you measure and calculate the camber at 30 degrees left and 30 degrees right. Your caster is the algebraic difference between the two. As an example, with the wheels turned 30 degrees right you might calculate the left wheel camber at +0.75 degree; with the wheels turned 30 degrees left the camber might be -3.25 degree. Your caster is +4.0 degrees.

And keep in mind that the 1/32" = 0.15 degree conversion is only good for the 12" length; over a 17" length each 1/32" is only 0.105 degree.

Norm

[This message has been edited by Norm Peterson (edited May 30, 2001).]

Frank88

AHAH!

Norm, this is the technique I was asking about in my original post. Someone on the corvetteforum mentioned it (not as well as you did) and noone could explain how/why it works. I still don't understand!

In your example, left wheel caster is +.75 - (-3.25) = +4.0 degrees. Why isn't it -3.25 - .75 = -2.5 degrees? I guess I'm trying to understand the algorithm better and how it relates to front-end geometry.

If you don't mind taking some time to provide more explanation, I'd appreciate it.

thanks!

Frank

Norm Peterson

I have to admit that I hadn't previously bothered to go any deeper into the math than what was required to get my alignments done. But here goes. (And to anybody whose geometry courses are more recent than mine - think 1st gen Camaro vintage here - feel free to jump in.)

First, you want the result of your calculations to be consistent with the accepted conventions for caster and camber signs. If you're looking for the range between -3.25 and +0.75 starting from -3.25 you're solving -3.25 - (+.75), which still gives 4.0 as the magnitude, only the sign is negative. It's still the range between -3.25 and +0.75.

Now for the nasty part of it if you're trying to develop some total camber equations.

The presence of the steering axis inclination (as viewed from the front) introduces some complications into the formulas. It's already established that caster becomes camber according to some function of steering angle. More specifically, positive caster adds negative camber on the outer wheel as it is turned (and adds positive camber on the inner wheel). But the effects of steering axis inclination work differently, adding +camber on both the outside wheel and the inside wheel. Fortunately for the purpose of setting caster you can take advantage of this symmetry about the straight ahead position and take camber measurements at equal right and left steering angles to cancel this out.

The topic of how caster, camber, and steering axis inclination are inter-related has come up somewhat indirectly at CamaroZ28.com but nobody has yet posted a specific set of formulas over there either. Geometrically it would seem that you're looking at camber being the slope of a line along the surface of a cone whose axis is through the centers of the ball joints and whose half angle [EDIT (I think) is the steering axis angle.] I realize that 3rd gens use struts, so the strut attachment to the chassis is probably the analogous location to the upper ball joint in a SLA design.

Completely off the top of my head (and therefore probably of no significance) is the thought that perhaps the 30 degree steering angle was specifically chosen based on the numerical value of the sine of 30 degrees being 0.5. I seem to also vaguely remember another angle of something closer to 25 degrees being used, possibly the angle that corresponds to the arctan of 0.5, which is approximately 26.5 degrees. Anybody???

Norm

[This message has been edited by Norm Peterson (edited May 31, 2001).]

Stuart Moss

Norm,

Good catch - you were correct in elaborating on your 1/32" per 0.15° factor for camber. When I plugged in your 1/32" into my formula, I did not get the angle you did (0.15°), but 0.105° as you stated (actually 0.105323). I knew you used a 12" (vice my 17") length when making your calculation. I should have stated the correct value (0.105° per 17") as you did.

Everything you stated is correct. "You're the man".

Frank88

Norm,

Thanks - that helped a lot. I'm going to think about this some more and check out the camaroz28 link you posted. It makes sense that the various alignment parameters are related, via the various linkages, control arms, etc.

Frank

Norm Peterson

Well, maybe it's closer to correct after all the edits I made this morning to my previous post regarding cone surfaces.

This thread sent me back to the old math books last night looking for formulas, and I still can't find one for the surface of a cone whose axis is inclined. And it occurred to me that my original description of the cone half angle was somewhat wide of the mark. That half angle is the steering axis inclination which is fixed at the angle the upright part of the spindle makes with the vertical. That's with the stub axle horizontal and the wheel is consequently at zero camber (and pointing straight ahead). Caster and camber settings only affect the inclination of the axis in space.

But thanks.

Norm



[This message has been edited by Norm Peterson (edited May 31, 2001).]

Norm Peterson

The reason that 30 degrees is used does in fact appear to be due to the value of the sine of 30 degrees being 0.5. Unless I've botched the derivation (wouldn't be the first time), total camber at any steer angle is the algebraic sum of the static camber setting, steering axis inclination times (1 - cosine(steer angle) ), and caster setting times sine(steer angle). As previously discussed, the effects of SAI cancel out as long as the right and left steer angles are the same. The initial camber setting is constant, of course. That leaves the camber range equal to caster times the range of the sine function between +30 degrees and -30 degrees, or 1.00.

Norm