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Discussion Starter #1
Which alignnment paramater(s) are affected by adding or not adding the drivers weight before alignment? Seems to me that caster and toe-in would remain the same. The last alignment shop I went to said that the alignment machine automatically compensated for a 165lb. driver in the drivers seat. I can't see how this can work without the alignment machine knowing the spring ratings.
 

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Which alignnment paramater(s) are affected by adding or not adding the drivers weight before alignment? Seems to me that caster and toe-in would remain the same. The last alignment shop I went to said that the alignment machine automatically compensated for a 165lb. driver in the drivers seat. I can't see how this can work without the alignment machine knowing the spring ratings.
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The original Alfa suspension manuals for the 105 series showed putting standard weights in the seat(s) roughly equal to what the occupants would be. Only makes sense to me, that you want the specs set with how the car will be loaded in the real world. When Glenn Oliveria and I did the alignment on my race Super, he had me sit in the seat.

Andrew
 

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Discussion Starter #4
I agree that it makes sense to set the alignment under the conditions that the car will be driven under and that adding weight is advised by the Alfa manual. But then again, is adding driver weight in the same realm as changing caster and camber on one side to compensate for road crown? Adding driver weight for alignment seems to be as controversial as oil viscosity when you visit other car forums, that's why I am curious as to which parameters change with the addition of weight and in what way they change. Under occasional spirited street driving will I even notice the change? I was on a hot rod forum that the poster swears that all of the race car shops that he has been to set ride height and corner balance with the driver in the car but set caster, camber, and toe with the driver out of the car. How much of a difference will it make with my 125# wife in the passenger seat? I copied the following question from a post I added to in the suspension forum:

Home shop caster setting
Will this work to get a fairly accurate caster setting: Use a laser level to assure that the floor is level where all 4 tires contact the floor (shim under the tires as necessary), set the front wheels going straight forward, place a 24" carpenter's level plumb(vertical) in a machinist's vice placed on the floor forward of the ball joints, measure the horizontal difference in the space between the threaded stems or (turning center countersinks) of the upper and lower ball joints and the level, measure the vertical distance between the threaded ends of the ball joints, then do the math to determine the angle? caster angle= tan- (horizontal measurement difference distance divided by the vertical measurement between the ball joints)
 

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I have wondered about the same thing. Changing the ride height definitely alters the camber (lowering the car gives negative camber) but I'm not sure about the caster.
The caster rod is attached at the top ball joint and, as far as I could tell ( but I'm happy to be corrected..), its the lower ball joint that moves up and down with shortened or lengthened springs as the angle of the lower wishbone changes. So the position of the caster rod probably doesn't change much, if at all.

I suppose the answer is to experiment to see how much the camber changes when someone sits in the car. I have a spirit level (bubble gauge) that gives an angle reading from vertical, for measuring camber so could give it a go.
I would guess it wont change much as I have tried standing on a front spring when I had them out (no, I don't know why I would do that either, its hard to balance!) and I couldn't see/feel any compression. I weigh about 170 lbs.
 

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Discussion Starter #6
Yes, I do plan to experiment with or without weight, that's why I was asking about which parameters change. Obviously toe and camber are the easiest to check at home. I don't have a spirit level that reads degrees but a regular level works if you measure the gap between the top and bottom of the rim between the level and use right angle inverse tangent math to get the degrees. If there is a 1/8" gap at the top of a 15" diameter rim from true vertical then the camber is negative 0.477 degrees. I think that my approach for measuring caster will work but there may be a variable that I'm not seeing.
 

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Yes, I do plan to experiment with or without weight, that's why I was asking about which parameters change. Obviously toe and camber are the easiest to check at home. I don't have a spirit level that reads degrees but a regular level works if you measure the gap between the top and bottom of the rim between the level and use right angle inverse tangent math to get the degrees. If there is a 1/8" gap at the top of a 15" diameter rim from true vertical then the camber is negative 0.477 degrees. I think that my approach for measuring caster will work but there may be a variable that I'm not seeing.
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Discussion Starter #8
Steve: Thanks, I like real world practical answers. I can be as anal and obsessive as the next guy, but putting 150 - 200 lbs on one side of the car just didn't make sense to me unless you're racing and looking for top performance. What do you think of my caster measurement approach? Am I correct in assuming that caster remains the same with the wheels turned to full left or right lock? It would be a lot easier to get measurements off of the ball joint stems with the wheel turned.
 

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Steve: Thanks, I like real world practical answers. I can be as anal and obsessive as the next guy, but putting 150 - 200 lbs on one side of the car just didn't make sense to me unless you're racing and looking for top performance. What do you think of my caster measurement approach? Am I correct in assuming that caster remains the same with the wheels turned to full left or right lock? It would be a lot easier to get measurements off of the ball joint stems with the wheel turned.
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Thanks for the write ups Steve, that's very informative and covers it well.
I've been trying to set my own parameters too as I have got fed up of tyre places, even with the full-on four wheel alignment gear, getting it wrong. Its easy to tell when there is too little positive caster as the steering is far too light and doesn't self-centre after turning. And that's how the tyre place set it last time :taz:
With the S4 power steering you can afford to have 2 - 3 degrees of caster and not worry about making it harder to turn the wheel.

Bob, I'll be really interested to see if your ingenious method works. It sounds like it should do but I guess the difficulty will be actually getting access to do the measurements accurately, given that you have to leave the wheels on.
 

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Thanks for the write ups Steve, that's very informative and covers it well.
I've been trying to set my own parameters too as I have got fed up of tyre places, even with the full-on four wheel alignment gear, getting it wrong. Its easy to tell when there is too little positive caster as the steering is far too light and doesn't self-centre after turning. And that's how the tyre place set it last time :taz:
With the S4 power steering you can afford to have 2 - 3 degrees of caster and not worry about making it harder to turn the wheel.

Bob, I'll be really interested to see if your ingenious method works. It sounds like it should do but I guess the difficulty will be actually getting access to do the measurements accurately, given that you have to leave the wheels on.
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Thanks for the links. That last one shows the camber gauge I have.

Apparently you can use it to measure the caster angle as you have suggested previously - put the wheels on turn plates then turn them to (the leaflet that came with it suggests) 20 degrees, set to zero, turn back and measure again.
So I plan to get some turn plates and have a go at that.
 

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There's been a bit of misinformation posted in this thread. For a quick read on the three basic alignment angles, camber caster and toe, please click here. For an even quicker read on the non-adjustable SAI/KPI (Steering Axis Inclination/KingPin Inclination), click here.
 

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I provided the two links above to address two pieces of misinformation posted earlier. The first;
...people use KPI or king pin ( in this case the uprite ) angle as viewed from the side ...
KPI (KingPin Inclination) is a term more accurately applied to vehicles with kingpins. SAI, or Steering Axis Inclination, is for vehicles without kingpins. It is a specific non-adjustable angle built into the suspension geometry and is viewed from the front or rear of the vehicle, not the side.
...[if] the uprite appears to be leaning backwards then that's neg kpi...
As viewed from the side, a backwards leaning upright has positive caster, not negative KPI.

Scrub radius and road crown pull compensation are discussions for another day.
 

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Discussion Starter #16
I respect both Stevexsm's and Pappajam's technical opinions and experience. I think that expressing differences in technical opinions, procedures, and terminology is what this board should be about and helps all of us understand our car's engineering better. At least that's what I'm looking for when I log on. I don't think that calling someone who enjoys driving a automatic spider a "girly boy" and should join a Miata club is in any way a positive contribution to this board. I was a gold subscription member, but why pay $40.00 a year to be insulted?

I actually logged on to give a FYI about an accurate and inexpensive level that can be used for alignment purposes. It's made by SRA Measurement Products Part# me-an-pro-lev-40. It's claimed to be accurate to 0.1 Degree in both vertical and horizontal positions. It's around $50.00 including shipping. $50.00 isn't pocket change but it's cheap considering the price of other engineering levels.
 

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+1 for those sentiments Bob. I enjoy driving my automatic car as much as I enjoy the manual. Horses for courses, as they.
Calling someone names on this (any) forum just reflects badly on the poster, really.

That level could be useful, I like the idea of the buzzer.
I'm still struggling to think how you would actually get it into position and make any accurate measurements with the wheel in the way, though.
If you have adjustable jack stands I guess you could measure the height off the floor to the bottom of the spring pan then jack the car up, take the wheel off and drop it back onto a jack stand under the pan at the correct height. That would have the effect of having the car at the correct height and give you access to the area you want to measure.
 

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I'm still struggling to think how you would actually get it into position and make any accurate measurements with the wheel in the way, though.
When I do my own alignments I use vinyl flooring squares for my alignment pads. I simply sandwich a thin layer of grease between two sheets.

I can vouch for the Digital Angle Gage. In my shop maintenance and set up guys use them all the time. We have also used them for inspection proposes in a pinch.

I do have to admit that in recent times I have been very spoiled by only having to adjust toe on modern cars.
 

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Discussion Starter #19 (Edited)
After being educated about the fact that the true caster angle isn't measured by the actual angle of the ball joint centers I will probably use the stem measurement only for the initial setup after the installation of the new lower ball joints, control arm bushings, and adjustable upper control arm.. A piece of 1/8" aluminum could be cut to whatever convoluted shape necessary to get around whatever is in the way. Both shapes need not be the same as long as the overall length from the stems is equal and held parallel to each other. I'm thinking about removing the cotter pin and castle nut and drilling the appropriate sized hole in the aluminum pieces and then holding them in place with the nut. I can use the digital gauge placed vertically on the rim with the tire turned 20 degrees, zero it out, and then turn it 20 degrees the other way to get the true caster reading (I'll probably have to add or subtract 90 degrees to get the true angle.) I read on another forum about a guy taking 4 pizza pans, putting 2 under each wheel with a coating of olive oil in between as his turntable. Probably worked well :thumbup:
 

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I read on another forum about a guy taking 4 pizza pans, putting 2 under each wheel with a coating of olive oil in between as his turntable. Probably worked well
Brilliant! What does he use for cars that aren't Italian??

That digital gauge does look cool, Jason. Not expensive either.
 
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