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944 String Alignment Reference Points

 
Old 07-09-2019, 01:18 PM
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nrider42
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Default 944 String Alignment Reference Points

Question for those of you who do their own string alignments, what reference points do you use to make your strings parallel? The published front and rear track widths are different (F:58.2, R:57.1). I usually set up a third string under the car which I center on the suspension mounting points and then set my outer strings from that center. Works well for me but I am feeling lazy

What points do you measure from to make your outer strings parallel?
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Old 07-09-2019, 02:23 PM
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I use 2 pieces of 3/4" conduit that I have milled slots in that the strings lie in, that way I know they are parallel to each other. Then I just get the measurements from the center of the wheel to string equal on each side.
I can use this on any car without ever worrying about track widths.
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Old 07-09-2019, 02:33 PM
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Establishing a centerline and working out from there is certainly the best policy. I did that and established permanent marks at the front and rear of the car. Then I used some 1/2" conduits to hold my strings. They are marked at a centerline and then a reasonable distance outward, equidistant. Being as this was a track car, I mounted plastic conduit supports on the front and rear of the car to hold the conduit in place. Line up the centerpoint of the conduit with your marks and the outboard marks should be reasonably parallel.

BTW, I'm not going to state this categorically but I think the spacers at the back hubs on a N/A car may serve to cause the front and track width to be the same.

I have always done my own alignments. Especially with a track car, it is a major PITA to trailer it to an alignment shop.

https://newhillgarage.com/2018/04/20...ignment-specs/
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Old 07-09-2019, 02:35 PM
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That makes sense. I guess it is really simple isn't it. As long as the front wheel center to string measurements are equal to each other and the rear wheel center to string measurements are equal to each other then it is parallel.

I like it when I think stupid things out loud in front of the internet....
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Old 07-09-2019, 05:01 PM
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Originally Posted by nrider42 View Post
That makes sense. I guess it is really simple isn't it. As long as the front wheel center to string measurements are equal to each other and the rear wheel center to string measurements are equal to each other then it is parallel.

I like it when I think stupid things out loud in front of the internet....
Nope, not necessarily! Think about it - if you have the strings diverging from the centre line by the same angle on both sides, then your conditions above would be met, but the strings would not be parallel.

This is why I think the best approach is as tc944 described - using 2 poles with slots milled at identical distances. This guarantees that the strings are parallel. Your next problem is making sure that you're aligning to the car's centre line (iow "thrust angle"). That's where the wheel centre to string measurements come in.
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Old 07-09-2019, 05:31 PM
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Understood. I was replying to tc944's conduit solution.....thinking through that track doesn't matter.
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Old 07-09-2019, 06:31 PM
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If the track widths are the same front to rear, and the wheels are the same width, and you are measuring to the 6 o'clock or 12 o'clock position on the front wheels, and you neglect camber effects, then equalizing the measurements without going off a centerline can get you pretty close. But if any of these factors are off, there will be no indication of a problem and as Divil says the lines may not be parallel. I just feel better working off a centerline every time.

"you are measuring to the 6 o'clock or 12 o'clock position on the front wheels" - Note- By definition you are going to **** the front wheels inward a little bit, so you have to measure at 6 or 12 when checking for parallelity. Which can be hard if your strings aren't set up at the right height.

"you neglect camber effects" - Note- if the front and rear wheels have different camber, then you are also not apples to apples when measuring against the wheels.
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Old 07-09-2019, 06:41 PM
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Originally Posted by harveyf View Post
If the track widths are the same front to rear, and the wheels are the same width, and you are measuring to the 6 o'clock or 12 o'clock position on the front wheels, and you neglect camber effects, then equalizing the measurements without going off a centerline can get you pretty close. But if any of these factors are off, there will be no indication of a problem and as Divil says the lines may not be parallel. I just feel better working off a centerline every time.

"you are measuring to the 6 o'clock or 12 o'clock position on the front wheels" - Note- By definition you are going to **** the front wheels inward a little bit, so you have to measure at 6 or 12 when checking for parallelity. Which can be hard if your strings aren't set up at the right height.

"you neglect camber effects" - Note- if the front and rear wheels have different camber, then you are also not apples to apples when measuring against the wheels.
Why not measure the string distance from the centre of the wheels, instead of the 12 or 6 o'clock position?
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Old 07-09-2019, 07:41 PM
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Originally Posted by divil View Post
Why not measure the string distance from the centre of the wheels, instead of the 12 or 6 o'clock position?
They mean the variability of the position of the spindle dependant on existing camber when setting up.

Personally I use the center at the grease cap...., and you are talking about someone who laser levels scales when balancing.

I use two 1" box tubes, notched for thread but after the original setup on each car, I mark, drill and tap holes in the car itself.

With the tube positions and orientation marked permanently, it takes me 5 minutes to attach with 8mm thread bolts.....and they don't move.

T
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Old 07-10-2019, 11:36 AM
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The OP didn't really mention this but if all you are trying to do is get close enough to drive to the alignment shop, then most any method will be close enough. If you are trying to do your own alignment then the best practices described above would be recommended.
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