Need a little help figuring something out

[Ron Sutton]

Lance, I think I remember you’re leaving town for a few days. Take this & digest, so you can plan to do this sometime after you return. This takes time & patience.

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In this post, I’ll lay out a method to measure all of the pivot points in your upper & lower A-arms … plus track width, sway bar, shock & spring points.

There are hundreds of ways to doing most things. I’m laying out one way I think most car guys can do in their garage. You will need some basic tools & creative body language when it comes to getting into difficult spots.

This method will take a little longer, but we will have accurate numbers … AND … as you make changes, you will need to take only a few measurements & we’ll still know where everything is.

These dimensions are important, so taking your time, measuring several times & even measuring different ways will insure we have accurate numbers.



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Tools:
You will need a good tape measure. Use just one … so if the end isn’t dead zero perfectly accurate, at least all the measurements are the same. Every 1/16” matters.

Tool check list or shopping list:
Good, readable tape measure.
4-6” dial or digital caliper.
Short laser level (6-10”)
String
2 Bob weights.
Chalk line (blue will come off your floor eventually. Red is not coming out … ever)
Roll of quality string
Removable masking tape (Blue 3M works best)
Sharpie fine point marker(s)
Brake Cleaner & paper towels
Note pad & pens

Sears has everything in one stop if you need something.

Laser levels
http://www.sears.com/shc/s/p_10153_12605_00948292000P
http://www.harborfreight.com/2-in-1-...vel-67800.html

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Pre-measure Ball Joints:
If you have some spare upper & lower joints ... great. If not, make a stop at your local, friendly auto parts store where you buy parts. You’ll need to borrow an upper & lower ball joint to measure at the counter.

Lance, you need a Moog K5208 for the upper & Moog K6145 for the lower. Unless your DSE upper A-arms have a special ball joint in them. Call DSE & find out “for sure” as this is CRITCAL.











Refer to the photos I’ve attached here. Take a ball joint & lean it all the way to the right & draw a Sharpie line on the housing … in line with the BJ pin. Now lean it left & do it again. Now straight up & do it. There is your true pivot center. Take your dial/digital calipers & measure from the pivot center to the top of the housing & again from the pivot center to the end of the stud.

Do both ball joints & write down all the numbers. When you’re under the car, getting to the top off the housing or the end of the stud will be WAY easier to achieve. You just need to do the math … along with measuring … to arrive at the true pivot center locations on your car.

What was the brake cleaner & paper towel for? To clean off your Sharpie marks on the ball joint housings.

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Before you start:
a. Plan for this to take half a day.
b. You’ll need a helper to hold the other end of the tape and to “spot” for you.
c. Work out how you’re going to put your weight in the seat. Don’t use a person. (We use lead)
d. Put your AutoX tires on & set the tire pressures just like you compete with.
e. Get the car as close to “race ready” as possible: fuel level, stuff out of (or in) the car, etc.
f. CRITICAL: Document all numbers & details on paper, so we can refer back later.

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Platform:
The tires & suspension have to be “loaded” just like the car is on the ground. So you can not use a chassis lift or jack stands. You can use a drive on lift.

The car needs to be on its tires, just like ride height, but you need to be able to get under it. We use 10” Joe’s Racing stands & simply add 10” to all of our height numbers.



You “may” be able to do this on the garage floor, but it is harder. Depending on ride height you may not be able to get under the car well, or at all. If you’re doing this on the floor, pick a spot as flat as possible with no dips.

I’ve seen guys use car ramps & stands … shimmed so all 4 to the exact same height. I’ve seen guys with shops use muffler & oil change pits, where they can walk under the car. So give this some thought on where & how works best for you.

If you rig something up to raise the car, all 4 stands need to be the EXACT same height. Any height will do, but they have to be the same. Whatever the number is, you will be subtracting it from your height numbers to get true numbers, as if the car was on the ground.

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Pull the car into your “space” straight. Make sure the front wheels are “dead true straight” as you roll it in & do NOT turn the steering wheel once you’re in your spot. Back up & do it again if you need to.

A simple way to check & confirm the front wheels are “dead true straight” … is to pull a long, taut string across rear tire & front tire on one side … at the same height (preferably axle centerline) … and pay attention to how it lays across the front tire. Do both sides.

If the car is toed-in, the gap between the string & front sidewall, of the front tires, should be the same on both sides. If the car is toed-out, the gap between the string & rear sidewall, of the front tires, should be the same on both sides. If a gap is bigger on one side, the steering is not straight.

You don’t want to have to turn the wheels … in their spot … and leave them, as there will be “tire bind” (unless you have some way of freely sliding one wheel). Get it true & back the car up 2’ & roll it into place again if you need to.

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3 types of measurements.
1. Height … from the ground up to the pivot point
2. Left or right … always from the car centerline
3. Forward or backwards … of the front axle spindle centerline.

What you’re measuring … in order:
a. Car ride height.
b. Car centerline.
c. Front axle centerline.
d. All four ball joints ... at true center of their pivot.
e. All 8 A-arm pivot centers (2 for each upper & lower A-arm).
f. Shock pivot centers
g. Spring end centers
h. Sway bar attachment points to A-arms.
i. Track width

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Here is detail for each area of measurements.

a. Car ride height.
Pick a spot on the bottom of the frame rails that will be easy to measure now & in the future. The further apart you go, the more accurate. Most racers usually pick a spot in front of the rear tires & behind the front tires … if the frame rails are wide at that point & out near the rocker panel. Either pick a spot with identifying holes or marks on the bottom side of the frame rails … or make something to permanently mark these spots. You’ll use these for the life of the car, no matter what changes you make.

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b. Car centerline.

Before we start … “mark down” … means using either the laser or plumb bob & string … to put a mark on the floor exactly where a point is. Some people use the term “transfer” … meaning to transfer a point on the chassis or suspension onto the ground.

I don’t like marking on my epoxy coated floors, so I put blue masking tape down first & write on it with the Sharpie marker.

This measuring process is difficult & somewhat subjective. Pick a section of the frame that looks symmetrical … and either go inside or outside (but use the same on both sides of the car) & “mark down” … putting a dot or “x” on the floor. Do this in 3 spots, using 3 different sections of the front frame. Then, do this in the rear, using 3 sections of the rear frame.




Now find the center of those 6 frame sections, using tape & sharpie again.

Next, with a friend’s help, pull your chalk line taut … down the center of the car … on the floor … and the string “should” hit all 6 frame section centers. If it doesn’t, either recheck your measurements and/or re-evaluate your choice of locations. Ultimately, you’re going to put a chalk line on the floor using the marks you trust.

That is the car centerline that everything is going to be measured from & to.

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c. Front axle centerline.

A simple way to do this is to pull a taut string behind the front tires, on the floor, and mark the string location on both sides. Do the same in the front. Split the difference & that is the front axle centerline. Problems only occur with this method with different tires, different pressures, suspension or tire bind from not rolling it into place straight.

Put a chalk line on the floor representing the front axle centerline. Many things, but not all, will need to be measured from & to this point.

For all things in front of the front axle centerline, express them in negative or minus numbers. Example: if something is 2 & 3/8” in front of the front spindle centerline, write it down as -2 & 3/8”.

Everything behind the front axle, express as positive numbers.


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d. Locate all four ball joints ... at true center of their pivot.

Since you have already pre-measured the ball joints, this part is not as tough as it would be if you were trying to find the pivot centers while measuring. Eyeballing these pivot centers ALWAYS leads to inaccurate data.

Use your measurements from the top off the housing, or the end of the stud, to the axle centerline & work out the math. Double check by eyeballing to see if your math places the pivot center where it actually is.
Your roll center locations & camber gain numbers will only be as accurate as your measurements. This is a time consuming & somewhat tedious operation. I always suggest people take the time to do it right the first time, so you don’t have to do it over (or suffer handling problems from incorrect tuning).

You need to measure the location of each ball joint in 3 directions … all based on the true pivot point of that ball joint. You need the …
1. Height … from the ground up to the pivot point
2. Left or right … always from the car centerline
3. Forward or backwards … of the front axle spindle centerline.

Reminder: for all things in front of the front axle centerline, express them in negative or minus numbers. Example: if something is 2 & 3/8” in front of the front spindle centerline, write it down as -2 & 3/8”. Everything behind the front axle, express as positive numbers.


I can’t stress this enough. Make sure your tape is both straight & a true 90 degrees to what you’re measuring. Having the tape measure angled any direction other than a true 90 degrees will produce incorrect numbers. This is hard to see when you’re holding the tape under the car in a tight spot.

Use your friend as a “spotter” to insure your tape is straight up & down for height measurements on 2 planes ... and 90 degrees to the car centerline & level for right & left distance measurements.

There are times when it is more accurate to …
• Use a tape and measure directly.
• Hang a plumb bob on a string off the point, or near it, and measure.



• Utilize the laser (and level) to point up or down & transfer the measurements.
• Use the level to extend a point out to where you can use the tape measure.
• You’ll just have to use your best judgment or try it different ways.

I like to mark on tape on the floor … so I don’t forget (I’m old). I put “points” on the tape along with the measurement … so I can find the point again easily to re-measure if I want or need to … and so I can re-check my measurements.

I check my numbers & recheck them several times. So when I capture them all … I KNOW THEY’RE RIGHT … and can trust the data & results.

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e. All 8 A-arm pivot centers (2 for each upper & lower A-arm).

You need to measure the location of all 8 A-arm pivots in 3 directions … all based on the true pivot point of the bushing. You need the …
1. Height … from the ground up to the pivot point
2. Left or right … always from the car centerline
3. Forward or backwards … of the front axle spindle centerline.

For the upper A-Arms … you can simply measure off the ends of the pivot shaft. For the lower A-arms, I need you to measure each bushing bolt … on both sides … and average the numbers.

For example: If the center of the bolt at front of the driver side lower A-arm is 8-11/16” in the front of the bushing & 8-9/16” in the back of the bushing … you will average that to 8-5/8”. That is the height of that bushing.

When measuring from the car centerline, the differences are bigger, because the lower A-arm is angled a lot. So, from car centerline, if the center of the bolt in front of the bushing is 10-1/16” & the center of the bolt on in the back of the same bushing is 10-7/16” … you will average that to 10-1/4”. That is the distance from the car centerline to the centerline of that bushing.

If this same bushing is 1-1/2” ahead of the axle centerline on one side & 1-7/8” ahead of the axle centerline on the other side … you will average that to 1-11/16” … and because it is AHEAD of the front axle centerline, you need to express it as a negative, so write it as -1-11/16”

We need all 3 dimensions on all 4 bushings.

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f. Shock pivot centers

The process should be getting simpler by now. You’re measuring to find shock pivot point centers. We need all 3 dimensions on all 4 front shock bushings.

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g. Spring end centers

A little tricky to measure … but we need measurements from the center of the spring top … to the front axle centerline & car centerline … and the height.

We need the same thing for the bottom of the spring … and for both front springs.

** Anyone who is following along with us … if you have coil-overs … all you need to do is locate the shock pivot centers, as the spring does whatever the shock does.

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h. Sway bar attachment points to A-arms.

I saved the simple stuff for the last two. We do not need measurements for height or distance to front axle centerline.

For this part, all we need are accurate measurements from the center of the car to the center if the connection points on the A-arm.

** Anyone following along with us, if your sway bar has linkages that mount off the side of the sway bar arm … you want to measure to the center of the connection points on the A-arm … NOT the center of the sway bar arm.

Sway bar arm length matters to calculate your actual sway bar rate. So now is a good time to measure & record it. Measure from center of main sway bar to center of pivot on sway bar arm … 90 degrees from the main sway bar … regardless of angle or shape of the arm.

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i. Track width

Just for clarification … “tread width” is outside to outside of the tread. “Track width” is center to center. A lot of people get those confused & our conversations get sidelined.

We need to know the track width … the true center to center of the front tire contact patches. Several options, but here is a quickie.

On the front side of the tires … measure from the outside of the tread width on one tire … across to the inside tread width on the other side. Do the same on the back side of the front tires … and average the two numbers … to account for any toe in or out.

If you get 55-1/2 in the front & 55-3/8” in the rear, average that to 55-7/16”.

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Tips:
• Remember to subtract the distance you raised the car up from ride height for all height measurements.
• Reminder: for all things in front of the front axle centerline, express them in negative or minus numbers. Example: if something is 2 & 3/8” in front of the front spindle centerline, write it down as - 2 & 3/8”. Everything behind the front axle, express as positive numbers.
• Your roll center locations & camber gain numbers will only be as accurate as your measurements & small #’s make a big difference. I measure everything I can on my cars with a digital caliper to the thousandth. It is that important.
• Take your time & be precise. Don’t just “eyeball it.”
• Getting true measurements is difficult. Experiment & be creative with measuring methods, but be accurate.
• This a time consuming & somewhat tedious operation. I always suggest people take the time to do it right the first time, so you don’t have to do it over (or suffer from incorrect tuning).
• Because you got frame heights on 4 corners of the car, you will be able to make many adjustments to the car, and know what changed & where you are, by rechecking frame heights.
• For example, if you lower the whole car ½” … all of your frame mounted pivots just went down ½” … and your ball joints did not. That is easy to change in the roll center programs & know what your geometry is then.


When you have the numbers, post them here on the Forum in an order that matches the numbers in this photo. After I enter them all, I’ll run calcs & post the graph.





We won’t be able to determine true roll angle or dive numbers until you get shock travel measurements from your June 30th AutoX event.

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If anyone has any questions, feel free to chime in on this thread.


Ron Sutton