How to do an alignment with a string system?

[FoxSTI]

Still not sure how the L ruler would help or how you are doing your alignment, but so far this is what I have come up with.
Maybe I am totally wrong and not considering some important items.

I have attempted to find the center of the car (chassis) and from there (center line) offset a parallel laser line at a know distance at both sides.
Then I take a measurement from the laser line to the center hub. Both measurements should be the same at least at each side of the car. (in my test car all 4 happened to be the same).
At that point, I imagine I just take measurements to the front and rear of each tire.

For instance, on the front passenger tire there was a delta of 3/16" (toe out).

All this testing of the setup was done with the car with the tires on, on my driveway which slopes and is not leveled. Once I level the car and out on hubstands, I should be able to get actual measurements and go from there.


please confirm this a correct approach. I am interested to learn how I can make it better and how any other tools can help me.
I have made up a graphical sheet to use as a record working sheet to make sure I use the same setup on the car every time.

again, not an expert so I am looking for feedback - but this seems a very easy process.

[fatbillybob]

I have attempted to find the center of the car (chassis) and from there (center line)

I look for simple. I look for fool proof. What you are doing works but you have the ability to introduce the 1st error that will carry and magnify itself with every additional measure. Finding chassis centerline is nearly impossible with any degree of accuracy IMO. But if you can truly find it then yes that will be a fine reference point. I can adjust my suspension based on where the wheels are not worrying about the centerline because the distance of centerline to wheel hubs is fixed. So the important thing is just the relationship of the wheels to each other. I would be willing to bet you that if you started with chassis centerline that I could prove to you that your thrust is not zero just because of the difficulty of finding and using chassis centerline.

[FoxSTI]

I look for simple. I look for fool proof. What you are doing works... Finding chassis centerline is nearly impossible with any degree of accuracy IMO.

It all depends on that centerline and making sure the lasers are parallel to it and to known point on the car.
If you take your time and do it with the proper tools you can find it very accurately. Then as I mentioned you can use your axles to QC. squareness of the setup or rig.

In essence we just need to be able to lay out a line on each side of the car parallel , not to the wheels but to a constant reference point.

but you have the ability to introduce the 1st error that will carry and magnify itself with every additional measure

You can do that in any instance things are not setup up properly. For instance referencing the axle nuts could also throw things off if it happens that one axle is 1/8" longer on one side because the factory goofed off.


Why don't you share how you keep thing simple and fool proof - would you mind?

Using laser level and "L" rules make for simple reproducible results because the reference points are now stupid simple

From reading several responses it seems like these setup ups are kind of a hidden art and not many want to share how they do it. I don't mind if the next guys knows how I do my alignment, all I care is about driving a better line on the course than him. No alignment can do that for you.

Anyway have a happy 4th folks (for those of us in the USA)
This is starting to sound like one those mine is better than yours.

[fatbillybob]

it is hard to put it down on paper. Takes 10 mins to show it. Like some people try and use laser level and ruler to get a flat floor. Some carry around long poles and strap levels on poles. Some use a bucket of water, aquarium tube and a ruler. There are many ways. Think about it and tell me which way introduces the least potential error and is the fastest and most convenient? Do the math on being 1/2 degree off with your laser beam over a 9ft wheel base is almost 1". That will totally jack your flat floor. With water all you have to do is read a ruler and your margin of error is 1/2 of the smallest division on that ruler. I have tried them all and pick my poison. I did not invent any of them so I'm not married to a technique. They all work. Ultimately you have to do what works for you. Everything has pluses and minuses.

[FoxSTI]

water level wins every-time for leveling unless you have a "total station".
The whole idea here for anyone who is interested in down their own alignment:

1- provide a leveled surface under the car
2- establish equidistant parallel lines (laser or strings) to the cars longitudinal axis on both side of the side - one one each side.
3- take measurements from those lines to point on the wheels or wheel stands.

Its very simple in principal. How you level your floor and how you establish those lines along side the car is where the "magic" comes into to plan and its up to the person doing the alignment to figure out.
For me it seems that if I am find the center of my chassis, that is a good reference, and if I can confirm and QC it with then hubs, then I am good.

[FoxSTI]

Today I decided to play w me wife's car. I laid a line along the center of the car, then offset a line to leach side 36".
I took measurement to the wheel hubcap on the rear and front axle. (I know this was just a test.

Here is what I found. Measurements where the same on both sides of the car. However the fronts where 2.25" to the string (laser) and the rear measurement was 2.75"
So there was a consistent 1/2" different between the front and the rear.

So here is my question. I thought that axles lengths were the same front and rear on cars. But apparently they are not - Or I screwed up laying out my lines.. (?)
Or my lasers are walking by the time they reach the front wheels?

If I had set the outside laser lines equidistant to all 4 hubcaps /axles, the lasers would be a smaller distance apart along the back wheels compared to the front.

[BryanPendleton]

I think most alignment shops reference toe to a 24in wheel, correct? The hubstands come with a toe bar that is 24in. So if you measure toe at the ends of those bars, you will likely be speaking the same language to most when they describe their toe settings.

I switched from Toe Plates (24" combined toe measurements) to SmartStrings (toe measurement on individual 15" wheel), so I too was curious about the conversion of values. It was really interesting to see how subtle of an angle change is actually being made. Since switching to SmartStrings, I also quickly switched to metric units as its so much easy to measure in MM as opposed to fractions of an inch.

Here is a quick table I threw together:

[albertg]

Thanks for the chart. I need to do an alignment before this weekend and I couldn't remember what was said on this thread about toe. I still always hear people talk about toe in fractions of an inch, but if you look at the chart you could be a bit off from each other. 3mm toe (just under 1/8) measured at a 24in wheel is the same as 2mm (just under 1/13) measured at a 16in wheel.