Home alignment

[BK911]

I came up with an economical solution to home alignment. Is it as accurate as a shop? No. Is it good enough for some performance street/autocross/DE's? Yes! And only about $12 in material and a couple of hours work!

Basically I created a square jig around the perimeter of my car. The two long sides are the same length, the two short sides are the same length, each corner is the same height as the center of my hubs, the distance from the string to the front r/l hubs are equal, and the distance from the string to the rear r/l hubs are equal. Then it was easy. Just measure the front of the rim to the string and compare to the rear of the rim to the string. Make the appropriate adjustment and re-measure. Repeat. Repeat. Repeat. You get the point!

Of course do the ride height, corner balance and camber before this. For the camber I used a level set to plumb and measured the top and botom of each rim from the plumb level. Then simple trig and Viola!

[Rot 911]

I can't tell from the pic, maybe an optical illusion due to the color of the floor, but does the jig attach to the car or rest on the floor and balanced up against the car?

[TimT]

There is a vendor out there selling something that looks quite similar to your set up for about $375 or so.

A few years ago at a Watkins Glen club race I remember seeing G&W Motorsports doing alignments on cup cars with strings.

[billwagnon]

How do you do caster?

[RoninLB]

Originally posted by BK911
The two long sides are the same length, the two short sides are the same length, each corner is the same height as the center of my hubs, the distance from the string to the front r/l hubs are equal, and the distance from the string to the rear r/l hubs are equal.

great work BK...two short sides being equal is imp. IMO because the distance from the side of front and rear wheels to the line probably will not be equal.......Ron

[BK911]

Caster? Dunno! I haven't gotten to that yet! I saw the set for $375, that's what gave me the idea. Half an hour at Home Depot and $12 later I was prepared to begin the assembly process. All the bars are attached to the car itself via pipe clamps. And yes, the distances from the hub to the string are different for the front and rear wheels, but the same left and right.

[TimT]

Set caster first. then camber, then fine tune toe..The strings come into play after you have your caster and camber resovled

[billwagnon]

How to do caster, though?

I would like to do my own alignment - my front tires are rather worn so I can't hurt them too much, but caster seems to be the deal breaker - a lot of guys say you need the alignment rack etc. but I keep thinking it's just geometry.

I did raise the height (that's where MY Labor Day weekend went!) and corner balance, and I quit driving the car til I can get it aligned or learn how to DIY it.

[Steve W]

I think there is a way to to measure caster, but I can't remember how I did it. It involves turning the front wheels something like 25 degrees? to the right, taking a camber measurement, and turning it 25 degrees to the left and taking another camber measurement. The difference was able to help you compute the caster.

[john_colasante]

Nice work. Let's explore this a little. How do you know you don't have a situation pictured below? Obviously I have exaggerated the chassis thrust.

[Steve W]

John, I would think if your rear toe was asymetrically out of wack as in your drawing, the rear end would steer to the right as in your drawing, and the front would have to steer right also to keep a straight line. Obviously, make sure your rear toe is correct by measuring the distance at the fore and aft rim edges from the string, and you should be ok.

[john_colasante]

Steve,

If you look at the diagram you will see that without specifically squaring the box around the car one cannot determine if the chassis has thrust. That was the point I was illustrating. Just measuring the toe from the string does not tell us the whole story here. We need some reference to the geometric centerline. Also without additional measurments we cannot be sure that one of the wheels is set back in the chassis.

[logician]

Hi,

Smart Racing Products (www.smartracingproducts.com) sells an alignment system that works as you propose. Check out the following links:

> http://www.smartracingproducts.com/pdf's/SmartStrings%20Web%20Flyer.pdf

> http://www.smartracingproducts.com/pdf's/SmartStrings%20Web%20Manual%20-%206-02.pdf

-Juan

[logician]

Hi,

Sorry, previous link didn't seem to work right. Try the following, and look for "Smart Strings" product about half way down the page:

http://www.smartracingproducts.com/ProdCat/AlSuTool/alsutools.htm

-Juan

[jluetjen]

Here's a thread where I outlined the process for doing a home alignment using the "String method". The process has been around for years. I proposed setting up the jigs on the floor, but I like DK's jigs better. I've just been trying to think of a way to mount them to the car. Anyhow, the process that I described already answers a few of your questions:

Just measuring the toe from the string does not tell us the whole story here. We need some reference to the geometric centerline. Also without additional measurments we cannot be sure that one of the wheels is set back in the chassis.

There are a couple of ways of looking at this problem.

1) If you measure the distance (right to left) between the lower suspension mounts on either side of the car and halve it -- you will have two points which represent the centerline of the suspension at each end of the car. If you run a string between those two points you will have the centerline of the car. Once you have the centerline, permenantly mark it at either end of the car using a punch for future reference. Carroll Smith outlined this method in his "...To Win" books. Grass Roots Motorsports described a clever twist to this where you get some butchers paper and tape it to the floor of your garage. Use a plumb-bob to mark the different points on the paper and then transfer the results back to the car using the plumb-bob.

2) As long as the distance between the center point of each front wheel and the string is equal, and the distance between the center point of each rear wheel and the string is equal, AND the two opposite sides of the parallelagram are equal, you should be OK. Any offset will be due to manufacturing tolerances of the suspension arms which are pretty small.

3) My car actually has a thrust angle of about 1/4 degree (unfortunately) because of a PO's misfortunate at Watkins Glen. I had no problems measuring it or dialing in the correct amount using the string method. As long as the parallelagram has equal length opposing sides, it works because the sides will be parallel (I believe that this is one of those Geometric rules from middle school. It's been soooo long! ).

4) Caster can be measured by turning the front wheels full right, measuring the camber, and then full left and doing the same thing. You then take the difference and that will be VERY close to the car's actual caster. Caster is a pretty "blunt instrument" -- the important thing is that it be fairly close to spec and most important: EQUAL ON BOTH SIDES. Otherwise your car will handle funny and pull to one side.

5) There is one "gotcha". If the car's chassis gets tweeked in an accident, you will need to readjust your jigs to take into account any movement of the chassis(tub) from it's original position.

PS: Don't undersell the accuracy of this method. While the equipment may not be accurate down to the 1/10 of a degree, chances are the operator will be more accurate then in a professional shop since s/he cares about how the car handles when the alignement is done.

[Tim L]

I have developed a system where you can check your alignment and make adjustments I think as good as any alignment shop. I purchased a laser level from harbor freight for $10 and got an aluminum bar that I cut to fit my rims. Then I attach the laser level to the bar and I hold the bar to the rim with a bungee cord. The first step is to make sure the car is level then set the camber front and rear. To do this I use a accurate machinist level and just hold it on the bar in the vertical position.(very easy). Then to set the toe in the rear you need a straight stick or bar of some sort as wide as your car and bar laser setup. On one end you mark a target and with the laser pointing forward from one rear wheel line the target up with the laser(I support the stick on two boxes that are the same height as the center of the wheels). Then attach the laser to the other rear wheel and aim it at the other side of the stick mark the stick at this point. Next move the stick to the rear and repeat the process. With the distance between the two marks you can calculate the total toe using trig functions(the toe of each wheel can be checked by measuring the distance from the front hubs to the laser when you have the laser pointing forward. The front is done the same as the rear and you only have to worry about total toe.

Tim

[Vin-barrett]

Has anyone made one of these alignment jigs for a later impact bumper car? I'd like to see how it was mounted

[T77911S]

this was basically the same setup i just had done on my car. the guy that did it was the meachanic for "spot" back in the 90's. stringing a car like this is very common among racers. he only did my toe, camber and weight balance, nothing with caster. he is running 3 deg neg camber on his 70. with toe settings, he gets no uneveven tire wear on the rear, which was my problem. my inside right rear was wearing very bad, even though an aligment was done by someone else just before i bought the car.
i did see a show where this dirt track guru was setting up a car. he set the caster by turning the wheels and checking the angle. for toe, he used this setup that looked like a big 'U". it slid under the car and he would measure form the front of the rim to the top of the U then do the same for the rear of the tire. much like stringing a car, except with a string, you can get the car square. measuring from the center of all 4 wheels to the string will center the car to the strings.

[aston@ultrasw.c]

I made up home alignment jigs and just for calibration I took it to Jack Furrier for a measurement only, no adjustment.

It only cost around $50 and confirmed all my numbers!

[stlrj]

Originally Posted by Steve W

I think there is a way to to measure caster, but I can't remember how I did it. It involves turning the front wheels something like 25 degrees? to the right, taking a camber measurement, and turning it 25 degrees to the left and taking another camber measurement. The difference was able to help you compute the caster.

I think you need to multiply the difference by four to give you your caster.

Ideally, if you could turn your wheels 90 degrees, your caster would be the exact difference of your camber readings. But since that is not possible, 1/4 the amount of turning ( 22.5 degrees ) would yield 1/4 the result, so multiplying by four should equal your total caster.

Sound about right?


Cheers,

Joe