Actually, I believe you have side 1 and 2 on this no matter which way you choose to measure. On the groun front and rear of the wheel, or targets front and rear of the car.

This worked well with the strings method too.

 

yes, you have side 1 and 2 both ways, but calculator doesnt allow you to calculate it that way. you need an angle, like the .25 degrees and then you can take your distances, which are side 1 and get your side 2.

since the marks at the bottom of the tires would give you the side 1 and you know the width of the tires, you can easily calculate side 2. if you want to calculate side 2 from one side and the desired angle, thats easy too. when doing camber for example, i always look for 17mm off vertical to tell me how far off or near i am to 2 degrees camber. (i know the side 1 19" and i know my desired angle , 2) so side 2 is easy to find.

mk

 

When adjusting the rear toe angle, the thrust angle is also set. That takes into account of how rear wheels track in relation to the front wheels. The front wheels must be used as a reference point for the rear thrust angle. Since the wheel base/rim size is wider on the rear, than the front, the calculations are less trivial.

 

For front toe, I park the car on the driveway with the front wheels pointing straight ahead. I'm sure the driveway is neither level nor flat, but it's not a cockeyed slope, and I can't see how it not being perfectly flat and level throws the toe measurement off very much. I set up 4 of my kids poster boards, the large foldout type that I saved from their school display projects, two in front of the car, two behind, about the same distance (eyeballed) from the car. I hold the laser level across the tires in the middle of the wheel - that's right, the tires. I haven't had time to make a mount for the level that would fit the rims. The tire walls seem even, at least for doing toe (camber, of course not). I shoot toward the poster boards and have my son mark the place on the boards where the laser dots are. The front boards are about 120" from the rear boards. If the distance between the dots at the front is less than the dots at the rear, I know I have some toe-in. I calculated the number once. It was small but it was in rather than out, my primary concern. My technical tip: Do this on a calm day, otherwise you'll be running around the car re-setting up the poster boards over and over each time the wind knocks them down. Feel free to bookmark and link to this post for future reference.

Now, this may be tongue-in-cheek, but it is what I do. I've read all the guides and admire all the technical charts, but I have had a real hard time wrapping my head around them. I need pictures to illustrate those thousands of words. I have a very hard time translating them into action. I figure I probably would flub it up if I tried anything more complicated.

 

Bill, I'm with you on not forcing folks to go through all the calculations. That's why I was thinking that a defined shape with dimensions and a known target angle (using the WSM .75 degree number as target) would simplify things for most people. MK's method is right on if you are trying to find out what the angle is now. Same with your method, although yours is geared more towards making sure you aren't toe'd out rather than getting an absolute number. The method I suggest really doesn't care what it is now, although you can always figure that out using MK math. I'm interested in getting it right, corrected from wherever it is now (don't really care..) to where it needs to be. So no need to calculate angles, cotangents of the inverse arc of the cosine of the moon's orbit. It's all just tape-measure stuff that most of us can handle. Adjust the tie rods until your readings say X and you are done.

I have enough of the aluminum square stock left to make another pair of fixtures, but the shipping to you would cost more than the metal cost. The angle pieces are from the bin at Home Depot, but after seeing how inexpensive that stuff is at Industrial Metal Supply up the freeway a few exits, I'd just get it all at one place. I used six stainless machine screws and some stainless locknuts to hold it together, some five-minute epoxy to bed the lasers during alignment, and a couple feet of plastic packing tape on the edges of the angles to protect the wheels. The lasers were about $13 each at H-F, and they come on sale for less if you have patience. So all in, less than $40, a couple hours for shopping and a couple hours for alignment and assembly. My normal shopping and assembly fee of $250/hr was waived just this once.

I may go ahead and do a real instruction on how to make them, how to align them (most important...) and how to use them. I have a lot of airplane and hotel time coming up, and this is the perfetc time to do instructions.

 

dr. bob: You've already posted some pictures, but I do need more of the process. Yes, aligning or checking the alignment of the lasers is a mystery to me. I figured if the lasers are not exactly shooting straight ahead, the error is the same all-around (except for vertical error), and since I'm using the distance between the front and back posters and the dot spacing difference, a small error will have no significant effect.

But I'd like to be able to do a more complete and technical alignment. I've read Captn Earl, but he does not cover things like homebrew caster measurement or even which way to move the adjusters to increase or decrease caster. I know this can be done with alignment slider plates and measuring camber at +20º/-20º. Better illustrations of rear toe and thrust alignment would be helpful. I've read descriptions, but I get easily lost in the verbage.

 

This was the next thing to talk about , and the most important. Its the main reason that home alingment systems can go wrong. you dont want a car "crabbing" down the road.

mk

 

Thats why using a level is the easiest way to do this. take the level, and press it agaist the rim or tire. whatever is easiest. mark the ground. there is no chance of the wind effecting this way of measuring. then, you measure the distance between the front part of the two front wheels and the rear part of the front two wheels, making sure the marks are near 18-19" apart (width of the rim). Then, measure the distance between the two sets of points.my fronts are usually:
71 and 3/8s" front to back. this means 0 toe.

if you are near 1/16" of an inch, you are right around spec of 15min or 1/4 degree.

no lasers, no mess, and real easy


mk

 

OK Mark, I think I figgered out why I was off on my first numbers vs. my second. I had to go back to the spec book and see again that the suggested front toe-in is .25 degrees (15 mins) not .75 degrees (45 mins).

So the difference between spreads at 86" difference in distance from the centerline of the front axle is 3/8". tan(.25) * 86 = .375 inches


Look at the attached diagram:

In my example, I used 30" between Line A and Line B, but that dimension is really unimportant. The critical dimension is the 86" between Line B and Line C.

In this same example, we are now looking for the difference between the distance between the beams measured at Line B, and the distance between the beams measured at Line C. If your target is the WSM alignment spec number of 15' (fifteen minutes, one quarter of one degree) of toe-in, the number at Line c needs to be 3/8" (0.375") less, as shown in the drawing. The actual distances will be affected by the width of the wheels, the offset, and the size of your measurement fixture. It's the difference between the two measurements that tells the angle.

Why choose 86"? It happens that 86" is a point where each 5' (five minutes) of angle results in a change of 1/8 inch in the difference number. The WSM allows 15 ' +5' tolerance, so your final difference can be between 3/8" and 1/2" and meet the WSM specs. It makes the measuring a little easier. 1/8" is a number that most can see on the tape measure.

 

dr, bob:

Your diagram is helpful to me. In order for this to work, you have to know the distance A. I don't get how you do that with a carpenter's square. If the wheel has camber, then the whole device is canted, so using a square as I visualize it will skew the laser beam center measurement on the ground outward from actual and your toe will end up being larger than you think. Maybe your device is compensates for different cambers. Anyway, that's why I shoot the laser to the rear as well and take the difference. Then distance A in your diagram does not matter. Here's a representation of my laser method with 4 posters.


ABCD is an isosceles trapezoid. Whether it is truly isosceles can be verified by measuring across from the corners (A-C = B-D). If it is, then the angle can be calculated directly with tangent or sine, depending on how you measure the distance between the posters. Actually that doesn't matter if you can measure all 4 sides of the trapezoid. Then you can use the trapezoid calculator below to get to toe for each side individually just in case you didn't have the wheels centered or the posters precisely set up. All that's required is that the lines between the front posters and the lines between the rear posters are parallel (top and base of trapezoid are parallel). That's what I do.

http://www.analyzemath.com/Geometry_...alculator.html

I plopped in what I found last time..
side a = 240"
side b = 85.2"
side c = 240"
side d = 87"

So, with the front dots 1.8" closer than the rear with the front and rear posters 240 inches apart at the dots, I get 0.2 degree toe-in on each side.

 

I posted the wrong calculator, this is the one I meant to post. You know the hyp. and one of the sides, so the angles will be calculated. Here's the right one:

http://www.1728.com/pythgorn.htm

 

Bill-

The carpenter's square is used to transfer the laser points to marks on the floor.

The lasers are "leveled" with the floor, so the effect of camber on the lasers is eliminated, and you do't need to precisely level the car front-to-back. Using the square on the floor, measure the height of the beam first, at line B and Line C in my diagram. Rotate the laser fixture on the wheel until the two heights are the same, indicating that the laser is pointing straight ahead from the car as it sits, beam parallel to the floor.

Now, go back to the two lines A & B, and mark the floor directly below where each beam crosses each line, using the square to find your mark. If your floor is uneven, use a plumb bob instead. I put a piece of blue tape on the floor, and mark with a pen on the tape where the middle of the beam is. When you have all four marks, lay a tape measure on the floor and see how far apart the marks are on each line. Distance at B = distance at A plus 3/8 of an inch if A and B are 86 inches apart and you have 15 minutes of toe-in. Spec allows up to 20 minutes of toe-in, which gives us half an inch difference instead of 3/8 inch.



I obviously need to take more pictures, maybe some video, to help some of this make sense. I've spent more than a casual amount of time teaching about numbers in a classroom environment at the university level. Mixed results, so teaching wasn't my thing obviously. As part of the Rose Parade effort, I have the duty to train people who help with the flow of the parade entries through the TV areas. I started off with tables of numbers, time-speed-distance stuff. HEGO syndrome (His Eyes Glazed Over) big time. Best reesults came from using wood blocks on a tabletop, with tape marks showing where things are. All smart people, just a not-so-hot instructor sometimes.

 

Bill--

Looking again at your diagram, all I did was move the whole measurement area out in front of the car, rather than having the car in the middle. Your method requires that you reposition the lasers from shoot-forward to shoot-backward, with the possibility of introducing an error when you do that. You also can't "shoot through" your posters, but you could use them at Line B in my diagram, measure between the marks, then move them 86" to line C and measure again.

Making the metal brackets instead of strapping the laser to the tire means I can zero the lasers so the beams are exactly parallel to the center of the square tube, and I don't need to do differential front and rear shots to zero out that error at every use. I looked at a few of the wood solutions popular on the 'net for homebrew, and for the same amount of fabrication and a few extra dollars in materials, we have repeatability as well as accuracy.

----

 

OK, I re-visualized how you use the square, and I see how easy that is. Hmmm... OK, I can just shoot forward then. That simplifies things. And I can still use the trapezoid calculator. Thanks for helping me see an easier way.

MK's way could work just as well. Measuring a 1/16th inch from the front to the rear of the wheel may be no less accurate than projecting and measuring a half-inch over a longer distance, as any errors are magnified.

 

Mark's method includes 1/16" difference total for both sides, and that's the smallest graduation on most measuring tapes. Extending the measurement field out to 86" makes it possible to use bigger values that are more appropriate for the tape. 3/8-1/2 inch is easy for us blind guys. I suspect that the 1/16" could easily be lost in two pen-widths of marks on the floor.


For those of us who run the same wheels all the time, we can speed the process next time by recording the readings from the first alignment we do, then measuring at any distance to a surface perpendicular to the front of the car, like a garage door. Get the distance between the car and the door and the space in between the beams on the door as your standard, and you can always just put the car the same distance from any vertical surface and verify that the beams are still the same distance apart. Say you work on the car before you take off for Nevada, and that work includes raising the car. When you get there, pull up to a handy wall, correct distance from it like at home, shoot the wall and measure to varify that the toe hasn't changed since home. Adjust as necessary to match your good home spread and you are assured that your toe is once again correct.

Simple repeatability.