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Like most hot roders, Locosters etc. I've been struggling to measure the toe in/out on my various cars for years. Tape measures take two people, the body work usually gets in the way for accurate measurements, professional gages cost too much for the number of times I'd use them etc etc.
While looking around on Internet I found a rather simple looking toe in gage for sale. I figured I could simplify it and reproduce it with stuff from my "spare parts" (some people call it my junk pile). Even if you have to buy all the parts new, you should be able to build one for less than $10. This gage is admittedly more complicated than others but it will give very consistent and accurate results.
No, those aren't my new secret super sticky sponge rubber tires!
Here is a look at the complete toe in/out gage. The supporting pipe is a 65" length of 1/2" diameter electrical conduit.
The 2" x 4" by 6" long blocks are used to space the gage away from the tires so your readings will be consistent. They also make it easier to slide the movable pointer on the pipe.
After this picture was made, I now use a straight piece of 1" x 2" length of wood long enough to sit behind or in front of both tires to rest the edge of the 2" x 4" blocks of wood against. The 1 x 2 would be placed between the forward end of the 2 x 4 blocks and the "tires" in this picture.
This allows me more latitude in where I place the 2x4 blocks. And it makes the measurements much more consistent.
Toe in is specified to be measured at the axle height on the rims.
The pointers should be long enough to touch the tire half way up the tire to get the truest reading of toe in/out. Measuring on the tire tread instead of the rim edge will cause a slight error in the reading since the radius that you are measuring is different between the rim and the tire tread. At the end of this page I give an example of how much error is introduced on my tire vs wheel combination.
The pointers need to be long enough to touch the tire at 1/2 of it's total height plus an inch or so. This will allow the pointer to lean against the tire. My pointers are 12" long and ~2" wide at the bottom. The pointer on the left is mounted stationary on the left end of the conduit support pipe. The pointer on the right slides on the support pipe when setting the gage up for measuring toe in/out.
I made the pointers from some thin scrap aluminum sheet that I had. The width at the bottom only has to be wide enough to allow you to drill the two mounting holes to match the couplers you are using.
This is the tip of the stationary pointer. In use the tip of the pointer is placed on a reference point on the tire tread. Note the short line located at the top of the point. This is an aid for setting the point on the tire when you move the gage to the other side of the tire.
Instructions for use of the gage are located at the end of this section.
This is a close up of the tip of the movable pointer. I riveted a short piece of a metal tape measure to the end of the pointer so I don't have to use another scale to read the toe in or toe out. You can also make this pointer pointed like the stationary one if you don't have a piece of a ruler to sacrifice to the cause.
A pop rivet holds the ruler on the pointer. The top edge of the ruler should be the same height as the tip of the other pointer.
This is an end view of the stationary pointer coupler. It is a normal 1/2" electrical conduit coupling adapter.
Notice the ridge in the center of the tube that is normally used to keep the two pieces conduit centered in the adapter.
Also notice that there is one washer on each set screw to give the pointer sheet metal a surface to seat on. The washer thickness should be such that the screw will seat on the conduit and hold the pointer tightly at the same time. The washers on both of my pointers are 1/16" thick.
This is and end view of the movable pointer's conduit coupler adapter.
Notice that the ridge in the center of this adapter has been removed by drilling and then filing the adapter smooth with a rat tail file. The coupler must just slide freely on the 1/2" conduit supporting pipe. There are washers on each side of the sheet metal so the end of the screws do NOT project through the adapter.
On the right side of the coupler you can see a piece of a spring clip that keeps the pointer and adapter in position on the conduit when in use. There is a better view of the clip in the next picture.
The movable pointer tensioner is the only semi-complicated part of making the toe in gage. The spring clip shown in the photo to the right, is from a gas powered lawn mower. It is normally used to hold the various cables (throttle, gear shifter for instance) against the operators handle.
WHAT! You say you don't have one? Take one off your lawn mower! Or you can probably get one from a lawn mower repair shop or where I do most of my shopping, the junk yard. It's amazing the stuff you can find in the bed of a junked pick up truck.
Drill two 1/4" diameter holes in a line on the side of the adapter opposite the set screws as shown in the photo. File the sides of the holes flat as shown to provide clearance for the "S" shaped end of the clip.
I had to bend the clip slightly to cause the "S" end to project deeper into the slot in the adapter.
This picture shows the spring clip that applies pressure on the conduit through the slot in the adapter. It is not necessary to use a ribbed adapter. I just happened to have this one when I made my gage.
That's it, now you can assemble the two pointers on to the conduit pipe. Don't forget the spacer washers.
1. These instructions assume that both tires to be measured have the same tread pattern.
2. It will simplify figuring out if you have toe in or toe out if you set the first reference point at the REAR of the tires. This will allow direct readout of toe in or toe out from the movable pointer. If you set the reference at the front of the tires first the readout is reversed (trust me on this).
Step 1. (Setup)
Having a helper at the left tire to do the left side settings will speed up the process.
Place the long 1" x 2" length of wood and the 2" x 4" wood blocks against the rear of the tires as shown in the photos to the right. Slide the gage under the car so the stationary pointer is on the left side tire as shown and both pointers are touching the tires. The [left] stationary pointer will be called the "primary pointer" from now on.
Step 2. (Setup cont'd)
Position yourself or your helper at the left tire.
Select a point on the tread where the edge of a tread block is vertical. Move the pointer and the pipe left or right so the tip of the pointer is exactly on an edge of the tread block. The spot on the tread where this pointer is positioned will be called the "reference point" for the rest of these instructions.
Rear view of left front tire with stationary point set to a reference point on the tire tread.
In these pictures I did not have the 1" x 2" length of wood between the 2" x 4" and the tire because I realized it helped after I took the pictures. The wood runs under the car to the tire on the other side.
Step 3. (Setup cont'd)
Position yourself at the right tire.
Hold the pipe so it doesn't move. Slide the movable pointer left or right on the pipe so that it rests against the tire with the center division of the ruler against the exact same tread pattern location where the reference point (left side) pointer is positioned on the left tire. In these pictures the pointers are on the left edge of the center rib of the tire tread.
Let's call the point on the tire tread at the ruler center division the "2nd reference point" from now on.
Quickly check that the primary pointer is still at the primary reference point. If not repeat steps 2 and 3.
Step 4. Reposition the gage.
Carefully remove the gage from under the car. Be very careful and do NOT allow the movable pointer to move on the pipe. This is the hardest part of taking a measurement.
Place the long 1" x 2" length of wood and the 2x4 wood blocks on the front side of the tires.
Rear view of right front tire with the ruler set to the same relative reference point on the tire tread. (And missing the long 1" x 2"" wood.)
|Step 5. Reposition the gage
Position yourself or your helper at the tire to your left (the right tire of the car).
Put the gage on top of the blocks with both pointers near the tires. Position the primary pointer against the tire tread so that it is positioned on the same edge of the tread as the original reference point. The accuracy of the measurement, depends on placing the pointer exactly on this new primary reference point.
Step 6. Taking the reading.
Position yourself at the tire to your right (the left tire of the car).
Check how far the 2nd reference point on the tread is from the center division of the movable pointer's ruler.
Step 7. Interpreting the reading.
If the 2nd reference point is exactly on the center division of the ruler you have neither toe in nor toe out.
If the 2nd reference point is towards the center of the car in relation to the center division of the ruler you have toe IN by the amount of reading off the center line.
If the 2nd reference point is towards the outside of the center division of the ruler you have toe OUT by the amount of reading off the center line.
A toe-out condition could correctly be called negative toe-in (for instance -1/8" toe-in) although it is common to call it +1/8" toe out.
1. If you are making other alignment adjustments, do the toe adjustment LAST.
2. If you make any adjustments, roll the car back and forth at least 1/2 tire revolution to allow the suspension to settle and to reposition the tires in relation to the chassis. To be consistent, roll the car forward to the original spot as the last movement.
3. To be completely accurate, toe measurements should be made from a height equal to the center of the rim AND at the rim (not the tire) edge. The extra diameter of the tire compared to the rim diameter -will- add a sight error to the toe measurement. This error will depend upon the size of the tire and the rim diameter.
4. You could measure lower down on the tread where the front to rear tread distance is equal to the rim max diameter and the reading should have no error.
As an example here is the error to be expected if you have 15" rims and tires with a maximum diameter of 22" and with a specification of +0.25° toe-in. (It makes the math for the example simpler to use degrees instead of fractional inches.) The formula is: (Diameter of measurement point) * Sin(angle in degrees).
Measured at 15" rim, toe-in should be 15 * Sin(0.25) = 0.065"
Measured at tire tread, toe-in should be 22 * Sin(0.25) = 0.096"
Using the 0.065" as the correct measurement the tread error is ~50% although the actual error in thousandths of an inch is very small.
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