I bought this Longacre toe tool about 20 years ago and was surprised to see it is still available new and unchanged.

After replacing everything in my rear suspension except my TAs, I drug my old guage out of retirement to do the initial toe. It just fits in front of the rear wheels and is simple to use.

http://www.longacreracing.com/products.aspx?itemid=1709&prodid=7237

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SR
73 TR6
86 930

Mine is much the same but consists of a 2x4 with two rods/pointers. One pointer is on a moverble shoe.

A bit more inexpensive tool for measuring/setting toe-in is a spring loaded "cafe curtain" rod. Like this.

To measure 'toe', first make sure that the wheels are in normal loaded state, after rolling car forward or backward at least one full revolution, straight ahead/back. Unscrew the rod so that the rod will hold when placed between the 'front' of the tires widest 'bulge' or the lip of the wheels, ideally at axle height but practically as high as possible. Scribe an erasable mark on the innermost rod at the slip joint. Roll the car forward to bring the rod to axle height or as far as possible. Scribe another line on the innermost rod. The distance between the 2 marks is the "toe' in or out. Same procedure for front or rear of car.

"ideally at axle height but practically as high as possible."

That is the crux of the matter!

Tony - Are you suggesting that an inability to achieve "axle height" in either/both direction side(s) invalidates a toe-in measurement as imprecise? Mathematically, an inaccuracy will be small due to the small measures that we are dealing with.m Equally important is the fact "correct" toe is about 50% flexible on either side.

Well the toe is an arbitary figure anyway, it depends on how you want the car to behave, what wheels and tires you use and the type and condition of your suspension bushings.

But IF you are going to measure anything, it is best to get the most accurate measurement possible, if only for reference information.

Our cars frame and drive train ride quite close to the ground, any straight line measurments from rim edge to rim edge that is possible, is going to be quite a bit lower than if a measurement could be taken at the optimal points which are at axel height on the rim.

For instance, if a toe in of 1/8" is desirable, the measurements taken at axle height would be 180 degrees apart on the circumference of the wheel rim. The measured difference sould be 1/4".

If the measurements can only be made 90 degrees apart on the rim the difference would be half that.

Possible inaccuracies are less the larger the measurement.

Sorry Tony, I think that you had better check your math. Toe of 1/8" is 1/8", not 1/4" Toe (total) of 1/8' is 1/16" per wheel. As to your 180 degrees versus 90 degrees, I don't understand your 50/50 proportion. Regardless. the angle of rotation capable due to the undercarriage, while less than 180 degrees, will be well larger than 90 degrees.

As one who is afflicted with a knack for math, maybe I can add something.

Ideally, toe measurements would be made at axle height--that is, 90 degrees either side of the vertical radius of the wheel. Measuring at a point below axle height will result in reading a fraction of the true toe-in. The fraction is the cosine of the angle below horizontal that the measurement is taken. Here is the error fraction for a few angles:



The table assumes measurements are taken at the periphery of a wheel with 26" outside diameter.

Angles off horizontal up to 20 or 30 degrees cause fairly small errors.

Ed



Edited 2 time(s). Last edit at 2019-02-11 01:04 AM by ed.h.

Thank you Ed, Math was never my strong point.

One of my mystakes was to think that if the measurement was not made a axle height on the rim, half the measurement could be taken at half axle height.
My erroneous thought was that half axle hight would be found on the rim at 45 degrees radially from a horizontal drawn at axle height.

My logic was: If the desired toe deviation at axle height is 1/8" (3 o'clock position) and there is zero deviation at the 6 o'clock position, then half way (bisecting that 90 degree angle) would yield half the deviation or 1/16"

But that is not the case. As can be seen on the chart or by doing a quick drawing.

However it does show that it is difficult to get a meaningful rim to rim measurment anywhere OTHER than at axel height.

My OTHER error was that toe deviation is taken as the change at one side of the rim. ie. With wheels parallel a rim to rim a measurement is taken (at axel height), then that measurement is reduced by 1/8" at the front, to give 1/8" toe in.

However when doing this the rim to rim measurement at the back is then increased by 1/8"
The differance between front and back measurments is 1/4" But that is not the toe measurement.

Oops!