I've always had toe adjusted in either mm or inches, but know some ppl that use degrees. When I thought about it, degrees makes more sense, since it would not change regardless of where the measurement is taken (w/ respect to wheel/tire and hub center). However, if measuring in inches (or mm), if I have 1/16" toe out, where is the 1/16" from with respect to the center of the hub?...is measured at the rim edge?...tire edge?...or am I thinking about this completing wrong? Just wondering how toe is measured in inches(mm)? Thanks.

 

Drop two plub-bobs from each edge (front and rear) to the ground and measure the difference between the two to the center-line of the vehicle. Or what's more common, measure the difference between the two front edges of the tires and rear edges of the tires at each end of the car and then take that difference and divide by two. However, most of the time toe is quoted in total toe not individual toe in which case you wouldn't measure by two.

This info could easily have been found through a Google search or something but I'm feeling generous.

btw, I'm not sure if alignment racks usually do toe from the wheels or tires. If you string the car though you usually do it from the edges of the tires.

 

It depends on how you're doing the alignment. If you're using a computerized rack, you're best to use degrees. If you're at the track, you'll probably use inches (using string, lasers, etc.) Because of common convention, and how alignments were done in the old days, most people still specify tow in inches (or mm). Degrees are a much better way to do measure it, however. There can be no confusion with the toe specification in degrees.

The problem arises that we have here; where do you take the toe measurement from, the tire OD, or at the rim, or somewhere else? Modern alignment racks measure degrees directly. If you request the number in inches, it is based an a reference tire outer diameter. If you have an alignment tech that knows his machine well, there is usually a submenu buried away somewhere that has an adjustable value for a reference tire diameter. Most don't know about it, or even understand that this affects the machine's toe output (when in inch or mm mode).

In the old days, (or today, at the track) they used to put chalk on your tires and lightly scribe a centerline on the tire. The tech then used a toe gauge to measure the difference between the track at the front of the tire and at the rear. The difference is total toe.

When using string, people usually measure to the rim, as it is an accurate, machined surface. If I were using this rig: Smart String I'd measure to the wheel. As long as you are consistent, it doesn't really matter where you measure from. If I used string, and then went to a rack, I'd probably convert my toe at the wheel measurement (per side, not total) to degrees.

HTH,
Steve

 

When I string my car I go to the wheel edges as well for the same reasons you said. I was under the impression that most people actually used tire-scribes and measured from the tires if they strung the car.

 

I probably shouldn't have said "people usually measure to the rim", as it seems to be a personal preference thing. If I make a toe change in the field, I usually use a toe gauge, or a plain old tape measure using the molded in grooves on my Hoosiers instead of a scribe line.

Steve

 

Thanks for the explanations guys! I've tried looking this info up on the net (google and others), but didn't find anything on how to measure in inches/mm. All I find is descriptions on what toe is (which I already know). It would seem to me that if measuring in inches/mm, it would be most consistent to use the wheel as a reference since changing tires, wear of tires, and possibly even air pressures would affect overall measurements. If measured using the wheel, even if you changed wheels (assuming same diameter wheel), the measurements would still be applicable. The alignment shop I go to uses the scribe line method, but I haven't been there in a while and forgot to ask him when I was there. Thanks again!

 

I haven't done a search here but I captured these directions in this forum some time ago - hope it helps:

toe is the difference between the front and rear of the tire, therefore you have to use diameter, not radius. It's really a simple hypotenuse triangle using

Rsin(deg) = toe

where R = tire OD

as a general rule of thumb you can alson use

(decimal deg / 2) = decimal inches

which is close enough in the realm of most toe angle ranges

24.5" sin(.08deg) = 0.034"

0.8/2 = 0.040" ---> 0.006" error is insignificant

most manufacturers have switched to angular toe measurements because they are independent of tire diameter. It's the wheel angle that's important to maintain regardless of tire diameter.