toe In question regarding where to take measurement!

[crash340]

Guys, im assuming the toe in measurements should be taken from rim edge to rim edge front and rear of the rim, so what I'm saying is if you have 14" rim and you set the toe in at say 1/8" then rim edge to rim edge on say and 18'' rim will not be 1/8", it has to be more if you dont adjust the tie rods and simply swap wheels! Am I on the right wave length or ?
Right now I just have a piece of straight pine say 2x1 that I hold against the tire as high as I can to get a tape measure under the pipes etc on each side and measure and adjust, like I think we most all do but to be accurate, at what point do you or are you supposed to take that measurement?

[Bullitt-]

Was getting an alignment a couple of weeks ago & was talking to the ole boy doing the work, said he used a string back in the day.
Something like this.  https://www.youtube.com/watch?v=0sguZ-gRF9I

[crash340]

Thanks bullitt, thats great but again the question still remains, fine if your setting no or zero toe in/out, but if your setting at for example 1/8" to you measure front to rear difference of the tire at say 24" or the rim at say 14" (for a 14"rim).
the method shown in that youtube vid is also a good way to check rear alignment and adjust, I will try it to check my rear for sure

[brads70]

I use these toe plates. It uses the outside of the tire so rim diameter doesn't matter.
http://www.summitracing.com/int/parts/aaf-all10119/overview/

[crash340]

so, they are 23'' long Brad, what toe in do you set yours at, if I used a similar plate at say 40'' long, then I couldnt use the same measurement right? so, when the specs call for a given measurement, what length plate or device/item is the given measurement based on? or, is it not that critical.

[brads70]

so, they are 23'' long Brad, what toe in do you set yours at, if I used a similar plate at say 40'' long, then I couldnt use the same measurement right? so, when the specs call for a given measurement, what length plate or device/item is the given measurement based on? or, is it not that critical.

I shoot for 1/16-1/8  I never really thought about that before? I know the electronic alignment machines use a hub that hooks to the wheel that's smaller than the wheel? I'd guess using trig and few inches in length won't make that much difference? 

[crash340]

Yeah, was just curious Brad, im the same, guess it is not that critical , just throwing it out there.

[HP2]

The difference in measurement at 23" vs 40" could be significant. If you are setting toe in inches, then tire diameter does matter and you want the toe to be set at the diameter of the tires you are using.

Typically, I set the front end up in the air, spin the tires and using a scribe or pencil mark a line in the center of the tread on each tire. Then it goes back down on the ground. Toe measurements are taken on this centerline front and back, as high up the tire as is feasible in back of the tire, usually limited by the exhaust and oil pan, and then at a comparable height in front of the tire.

[Chryco Psycho]

I measure as high as possible in a straight line under the frame rail across the front & rear of the tires using the exact same place in the tread front to rear & try to get 1/16" toe in

[crash340]

But what if the diameter of your tire Neil? Mine is more than likely different so I can't just say, set it at 1/16", that's the debate I'm on about.  That is exactly how I do it as well and I set mine up at 1/16, but mine won't be the same as yours unless out rolling diameter is exactly the same.

[Bullitt-]

I've looked up several different cars alignment specs in the meantime...from a 70's ebody , 2000s Mustang to a modern Challenger. none really answer your question of where to measure but everything I've ever seen referenced the outer edge.
Common theme...Total toe 1/16-1/8 although the modern Challenger tends to be expressed in degrees 0.20*.

You might find this article interesting  http://www.allpar.com/history/mopar/front-end-alignment.html

[HP2]

Alignment specs are going to call out toe in degrees because alignment racks can more accurately dial this in using the outer edge of the rim with their laser sites and the factory tire diameters that are all loaded in their databases. Toe in inches is a hold over from earlier days, but it also is a lot easier to achieve under the shade tree than it is to do all the trigonometry to figure out the degrees based on tire diameter.  To achieve 1/16" toe in on a 26" tire is something like .18 degrees. Maybe a new phone app can get into that small a detail, but I'm pretty confident none of my angle finders in my toolbox can split it that low.

FWIW, new Challenger tires are 28" in diameter compared to  a classic that could range from 24" to 30" depending on how you have it optioned and your intended application.

[crash340]

Thanks for the input guys, was just something I was thowing out there, over engineered thoughts I guess. got my head thinking a little. An angle measurement wouldl be more correct I believe however, under the shade of my car port, two bids of stick and two builders tape measures will do me for now.