How do you get toe in degrees from mm-figures?

[Frank N. O.]

I need a toe-in figure for a car in degrees, but I only have it in mm. I tried using pythagoras with half the rim-diameter and the toe in mm but that gives a way too big figure. For instance from a pdf DMC-12 manual I read that there is 3mm toe-in per wheel f/r but with a 14" front rim, that gives a toe-in of almost 10 degrees, and another printed DMC-12 manual I have lists the toe-in as 0.5 degrees toe-in front and rear. Any ideas? Matt?

Frank

[Justin Martin]

Here's a spreadsheet that I made several years ago which converts toe in inches to degrees, just convert from mm to inches and use that.

[Frank N. O.]

Thank you very much :) And I just used your other research to estimate cog as well :cool:

Frank

[MATT]

I'm just a lowly mechanic-in-training. I have a computer that converts it for me, has all the specs. in a database. Actually, the class I'm taking, aimed at helping potential alignment technicians, is explaining many of the principles behind it. Most don't bother paying much attention simply because all they want to do is wrench. But I do try to understand it better. If I can understand all the geometry, different kinds of suspensions, etc. it will help a lot in diagnosing problems that can otherwise be unseen. Definitely can make myself a better technician by doing so. I'm trying :)

However I have no clue as far as the conversions go. And here in the U.S., we use fractions of an inch rather than millimeters. The machine that's used by our shop measures in inches only for toe. Some manufacturers specify with degrees, some with an inch/millimeter measurement. Ours just stores all the specs in inches. I think new vehicles are trending towards toe measurements in degrees, though. So at some point a software update may change that for us.

[Frank N. O.]

Well Matt I have it in inches too, 0.04 in total toe-in front, that would be 1/25 in right?

Btw do you know what a "steering axis inclin." (14 degrees 5' )(front) is?
And what a "thrust angle" (zero degrees) is (rear suspension)?
It's for/from a 94-95 RX7 US-model btw and that has double-wishbones f/r.

Greetings
Frank

[MATT]

Well Matt I have it in inches too, 0.04 in total toe-in front, that would be 1/25 in right?

Btw do you know what a "steering axis inclin." (14 degrees 5' )(front) is?
And what a "thrust angle" (zero degrees) is (rear suspension)?
It's for/from a 94-95 RX7 US-model btw and that has double-wishbones f/r.

Greetings
Frank

Thrust Angle is the combined toe of both rear wheels, essentially.

Steering Axis Inclination is considered to be more of a diagnostic measurement than anything else. Not really adjustable...

I don't completely understand what it is myself. It's similar to caster...

I found this definition: "Definition: The angle formed by a line that runs through the upper and lower steering pivots with respect to vertical. On a SLA suspension, the line runs through the upper and lower ball joints. On a MacPherson strut suspension, the line runs through the lower ball joint and upper strut mount or bearing plate. Viewed from the front, SAI is also the inward tilt of the steering axis. Like caster, it provides directional stability. But it also reduces steering effort by reducing the scrub radius. SAI is a built-in nonadjustable angle and is used with camber and the included angle to diagnose bent spindles, struts and mislocated crossmembers."

Taken from http://autorepair.about.com/library/glossary/bldef-748a.htm

And yes, .04" = 1/25"

[Frank N. O.]

Ok that is weird. The toe-in measurement for both front and reas specifically says total and not per wheel, so how can the total toe-in be 1mm in the front and 2mm in the back if several sources say that no matter what mod you do or not to the RX7 you have to keep the thrust-angle at zero. The 206 was tested and found the toe was combined zero but that was because one wheel was -0.16 degrees and the other was +0.16 degrees and that wasn't supposed to be.

Hmmm, strange, but thanks for answering anyway :wave:
Frank