I searched! Really! Both here and on the Internet in general, and I can't find an official converter of toe-in inches to degrees.

The last big truck spring and alignment shop I knew of in Northern VA is gone, and my local shop only does toe-in in degrees. I have the specs for my 51 F1, both from Julie's posts and the Ford manual, plus everyone's opinion that it should be more toe-in than the factory spec of 0-1/16.

I taped measured ~1/8, and the shop measured 0.41 degrees, then set it to 0.05 degrees, which seems too low, but how do I know?

Does anyone have a converter, or knowledge of what degrees 1/8" would be with stock size tires? I found some online, but they didn't come from a source reputable enough for me to take the figures to the alignment shop and say "look here - do this."

Recommendations for a spring and alignment shop in No VA would be great, too!

Thanks,
Jonas

 

They should be able to switch there alignment machine to inch'' with a few click of a mouse.

 

I looked up the specs for a 1998 F-150 which I thought might have similar height tires and it calls for .06 degrees or .03 inches.
That is with tires approx 28" high. The tire dia. would change the toe in measurement in inches but probably not signeficantly.

1/8" woud be .125 so that should be approx. .25 degrees.

.05 degrees would be .025" or 1/40"

 

alignment machines now use degrees because that is tire size independent. If you have the stock beam axle set the toe using a tape measure or string method to 1/8" toe-in and all will be good. There is no conversion factor between degrees and inches because there would need to be one for every different tire diameter. You could calculate what the degree equivilant would be using plane geometry (yea that math you learned in high school that you thought you'd never need to use). At least the calculations are easier now with pocket calculators.

 

This may sound stupid but.......setting the toe on these trucks correctly is VERY simple. It's just a matter of getting a rod or string and after a few roll ups and backs turning the tie rod such that the front of the tires are 1/16 (3/32-1/8 is better for freeway speeds) at the farthest points forward and back. Once you get it correctly set, take it to the alignment shop and ask them to measure the degrees for future reference with your tire size.

To do it trigonametrically, you would draw an imaginary box with the front and back edges being parallel to each other, and the length of those two line being the distance between the inside tire walls at the center of the tire. Then the two sides of the box would be parallel and they would be the length of the tire diameter. All angles are originally 90 degrees.

Then you would shorten the front line by 1/16th and lengthen the back line by 1/16th and calculate the angle change of the two front corners from 90 degrees to the new angle (and it will be larger than 90 degrees). This forms a trapazoid out of your rectanglular box. Lastly, you would draw a new line from the intersection of the top and new side lines (now canted inward from the toe adjustment) straight down to and perpendicular to the bottom line.

In this case lets label your triangle with sides a, b, and c

Where "a" is the back line; "b" is the new straight line; and "c" is the angled line that your tire is now sitting at.

b/a is the Cotangent of your angle in degrees.

So, I'll measure mine and we can do some numbers

Tire diameter is 28"
Distance between the tires at the center started at exactly 54 inches
After adjusting for toe the distance between tires in front is 53 1/16 (toe in = 1/8 total)
After adjusting for the toe the distance in the back is 54 1/16.

Thus the back line is 1/8 inch long - right? (imagine in your mind that you move the truck sideways 1/16 inch so the original tire line and the angled tire line touch in the front).

So "a" = 1/16" (or .0625") because one side is half the amount (the other half being on the other side)
and "b" = 28"

So 28/.0625= 448 = Cotangent of the angle

The angle would be 0.1279263661739degrees.

So simply stated your alignment angle of the tire is going to be the Cotangent of your tire diameter divided by half the amount of the toe in (the amount one tire gets toed in) distance.
.
Aren't you glad you asked

Test tomorrow!

 

Actually, because the tire diameter doesn't change you would use the Sine of the included angle. Using a 28" diameter tire, and a total of 1/8" toe-in, it would be 1/16" toe-in per side. The sine of the angle would be .0625/28 =.00223 which equates to an angle of 0.13* per side. Now aren't you glad you asked...

Because the angle is so small, the sine and the tangent are almost the same so either will give you degrees that are too close for any of the alignment machines to differentiate.

 

and the other responses.
In my searches I had found the formulas.
However, I didn't think taking that to the alignment shop to 'splain it to them would work very well, so I was looking for a converter from an official source, like Hunter Engineering or somebody.

So, Hunter Engineering sent me a conversion chart (after I started this thread), which doesn't take tire diameter into account. Apparently the small variations in tire diameter we use on these trucks doesn't really matter much in converting 1/16 or 1/8 to degrees. The chart is a pdf, so how do I post it?

Anyway, their chart says 1/16: = 0.12*, 1/8" = 0.25*.
Another homemade Excel converter I found which does accept different tire diameters, using the original 6.50-15 tire diameter of ~25.6" says 1/16" = 0.15*, 1/8" = 0.27-0.28*.

So, I've emailed my shop and told them I'd like to come back in to have some more toe cranked in. Yes, I heard the tape measure idea, and as I mentioned I've done it, but I paid them to check everything and adjust the toe, so I'm going to have them do the toe correctly. FYI, camber is 0.4* left, 1.0* right, caster 1.1* left, 1.5* right. Camber's close enough, the shop said the variation was actually good for crowned roads. I could use more caster, perhaps I'll get some 2* shims. I know some of you recommend more caster, but I drive 50mph max and think the factory specs will do fine.

Thanks again for everybody's input.
Once I figure out how to post pics, I'll show you the pins, bushings, hangers, etc. I pulled out of it. Yikes.

Jonas

 

Sine, Cosine, Tangent

Ollie Had A Headache Over Algebra

Opposite/Hypoteneuse Adjacent/Hypoteneuse Opposite/Adjacent

Never mind Cotangents and that other stuff, 'cause I don't have a mnemonic for them!

 

As long as it goes straight hands off, doesn't wander or tramline (follow crocks or seams in the pavement) to suit you, you're good to go.

 

Well, that's not quite true since after you toe the wheel you can't use the diameter of the tire to measure the length of the hypotenuse by physical law it is now longer.

Here's a drawing representation:



I adjusted the numbers in my previous post (I don't generally do math on Fridays to begin with so I had to fix it) and we all did come up with the same numbers. Jonas found the answer with another source. But in the future if you need a formula, it's listed and it's correct now.

One thing I compensated for in my calculations above was to cut the toe distance in half in the calculations because the toe in is actually the sum of the distance both tires are canted in - so the value of the "a" is half of what I originally said. But there is a simple calculation and the deduction is still the same as corrected: The cotangent of the angle of toe in is the tire diameter divided by half the toe in value. So for future reference that's the formula.

PS You seem to be on top of the specs, but I'll post the specs just for future reference and use: