Okay .. people always say, ``run 1/8" toe out'', but every alignment shop I have been to measures toe in decimal!! Most of the printouts look like they have a degree symbol next to the value. I have only seen one which has " for inch, but still in decimal.

Now, 1/8 == .125. I have always ran 0.05-0.06 toe out per side, which should be .12 ~= 1/8, if the readings are in inches. If not, how to convert 1/8" to decimal degrees?

SPiFF, who wishes people would just use the metric system.

 

When toe is expressed as a decimal, it is typically a straight coversion - inches to inches. I haven't run into a case where it is measured in degrees...

K

 

The formula to convert inches to degrees is very long and varies by tire diameter (not wheel diameter)..Better just have your alignment shop push the little tab that states "Measure in inches" All decent aligners have the fucntion to convert. If your alignment tech doesn't know how to do it......Let me know what machine he has and I can walk him through it..

Jeff

 

Just use a little trigonometry to convert.

The total diameter of your tire is the hypotenuse of the triangle, and the degree measurement is the angle at the "small end" of the triangle.

So by thinking back to the last geometry class you had:

Toe in Inches = Tire Diameter*sin(toe in degrees)

Now that wasn't so hard was it?


<<<Glorified mathmatician

 

Thanks guys. All the print outs I have, but one, are in degress, so my -0.05 deg is ~ -0.02". I will have to ask if they can set the thing to inches or get them to set me to -0.15 deg each side.

 

Toe in Inches = Tire Diameter*sin(toe in degrees)<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Def &raquo;</TD></TR><TR><TD CLASS="quote">Just use a little trigonometry to convert.

The total diameter of your tire is the hypotenuse of the triangle, and the degree measurement is the angle at the "small end" of the triangle.

So by thinking back to the last geometry class you had:

Toe in Inches = Tire Diameter*sin(toe in degrees)

Now that wasn't so hard was it?
</TD></TR></TABLE>

I was just talking to a very good friend of mine the other day about this exact subject. He has a set of parents (he's a techer) who flat out told him..." I have yet to use geometry in the 15 years I've been out of high school, I'm not making my kid learn this stuff"..

NOW I figure out I should have paid attanetion...

What's a *sin anyway??

Jeff

 

the * symbol is mutiply.

 

and sin, as in sine. Look at your scientific calculator and you will see it. You will also need the inverse sine to do the conversions. Trig has 3 basic functions, sine, cosine and tangent. For more info, refer to any ol' geometry/trigonometry book.

 

I don't own either...I fix Hondas

Jeff

 

windows has a calculator built-in, and the option to be a scientific one... See, you do own one after all. You just didn't know it
As far as the book, if you really care, Amazon is your friend. Or Google, for that matter.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Def &raquo;</TD></TR><TR><TD CLASS="quote">Just use a little trigonometry to convert.

The total diameter of your tire is the hypotenuse of the triangle, and the degree measurement is the angle at the "small end" of the triangle.

So by thinking back to the last geometry class you had:

Toe in Inches = Tire Diameter*sin(toe in degrees)

Now that wasn't so hard was it?


&lt;&lt;&lt;Glorified mathmatician</TD></TR></TABLE>

I should know this, seeing as how I took two calculus classes and did well a few years ago.

But i'm not following this formula. The answers I am getting CANNOT be right.

First, I was trying to figure out the dude at the acura dealer actually set my toe to last time. I told him "1/8 total toe out" and he came back with 0.06 degrees on each side, which is not the same as 0.06125" (which would be 1/16"). No luck figuring out what he set my toe to in degrees.

Second, I tried to follow the formula above to figure out what I should actually be asking for. No luck. Apparently, I'm dumber than I remember being.

Please spell it out for me since I'm stumped and annoyed with myself.

 

well, if he set it to 0.06 deg, you got 1/64th toe out on each side. And you wanted 1/8th total toe = 1/16th each side.

So, if he set your toe to 0.06 INCH on each side, you're ok.

here are the calculations = which are all wrong since I am only using the wheel diameter. go out and measure the wheel+tire diameter and plug into the formulas.
sine (toe angle) = (toe in inches) / (wheel dia in inches)
toe = sine(angle) * wheel dia.
toe = sine(0.06) * 15 (I'm assuming stock dia. wheels) = 0.0157 ~ 1/64th

toe angle = inverse sine(toe/wheel diameter)
angle = asin(0.0625/15) = 0.24deg

hth

 

Gotcha. I was using Sin, but using the 'adjacent' side as the tire diameter instead of the hypotenuse.

Me.

 

I'm trying to get an alignment done today and the shop that replaced my spindle/upright (I know, I should have done it myself but ran out of time) is taking it to get aligned and when I told him 1/8" total toe out he was confused that it wasn't in degrees. Granted, he's not the one doing the alignment, and maybe the guy that is doing it, will understand to convert it from inches to degrees.

If they don't though, someone want to tell me what 1/16" for each side is, in degrees? I don't trust myself trying to use that formula without a scientific calculator handy (and wouldn't anyway, lol). My wheels are 15", with 205/50 tires.

thanks

 

1/16th on each side should show up as 0.07 degrees.

I just had my alignment done at a friend's shop and watched the whole thing done in degrees.

 

that was fast. so cool man.
for you!

thanks!

 

Good luck with the alignment.

I highly recommend getting your alignment done by a friend (if one works at a shop) or a friend of a friend. I learned a ton about alignment, suspension, etc, just from asking questions/watching my friend do my alignment. MUCH better than trying to explain that you actually want toe out to some goofy guy who can't understand why you want an alignment that is out of spec....

BTW - interesting fact I didn't know: If you set your toe to zero in the rear, they will toe OUT to 0.04 degrees (1/28th of an inch I believe) when turning because of the big ole' trailing arm bushing. I never understood why setting the rear to zero would help the car rotate/turn in. but knowing that it is actually 0.04 out when turning in.... makes sense now. I'm sure a lot of you already know that, but I had no idea.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris N &raquo;</TD></TR><TR><TD CLASS="quote">1/16th on each side should show up as 0.07 degrees.

I just had my alignment done at a friend's shop and watched the whole thing done in degrees.</TD></TR></TABLE>

Looking at SJR's calculation above, 1/16th on each side yields .24 degrees. ???

Sorry to bring it back from the dead...

 

SOH CAH TOA pwns all!

 

arumph.
if you read the whole post, it mentions that I used a bunk value for the wheel diameter. You need to use the diameter of the entire wheel (tire + rim). So go measure the total diameter of your wheel + tire assembly and plug it into the formula.

 

Right, but isn't toe normally measured at the wheel edge, rather than the tire edge?

Also, wouldn't you use the tangent instead of sine? Tan (angle) = opp/adj = toe measurement (in inches)/wheel diameter. ???

Using a 205/50R15, I get 1/16in. of toe = 0.16 degrees.

Are my calculations incorrect?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by STSDA3 &raquo;</TD></TR><TR><TD CLASS="quote">Right, but isn't toe normally measured at the wheel edge, rather than the tire edge?

Also, wouldn't you use the tangent instead of sine? Tan (angle) = opp/adj = toe measurement (in inches)/wheel diameter. ???

Using a 205/50R15, I get 1/16in. of toe = 0.16 degrees.

Are my calculations incorrect?</TD></TR></TABLE>

nope, the adjacent side of the triangle isn't wheel diameter, but the vertical distance from the wheel's edge to the vertex of the triangle. The hypotneuse is the wheel diameter, and is known or measureable, and the toe is measurable or given, so the easiest thing would be to use sin, since toe = opposite, and wheel diam. = hyp.

 

Is it becoming clear why the measuring machines do it in degrees instead of inches. If you will do it in degrees, wheel and tire measurements don't matter.

 

ding-ding-ding! we have a winner. For the shadetree mechanic though, the ol' ruler works.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SJR &raquo;</TD></TR><TR><TD CLASS="quote"> the ol' ruler works.</TD></TR></TABLE>



If you want to be pimpy you can get one of these though: