Alignment Toe Question
 

Should I measure toe from tire tread or wheel rim?:iono:

From the wheel. How are you doing the measuring?

- Andrew

I'm pretty sure the reported/standard measurement in units of length is at the tire tread, not the wheel.

25" tire OD, 1/8" (0.125") toe-in conversion to degrees = (0.125"/25")*180°/pi = 0.29°

If you measured at the wheel, 1/8" (0.125") toe would equate to (0.125"/17")*180°/pi = 0.42°, that's a big difference!

What are you using? The rim provides a better place to measure with strings because the tire sidewall is not perfectly straight or parallel to the wheel surface so it is hard to measure precisely on 2 places on 4 tires. However, yes, that distance is shorter so it's a little harder to measure and adjust accurately. You could lean a rectangle of plywood against the tire like a toe plate and measure to the edges of that instead.

Typically the wheel. The tire is too dynamic.

One good technique I've seen involves using a nail to just slightly score a center line on the tread of the tire as you spin it. Just enough mark to be visible. I suppose a good sharpie would work too. Then you measure to that line that you marked from a fixed point while the wheel turned. Still, the wheel is better.

ZDan's point about the difference of measurement is a good one but the spec is measured to the wheel as a standard. If you've ever watched a professional alignment, all the machines I've ever seen used are measuring to the wheel. Otherwise different tires, pressures, or even states of wear would be impacting alignment settings.

It depends on the method. There are easy-ish methods to accommodate for either but it depends on how your doing your measuring. Many people that do at home alignments with toe plates measure at the tire but I would prefer not to do that.

There's at least 1 set of toe plates that are specifically designed to measure from the wheel, and if you're using strings it's not a big deal to use the wheel and IMO is preferable.

- Andrew

The problem with using the wheel is that direct inches or millimeters of measured toe are not the same as the industry-standard which alignment specs are given in. You have to scale based on tire OD/wheel OD to get the conventional toe dimension.

0.125 inches of toe measured at the wheel on a 17" wheel with 25" tire = (25/17)*0.125" = 0.22 inches of toe in the standard measurement.

Again, it's a big difference and if you don't account for it you'll end up giving yourself way more toe than desired or intended...

Probably best to just convert directly to degrees which I prefer for units anyway, to remove ambiguity.

0.125" at 17" wheel = (.125/17)*180/pi = 0.42° (calculation for reference only, way too much for any usage IMO)

I measured with string at the rim edges. Autox specific alignment. Not a daily driver. I set 1/8 " toe out front. 1/8 toe in rear. I've got tarmac2's. Is that an OK starting point Andrew? Thanks everyone for your help. GREAT forum!

Like I said above, 1/8" (0.125") *at the wheel* is 0.42°, IMO way too much for any usage. I prefer close to zero toe at both ends, but anyway I don't think you'd want more than 1/8" of front toe-out *at the tire*, which is 0.085" or a little less than 3/32" *at the wheel*, or 0.29°.

All that toe-in at the back of the car is, IMO, good for nothing and bad for everything, including turn-in responsiveness which I would think you'd want for autoX. I would run zero to no more than 1/16" rear toe-in *at the tire*, or 0.0425" *at the wheel*, about 1.5/32", or 0.14°

As the above numbers illustrate, you have to be able to measure distances more precisely at the wheel to make up for the fact that the measurements are only ~17" apart instead of ~25" at the tire tread...

IMO yeah that's too much toe. 0 up front or close to it at least as a starting point. 1/16 in at the rear as a starting point.

Converting to degrees is a good way to be sure you're doing it right.

- Andrew

So, when you're talking of 1/16, you're talking in inches, right?

Yes, freedom units.

:lol:

I think here in Italy we measure toe at the rim edge, can you please tell me what 1/16 of inch is with 17" rims? I have total rear toe in of 1,6 mm... Thanks!

1/16 of inch is 25.2mm/16=1.575mm, when 1mm toe for 17" rims is about 7' this means 1/16 is 1.575x7'=11' toe!
I think I am the only one that uses toe out (1mm) front and parallel rear wheels for DD in our very slippery roads...

You might want to check your math on that one.

1/16 over 17" is more like 0.2º of toe.

other thing is a cambered tire creates a thrust force in that direction so it may be a good idea to have a small amount of toe out with a lot of camber. If you have in the ballpark of 1.5-2 degrees of negative camber that would be an alright amount of tie.

https://robrobinette.com/ConvertToeInchesToDegrees.htm
If you set toe in inches 0.0625 (1/16) and tire diameter to 17" (24.6") then the result is 0.072...where am I wrong?

Well, which is it?

And .07 is not 7 degrees- It's .07 degrees.

Also 7' is not the right symbol for degrees assuming that is what you meant. With regard to angles that is the symbol for a "minute," which is 1/60th of a degree. To get a degree symbol (º) type alt+167

I mean minutes not degrees as alignment machines read minutes or mm locally, but I am really confused now, how much is then 1/16" to minutes or mm?

Units for alignment can be confusing...
' in this context is arc-minutes, not feet.
1 arc-minute = 1/60 = 0.0167°

1/16 inch toe-in at 17in. is (1/16")/17" = 0.0037 radians = 0.21° = 12.6' (arc-minutes)
1/16 in. toe-in at 25 in. is (1/16")/25" = 0.0025 radians = 0.14° = 8.6' (arc-minutes)

Personally I wouldn't want more than 0.1° toe-in, and preferably closer to zero...

I run zero toe rear and 1mm toe out per wheel front with -1.4 degrees camber all around for DD but I believe a pyrometer is a "must" have for those that use their cars on track.

I like to just use degrees and decimals at each corner, seems that's how most printouts I've see are. Then you don't have to worry about that whole how big is the wheel thing. And not that it makes much of a difference but the points you're measuring on a rim are going to be farther apart than the wheel size by like a whole inch.

Other thing I rarely see mentioned is the effect of camber thrust. Leaning a tire over creates a side force that wants to pull the tire in that direction. Some books indicate in the ballpark of the equivalent of 0.1 degree of toe per degree of camber. So, maybe it's a good idea to have a little toe out with a good amount of negative camber to make the tires roll straighter and reduce scrubbing and the tires both trying to turn in. On the other hand compliance in the suspension and steering might generate some toe out from tire drag. And also toe out will make scrubbing on the inside tire worse in a corner.

And here I am worrying about hundredths of a degree while people can't even sort out how many degrees of toe they even have!

I currently have 0.02° toe out up front, 0.05° toe in rear... Basically zero...

Small correction... An inch is ~25.4mm

We live in different parts of the world, it doesn't mean people don't know how many degrees toe have but how to convert from one system to other, they have minutes or mm, so simple!
By the way how many mm toe you have? :lol:

Don't most dyno rigs allow selecting different measure units for toe, whichever seem more convenient? I don't get much all the fuss about converting.

Alignment machines may be allow it, their operators don't know very often how to do it if you know what I mean...

I don't figure you need to care about inches very often. :lol:lucky you. Just wanted to note in case government contractors building satellites decided to use your post as a reference...



No idea how many mm toe I have, because it's a useless conversion for the way I do alignments. About that much. Might be 0.5mm toe in rear, 0.2mm toe out front (using the tire) if I didn't mess up the math. Which is interesting, because that means on this car each hundredth of a degree of toe might be just about one tenth of a millimeter of toe.


I've been told my alignment setup has about 4x the resolution of the best laser alignment setups... It also can take 10x as long to do a proper alignment... partly because of cramped quarters in my garage...

And here I am worrying about some minutes while people can't even sort out how many mm of toe they even have! :bow:

cjd: if you want to dvelve as deep in alignment precision .. remember that it changes depending on load. Was your alignment done with you sitting in car or not? :)

And how level is the car, how good are the slip plates, how accurately can you determine the centerline of the chassis, how does that relate to the position of the suspension and wheels, etc.

1mm at the rim is about 0.1 degrees. Which I suppose is a pretty good reason to measure in mm instead of fractions of an inch.

Hey, at least I know that radians and minutes and degrees all exist. I'm mostly just too lazy to do the math most days. :bonk:



Me? no. An approximate representation, give or take? Yes. Gas in tank too, I know... I'm not as worried about the level of precision, just found it vaguely funny.


I got that at the wheel, not the rim. Rounding differences probably...

I don't convert often degrees to minutes cause I have my own alignment specifications based in my experience and my tire pyrometer not the forum, I just tried to help and according to ZDan's calculations it was 8.6' instead of ~7' I wrote, so wrong that worth long conversation, keep your ironic comments I keep my fault, we are so different...