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!