It can be done with either unit of measure. I had only seen specs in degrees for the Passat, but I used to used inches when I aligned cars in the shop (many years ago).

 

While I don't know, I'll say that .16 inches is easier to measure than .16 degrees. Someone who is more up to speed on math should correct me if way off, but .16 degrees from straight ahead would only move the edge of my 16" rim about .025", less than a spark plug gap.

I figured that from the center of my wheel to the rim edge is about 8.5": X = 8.5 * Tan .16, so X = .025".

 

Thanks for the replies. I did some geometry using autocad. The following applies to standard 15" rims and tires for a GLS Passat B5 (mine is a 2003).

The official VW spec for toe-in for each wheel is 10' +/- 2'. This is 10 "minutes", where a minute is 1/60 of a degree. So, 10' equals 0.167 degrees.

Since the OD of the wheel/tire is 25" across, this 10 "minutes" per wheel translates to 0.145" (inches) of total toe-in. (The distance between the rear of the tires minus the distance between the front of the tires.)

I used a 59" stick and two finishing nails, together with a micro-caliper to measure the distance between the front and rear of the tires (total toe). The Michelin Primacy tires have a thin groove at the exact center of the tread, and a #4 finishing nail fits in that groove perfectly. So the measurement using this setup is very accurate and precise.

But because of the clearance from the undercarriage, you cannot measure high enough up on the tires to get to the exact front and rear centerline points. You have to measure a few inches below the centerline. The distance between these points is 23.5", not the full 25" OD. Accounting for this, the total toe-in between these points is 0.137" (not 0.145").

Also from geometry, a change of "X" on each tie rod end will result in a change of 7.83X on the total toe (as measure at the points slightly below the centerline, as mentioned). For example, if you extended each tie rod end out by 1mm, you will increase the toe-in by 7.83mm.

When you consider that the tie rod ends have a thread of 1.5mm per turn, you can readily determine how much to turn each tie rod adjusting nut to bring the toe-in into spec.

For example:

If you measure the toe-in to be 0.10", you would have to increase the toe-in by 0.037" to bring it into spec (0.137"). (Again, as measured at the points slightly below the centerline, as high up as you can get when the tires are bearing the load of the car.)

Using the factor of 7.83, that means you would have to adjust each tie rod out by 0.037" / 7.83, which equals 0.0047". Converting from inches to mm (25.4 mm per inch), this equals 0.0047" x 25.4 = 0.12mm.

Since the tie-rod threads are 1.5mm per turn, you can divide 0.12mm / 1.5mm = 0.08 turns. 0.08 x 360 degrees = 29 degrees. This means you would have to turn each tie rod adjusting nut by only 29 degrees to bring the total toe-in to spec.

I verified that these factors are correct, by actually doing the adjustments. When I did the final check, the toe-in was exact to within +/- 1' (one minute).

Details on the stick measurement tool:

You can go to home depot and buy 5 ft of thin wood moulding. The 3/4" x 1/4" is the perfect cross section. Will cost about $4.

Cut this to exactly 59.5". Exactly one inch from the end of the stick, drill a hole slightly smaller than a #4 finishing nail. Grind off the point of the finishing nail. Then force the nail through the hole so that it sticks out about 3/16". This nail will center that end of the stick in the center groove of the tire. (You will need to use a cinderblock and a short 12" stick to wedge against the measuring stick next to the nail, to get it to stay securely in the tire groove. It works great.)

On the other end of the stick, make sure that the end is perfectly square. You may want to rub a little wood glue on the end so that it hardens and preserves the surface, because you will be measuring from this end with the micro-caliper for very accurate measurements.

Grind off the end of another #4 finishing nail to insert it solo into the center groove of the opposite tire.

There will be about a 1" gap between the end of the stick and the nail sticking out of the tire groove. This is where you use your micro-caliper to obtain very accurate and precise measurements. Remember to measure at the very base of the nail sticking out of the tire groove, and try to keep the nail perpendicular to the tire. You only need to measure this gap. The length of the stick does not matter because it cancels out when you subtract the front distance from the rear distance. So write down the gap measurement when doing the rear, and write it down for the front, and then subtract. This is the total toe-in measurement.