Wheel tracking for 1800S
 

The original service manual quotes Toe-in 0 to 4mm (5/32").
How does this equate to the individual toe and total toe, quoted in degrees as used in modern laser equipment?

I think it would be total toe since Volvo's of this vintage do not have provision for left and right toe adjustments. Vehicles with rack and pinion steering have an adjustment on each individual tie rod which is why you have a left and right toe values which are typically the same on every car that I have seen and sum to the 'total toe in'.

Equating to degrees is a problem since Volvo does not specify toe in in degrees. To figure out what the degree value for the toe in is, you would have to set the car on turn plates, loosen the toe adjustment and adjust using the rim or tire centerlines to establish 0 toe in. Then adjust the toe in to Volvo's 4 mm spec and read the change in angle. Presumably, if the specs in degrees reside in the alignment computer somebody has done this already. Because the laser alignment tool establishes a vehicle centerline it will report the angles relative to that centerline and give you a left and right toe value; but, you can't modify the individual values. If the total toe is correct; but, the left and right toe are significantly different that is likely an indication that something is bent.

Absent somebody doing an actual test on an 1800, you have to hope that whatever total toe value is loaded into the alignment system matches up with Volvo's 4 mm spec.

The service manual quote is for total toe in I believe.

Found this on line.

https://robrobinette.com/ConvertToeInchesToDegrees.htm

That conversion is correct. The thing to remember is that Volvo's toe measurement is based upon the original tire diameter. Don't use the diameter of the tires that may be on the car at present to calculate the toe angle unless they happen to be the OEM size. You could use the OEM tire diameter to calculate an equivalent toe angle and then apply that toe angle to your current tire size.

Isn't the diameter of the rim the size that matters? Tracking is measured at the rim edge.

X2

That seems to me most likely - I've not got my bits of string and home made camber angle out to do the wheel alignment on my PV yet (not quite reached that stage!) but on other vehicle types the measurements I've had to make have always been from the wheel rim.

I'd be surprised to learn that Volvo measured from tyres (but hey - you know - weirder things have happened in the last ten years)

Using degrees largely takes inch/mm measurements out of the equation when the gauges are clamped to the rims. Hopefully the rims aren't buckled.

Yes and no.

Modern alignment systems use a fixture that attaches to the rim and reports the angle / toe in of the wheel relative to the vehicle center line in degrees. It is using the rim 'edge' to define the center plane of the wheel and the diameter of the rim is irrelevant. Accurate measurement requires straight rim edges and correct fitting of the fixture to the rim. If your vehicle dog tracks I believe this also bodges the measurement because it skews the centerline.

There are fixtures for home alignments that attach to the outside edge of the rim that create lines parallel to the planes of both wheels and you can measure the distances between these two fixtures to determine toe in. But, the measurements must be made at a separation corresponding to the OEM tire diameter if you want to use Volvo's toe measurement value.

Vintage Volvo predate modern alignment systems. If you check the original Volvo green book service manual, you will see that Volvo defines toe in as the difference in the distances between the front and back of the tires as measured at the height of the center of the hub, exactly as shown in that link provided by C1800. In that case, the correct diameter of the tires is absolutely important if you are using the Volvo specified measurement. If your tire diameter is smaller than OEM, you can use that calculator with the OEM tire diameter and Volvo's spec to calculate the recommended toe in in degrees. Toe in measured in degrees is a better measurement because it is invariant to the diameter of the tire. However, toe in specified in mm or inches was the norm because most alignment shops in the '60s and '70s could not measure angles.