Toe per wheel, axle totals and thrust angle from string line measurements, with the setup sheet saved on your phone so it comes back to the paddock with you. Two strings outside the car, a steel rule and this page will get a club race car within a couple of minutes of where it should be on every wheel. The numbers are only as good as the strings and the rule, so the page checks the string setup as well as doing the sums, and tells you how much error the strings are putting in.
Vehicle
String Setup Check
Every toe number on this page is measured against the strings, so any error in the strings goes straight into the answer. Two things matter. The strings must be parallel to each other, and they must be parallel to the car. The first you have to get right. The second this page can measure and take out for you.
Hub gaps - string to hub centre
String separation - are the strings parallel?
Rim Measurements
String to rim at hub height, on the same rim surface front and back. Leading is the edge nearest the front of the car. The layout below is the car seen from above, so the left column is the left side of the car.
Alignment Results
Toe Targets
Positive for toe in. Enter it per wheel or as an axle total, whichever your setup sheet uses. An axle total is split equally between the two wheels. Every corner above then shows which way to go, how far, and how much the leading gap has to change relative to the trailing gap to get there.
Setup Sheet
Saved sheets
Accuracy And Method
toe = atan(Δ / span)
axle total = left toe + right toe
thrust angle = (rear left toe - rear right toe) / 2 (positive points right)
front toe to thrust line: left - thrust, right + thrust
string rotation = ((RL - RR) - (FL - FR)) / (2 × wheelbase) from hub gaps
Δ for a target = span × tan(target)
1° = 60 minutes. Span is the distance between the two points you measured to on the rim.
What You Need To Do This Properly
String Alignment Questions
Parallel to each other, yes. Square to the car, not if you take the hub gaps. Non-parallel strings put an error into the axle totals that nothing on the page can separate out, so set the separation equal at both stands before you measure anything.
Once they are parallel, a small rotation relative to the car only shifts toe from one side of the car to the other. The hub gaps measure how much, and the correction tick box takes it out. You still want it close, because the correction relies on the hubs being symmetrical.
Because the car drives along its thrust line, not its centreline. If the rear wheels have uneven toe, the rear axle steers the car slightly, and the driver holds a little opposite lock to go straight. Setting the front toe equal side to side relative to the centreline then leaves the wheel off centre.
Fix the rear first so the thrust angle is close to zero, then set the front. If the rear cannot be adjusted, set the front to the "relative to thrust line" figures instead of the plain ones. That gives a straight steering wheel with the car crabbing very slightly.
Only if you know the diameter it was quoted at. A millimetre toe figure is a distance across a wheel, so the same angle is a bigger number on a bigger wheel. 1 mm over a 457 mm span is 7.5 minutes. 1 mm over a 492 mm span is 7.0 minutes. Spec sheets are often quoted at a reference diameter that is neither of those.
If the sheet does not say, ask whoever wrote it. If you know the diameter, convert to minutes yourself and enter minutes. Selecting mm here uses your own measuring span, which is only right if the spec was quoted at that span.
With strings and a decent rule, about two minutes per wheel is realistic and repeatable. Better than that and you are inside the reading error. That is why the tolerance defaults to two minutes. Getting both sides of an axle equal matters more than getting the total exactly on the number, because unequal toe on the rear is a thrust angle and unequal toe on the front is a crooked steering wheel.
Always roll the car back and forward and remeasure after an adjustment. Tyres and bushes hold load after a car has been jacked, and the first reading after lowering it is rarely the one it settles at.