Toe-in - What Does It Mean Exactly?

[Pawel66]

I need to set it again, as I replaced the steering box and when steering box was installed centered, marks on pitman arm and shaft aligned, mark on steering spindle up - the steering wheel is not in center when driving.

I refreshed the specs again, they say Toe-in (rolled average) 2 +/- 1mm or 0deg 20' +/- 10'

There is a note as well: Try for toe-in 2mm or 0deg 20'. I guess the note says "get it exactly" 2mm or 20'.

Two questions:
1. "Rolled average" - of what?
2. The 20' parameter - is it the angle between the two wheels or the angle between a wheel and a line parallel to car axis?

Never thougth of that before and my lack of car mechanics education makes me ask this question.

[MikeSimon]

I will try, but others may disagree:

The "rolled average" is the value between the measurements before and after you "roll" the car for one wheel rotation.
The 20' (minute) value is the angle between the straight line through the wheel plane and the straight line parallel to the longitudinal centerline of the car.
Measuring the toe-in (and camber etc.) usually requires some extensive alignment set-up that few home mechanics have access to. How are you going to do this?

[Pawel66]

In a specialized shop. I did this at the dealer, but their machine broke down and I prefer not to wait.

So 20' angle for each wheel... feels a lot, but it is what it is..

Thank you Mike!

[FGN59]

Maybe you are being misled by the notation : 20’ is a third of a degree, which is not very much; not to be confused with 20º, which is indeed a lot for a car’s front wheels. You probably couldn’t drive the car without hearing the tires squeaking to their death if you could drive at all.

Working with degrees and minutes, inches and feet, meters and centimetres, metric and US tons, etc. sometimes gets to you. One of the joys of a multipolar world and international forum.

[Pawel66]

Thank you! Yes, I am aware of 20' being less than half a degree - still seemed a lot to me somehow even though I did not have a lot of reference. With 4deg caster it seems a lot has been done to keep the car driving straight with power steering...

[FGN59]

I’m sure you know that: caster angle is what brings the wheels back to center when you let go of the steering wheel after a turn. Toe in helps keep the car in a straight line. You need both working together. Sorry if I’m pushing on an open door.

Power steering probably helps also a little bit, but it is not really designed to keep the car straight, unless it is actually designed to, as in the Citroen CX and SM for instance (where if you let go of the steering wheel, it will actually automatically center itself back).

[Pawel66]

No, good discussion.

I think the caster also helps keep the straight line.

I think PS with lightness of steering wheel operation it provides, regardless of speed, is a challenge to keep the car straight at high speeds. In modern days, it is resolved differently, but in the 60ies they, perhaps, configured the suspension in such a way that it helped keep the car straight.

The caster of 4* is there for cars with powers steering only for W113.

Just my uneducated thinking. 

[FGN59]

Yes, caster helps a little bit, but if the toe-in is wrong, it will not be enough to keep the car going straight. That’s why you sometimes have cars that drift either left or right, it is almost always the toe-in which is wrong, usually on one side (after a shock or a bump).

And you’re right, power steering goes with a bit higher caster angle.

On my previous ’oldie’, a 1962 Jaguar MkII (with an extremely heavy cast iron V6), the original steering was not assisted (very rare option). I made the mistake of having an electric power steering installed, not adjustable. For parking and city driving, a dream. For high (or even moderate) speed driving, not exactly a nightmare, but much too sensitive for ease of mind. You had to concentrate all the time to keep the car in a straight line.