Tracking explanation please

Wig

Just had the tracking done, there was inner wear on both fronts.

He used a laser thingy

First he checked the back axle was straight (fixed axle no adjustment possible just checking) both rears were on '5' (+5?) on the front scale.

So that was fine, then he swapped the laser thingy from front wheels to back wheels, and vice versa, and I think he did swapped the laser from left rear to front right, whether this was deliberate or just how it randomly happened I don't know.

Then he said "we adjust the front before we look at the back" (i.e. before we look at how the fronts align with the back) Unfortunatly I didn't get the reading before it was adjusted. But it was adjusted to be towed out +1 on both fronts +1 in the green zone.

Then he said "now we check the back" and the rear left was 7 and the rear right was 9 (I think) They made some maths numbers in their heads I didn't hear what they were trying to work out, but they ended up adjusting something so that both rears were now on 8.


I got the feeling that the adjustment for +1 on both fronts was adjusted on a different part from the next adjustment which lined up the fronts to the rear. Like maybe the first was a toe adjust and the second was a castor adjustment but I have no idea really.

Then after he had the rear set he checked what had changed on the toe, and I think he said now its 2 & 0 (but I can't be sure) but then he definately did say something like "so the difference between them is still the same" i.e. before the difference was 2 degrees +1 toe out to +1 toe out on the other side is a difference of 2 degrees.

And with that he was satisfied and test drove the car to check it was going straight - which it was.

I was left wondering.... (if the above is accurate description of what happened....) are the fronts now actually set to +2 and 0 toe or are they still +1 on both sides and it is just a quirk of the way it was adjusted. Is it a problem that one would be 2 and the other 0 ? Does this all sound normal procedure? Anyone able to confirm if it sounds right and why what he was saying is correct?

daveyjp

Did they change the front tyres before doing the work?

Hammyman

Yes, what he said was correct. If he hadn't done it the way he had, you can end up with the tracking being correct on the front axle but the car crabbing sideways down the road.

flashg67

If I can recall the course I went on for the laser tracking thingy (many years ago), you adjust the fronts to the manufacturers tolerances, then use the rear readings to ensure all four wheels are running straight. It's difficult without a diagram, but in essence, there's no point having the front wheel running correctly, if the rears are not running 'in line' with the fronts. It's to account for the fact that no car is ever built exactly true and square - what I seem to remember is called 'thrust angle'

As long as the front total toe 'adds' up to the correct setting, then that's fine. EG if the setting you need is +1 then it's ok to have one side at +2 and the other at -1

What you have described sounds pretty much how I remeber being told it should be done - I'm sure with the guages in my hand it would all come back to me!


Edit - Hammyman beat me too it and put it much more succintly....

Wig

daveyjp wrote: »

Did they change the front tyres before doing the work?

No, I did, two new tyres.

Wig

flashg67 wrote: »

Edit - Hammyman beat me too it and put it much more succintly....

I appreciate all replies but I prefer your more detailed reply, I need it explained in detail.

Do you think the first adjustment was "toe" and the second adjustment was on a different component like for castor?

What's the name of these bits that are adjusted for toe and castor?

Wig

Wig wrote: »

So that was fine, then he swapped the laser thingy from front wheels to back wheels, and vice versa, and I think he did swapped the laser from left rear to front right, whether this was deliberate or just how it randomly happened I don't know.

I just realised this would make sense because he would want the green to be on the outside of the car and the red to be on the inside of the car so these laser thingys are 'handed' so you always see them as the 'left one' and the 'right one' depending if you are looking at them on the front from the rear or on the rear from the front. If he had not swapped them diagonally the green zone would have been on the inside of the car and also they would logically only fit on those diagonally opposite wheels otherwise the scales would be at the rear of the front wheels....So that makes sense.

Strider590

I was under the impression the rear had to be aligned before the front........ Which makes sense as the rears don't change direction and should be set up in line with the chassis.

Wig

Strider590 wrote: »

I was under the impression the rear had to be aligned before the front........ Which makes sense as the rears don't change direction and should be set up in line with the chassis.

Yes, he checked the rears were aligned (with the chassis if you like) first....... but you (or they) don't align the fronts respective to the rear until the toe is set for the front.

flashg67

As most cars aren't adjustable at the rear (well not easily anyway), the rears are assumed to be 'fixed' and the adjustable front wheel are used to make adjustments as needed. Toe is adjusted by moving the track rod at each end of the steering rack to make the steering rack in effect, shorter or longer which in turn pushes the wheels in or out individually until they are straight. Cars are set with a toe in or out when static to account for loads & movement when the car is moving.

I do recall some Toyotas had adjustable track rods on the rears (and I'm sure we used to charge for adjusting it twice!)

It is unlikely that the camber or castor was adjusted - this usually needs more sophisticated gear, takes longer and is more costly. On most cars, camber and/or castor is not easily adjustable - if it's miles out, usually something is bent!

If you've not nodded off yet, this may explain it better - http://www.familycar.com/alignment.htm

in_the_Cotswolds

Tracking (toe) and on some cars, VW, Vauxhall, Saab etc, camber is adjustable.

Altering the camber affects the tracking so it has to be checked and adjusted after. However tracking doesn't alter the camber.

Castor is set at the factory.