Tracking.....

[aceparts_com]

OK, my car has always wondered off to the left, always. I've had the alignment done 4 times over the last three years and it's still going left. I've just fitted new tyres and now notice that although it's going left, when holding the wheel dead ahead the car will go right slightly.
As it didn't do this before i'm asuming the new tyres are either not yet bedded in (20 miles) or the old ones had worn funny.

Also, how is it possible to have only one wheel toeing in or out? What is the reference point for the one wheel? Surely they'd both be in or out to the same degree?

[up-the-dubs]

A smack of a pot hole or sharp impact will knock one wheel out but not necessarily the other. The tracking is fixable, bring it to a different place, have them put the readings on the reciept to show the other clowns. They may need their machiene re-calibrated.

If they say it's straight, there may be something bent that the tracking doesn't highlight, though the fitter should notice it.

[GreenV8S]

You can have the toe-in wrong on one side on the back wheels - obviously on the front it isn't possible to apportion the toe-in to one side or the other because you can always turn the steering to even them up. What sort of alignment checks have you had done? If it's a full 3D check then that ought to tell you whether the front and rear axles are square to the centerline of the car and the two sides are symmetrical. If all looks good, perhaps the corners weights are out?

[leorest]

This is how I understand it.
Each front wheel toe angle is referenced from the thrust line, which is the average of the rear wheel toe angles. Each rear wheel toe angle is referenced to the chassis.
A proper alignment process should centre and lock the steering rack before measuring/adjusting any toe settings.
If you think about this you will see it is possible to get one wheel toe setting out of spec.

I think you need to find someone reputable who you can trust to do your alignments.

[aceparts_com]

Thanks guys, you've answered all my questions especially with reference to the thrust line.

I've just discovered that I've actually broken my strut brace - so no one can accuse me of not trying hard on the track
The car has always followed the camber of the road so I'm not over worried about the drift to the left but it's probably time to get it checked again (3rd time this year)

[Sam_68]

aceparts_com said:

I've just discovered that I've actually broken my strut brace - so no one can accuse me of not trying hard on the track

If you've stressed the chassis enough to break a strut brace, the wheel alignments are going to be all over the place!

If you drive that hard, I'd suggest that you need adjust wishbones/suspension links so that you can get regular 4-wheel geo and adjust out any alignment problems.

[aceparts_com]

Update.... I've done about 100 miles since the fitting of the new tyres and the car is now 95% perfect - it was only 50% before. What is it with new tyres that can make the steering so crap?
BTW, my car has ALWAYS gone slightly to the left, always and it's been set up 5 times in the last 3 years. I guess very wide tyres and UK roads just don't mix

[leorest]

In a discussion with Chris Franklin (of Centregravity) he said, for road use it is good practice to set-up so that there is a slight tendency to steer left which with a drivers lapse of concentration would be safer than the alternative! Made sense to me.

"What is it with new tyres that can make the steering so crap?" This is just speculation but there are marks (dots on the walls and lines in the tread grooves) placed on the tyre indicating dynamic and static balance and dimensional (?) variations on production. If a tyre is out of balance on its right hand wall and the tyre on the other end of the same axle is also out of balance on the right hand wall then as it starts to vibrate this will make both tyres tend to steer (like procession of the earth?) in the same direction. If you transpose one tyre on its rim then each tyre's manufacturing errors would tend to cancel each other out rather than add! Remember that the balancing done by your wheelwright cannot 100% compensate for all of the manufacturing inconsistencies so fitting the tyres so the errors subtract instead of add can make the difference!

Not very well explained but I hope it makes sense to someone

[aceparts_com]

That's interesting as when they were first fitted it felt as though they weren't really balanced at all. Now they've smoothed out, about 95% too.

F'ing cars - we just love them