We took the wife’s car in this weekend to get a new set of tires put on. (2002 Camry with about 36000 miles on it.) The guy at the tire store told us that they would also do a free alignment check while they were putting the tires on. A couple hours later he calls and tells me that the front end looks OK but the back end needs alignment, and that if they align the back end it’s going to throw the front end out of alignment – long story short, both ends need an alignment and it’s going to cost another $75. I told him to go ahead and do it, but got to thinking about it later and it just seemed fishy. Is what he told me possible – specifically, what would cause the back end to be out of alignment, and why would aligning the back end affect the front end – or was it just a scam to drain my wallet of an additional $75?
Just for everyone’s edification, it’s wheel alignment, not tire alignment.
Back to the question at hand: the info as related is plausible. Some further explanation might have been helpful.
Presumably the front wheel alignment angles (caster, camber, and toe-in) were within specs, and I would further guess that the thrust angle (correlation between front and rear toe-in) was also within spec. Thus without adjusting anything, the car should go reasonably straight and the front tires should wear normally.
However, it appears that the rear toe-in was off. This could cause premature wear of the rear tires. The cure is to adjust the rear toe-in. That takes care of the rear, but unfortunately can’t help but change the thrust angle. Thus in order for the car as a whole to be in proper alignment, it is necessary to then adjust the front toe-in so that it’s in synch with the rear.
Some further notes:
Front caster is not adjustable on this car. If it’s off, the cure is replacing a bent or worn part. Front camber and toe-in are adjustable.
Caster does not apply in the rear (applies only to wheels that steer). Rear camber is not adjustable on this car (camber off = replace faulty parts). Rear toe-in is adjustable.
[Thrust angle](http://www.familycar.com/Alignment.htm#Thrust Angle) has to do with both front and rear toe-in being symmetrical to the center line of the car. It’s possible to have the front and rear toe-in each okay in and of itself, but on different theoretical axes to where the car won’t go straight down the road. Any change in toe-in, front or rear, can affect the thrust angle, so for proper alignment the front and rear need to be coordinated.
As to how these things get out of alignment, sometimes we never know. The chief suspect is impact from potholes or curbs.
Okay, here’s a dumb question – I know I need to get the alignment adjusted. Can I just take it to a normal mechanic, or do I need to take it to a tire place or other specialist?
It needs to go to a shop with an alignment machine. Probably the great majority of tire shops and dealerships have one, but probably most general repair shops don’t.
Thanks for the info!
Thanks Gary T. Funny you should say that. The guy that sold me the tires was a real yakker. I’m surprised I got out of there with both ears intact. It would have been nice if he could have used his gift of gab to explain this a little better.