If you're wondering whether your car needs an alignment, first look at your tires. Uneven tire wear -- often, more wear on the outside of some tires -- is a prime indicator that your car is likely out of alignment. Here are a few more indicators:
1 - your car seems to be drifting to one side, even when you think you're driving straight
2 - your steering wheel vibrates
3 - you are driving straight, but your steering wheel isn't centered
If none of these indicators occurs but it's been a while since your last alignment, check your owner's manual to see how often the manufacturer recommends having this service.
