How do you know if your car needs a new timing belt?

The manufacturer's mileage recommendation has been met. Something like 60 to 100 thousand miles. The appearance of the belt won't usually change, and an inspection won't tell you anything.

If the belt breaks, there's a good chance the engine will be severely damaged. The damage is instant; the valves hit the pistons and bend or break. So unlike a lot of maintenance jobs, you don't want to wait for it to fail. It's not like the serpentine belt (the one you can see.) If the serpentine belt fails, the car won't necessarily be damaged right away (but it might overheat, the battery won't charge, and the Power Steering will be manual).