It's probably safe to say that no car owner ever wants to call a tow truck; not only is there is the expense but also the wait in traffic, and then seeing your car being loaded onto the back of chains and dragged to a nearby shop. However, as unpleasant as it might seem, continuing to drive your car rather than having it towed when it needs repairs can mean even more expensive fixes once you do get to a shop. Consider when your car problems mean that you should call for a tow, to protect your car and avoid unnecessary repair bills.
Grinding sounds often come from the brakes, when the pads are very worn down; you may hear metal-to-metal contact of the pads with the rotors when there is no more cushioning around the pad itself. When you hear this sound, and especially if it's severe and loud and you notice what feels like strong resistance or pulling from one tyre, call for a tow. The brake pad is probably almost gone and continuing to drive can mean having it slip and, in turn, having your car slam to a stop.
That grinding could also be the brake parts, called clips, that hold the pad in place. If the pads are very worn down, the clips may then be rubbing against the rotors. These clips are very expensive to replace. This metal-to-metal contact also causes severe damage to the rotor itself; continuing to drive can mean that the rotors also will need replacing.
If your car's steering wheel shakes, this often is the result of one tyre shaking and that vibration is then carried all the way to the steering wheel. Severe shaking may mean that the tyre is not securely connected to the car; the lug nuts may have broken, or you may have a broken strut, which is a long vertical metal piece that connects the tyres to the car's body. When the car has a broken strut, the tyre is not securely connected to the car and it begins to shake when you drive.
In both these cases, you may be at risk for the tyre actually coming off the car. Not only is this dangerous for other drivers but your own car's rotors can slam against the pavement when a wheel comes off, causing severe damage. To avoid having to replace the rotors and a missing tyre, it's better to call for a tow when you feel severe shaking in the car.