Here is how gps works. Taken from a website: A GPS receiver's job is to locate four or more of these satellites, figure out the distanc*e to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration. So if you drop or have bad signal you suffer erros in data. So just do what Looigi says and supplement with sensors. If you don't care that much don't put the sensors on. I ride with a buddy who never put the sensors on his bike.