Q: I just had my calipers switched now smoke is coming from tires rpm goes up and speedometer won't go over 40

Hi There, It sounds like you may have a caliper that is sticking causing excessive heat to be generated at the rotor as a result of the caliper trying to stop the rotor. A few different things can make the brakes stick or lock up. The master cylinder may be causing this if it has not been properly bled. If you loosen the lines to the master cylinder and they free up, this is where your problem stems from. In other cases, the problem may be in the brake lines cause the pressure to continue to maintain in the caliper resulting in them sticking as well. Try cracking the bleeder valve to see if this frees them up. If this does not free them up, you may have a caliper that could have a damaged piston that may be causing them to stick. I would recommend having an expert from YourMechanic come to your location to diagnose your braking system.