You did not mention if the motor runs on AC or DC.
Lets assume you meant DC. The solid state relays are usually only for AC switching as they switch on zero crossing though I dare say there are DC versions, even more expensive, available.
If your motor runs on DC you can try a reverse biased diode across its connection to suppress the arcing at the relay contacts.
You should also put a reverse bias diode across the relay coil to protect the computer driving it from the back EMF generated spikes.
Klaus