Tesla Motors Inc (NASDAQ:TSLA) fans spotted an unusual car made by the electric vehicle company. It was spotted near the University of California – Santa Cruz. First look of the car had heavy test equipment on its top. Each wheel of the vehicle was fitted with an external odometer, which is used to note and record the rotation of each wheel. It bears the California “manufacturer” license plates.

tesla model S or X

Theory: it’s Tesla’s all-wheel drive car

Many say that it’s the early prototype of Tesla Motors Inc (NASDAQ:TSLA)’s all-wheel drive Model S. Others argue that it’s the test mule for the upcoming Model X. Transport Evolved spoke to several people, who claimed that it was a Model X test mule with all-wheel drive. The extra weight on the roof would help it maintain the center of gravity. Auto experts said that the Tesla used the weighted box on the roof to adjust for the higher COG of the Model X.

Tesla Model S or X

Tesla Motors Inc (NASDAQ:TSLA) founder Elon Musk has promised to bring a Model S with all-wheel drive. However, that’s unlikely to hit the markets until the Model X enters production in 2015. JB Straubel, chief technology officer at Tesla, recently said that the Model S all-wheel drive system will be an “energy-neutral option. That means it won’t affect the sedan’s electric range.”

Tesla Model X wheelbase to be same as Model S

Tesla Motors Inc (NASDAQ:TSLA) has clarified that the Model X will offer an all-wheel drive. The crossover will come with a separate motor to power its front wheels. The wheelbase of the Model X will be the same as the Model S, but its length could be 5cm more or less than the current sedan.

What do you think? Is Tesla Motors Inc (NASDAQ:TSLA) testing the AWD version of Model S? Or is it the upcoming Model X? It could also be something entirely different – perhaps the company’s first self-driving vehicle prototype.

Tesla Motors Inc (NASDAQ:TSLA) shares ticked up 0.40% to $255.86 in pre-market trading Wednesday.