INFLUENTIAL US magazine Consumer Reports has declined to recommend Tesla's Model 3 sedan, saying it braked slower than a full-sized pick-up truck.
The car is seen as crucial to the electric car company's profitability at a time when it is battling to reverse production shortfalls, confronting reports of crashes involving its vehicles and facing increased scepticism over its finances.
On Twitter, company co-founder Elon Musk said the fully loaded Model 3, with all-wheel drive, a dual motor and a 499km range - but excluding its vaunted Autopilot feature - would cost $US78,000 ($A103,000).
The company has not yet begun to make the cheaper $US35,000 ($A46,000) price version that Tesla originally claimed would make it a mass-market vehicle.
Consumer Reports, however, declined to recommend the Model 3 and criticised it for having overly long stopping distances and a difficult-to-use centre touchscreen.
The highly influential magazine, which provides an annual rating of vehicles sold in the United States, said even though its tests found plenty to like about the Model 3 and it was a thrill to drive, it had "big flaws".
Tesla's stopping distance of 46m when braking at 100km per hour was "far worse" than any contemporary car tested by the magazine and about 2m longer than the stopping distance of a Ford F-150 full-sized pick-up, it said.
Tesla said its own testing had found braking distances of 40m on average using the 18-inch Michelin all-season tyre, and as low as 38m with all tyres currently available.
Meanwhile, a Tesla Model S sedan has crashed, killing the driver, in the San Francisco Bay Area, one of a recent spate of crashes, some of which involved fire and some of which took place while the company's semi-autonomous Autopilot technology was engaged.
In the latest case, the car launched off a rural county road into a nearby pond more than 18m from the road, state and local law enforcement said.
Tesla said it did not yet know the facts and had not yet received data from the car, but was co-operating with local authorities.