What’s Stronger – a Toyota Prius or a Tesla Roadster in a crash test?… Well a Tesla Roadster was ‘bound to crash sometime with all that torque – so we caught one on camera.
Quote: “An Autopia reader spotted this accident involving a Tesla Roadster, Volkswagen Tuareg and the Toyota Prius. The story goes the Tesla was stopped behind the Touareg at a red light when a Prius rear-ended it and pushed it under the SUV. From what we know all passengers were fine.
Tesla has been engaging in intensive durability and validation testing of final prototype cars.
As part of this final testing – a Tesla Roadster ran for 245 miles on the combined EPA cycle on a single charge (235 on the EPA highway cycle, 255 on the EPA city cycle.)
Separately – a validation prototype Tesla Roadster successfully passed static and dynamic side-intrusion crash tests, the only tests that were not passed in the earlier prototype phase.
In other performance testing – a validation prototype Tesla Roadster accelerated consistently from 0 to 60 mph in under 4 seconds.
Tesla Motors has initiated a unique program – inviting customers to participate in durability and validation testing by road-testing our validation prototypes and providing feedback to marketing & engineering teams. Customers have shared their feedback on the Tesla Motors blog and with other customers in a members-only online forum.
The announcement of this production schedule represents a change from the previously stated goal of fall 2007. In the last letter to customers in August, former CEO Martin Eberhard indicated that the production schedule was subject to successful completion of crash testing and durability testing. This new schedule represents the decision to continue with additional durability and validation testing prior to start of production and shipping of cars to customers.
In an announcement earlier this year, Tesla notified customers that the EPA range of the car was not likely to reach the original goal of 250, & instead would be closer to 200 miles based on progress at that time. Since then, Tesla engineers have worked diligently to improve on this critical performance metric – and the results of the effort over the last months have been extraordinary.
The EPA cycle test result was observed by CARB (California Air Resources Board) staff & is expected to be formally certified by EPA in the near future – as is standard procedure.
The range of the Tesla Roadster is by far the highest range ever achieved by a production EV. The next closest was the 1999 EV1 using nickel metal-hydride batteries, which achieved a 140 mile range rating. No other EV currently being developed has completed an official test for range using the EPA standard protocols.
In a battery-powered electric vehicle, regenerative braking (also called regen) is the conversion of the vehicle’s kinetic energy into chemical energy stored in the battery, where it can be used later to drive the vehicle. It is braking because it also serves to slow the vehicle. It is regenerative because the energy is recaptured in the battery where it can be used again.
The kinetic energy stored in a moving vehicle is related to the mass and speed of the vehicle by the equation E = ½mv². All else being equal – if your car is twice as heavy it has twice the kinetic energy & if it is moving twice as fast it has four times the kinetic energy. Any time your car slows down the kinetic energy stored in the vehicle has to go somewhere. Let’s take a look at where this energy goes. There is always some kinetic energy consumed by the rolling resistance, mechanical friction, & aerodynamics of your car. These bits of energy go into heating the road, the surrounding air – and various spinning parts in your car. But the vast majority of the kinetic energy is converted into heat by your brake pads when you stomp on the brakes. In the Tesla Roadster, regenerative braking recovers some energy that would otherwise have been wasted in the brakes.
How much energy does it recover?
Unfortunately, the adage “your mileage may vary” applies to regen as well. The amount of energy you can recover depends on how and where you drive. From the powertrain point of view it looks pretty good. The energy conversion efficiencies from chemical to electrical (battery), DC current to AC current (inverter) – electrical to mechanical (motor) – and torque to force (transmission and wheels) are all quite high and work just as efficiently returning energy into the battery. The bigger problem is aerodynamic losses and higher speeds and rolling friction of the tires. These both act to slow the car, but the energy dissipated cannot be recovered. We must also remember that – even though the battery-to-wheel conversion efficiency is pretty good (up to 80% or so), the energy makes a full circle back into the battery & it gets converted twice for a net efficiency of at most 80% * 80% = 64%.
Acceleration testing was performed by Tesla staff using GPS instrumentation with traction control on. Additional testing is planned with third parties in the near future.
RELATED NEWS & LINKS
A blog by Tesla engineer Andrew Simpson on the range and performance testing can be found at the following link: http://www.teslamotors.com/blog4/?p=60
Blogs featuring unedited writeups of our customers’ experiences driving the Tesla Roadster can be found at http://www.teslamotors.com/blog5/?p=55
Tesla Motors CEO Michael Mark’s letter to customers can be found on the Tesla Motors website at http://www.teslamotors.com
Additional information on EPA range testing procedures for the Tesla Roadster can be found on the following blog, published last May on the Tesla website : http://www.teslamotors.com/blog4/?p=57