Two fundamentals of improving the performance of a car is:
1. Add Power
2. Reduce Weight (or "add lightness" as Lotus would say).
While adding power to an internal combustion engine (ICE) vehicle is straightforward, it is much less so for an EV. In addition to the complexity of modifying the drivetrain of an EV, there's a risk of voiding the warranty of your expensive Tesla Model S, X, or 3.
First, let's address an important question- Why are we seeking to improve the performance of our Tesla Model S?
Faster quarter mile time? Being able to go faster is awesome, but a few tenths faster isn't a differentiator on a day to day basis when the Model S has plenty of off the line acceleration.
Faster than legendary sports cars around our local race course? Maybe. More to come on this topic....
So far, none of the above moves the needle for our real world application. The performance we really wanted was to improve was range. Being fairly new to EVs, we realized that range anxiety is REAL. So how do we accomplish this goal without violating the terms of the Tesla warranty (i.e. hacking the drivetrain)?The most sensible solution to start with is weight reduction. There are a few variables to reducing the weight of a car. Some include: overall weight, weight distribution, center of gravity (Teslas already have a very low center of gravity due to battery placement), and unsprung weight.
Removing the interior pieces to shed weight would mean sacrificing many of the luxuries and creature comforts that the Model S offers. Additionally, we would need to decrease weight by hundreds of pounds to realize a noticeable gain in range. This led us to looking at unsprung weight.
Unsprung weight is defined as any part of the vehicle not supported by the suspension. This includes axles, wheels/tires, suspension arms, brakes, etc.
Our first modification was lighter brake rotors. Manufactured by Girodisc, the ULTRAdisc rotor is a direct replacement rotor for the Tesla Model S and X. It is straightforward install and requires no modifications. A complete set of these front and rear rotors is 22 pounds lighter than the Tesla original equipment. Per our strategic partner, Rays Engineering, each 2.2 lbs of unsprung weight is equivalent to reducing 33 lbs of overall vehicle weight. This means that replacing the OEM rotors for the ULTRAdiscs would be equal to removing 330 lbs from your Model S/X.
To test the effectiveness of these rotors, we recorded energy usage with brake regen off during every day driving (office, food, rush hour traffic, day care, etc.) for ~1,700 miles. We performed the same tests before and after and mimicked our driving style (normal acceleration, 80+mph cruising speeds, etc.) to the best of our ability.
The result was 8.4% less energy used with the lighter rotors. This is good for 20+ miles of extra range in our Model S P100D! 20 miles is a significant increase and can be the difference between making it to the charger and calling a tow truck.
For more details and pricing, please click here to see our ULTRAdiscs product page. Our rotors ship free within the continental US!
Next, we'll continue down the path of reducing unsprung weight via wheels and tires. Meanwhile, please chime in on hacks on increasing range and thus decreasing range anxiety!