Best Understanding Memo: Electric Vehicles on Road Courses
A Guide for Driving Coaches and Track Day Participants
Context
Race tracks across the nation are seeing an increasing number of electric vehicles showing up for High Performance Driving Experience (HPDE) events and Hooked on Driving is no exception. And of course, California is leading the adoption curve of this exciting trend. But EVs bring a unique set of performance capabilities, peculiarities and challenges for drivers and coaches alike that everyone should be aware of.
EV Dynamics on Racetracks
Powertrain
Most EVs we see at the track are dual motor variants, typically with a higher output motor on the rear axle. More efficient or less expensive models omit the front motor, and are typically RWD only. All EVs on sale today ship with open differentials on both axles. Model S Plaid has two rear motors (plus one front motor). Some EV exotics like Lucid Sapphire and Pininfarina Batista have four compact motors that can do front plus rear torque vectoring. Aftermarket suppliers are beginning to provide LSD and other high-performance differentials into both the front and rear axle of these open differential cars.
Static Weight Distribution
Most EVs have near perfect download on all four tires when the car is parked. This all but obviates the need to do a corner balance, as the cross weights on a scale are nearly perfect even with the driver in the seat. The battery pack is most often placed between the front firewall and the rear bench seats. A good rule of thumb is that a 75 kWh pack will weigh around 1100 pounds, inclusive of the water cooling channels. Air cooled pack assemblies will weigh subtatnially less but are all but theoretical at this point (Mercedes EQXX), because a stationary car can explode if the pack temperature exceeds 150F. Larger sedans have 100 kWH packs, and long range pickups and SUVs have packs from 135 kWh to 200 kWh.
A Tesla Model 3 performance weighs 4000 pounds, Model S (all trims) at 4800 pounds, Taycan/E-Tron GT sedans at 5300 pounds. I expect the 2025 Porsche Boxster EV with dual motors to also weigh close to 3600 pounds with a 60 kWh pack.
Handling and Braking
The best way to describe a performance EV’s handling is like a Porsche Boxster with 1000 pounds of ballast for race day. You’re effectively dealing with a perfect mid-engine weight distribution. The nose has the characteristic of feeling very light, as there’s nothing fore of the axle line. The motor and inverter combination weighs about 150 pounds, and less in newer applications in exotic vehicles. The steering ratios are typically very quick in EVs, making them feel sporty and responsive. 48V low voltage system architectures will see the introduction of both steer-by-wire and completely dynamic steering ratios, with F1 car-like lock-to-lock of <360 degrees. Just when we had finally accepted electronic power assisted steering (EPAS) in sportscars, the game is changing again.
The center of gravity in an internal combustion engine (ICE) car is typically about where the driver’s right elbow is, when their arm is on the stick shift. The center of gravity in a battery electric vehicle (BEV) is behind the driver in the center of the car very close to the floor. When you wiggle the steering wheel at speed in an ICE car, you can feel the tilt left to right like an airplane. When you wiggle the steering wheel at speed in a BEV, you feel the car rotate on center on like a top. You can actually feel the rubber in front and rear arm suspension bushings compressing and squishing, diagonally from front left to rear right.
EVs do not reveal their weight in cornering, because they are so well centered. A 3500 pound front engine ICE car will feel equal in handling to a 4000 pound EV. Braking is where the weight of the EV becomes apparent, especially in heavier cars like Taycan which we would liken to slowing down a Porsche Cayenne Turbo. The brake pedal also takes on mid-engine or rear-engine characteristics, where at the threshold of ABS it can feel a bit like a wooden pedal (e.g. Audi R8, Lamborghini). Front engine sports cars have much more confident braking.
Some EVs use permanent magnet motors on both axles, while others use a combination of a permanent magnet on one axle and an AC propulsion motor on the opposite axle. The latter are a bit more playful mid-corner to corner exit, as the different delivery characteristics express themselves under load. AC motors deliver on-demand and more explosive feeling power, where permanent magnets tend to build steadily. EV throttles are very precise, allowing a careful driver to call up very small amounts of power in steady 5-10 horsepower increments. This makes throttle steering on edge extremely fun!
Note that EV brakes, even on performance or enthusiast models, are not up to the task of racetrack duty (with the exception of Porsche products). They are equipped like a base model VW Golf or Audi A3. The reason is most drivers use regenerative braking on the streets and the brakes are really there for emergency stops or stops exceeding -0.2 Geforce of braking (the maximum of regenerative on the street). Track mode in the vehicles can increase the braking force to -0.3 Geforce. Maximum braking force on level racetrack asphalt with 200 treadwear tires is typically -1.3 Geforce to -1.4 Geforce. The friction brakes must do the residual -1.0 Geforce of braking.
For safety and consistency reasons, we highly recommend turning OFF regenerative braking on the racetrack (set to 5% or “low” regeneration). The reason is that using throttle is exothermic (expends heat) and using regeneration is endothermic (returns heat to the battery). When the battery reaches its thermal safety maximum around 135F, regeneration will turn off – and the car will miss its braking point compared to the previous lap.
Stability Control systems
There is no such thing as an EV without a computer controlling the powertrain. When you have motors that can dump 300 lb/ft of torque at 200 RPM (not a typo), the computer must prevent the driver from snapping the half shafts clean off the vehicle. They rev to about 16,000 RPM on an 8:1 fixed gearbox, and some have a second gear transmission at 16:1. The cars have both dynamic traction control (DTC) and dynamic stability control (DSC). So called “track mode” programs will loosen “only” the DSC program to allow for more rotation before throttle discipline is electronically applied. Stability can be adjusted on a scale of 1 to 10, where 1 still has substantial intervention (like BMW MDM mode) and 10 is fully ON as in street driving. They also have low speed drift modes for parking lots and proper drift pads.
DTC can be disabled with a hardware defeat device installed on the CAN bus. This also allows customizable rotation (DSC loosening) of the vehicle up to specific yaw angles at specific speeds. For example, you could allow 10 degrees of slip at 30 MPH and 5 degrees of slip at 90 MPH, with the middle range dynamically adjusting down (e.g. 7.5 degrees at 60 MPH). DTC defeat also removes most of the throttle governor when the vehicle is moving, which allows more tire slip and the ability of the car to go sideways.
BEVs on Track, In Practice
Note that EVs are extremely easy to drive for students and HDPE drivers because of the miracles performed by direct drive motors with DSC and DTC. Remember, engine cutoff can occur in 1 millisecond and re-engage 1 millisecond later. In theory, it can change the power output on/off 1000 times per second. The passive physics of a BEV vehicle make a spin into almost a comedically safe event (in the center of the track, perfect 360) compared to other vehicles (front engine, RWD) which have a tendency to loop into the wall or off of the track.
Imagine a scenario of a BEV with a 180 horsepower front motor and 280 horsepower rear motor. In street operation at low throttle, the front motor is off and the rear motor pushes the car. In track operation at full throttle, both motors are pushing maximum output at speeds between 40 MPH and 120 MPH. After the apex of the first turn, the driver gets back on full throttle while the wheel is still turned but straightening towards the corner exit and track out point. The EV will happily obey this driver input and the car zooms away. What the driver doesn’t know is the rear axle had no more lateral grip to give and no more available traction for forward acceleration. Remember, a tire can only do 1 thing (well) at a time – brake/accelerate OR change lateral direction. So the computer uses the 180 horsepower on the front axle, diffused through the open differential, and pulls the car out of a turn.
Power Delivery
Advanced drivers tend to have excellent throttle discipline. When disabling DTC with a hardware defeat device in an EV, drivers have to remap their brain to how powerful these cars are at very low throttle input — when uncorked. Even 5% throttle input leaving the apex would slide the car quickly, and switch to a busy hands exercise to correct the vehicle’s course at a wider radius to get back on line. Applying perhaps 20-25% throttle input will spin the car immediately as you’re effectively calling up nearly 400 lb/ft of torque albeit at lower horsepower. Coaching novices to not use 100% throttle exiting the turn in an EV until the wheel is straight is a good habit for advanced drivers progressing in the sport to develop. But even when we ignore this and continue to do it anyway, the EV car will compensate for this. This phenomenon still saves the driver even in track mode, where spins are more possible but still unlikely if you can correct steering within a “Three Mississippi” count.
Aftermarket Parts
Drivers who make a hobby out of track driving in their EVs will likely need to upgrade their braking system completely, with the lone exception of the Porsche Taycan and its siblings. In very high output applications like Tesla Plaid, throttle discipline in straights is absolutely necessary to finish the track day in one piece with streetable brakes. A good rule of thumb would be cutting the top speed from 160 MPH to 120 MPH, or even 100 MPH on some alternating laps. A Tesla Plaid with its extra speed and weight has double the kinetic energy to a Model 3 Performance going into T2 at Laguna, at 5 million and 2.5 million kilojoules, respectively. Mind you, the speed is matching a GT2 RS and the weight is 1400 pounds extra. Stoptech, Brembo, Girodisc, and others make aftermarket rotors sets and caliper sets. Aftermarket pads are available with the popularity of EVs.
EV suspensions are often double wishbone front and multi-link rear, with steel dampers on the mid-level cars and air suspension on the luxury cars. As is typical with all other cars, adjustable arms allow you to set a static alignment. EV is particularly hard on the lower control arm bushing, which tends to fail first. They also have rear subframe mounts which squish and deflect and rot. Very high spring rates are used in aftermarket kits, likely because of the motion ratios and total weight.
Limitations
Some EVs will overheat after 5 hot laps, though software updates and programming typically addresses this over time. Just let the car cool down for a lap and then resume pace. The root cause is the motors heat up to 250F, and they share a cooling circuit with the battery which needs to stay below 140F. At around 130F, the car will begin to cut power about 33% to continue the lap. At 135F it will cut power further, perhaps 50% or greater. Exotic EVs use a seperate cooling loop and air-water heat exchangers for the battery and each motor. Note that an external transmission oil cooler on the rear motor can help keep that temperature in check.
Despite the weight, EVs are extremely on tires at the track. The very even tire download and direct DSC/DTC system prevent wheel overspin and preserve tire life. The factory alignment can damage tires on track with suboptimal camber and toe. The air suspension cars also suffer from more inside tire wear when the car is in the low suspension setting.
Charging at the Track in Northern California
The garages at Laguna Seca and Sonoma have specific 30A power adapters, that convert to a dryer plug which accepts a native EV wall charger. These charge at a speed of about 7 kW, which can top off the battery between sessions (6-7% per hour) and help the car “cool off” as the fans run on overdrive. Thunderhill has RV plugs which are also good for 30A, and a Level 2 charger near the gas station. Laguna Seca and Thunderhill East both now have onsite Tesla Supercharging stations (400V DC fast charging), but beware as these cook the battery to 130F sending you on track near thermal maximum. Willows, CA, has charging at WalMart from Electrify America, which accommodates both CCS charging at 150 kW and CHADEMO charging with a vehicle adapter at around 44 kW. Sonoma has supercharging 15 minutes up the road in Novato at a Costco, Level 2 chargers in the garages, and 30A plugs next to the gas station if you have the requisite adapters. Here are the adapters you may need: 1, 2, 3, 4.