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08/01/2019
Model 3 state-of-the-art tires on tesla's latest "star"

Telsa

 

One of the most anticipated cars in recent years, Tesla’s Model 3, after finally achieving a sufficient production stability, is now ready to satisfy the desire of a long list of clients whose bookings have been accumulating ever since its presentation.

Nicodemo Angì

One of the most anticipated cars in recent years, Tesla’s Model 3, after finally achieving a sufficient production stability, is now ready to satisfy the desire of a long list of clients whose bookings have been accumulating ever since its presentation. Now that "production hell", as indicated by ElonMusk, is behind us, interesting details about this highly anticipated car are beginning to come to light. Autocar magazine, for example, was able to speak with several engineers of the Californian manufacturer, obtaining interesting information on floor pan, tires, suspensions and brakes.

 

Starting with a blank sheet

First of all, it should be noted that Tesla has been around for less than 20 years and "learned the ropes" with its first Roadster, developed by turning a second series Lotus Elise into electric. After this beginning, the California-based company developed all the following models on its own, thus optimizing not only production but also qualities such as handling and comfort. Safety also benefits from this blank sheet approach: the Model 3 has proven to be one of the safest cars ever since crash tests began. The clean-sheet approach allowed Tesla engineers to make the most of the reduced vertical dimensions of the electric motors; in addition, Tesla couples them with electronic control systems which share the same cooling system with the motor. The resulting unit is very compact and fits between two wheels on the same axle, together with a single speed transmission and diff. The cabling is thus rather simple (2 high voltage cables coming from the battery and control signals) benefitting weight, size and ease of production.

 

What about weight?

The heavy and flat battery packs have been placed under the floor, and this lowers the centre of gravity even further ensuring more than adequate driving precision and performance despite what the scale says: the Model 3 Long Range all-wheel drive weighs about 1,850 kg but has a top speed of 233 km/h and sprints from 0 to 60 mph (96.6 km/h) in 4.5 seconds. The “skateboard” design makes the car fun to drive thanks to excellent road handling and reduced lateral load when cornering but does have a side effect. The low centre of gravity and reduced vertical force build-up through the outside pair of tires generates not enough grip when they corner.

The search for greater grip must be combined with the fact that, as with any electric car, the Model 3 tires are called upon to minimize rolling resistance and, at the same time, withstand large, continual torque input. Electric motors deliver their maximum torque almost immediately, while regenerative braking engages only the drive wheels (in rear-wheel drive versions) when braking does not involve traditional discs.

 

Meeting the challenge

We are not surprised then to learn that a specific study of tires, in collaboration with top tire manufacturers, began as early as 2015. The Model 3 tires, just as for other Tesla, have a ring of noise absorbing foam, a sophisticated yet almost compulsory solution given the low level of noise produced by electric power-trains. Positioning the electronic control systems with the power unit reduces noise emissions even further and has therefore made the choice of “silent” tires an obvious choice.

The Model 3 has 18 x 8.5" standard wheels with 235/45 tires (Michelin Primacy MXM4 as OEM), but 19 x 8.5" wheels are also available for 235/40 Continental ProContact RX tires while the Performance version has the option of 20 x 8.5" wheels. In this case, the tires are 235/35 Michelin Pilot Sport 4S but it is possible to fit a set of 275/30 at the rear as well as 265/35 on the 19" wheels.

In the USA (the Model 3 is still to make its debut in Europe) Tesla offers also kits consisting of wheels and winter tires. The 18" wheel kit uses Pirelli Winter Sottozero 2 tires, while the 19" wheel kit is fitted with Pirelli Winter Sottozero 3 tires. Great care in the design is also evident in the suspension layout and braking system, working hand in hand with the wheels.

 

Ground-breaking suspensions

Each rear wheel has six degrees of freedom – five links and one damper, similar to a double wishbone – but the links have been split to give better control over the forces transmitted through the tire’s contact patch. The double-wishbone front suspension have the lower arm made up of two separate tie rods, tied to different points of the hub holder. In this way the steering axis (the one around which the hub holder rotates) becomes “semi-virtual”, varying as the wheels rotate. In this way, the front axle grip is maximised in any situation for greater safety and driving precision. These suspensions have also been designed to provide maximum protection in case of a frontal collision. Apart from the direct injury that can occur in accidents, doors can jam and EV batteries can be threatened too. To counter this, “sacrificial” links are designed to snap when the front wheels and suspensions take a hit. That allows the wheel to rotate around a third link, moving the wheel outside of the body and pushing the car, the occupants and the batteries away from the point of impact. The additional motor in all-wheel-drive variants sits on two mounts in the ‘V’ of the front sub-frame and pivots backwards into a void in the event of a collision. The electric power steering system has a rapid 10:1 ratio, giving two turns lock-to-lock.

Low frequencies and long-lasting brakes

The system has full redundancy with separate power feeds taken directly from the high-voltage battery, two electronic control modules and two inverters providing ‘hot backup’ if one fails. Tesla’s engineering team opted to fit more expensive four-pot brake callipers at the front of the Model 3 rather than a cheaper, single-piston sliding version for superior pedal response. That also allowed the firm to design its own piston seals that fully retract the brake pads after braking, cutting drag and boosting the available driving range. The discs themselves have been designed to last for the entire life of the car about 240,000 km, which is possible because the Model 3’s regenerative braking system reduces friction, an important factor in lengthening any vehicle’s mileage. Rust could be an issue over that time, so engineers developed new anti-corrosion system. Refining the Model 3’s suspension settings to ensure the car would be comfortable, the Californian company’s engineers turned to a study by the space agency on the limits of human capability, which included research into how long the body can be subjected to a certain frequency without feeling uncomfortable. Tesla says the suspensions of most cars are sprung and damped to move at between 1.0Hz and 3.0Hz., the equivalent of a brisk walk or a slow run, guaranteeing a comfortable yet sporty feel that harmonises with the performance of the power-train.

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