
Tesla Model S: 20″ Ultralight Wheel

Tesla offers two sizes for the Model S, a 19″ and a 21″ wheel. For more details on the stock wheel options, please refer to an older post about Tesla’s wheel offerings. A common opinion seems to be that 21″ wheels are too large for comfortable use, and are a lot more susceptible to pothole damage, so a slightly smaller wheel with a diameter of 20″ might be a feasible alternative. With this goal in mind, after spending about three months researching, planning and getting all the parts, I eventually completed my thoroughly planned wheel and tire setup for my 2014 Tesla Model S P85.

General Wheel Expectations

I was trying to find a set of wheels in 20″ that will fit the style of the car, be lighter than the stock 19″ wheels and have a very high load rating. Ideally, they would be identical to Tesla specifications, including pitch circle diameter, center bore and generally a good and safe fit. Unfortunately, if you are interested in a set of wheels that is wider on the rear axle, this complicates the matter tremendously. A wider wheel on the rear axle means you have to check the available space between the suspension, the effect of the offset value and the width of the wheel to the actual dimensional changes. Plus the desired wheel model needs to be available in both sizes. Here’s a list of requirements that I have set myself:

20″ lightweight wheels

very high load rating

as close to stock specifications as possible (64.1mm, 5/120, stock was 8.0Jx19 +40mm offset)

staggered setup, meaning rear tires shall be wider

single-piece, low-cost

using existing wheels from the market, no custom made forged wheels as they are too expensive

tires must protect the wheels from easily getting damaged on curbs

Calculating and Estimating Wheel Dimensions

From the comparison of many different setups that others have done, I saw that 285-295 seems to be the maximum you can put into the rear wheel wells of a Tesla Model S. The front seems to be limited to 245-255 at most. After comparing images of a lot of different size combinations, I realized that with a 285 tire, I have to use a wheel with a maximum width of 10.0″ to ensure there is enough rubber to cover the aluminum of the wheel. For the front, an increase in width from 8.0″ to 8.5″ was possible without compromising this requirement too much and keeping a similar look to the tire/wheel combination for front and rear. So this basically set the limitations for the dimensions. The offset was the last variable to figure out. It is a value that cannot be easily changed and is often limited by what third-party manufacturers have made for other cars on the market. The furthest I wanted to go out on the front was 5mm, resulting in an offset of +35mm. For the rear, considering the wheel is getting much wider, I did not want to go out too much either, and luckily I found a set that matched with an offset of +38mm on the rear axle. For the tire’s rolling circumference I wanted to be as close to stock as possible, maybe slightly larger for the speedometer to be more accurate. Front and rear circumferences should be as close to each other as possible, but considering the stock staggered setup with 21″ wheels is much worse here, this shouldn’t be an issue, especially with a rear-wheel drive only vehicle. So here are the specifications that I had decided on:

Front: 245/40R20 on 8.5Jx20 with +35mm offset

Rear: 285/35R20 on 10.0Jx20 with +38mm offset

Fitting the Wheel

The next challenge was actually installing the wheels. I acquired a set of third-party tire pressure monitoring sensors for the new wheels. I needed to go with the older generation sensors as I am below VIN 50600. Newer Tesla Model S and X require a different type of sensor and are not compatible with each other. Be sure to purchase the correct ones, if you do.

With those in place, I had to come up with a solution for centering the wheels, as unfortunately the center bore of the wheel was not 64.1mm as specified by Tesla, but 74.1mm instead. It is quite common for third-party wheels to have larger center bores to ensure a broader vehicle compatibility. To make them fit, they are supplied with correctly sized plastic rings that step down the center bore from the wheel to your specific vehicle. The Tesla, however, has a very shallow centering element on the end of the axle. This meant that a plastic centering ring will be pretty much useless as there wouldn’t be any reasonable contact area to take any force at all. I, therefore, decided to design and manufacture a set of custom made aluminum rings that are flat on the vehicle side to ensure maximum contact to the Tesla axle, and have a relatively long centering cylinder going into the wheel. The tolerances worked out great. I decided to fix the rings to the axle of the car by sticking to 64.1mm as close as possible without adding anything to overcome tolerances. This allowed me to install them easily by heating them up with a hot air gun, which expands the rings and then let’s you install them on the vehicle’s axle. After they cooled down, the rings were seated firmly and would not fall off by themselves. Removing them in the future will be easy, but might require the application of a little bit of heat.

Another issue that came up with the new set of wheels were the lug nuts. I needed to find a set of lug nuts that would be slim enough to fit in the new wheels and long enough to enclose all of the thread from the bolts. The original Tesla lug nuts would not fit, because they were too wide. I ordered a 41mm long and 19mm slim set of M14x1.5mm lug nuts. They were an ideal fit, but are not the finest ones available. Future plans will be to acquire a set of 65315BK from McGard, or the chrome equivalent. They are an excellent fit, prevent theft and have a separated seat for increased mechanical safety.

Last but not least, I wanted to have a set of center caps that showcased the Tesla logo, just like the factory wheels. So I ordered a set of custom made stickers that I installed into the caps that came with the wheels.

The Ultralight Wheel

I have purchased the TEC Speedwheels GT6 Ultralight wheel in the color black. It features a 10 spoke lightweight design, has a polished outer ring and has an increased load rating of up to 900kg. It is available in the dimensions specified above and was available for a rather low price. The full set of wheels was just under 1000 Euros. They came with no accessories other than the center caps with the TEC Speedwheels logo. Both the front and the rear wheel share a PCD of 5/120 with a center bore of 74.1mm.

Getting these wheels approved for use in Germany required me to have a set of documents proving the wheels have been tested by the manufacturer and have been approved to be used on other vehicles before. The technical assessment report by the TÜV is sufficient, because the wheels have an ABE, a generalized approval that is published under the KBA ABE number. There are various reports for these two type of wheels, depending on the vehicle that was assessed. If you take a copy of those documents, and your vehicle with the wheels fitted, to the TÜV / Dekra representative, they will verify the data and check for mechanical complications. In this case, there are no complications. We have evaluated all possible scenarios with my P85, which is equipped with the Smart Air Suspension. Keep in mind that the standard coilover suspension will behave differently. For more technical information on the front and rear wheel, please refer to the following table:

KBA ABE Number 50445 50456 Part Number GT6-8520 W6 GT6-1020 W6 Tire Dimensions 245/40R20 285/35ZR20 Diameter and Changes Relative to 19″ 704,0mm / +0,13% 707,5mm / +0,63% Wheel Dimensions 8.5Jx20H2 10.0Jx20H2 Offset +35mm +38mm Mass 11,7kg 12,0kg Wheel Dimension Changes Relative to 19″ (Outside / Inside) +11,4mm / +1,3mm +27,4mm / +23,4mm Tire Dimension Changes Relative to 19″ (Outside / Inside) +5mm / -5mm +22mm / +18mm

The Street Version of the Formula E Tire

Finding a suitable tire that also matches the staggered setup desired is another challenge. For summer tires, I decided to go with the Michelin Pilot Sport 4S tire as it is a very new ultra-high performance tire they just released end of 2016. It is the successor to the all-outperforming Michelin Pilot Super Sport tire that has been on the market for over 6 years now. It has been designed together with the Formula E tire and differs only marginally. Could there be a better choice for an all-electric high-performance sedan? Luckily, both dimensions were available without manufacturer ratings, such as N0, RO1, *, MO, MGT, etc. These ratings have an effect on the tires and I would not recommend mixing different ratings per vehicle, unless specifically designed for that. For example, the Lotus Evora is set up to be driven with a set of Pirelli P-Zero MO (Mercedes-Benz) tires on the front and MO1 (AMG) on the rear. In case of the Michelin Pilot Sport 4S, both the front and rear tires carry the XL (extra load) rating, being an ideal match for the heavy Tesla Model S. The tires features a new hybrid compound technology by using a softer compound on the inner shoulder during easy driving conditions and for wet braking performance, and a harder compound for dry cornering in heavy load conditions on the outer shoulder of the tire. Michelin reports a longevity of the tires of up to 52032 km, comparing to 29658km on the Continental SportContact 6 tire, just as an example.

Conclusion

I have been using this set of wheels and tires for over 25,000km now, including my 4250km long road trip through Europe. So far I have had a total average power consumption of 188 Wh/km (303 Wh/mi) which is only slightly more than the stock 19″ setup with the Goodyear Eagle RS-A2 all-seasons tire that I’ve been using before, which averages to about 184 Wh/km (296 Wh/mi). The wheels are excellent quality, no imbalance could be detected and they have some great looks. The feedback I have received so far is 100% positive. They match the old front facia quite well, with the black/chrome-outline design cue on both the vehicle’s front and the wheels. The tires are excellent as well. Awesome grip, very low wear on the thread and amazing wet handling capabilities, which was something the old RS-A2 tires were absolutely incapable of handling. Overall, the power consumption is much better than I anticipated. If you are in a stop-and-go type of traffic, ranging up to 60-80 kph, you are actually looking at a strong energy saving over the stock 19″ wheels, due to the lower total weight of both the rear and front tire and wheel combinations. I have seen as low as 150 Wh/km (241 Wh/mi) during those scenarios. Long distance, high speed travels, however, will cost you a bit more electricity due to the higher contact area of the rear tires and the amazing grip of the new tires.

If you are interested in a set of these wheels, feel free to contact me and I will be able to assist you in acquiring these for your Tesla. The wheels, tires and TPMS can be purchased independently, of course. I can provide the accessories kit, if desired, which will include the Tesla center caps, aluminium centering rings, lug nuts and a copy of the documents to aid in the process of getting the wheels approved for your Tesla.