Tesla Model 3 aero+ package

[Vekke]

I have been wondering little while which car should be my next project car and at the moment I think it will be the Model 3. There is a new Highland version coming which will get better than previous models, but here we focus on the same things that in all of my previous projects and its aerodynamics and NVH. These mods can be done to all model 3 models as all of them have the same problems with tire noise and harsh suspension.

At the moment I don`t have my own model 3, but that does not stop me to design the parts ready when I will have one in my hands.

Planned first mods will be the wheels and tires as in all of the previous projects this has big impact to the cars performance.
Stock tire size is 235/45R18 load index 98 with 8,5x18ET40 wheels. That low profile makes the suspension sporty on small bumbs. What would then be the best economical tire size for this car model?
Well it all starts what are the max axle mass-->1225kg for rear axle so it leads to 612,5kg per tire. For my own use best would be 175/60R18 but their load index is only 85 -->515kg thats not enough
If you want to fill the law letter in europe you need more load carrying capasity which lead us to different size as only one will meet the design goals smoother ride and less noise. That size is 195/60R18 which has 96 load index -->710kg per wheel. This means they have more than enough load carrying capasity.

https://www.willtheyfit.com/index.ph...h=7&offset2=22

For the wheels 195 wide tire widest wheel you can install it legally is 7 inch wide wheel so that what we have to use here. 7x18 with ET 22 you get the wheel outer edge close to where it is with stock wheel.

From that calculation you can see that these new tires have 3,26% bigger diameter, which leads to softer ride. I tested this with my ID3 which had lowered suspension and it was still nice and softer ride with 195/55R20 tires than the stock 18". Narrower tires lead to less noise in general. From that picture you can also see that tire will come 37.1mm further away from the suspension strut --> this leads you can make more smooth undertray. In general the 20mm narrower tire should have 0,01 lower drag. So here we make tires 40mm narrower so drag should drop 0,02. Wheels will be fully blocked so no cooling for brakes.

Rough start calculation what car should reach in stock condition:
https://ecomodder.com/forum/tool-aero-rolling-resistance.php?Weight=1900&WeightUnits=kg&CRR=.007 &Cd=.23&FrontalArea=2.22&FrontalAreaUnits=m^2&Fuel Wh=33557&IceEfficiency=.22&DrivetrainEfficiency=.8 5&ParasiticOverhead=100&rho=1.204&FromToStep=40-65-1

Now to get correct results that 10,259 you need to add 15% more for drivetrain efficiency -->12,1kwh @ 100km/h. people have tested the consumption at some road has been around 13 kwh. That difference can come from weather and road conditions.

https://cleantechnica.com/2018/08/19...r-on-highways/

Now if you lower the drag 0,02 and rolling resistance 0,001 less you get consumption down to 10,8. That is a 10,7% improvement just by changing tires. Now you cannot be sure you get all the benefits of you narrow tires if you dont modify also the front tire deflectors. At least they should be made smaller, but I think same type as in my ID3 would be more efficient.

https://ecomodder.com/forum/tool-aer...ToStep=40-65-1

I think at those deflectors you can gain 0,01 more good with the drag and small gains here and there another 0,01. So cars drag should drop under 0,20 range =10,4kwh
0,19 range = 10,1 kwh

If you play with the numbers you realise that the rolling resistance is very important with these heavy cars. Thats why the selected tire model will be Micheling e-primacy which is at the moment the best tire out there in the A rolling resistane class. The OEM Model 3 tires are with B or C rolling resistance label.

Number wise it seems possible to improve the model 3 efficiency close to 15% relatively easy.

[freebeard]

What would be the ROI?

The 165/65 R15 (smallest size) would be appropriate for my 1971 Superbeetle, but I guess it's for Europe, by Europe.

I still miss getting the Eropean Klebers in 145-15.

[Vekke]

ROI for the wheel and tire combo is more difficult to calculate in the ev world at least. Do you calculate just the energy costs for 0,4€/kwh at fast chargers. With that you get 1500€ investment/0,4=3750kWh-->payback 375000km driven. Not very tempting.

If you have to replace the tires anyhow it drops the costs to half when you just buy new wheels. Payback 187500km already much reasonable. Also you can sell your old wheel bringing the costs down even more. Or if you have a new car and you need second set of wheel anyhow then the aftermarket solution is already cheaper than OEM solution.

If you calculate any value to your time standing at the charger, which was main reason I sold my ID3 where one charging trip was 50 minutes of time wasted. 10 minute drive to charger and 30 minute charge and drive back 10 minutes. Lets here put a hourly rate of minimum 15€/h. To drive 10% longer means you can drive with the same charge amount 18750 more km. With consumption of 14 kwh in real life per 100km that means 428km per charge (60kwh of energy charged) -->43,8 charger visits less-->36,5 hours of you time saved-->547€. Now you can calculate this with your own numbers.

Do these e primacys last more km than the grippier stock size. My guess would yes they do last more. That also impacts the ROI.

However to get the car more silent is priceless or diffucult to put value on that.

Get more comfort/softer ride same thing what you value or want from your car.

Do you start to calculate how much more does it cost to have 10% bigger battery? However more efficient car is faster to drive on longer journeys at least on theory level as you need less energy to load into the battery.

So there is so many things that tire wheel change impacts its not a easy task to say what is the ROI for this change. From 1-5 years is my estimate.

In Teslas minimum Wheel size is about 18". In model 3 you migth be able to fit also 17" but there is more to this story. Here I am talking only the Model 3, but that same size will work also on Model Y and Model S Teslas and most all other evs out there as well. You just need correct offset wheels. In Model S I need to make custom wheels, but that is the case anyhow if I want more aerodynamic wheels.