Friday, July 17, 2020

DIY - Eibach Lower Springs - Positive Wh/mi results

I specifically bought a P3D- because I wanted to make my own version P3D, by putting in better parts the Performance Upgrade Package aka PUP. Or even perhaps a P3D+ but with a twist such that I don't want a fully track dedicated car (as I have my GT-R) but I want it to be comfortable and fact if possible more efficient than an LR AWD model. So the journey started by looking at brakes, aero parts, suspension components and eventually tires + wheels. I want it to come in under the cost of the Tesla PUP but with better parts.

Two piece rotors shave of approximately 14-16lb depending on front rotor size option. This is both sprung and unsprung weight. Sprung weight is not enough to make a considerable efficiency difference and the problem with the unsprung weight is that it is too close to the rotational axis i.e. lighter rotor hats not lighter rotors themselves. Therefore, maybe a last choice more for better braking and not efficiency, specially considering a $2,000-$2,200 cost, but I will first consider better brake fluids and lines.

One sure way to make a positive impact is aero. I first look at front splitters and rear spoiler. Anyone who watches any form of racing will know that the Model 3 "carbon" spoilers stuck on with 3M tape do absolutely nothing for considerable downforce. If my assumption is not correct, I should be able to put about 30-50lb of pressure on a spoiler stuck to a trunk with 3M tape and not have it snap off. 😅Therefore, it purely cosmetic unless bolted on and not worth the $1000 IMHO. A better rear under diffuser would take care of eddy currents behind the car. 

The front splitter is also a crock. Studying the front aero changes over 4 iterations of the current generation GT-R for the last 12 years has revealed what works and does not work in terms of aero. I don't care what a self funded CFD study states, the speeds at which you need to go to achieve ~5% efficiency simply by putting some additional plastic is not practical even for every day highway driving speeds. Visual inspection of the front of a Model 3 shows its pretty damn good aero design, if anything aftermarket products simply seem to cover the wheel opening slightly more, pushing the air out sideways. Perhaps sharing raw CFD data for a peer review would be one sure way for a vendor to stand behind product claims by manufacturers. Instead I believe that a more aero front under diffuser would help reduce the gap between the car and ground more cost effectively. This is what Nissan did to the GT-R after lap upon lap of Nürburgring testing.

So I next looked at lowering springs and for $324 the Eibach E10-87-001-02-22 PRO-KIT Performance Springs is one of the most cost effective ways to improve aero. Indeed my GT-R is lower and I can barely fit 2 fingers compared to my Model 3 in which I can fit 4 fingers between the tire and body. Lowering the car over an inch reduces drag, all around...period. Anyone an F1 tech fans? You know exactly what I am talking about. It also improves handling and could enhance ride quality. Bonus was that the springs are available on Amazon which means I can use gift cards to pay for it.

First off, I am extremely happy with the way the car looks with these springs on. This is how it should have been from the factory, IMHO.

Visual Comparison of before and after springs

Secondly, it is much more compliant on bumps due to the dual rate springs. The best way I can describe this improvement is that I can hear the tires hit road imperfections, but not feel them anymore. Before, I could immediately feel them as well as hear them. Handling is same to only slightly better, steering is very neutral as it was before. As you can see from my post about track mode, I do beat it up on back roads and these are not always the smoothest surfaces so compliance was important for me, I don't want it so stiff that it is unstable.

As for the Wh/mi, huge improvements here...

I have driven ~740 miles since installing the springs and my lifetime Wh/mi has dropped from 287Wh/mi to 277Wh/mi rather quickly and continue to drop the more I drive these days.

No, this is not purely weather related because at the end of winter specifically on day light savings switchover in March. I call it my season Trip Meter.  I recorded the lifetime as 290Wh/mi and driving ~3500 miles since then during warmer spring and summer months had only reduced lifetime from 290Whi/mi to 287Wh/mi, at which point I installed springs. So net huge positive effect for efficiency.

10 Wh/mi drop over ~740miles

For those that want to do this DIY install too, I have taken detailed pictures and outlined the steps and gotchas to ensure your DIY goes smoother than mine since there were many subtle lesson along the way. Even though I am mechanically inclined and have changed all 4 struts myself on the GT-R which is way more complex, the Model 3 proved to be a different DIY learning experience. Many YouTube videos seem to leave out subtleties, which I have tried to capture.

On the topic of suspension settling. After I installed all 4 springs, I measured the distance from the grounds along the center of the wheel axis the top of the body, it was ~28" all around, while in my garage.

After spring change - rear & front heights

I drove around for about 30-40 miles to return spring compressor, run some errands. This was the height after 2 days and before I went to the alignment shop.

Car settled ~1" day after springs were installed.

So the settling is ~1" all around. I think this is important to have happen BEFORE the 4-wheel alignment.

Lastly as for the alignment, I told the shop that I had lowered the car and the only thing that was out was the front and rear tow. The camber and caster were good, so job well done on my part to not mess up the alignment while changing springs. In fact, I have since day 1 from Tesla, had to have the car realigned and always had to hold the steering wheel 2-4 degree right to go straight, but the car did not pull to one side. The car drove exactly the same after replacing the spring. Of course, the alignment shop corrected it and the car is very neutral now.

I have broken the post into 4 sections for reusability.

Part 1. Removal of Rear Diffuser
Part 2. Replacing Rear Springs
Part 3. Removal of Front Trunk
Part 4. Replacing Front Springs