Bozi Tatarevic Profile picture
Apr 1 17 tweets 4 min read Read on X
The battery issues in the No. 2 and the No. 21 and the disqualification of the No. 43 at Martinsville are likely all related.

Let's talk about weight at Martinsville and what happened to those cars. Image
Let's start with the basics of what makes a car race well at Martinsville and discuss some concepts of the physics of a race car.

The first thing we need to consider is lateral stability which in its simplest explanation is a gauge of how well a car stays in a straight line.
Having great lateral stability helps a driver have better control of a race car but the nature of an oval track means that there is centrifugal force once the car reaches a corner.

This force tries to push to car towards the outside of a turn.
The level of centrifugal force felt by the driver is directly related to the location and height of the weight.

Center of gravity is a theoretical point where the sum of the weight is evenly balanced and the lower it is the better that a car will handle. Image
With that in mind, crew chiefs and engineers will try to do whatever they can to move weight away from tall places in the car and concentrate it towards the bottom and center of the car at a track like Martinsville in order to maximize handling for the driver.
One of the places where they can shift weight is the alternator since it sits at the front of the engine and installing a lighter alternator means that they can shift that weight to the ballast container at the center of the car and improve the handling. Image
The likely case for the No. 2 and No. 21 is that they ran a modified alternator that was overworked due to how lightweight its components were and eventually just failed. In that scenario, the battery inside the car can no longer recharge and has to be replaced when low.
There are multiple factors at play specifically at Martinsville that work against a lighter duty alternator because of the additional electrical load from things like brake fans, radiator fans, and driver cool suit systems. All of these components running have an impact.
The batteries themselves are also often on the edge of their capabilities because teams will install the lightest versions they can in order to again maximize that weight so they only have so much capacity.

Martinsville batteries are maybe rated for 40-50Ah.
The best way that I can describe the battery situation is telling a runner before a marathon that they can have one granola bar in order to be light for the race and then trying to maintain for the whole race on that minimal amount of calories.
Teams typically pack 1 or 2 spare batteries per car as they don't expect to swap them often so the situation we saw at Martinsville resulted in the No. 2 running out of batteries because they used up the whole allotment for their organization.
All of those same handling and weight factors were likely in play for the No. 43 and trying to make it as light as possible but they just ran too close of the edge of that weight allowance and crossed the line by being too light at the end of the race.
Teams will often find ways to shift or remove some weight that might be in the car before a race which is how they can end up at a different weight post race in addition to things like damage that might result in parts being lost from the car.
NASCAR gives teams a margin for race damage but just like drivers often use up that 5mph margin for pit lane speed, crew chiefs and engineers will push their cars to the edge of the margin that NASCAR gives them for weight and occasionally will go over as we saw with the No. 43.
NASCAR also gives teams an opportunity to refill fluids to account for changes during the races and will usually allow them to roll a car across the scales multiple times just to be sure they got it right.
Unfortunately, the margins at Martinsville are incredibly tight and it is not surprising to see many teams be within a pound or two of the minimum in post-race so seeing someone get disqualified for missing weight was not a huge surprise.
If you really want to get into all the nerdy facts of setup for Martinsville, I recommend this story from @AedanMcHugh at the @the_autopian which explains the concepts in great detail: theautopian.com/how-teams-try-…Image

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More from @BoziTatarevic

Feb 19
The No. 19 of Chase Briscoe was hit with a large penalty for modification of a single source supplied
part under the following sections of the rulebook:

-Sections 14.1.C&D&S: Overall Assembled Vehicle
Rules
-Section 14.5.8.A: Spoiler

Let's dig into the details of the parts. Image
Cup series cars are required to run a 7″ x 60″ spoiler face (F) on a tall spoiler base (E) for superspeedway races which is shown on the bottom half of this illustration. Image
NASCAR runs such a large spoiler base in order to slow the cars down and teams obviously want to find ways to make speed so getting air away from the spoiler is a priority whenever possible but NASCAR tries to make sure that the spoilers cannot flex through multiple methods. Image
Read 21 tweets
Feb 14
We saw that pit crew members from @JoeGibbsRacing had tablets that would light up in green as a car reached its fuel fill target to tell the driver and fueler that the car can take off.

Let's dig into how this works and how they choose the time when it should change colors. Image
In this video we see a fuel only pit stop on the No. 11 of Denny Hamlin in the Duels last night.

Due to the distance of the race being so short, the car does not need a full fill of fuel so teams try to predict exactly how much fuel to add in order to maximize track position.
In the first part of the stop, we see the fueler approach the car and as soon as he plugs in, the crew member at the front of the car presses a button to start the timer on the tablet. The timer starts with a yellow bar that counts down and turns green at a predetermined time. Image
Read 15 tweets
Feb 11
NASCAR has added torque sensor details to the rule book.

Ramping up testing with torque sensors is a significant step towards possibly allowing new engine types which could potentially lead to a new OEM.

Let's get into the details of how it all works and what it means. Image
A very simplified way to explain a torque sensor is that it is like a mobile dyno because the sensor is mounted on the driveshafts/axles leading to the wheels which allows it to calculate a torque output figure at the wheels. Image
Once a car is moving, the driveshaft produces a magnetic field which is detected by the torque sensor surrounding it. That magnetic field is converted to measurable voltage which corresponds to a given torque figure that can be transmitted over the cars data system. Image
Read 17 tweets
Feb 10
The car that Kendrick Lamar used on stage last night at the Super Bowl half time show is a real Buick Grand National.

Let's dig into some of the details and see where it came from and how it was modified. Image
My search for the car started with this great story from @WaterSlicer that gave me a hint of the car being for sale in Riverside, CA at some point.

wired.com/story/true-sto…Image
I did a little digging and noticed that there is small used car lot called Effortless Motors in Riverside, CA that specializes in specialty cars and has 5-10 cars in inventory at any given time. Their Instagram shows a 1987 Grand National for sale late last year. Image
Read 12 tweets
Feb 10
Kendrick Lamar owns an authentic 1987 Buick GNX.

GNX stands for Grand National Experimental and only 547 were built. Kendrick owns number 191.

He is deeply ingrained in Grand National lore and has even mentioned internal GM build codes for the GNX in the past. Image
From a post announcing the purchase of his GNX:

"make you realize the only thing that matters in life is that original paper work. that TL2 code"

T2L was an internal GM RPO code that marked a Grand National destined to be turned into a GNX. Image
Those 547 Grand Nationals were sent to American Specialty Cars (ASC) McLaren Performance Technologies where they got a big turbo and big intercooler among other upgrades.

They can easily be identified by the GNX turbo heat shield as seen in one of the photos in the post above. Image
Read 12 tweets
Oct 1, 2024
Listening to Actions Detrimental and feel like @dennyhamlin might need a whiteboard for a technical explainers to @jareddallen and @TravisRockhold.

Here is a good illustration to add to his explanation on why Xfinity cars can get close and pass but Cup cars can't. Image
If you look at the car when they're far apart, you can see how the air comes off the spoiler of the leading car and and also how the following car can get air under the splitter. The cars will be somewhat comparable in how they perform in these situations. Image
Once the cars get close, we can see the airflow from the leading car now joins the airflow from the following car which takes air away from the spoiler of the leading car. Which results in a loss of downforce for an overbody dependent car like the Xfinity car. Image
Read 12 tweets

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