What matters tonight at Bristol Motor Speedway and how might cautions dictate the course of the event? Let’s dive into the analytics and trends shaping tonight’s playoff elimination race (7:30 p.m. ET on NBCSN).
Cautions famously shape races at Bristol
If Bristol’s advertising, with images of bumping and running, spinning and crashing, helmet-throwing and fist-throwing, isn’t totally clear, the reputation of the half-mile track is built on contact. A byproduct of close-proximity racing, contact leads to cautions, lots of them, and those frequent yellow flags shape most contests at the facility.
Despite its last event acting as an outlier — just five cautions and a rare green-flag pit cycle — the ingredients for success at Bristol have been short runs and restarts. But the traditional methods of overachieving in both, having a fast short-run car and executing good restart technique, matter less than what most might believe.
In the 2020 spring race, the correlation between short-run speed rank and finishing position was a coefficient of -0.1, signifying a weak relationship.
In the same race, restart performance wasn’t as much of a deciding factor as restart groove placement. Three drivers who finished inside the top five of that race, Brad Keselowski, Jimmie Johnson and Erik Jones, were boosted by a Lap 496 restart, assigned to spots in an outside groove that retained position on 98% of attempts across both Bristol races last year. The combined positional net of those three drivers on restarts that day was -11.
Between the fall race of 2012 through last year’s spring race (a span of 16 events) Bristol averaged 10.8 cautions per contest, signifying high restart totals and subsequent short runs. And while both are important facets of a race, those who benefit most are not necessarily the best performers.
Knowledge, more so than talent, is key in navigating the track’s storied volatility and quantifiable randomness.
Bristol’s inside line is a dud on restarts
VIDEO: Bristol's restarting grooves are imbalanced, a dynamic necessitating the choose rule.@AlanCavanna and @DavidSmithMA discuss what might be the most important moments of this weekend's race. #ItsBristolBaby
— Positive Regression (@PosRegPod) September 17, 2021
This week's episode: https://t.co/BB3P2Bix10 pic.twitter.com/5a4SYeBnyF
The restart dynamic at Bristol is one necessitating the existence of the choose rule.
Occupants of the outside groove within the first seven rows retained position on 98% of attempts last season — and 100% of attempts in the fall playoff race — a wide difference when compared to the inside groove’s rate of 16%. The choose rule indeed makes this disparity easier to stomach, but selecting the inside groove as a bid for offense isn’t realistic for most drivers:
- Across 22 clean restarts, the inside car on the first row passed for the lead just once: Keselowski, on Matt DiBenedetto, just after lap 68 of last year’s spring race.
- Only Denny Hamlin and Joey Logano were able to defend non-preferred groove positions on at least four attempts last season. The only other drivers to defend such a position more than once were Kyle Busch, Chase Elliott and John Hunter Nemechek.
- The difference in positional net between those restarting from the outside groove within the first seven rows (+220 positions) and those restarting from the inside (-267) was 487 spots. That was the biggest two-race total of any track in 2020.
But this doesn’t mean we’ll see big positional swings on every restart, as that total is inflated due to the number of cautions. Per slot, the average gain doesn’t surpass +2.09 and the average loss isn’t lower than -1.95. While the gains and losses are consistent — there weren’t any aberrations to toss out — choosing a lane should be a relatively simple task for pragmatic teams:
Six of the 10 best restart slots originate from the outside groove. The 12th-place slot practically guarantees a 10th-place running position after two green-flag laps.
Bristol caters to track position above all
Between the spring and fall races of 2020, speed as a correlative measure of success moved from random (a coefficient of +0.34) to something a little more concrete (+0.7). While no one is likely to win tonight’s race with a slow car, a top-end speed potential clearly isn’t what’s most important.
Track position, as always the case in auto racing, is premium real estate. It’s made more valuable because of the choose rule and can realistically be achieved by a number of methods.
First comes straightforward passing. While track position is paramount, its need doesn’t reflect the ability of good drivers to pass efficiently. Both Elliott (69.77%) and Busch (68.04%), regularly among the best passers on 750-horsepower tracks, turned in robust adjusted pass efficiencies in last fall’s race, helping to result in finishes of seventh and second, respectively. Busch also registered a 61.61% mark in the spring race en route to a fourth-place finish.
Pit stops or electing to not stop also tends to influence outcomes of stages and results. Bristol’s low tire wear yields a lap-time degradation of 0.4-0.5 seconds, which doesn’t do much to equalize the advantages provided by clean air. This was evident in 2019 when Ty Dillon stole a stage win after eschewing pit road to restart from the outside of the front row.
But ultimately, restarts, especially in quick succession towards the end of a race, compound track position in a way that’s both advantageous and lasting. Repeat attempts from the preferred groove — like Keselowski had in the final 30 laps of last year’s spring race — are able to craft entire outings and, in his case, put him in position to capitalize on the possible mishaps of others.