Like so many things in 2020, the 25 Hours of Thunderhill Presented by Hawk Performance was canceled because of the COVID-19 pandemic. For 2021, there has been a surge of renewed interest in the longest closed-course endurance race in North America, which is back on for 2021 and scheduled to take place Dec. 3-5! Registration opens August 1.

To help you prepare, the staff at Speed News has interviewed teams that have been successful at the 25. We wanted to share what it takes to get there, what it takes to finish — and what it takes to win.

We talked to Ron Carroll, the former team manager and crew chief for Davidson Racing, who won the race overall in 2015. Carroll has worked professionally in racing for years and has contacts all over the country that he pulled in for The 25. He used crew members from IRL, World Challenge, and Grand Am, and drivers who have raced Daytona and Le Mans. “For the pro drivers, this is the most diverse race because of the darkness at night. Daytona at night is essentially driving in the daytime because they have so many lights on that track. The differential speeds at The 25 are way larger than the pros see in different series. Running alongside the amateur drivers, and the weather changes, the pro drivers love it and I (had) a waiting list of drivers who want to race every year for Bob Davidson’s team.”

We also spoke with Peter Guagenti, former crew chief of El Diablo Motorsports, who won the E0 class three times. “You invest your life into this race. As the crew chief, I am up for 40 hours straight and it can be a thankless job. The driver gets a trophy, and the crew gets sleep deprivation.” Peter Guagenti compared his experiences at the 25 to the experiences pro teams face at LeMans. “I’m a motorsports competitor and a fan. I’ve been to Le Mans. When you watch the documentary “The Truth in 24,” which follows the Audi team to their Le Mans victory, that experience as depicted in the film, is the exact same experience I get from The 25 Hours of Thunderhill.”

We also spoke with Rob and John Gibson, chief principals and drivers of RJ Racing, who are three-time winners of the popular and competitive E3 class. According to Rob Gibson, deciding to take on the 25 Hours is like trying to decide if you want to have a kid.

“Don’t wait until you think you are ready, because you will never be ready. Just do it. Jump in with both feet.” His younger brother John said the 25 is the chance for amateurs to feel what it is like to run a professional race. “There is assigned paddock parking, you have media there. (One) year, Al Unser was running. I raced in the same race as Al Unser! Can you believe it?”

These three teams provided advice, tips, and strategy to help a new team come to the event, enjoy the experience and maybe even win. We talked about vehicle choice, budgets, crew members, lodging, food, car preparation, strategy, brakes, tires, driver options and bad luck. The 25 Hours of Thunderhill encompasses all of those issues, and the team that can best overcome them stands the best chance for success.

We publish this story now, in July, because there is still more than enough time for you to prepare.

The car you choose to compete with ultimately will decide your endurance class (ESR, ES, E0, E1, E2, or E3) and, more importantly, it also will decide your fate. Deciding on what platform to begin with can be the most important decision you make. El Diablo Motorsports uses a tried-and-true 1992 BMW E36 M3.

“You want to run a chassis that people have already raced, so you know where the problems are,” Guagenti said. “This car has a lot of aftermarket support and lots of shops understand them and can give you good advice on what to do, but more importantly what not to do.” According to Guagenti, showing up with an unproven vehicle doesn’t correlate to a solid finish. “I’ve seen teams show up at Thunderhill with brand-new cars, straight from the factory, and it has never worked out well.”

Carroll agrees with that sentiment and has had races where cars didn’t finish because of unproven platforms. “We showed up with a car that wasn’t finished. We shouldn’t have brought it. It wasn’t ready. We had a delay from an engine builder and got the engine two days before the race. During testing, the engine sucked a valve and blew up. Lesson learned, come prepared or don’t show up.” Carroll came back with a vengeance, redesigning the car from the ground up, testing it extensively, and won the overall title in 2014.

RJ Racing also uses a simple, tested and reliable platform, a Mazda Miata. “We know the Miata is tough and can last. But we prepare the car and go through every system before the race. You don’t want to show up at Thunderhill with a big question mark on the roof of your car. You don’t want any doubt about its ability to finish the race.” The results don’t lie. The Mazda Miata was the only vehicle to win the E3 class until 2019.


Bring a spare of everything, even an engine, when you compete in the 25 Hours of Thunderhill. Some teams go so far as to bring a whole spare car.

The 25 Hours of Thunderhill can be hard on equipment, even brand-new stuff. Each team discussed what they bring to the event for insurance. Carroll brings everything. “Minus the chassis itself, I bring a spare of everything. Suspension for every corner, ready to bolt on with alignment settings already built into the units. Engines, trannys, complete front noses, splitters, you name it, we bring it.” It is important for Davidson Racing to bring all of its spares because it competed in the event in a BMW-powered Norma M20F, a specially built, one-of-a-kind-in-the-U.S. racecar. Miata teams can run to Pick-n-Pull in Chico, Calif., for a lower control arm, if needed, but you won’t find Norma parts at a junkyard.

RJ Racing brings plenty of spares, according to Rob Gibson. “We always have a spare coil pack, spare hubs, spare brakes, and a backup transmission. My brother, John, organizes our spares and charts them. We not only have bins with labels on them, for example ‘right front spindle,’ but in that bin we will have the installation instructions and torque specs listed so whoever is doing the swap won’t have to look up the information. It’s all right there.”

The trick to bringing spares is two-fold: know your vehicle’s weak points and bring a spare vehicle. That is what El Diablo Motorsports does according to Guagenti.

“We have our endurance car on track and we have a sprint car in the paddock in case we need a spare part. Even though we bring specific spares, like coil-overs, ready to go, body panels, front splitters, etcetera, we still bring the entire spare car. In the past, we have allowed other BMW teams to borrow parts from the car. Later in that same race, we desperately needed a welder and the same team that borrowed parts from us, loaned us their welder and got us back into the race, which we were able to win. Sort of like a racing karma.”

However, even brand-new parts can fail, and it has happened to El Diablo. “We have seen brand-new and rebuilt half shafts fail. We have found that non-OEM parts often lack the OEM build quality.” Not only can parts fail, but parts can get bent by someone else. Oftentimes, with different closing speeds among six classes, the 25 can be a contact sport. Having parts at the ready will help the team overcome an unforeseen situation.

“Prepare for everything,” Carroll said. “Because everything will happen.”


The number of tires you bring varies with the type of car you are racing, but expect a sizeable tire budget to get through the 25 Hours of Thunderhill.

At the top end of the spectrum in the ESR class, Davidson Racing brought 16 to 18 sets of tires, plus six to eight sets of softer-compound tires for night racing, and rains, just in case. “We do four tires every pit stop,” Carroll said. “We run a softer compound at night, which wouldn’t last a two-hour stint during the warmer temperatures during the day.”

In the middle of the spectrum, the E0 class, El Diablo Motorsports runs only four sets of tires. “We run the Hankook racing tire,” Guagenti said. “We get BFG tire performance with a Nitto tire longevity, which makes the Hankook tire optimal for the 25-hour race. We can get eight hours per tire based on our rotation schedule.” Cars running in the E3 through E0 class range can change only one tire per pit stop on pit lane. If a team wants to change more tires, they will have to drive behind the wall into the paddock pursuant to NASA endurance racing rules.

Asked if they prefer the strategy of going behind the wall for a four-tire change versus a single-tire change after fueling during a pit stop, the Gibson brothers got real quiet. “Um, you’ll have to come to the race and watch what we do to find out. We don’t want to give everything away here.” RJ Racing runs Hoosier Racing tires on its Miata and it is always the right front at Thunderhill that needs replacing first. RJ Racing brings four sets of Hoosiers for the race plus a fifth set for testing and spares. Their budget just for tires is around $3,000 for the race.


Cross-training crew members so they can do lots of different jobs on the car is key.

Spare parts and new tires don’t jump onto the cars all by themselves. That requires a crew, a 25-hours-around-the-clock pit crew to be specific. Davidson Racing pays professional crew members to go over the wall. Their fueler and their tire changers were from Grand Am or IRL, and they are fast. Additional crew were full-time employees of Carroll, and together they managed the race strategy and logistics. Crew size for Davidson Racing: 35 members.

El Diablo uses 12 crew members, who are all volunteers from the BMW community who have raced together for years. “Our team is the family and friends group,” Guagenti said. “Our crew is dedicated. Even though we schedule them time to sleep, they want to stay up and see the race through.”

RJ Racing runs a lean eight- to 10-person crew and cross-trains each member for everyone’s job, so if a member is missing, anyone can fill in. “Our crew is comprised of all engineering students from local universities,” said Rob Gibson. “NASA had an event called ‘Pit Crew For a Day’ at California Speedway a number of years back. We connected with a few enthusiastic guys from that and they have been with the team ever since.” RJ Racing has a formulated pit crew rotation schedule to ensure their team members get some rest.

One thing that came up universally while talking to each of the teams was the use of spreadsheets. While asking the teams about their crew sizes, we heard things like, “Hold on, let me pull up the spreadsheet and tell you exactly how many we had.” Or, “Just a moment, I have that here in my spreadsheet.” Organization is a key component of success at the 25. Excel is your friend.


Napoleon Bonaparte famously said, “An army marches on its stomach.” The same is true of a race team at the 25 Hours of Thunderhill. Have lots of warm meals on hand to keep your drivers and crew fed.

Just like he leaves the pit crewing and the driving to the professionals, Carroll also leaves feeding the crew to the professionals. “I’ve used the Thunderhill Grill catering service and I’ve used Nancy’s Diner in town (Willows, Calif). I’m thinking of bringing in a food truck and parking it at the end of my stall to cook for the crew all night.”

El Diablo Motorsports has a team mom named Gina, who prepares meals weeks in advance. “She never lets the crew get hungry,” Guagenti said. “She makes soups and stews to keep the crew warm at night, easy to prepare and it keeps the budget tight. She has been doing it for our team since our very first 25 Hour.

RJ Racing has a hospitality chief named Jennifer, who keeps their crew fed and happy. “She comes out every year for the 25 Hour and takes care of everyone,” said Rob Gibson. To borrow a quote from Napoleon Bonaparte, “An army marches on its stomach,” and it can be argued a race crew works off its stomach, too. So, keep the crew warm and fed, and they will be happy to replace the second splitter you knocked of during an off in Turn 1.


Having a place for the crew to rest is as important as food. They may not want to sleep away eight hours of the race, but they don’t want to nap in the cold in a fold-up chair, either. Sure, Saturday night a lot of people stay up all night, but that doesn’t take care of Thursday night after practice, Friday night after qualifying and for a lot of team members, Sunday night to completely crash after the adrenaline wears off.

Davidson Racing rents four bunkhouse trailers and sets them up at the track to house the people Carroll flies in to crew. Local hotel rooms will house fulltime staff and drivers during the week. During the race, one of the bunkhouse trailers will be for drivers only.

El Diablo Motorsports uses local hotels during the week for lodging and then rents RVs for the crew and drivers during the race. The crew double-bunks, and drivers get their own rooms. They have one RV assigned to crew and one assigned to drivers. “I don’t want crew members leaving the track during the race to go to a hotel,” said Guagenti. “I have had situations in the middle of the night where I needed a full crew immediately. Once we needed to replace the entire nose of our BMW. I had eight guys jump on the car, and they got the job done in seven minutes, which was amazing, and we won the race. If they were at a hotel, we never could have replaced the nose as quickly with only two or three people and we would have lost.”

RJ Racing runs a tighter ship for its crew, literally. “We use the Navy hot bunk system,” said Rob Gibson. “Once one crew member jumps out of a bed in our RV at the track then another crew member can jump in.”


This race is often won in the pits, so having a pit strategy and well-rehearsed fueling and driver-change procedures is essential.

“Being behind the wall is not good pit strategy,” said Guagenti. “I’ve learned, well, we have all learned, from watching Audi at Le Mans: less time in the pits equals racing success. We have the fastest pit stops in the lane, and a lot of our success comes from that. We can track exit, dump two 5-gallon jugs — the max allowed during one stop in E3 through E0 classes — and be back on the track in 40 seconds.”

RJ Racing uses a similar strategy. “We can get our driver in the car during the same amount of time it takes to dump two jugs of fuel,” said Rob Gibson. “This way we can make a driver swap and it isn’t a strategy decision regarding a longer pit stop. We can put a fresh driver in without adding time to our stop, and be more competitive on track.”

According to Carroll, the drama of the race is in the pits. “It is mind-blowing. I love watching different scenarios play out on pit lanes. It is interesting to see what other teams are dealing with during the 25 hour. Essentially the 25 Hours of Thunderhill is an entire season of sprint racing in one night.”


All teams interviewed for this story have won their class and overall. They all said the same thing: Find a brake setup that lasts the entire race.

While discussing pit stops, the subject of brakes came up, and all of the winning teams had the same strategy and advice: Find a set that lasts the whole race. Changing brake rotors and pads can be time consuming and difficult under race conditions because brake components are incredibly hot. Each of the teams found brake combinations — rotors, calipers, and pads — that can last the entire race. RJ Racing uses Porterfield Brakes with a pad they refer to as “The RJ Racing Special,” which will last through practice and the race. El Diablo Motorsports uses Brembo brake calipers with Performance Friction pads and they also can get through the entire race on one set.


Here is where the conversation about the 25 got a bit sticky. Nobody really wanted to talk dollars and cents. It could be because if anyone added it all up they might have a coronary. But Carroll’s statement that the 25 Hour is an entire season of racing helps you understand how costly the race can be. This sentiment was shared by Guagenti, who indicated running El Diablo Motorsports for the 25 Hour weekend cost about as much as an entire season of sprint racing. After some prying, we estimate — not including the car — that to run an E3 Mazda Miata with a volunteer crew would be approximately $7,000 to $15,000. An E0 BMW ride would be between $15,000 and $25,000.

And ESR? Chasing the overall win? Paying professional drivers and crew? That number wasn’t even hinted at. Data from previous ES winners running GT3 Porches on Michelins were in the neighborhood of $200,000. Does that sound like a lot to you? The crazy thing is, that kind of money doesn’t, by any means, guarantee a win. Nobody can buy a win here. It can only be earned.


Having pay-to-play drivers helps defer the costs of running the race. A majority of the teams at the event use this model. Each of the teams interviewed agreed the optimal number of drivers for a car was four.

Obviously, due to the cost of the event, funding the party is a challenge. A lot of teams are comprised of pay-to-play drivers, which help defer the overall financial hit. This concept is used by a majority of the teams at the event. Each of the teams interviewed agreed the optimal number of drivers for a car is four. That number gives each driver plenty of seat time and plenty of rest. Any number below four means drivers have to do extra stints, every number above four means drivers get limited track time. The question was how do you pick the drivers?

“Nobody drives an El Diablo car that we don’t know personally or hasn’t been vetted by someone we trust,” said Guagenti. “We don’t use anyone that is an unknown quantity.” RJ Racing talked about not just who they pick to be a driver on their team, but where they use them. “We want our drivers to be comfortable,” said John Gibson. “Some people don’t like racing at night so we use them in the day. But that does complicate our schedule. We have a comprehensive driver’s agreement that our drivers have to sign (the Gibson brothers are attorneys), which gives the crew chief the ultimate decision to pull a driver from the seat if it will benefit the team.”

Davidson Racing doesn’t have the same sort of issues with their drivers. “Pro drivers are used to being directed and so they listen,” said Carroll. “I have a specific meeting with my drivers after NASA’s drivers meeting Friday night. I tell them what I want and how I want to run the race. Our biggest issue is drivers missing yellow flags.”

The one thing that all of the teams agreed on was that they wanted drivers with a good head on their shoulders. Nobody wants a driver who is going to do something stupid and put the entire race at risk and end up on the trailer.


Teams interviewed for this story differed on the use of spotters. Some felt they were valuable. Others, not so much.

Spotting is an asset to a driver, especially in crowded races like The 25 Hours of Thunderhill, with upward of 70 cars on track and six different classes all running different speeds. Davidson Racing uses a spotter in the tower for the entire 25 hours. “We try to rotate the spotter out every two hours,” said Carroll. “It can be a long night up in the tower and I have six guys to rotate in and out. Regardless of having the spotters’ assistance, I make my drivers run with their headlights on during the entire race and direct them to flash their lights during passes. Spotters can warn drivers of slower cars, yellow flags, and stupid problems. They are invaluable.”

El Diablo Motorsports had a completely different strategy, “Spotters are useless at night,” said Guagenti. “We keep one radio in the pits to talk with the driver. If we are really chasing down the leader in the morning we might go on the hill and help spot. Other than that, it is up to our drivers to have situational awareness.”

RJ Racing was in the middle on the spotter issue. “We run one at the beginning of the race when it is really crowded and one at the end of the race. Other than that, it is a single radio at the pit wall.”


In ESR, finishing without a major mechanical problem is everything. When you look at the statistics of 25 Hour finishes for ESR cars, easily the fastest cars on the track, they have seldom won overall.

RJ Racing has won its class three times and they have never had the fastest car in E3. Their strategy is to bring a prepared car, run consistent laps, have solid quick pit stops and finish the race strong. This strategy has worked well for them.

El Diablo Motorsports has a different strategy: a 25-hour all-out-sprint. In the E0 class, the fastest car wins the class and therefore their pace is hard and aggressive.

In ESR, finishing without a major mechanical problem is everything. When you look at the statistics of 25 Hour finishes for ESR cars, easily the fastest cars on the track, they have seldom won overall. ES class Porsches hold that record, and the first-in-class ESR car is often beaten by E0, E1 and E2 cars simply due to too much time behind the wall. You can’t win this race while sitting on jack stands.


We asked each of the teams what advice they would pass down to a new team thinking of taking on the 25 Hours of Thunderhill for the first time. Guagenti from El Diablo Motorsport said, “Come in with a positive outlook. Don’t be afraid to fail. You are not going to win on your first time out. The car needs to be built, done and ready to go before test day on Thursday and all of your drivers need to have driven it. If you are fiddling with the car at the track, you are done.”

The Gibson brothers of RJ Racing said, “It is the ultimate team challenge. There is no one single thing that is the key to success. In this race, it is everything that is the key to success. Bring the car across the finish line in one piece and that will guarantee you a solid finish. Our philosophy is that we do things a particular way. There is the right way, the wrong way, and the RJ Racing way. This race is hard. We work on it all year long. Everything we do during the season is prepping for the 25.”

Carroll admitted he actually hates this race, but still comes every year. “I do, I hate this race. It is very difficult and I always come to win. I stress out about everything. I’m on edge. I don’t sleep at all. I stay up for 38 hours. The race is so unpredictable you just never know what it’s going to throw at you.”

In December 2014, what The 25 Hours of Thunderhill threw at Carroll and Davidson Racing was the overall victory — a victory Carroll had been chasing since the inception of the event. He’ll never forget the race he won, but he’ll also never forget the races he lost. Especially the ones that were close.

The 25 has that effect on people. For racers, it is a pilgrimage, an Everest, a moon landing. It is a goal to be conquered. Just finishing the race is an accomplishment. Standing on the podium is an enormous achievement. And winning, well, it is the ultimate triumph. The question that remains, where will you finish? On December 5, 2021, NASA will crown an overall winner and six class winners. Will you be one of them?



Davidson Racing was managed by Ron Carroll, no stranger to professional motorsports. The team won the 2014 25 Hours of Thunderhill in a BMW-powered Norma M20F. The car was a hill climb champion in France, purchased by Davidson Racing and converted for endurance racing.


The team name comes from the property near Mt. Diablo in Northern California where the team of friends and family built and maintains their BMW E3 inside a barn. The team is owned by Scott Smith and Lance Boicelli. The team has won the E0 class of the 25 Hours of Thunderhill three times.


The initials RJ Racing come from brothers Rob and John Gibson, attorneys out of Southern California who won the 25 Hours of Thunderhill E3 class three times in four years. Their orange and blue (or is it blue and orange?) Mazda Miata has been a strong platform for the team.

Image courtesy of Brett Becker

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