Marshall Pruett’s Racing Tech Mailbag for May 8

Marshall Pruett’s Racing Tech Mailbag for May 8

Insights & Analysis

Marshall Pruett’s Racing Tech Mailbag for May 8


Hi all – apologies for the delay since my last Mailbag. Please fire away with your tech questions about F1, IndyCar, TUDOR Championship, WEC, Pirelli World Challenge or whatever else that comes to mind from the world of road racing. Please send them to PruettsTechMailbag@Racer.comWe can’t guarantee your letter will be published, but I will always reply. -Marshall Pruett

Q: I understand tire graining is bad and reduces lap time etc. but what exactly is graining and what causes it?
Brad, Bloomington, IN

MP: Graining is a term used to describe an excess of abrasion between the surface of the tire and the road. “Graining” gives the impression of the rubber being turned into small granules, but the better image might be of road rash where the tire’s “skin” is roughed up. You can induce graining by sliding a tire and by spinning the tires repeatedly with the tire pressures either too high or low, or the camber settings leaning on the inner or outer edge of the tire too much. Once graining sets in, you have less of an effective contact patch to provide grip and traction, which then reduces your cornering or acceleration capabilities. Provided a driver does what he/she can to minimize graining by taxing the offending tire or tires as little as possible, the problem can be managed, but that isn’t always possible.

Q: When IndyCar drivers talk about practice times, there are often comments made about “foreign rubber.” Please elaborate. What are the effects of the different rubber compounds laid down by other series?
Gordon, Dallas

PS: Your column is appointment reading for me to learn more about the technical side of IndyCar I am continuing to learn growing my appreciation of my favorite form of motorsport. KEEP IT UP!

MP: Thanks, Gordon. There’s no hard rule here, but different rubber being laid down can be a significant issue when going from rubber being shed by street-based tires to slicks, for example. The most extreme scenario would be Indy cars or sports cars taking to the track after drift cars have done some lapping. Rather than driving over a track surface with embedded rubber to meet the Firestone slicks, you have lots of tiny chunks of hard street rubber – like little ball bearings – that interfere. Going from one type of slick – from the junior open-wheel categories – to IndyCar rubber tends to be much less of an issue, and if you’re racing in the TUDOR Championship, there’s three different brands of rubber being put down on every lap. Mold release agents and general differences in chemistry can lead to disparities in grip with one brand of tire running over what has been put down by another, but it’s just a part of life these days with packed schedules aimed at entertaining the fans with multiple series.

Q: Regarding the underbody of an IndyCar, it is very large and can create serious lift. It creates so much downforce too, though, so it becomes hard to minimize it without losing a lot of the crucial downforce that keeps the car to the road. My solution may not be possible but what if you put two hollow tunnels on the bottom? Maybe 2″ in height, and they go all the way through to the rear of the car. Inside this little tunnel, have little tiny wings or prongs evenly spaced inside throughout to produce low air pressure in certain places. The goal would be to funnel air into them, hopefully creating a vacuum effect not only between the bottom of the car and the road but also another vacuum just above that. I’m not sure if it would be possible since the tires would interfere with airflow. The idea is to make it like a two-story building with the windows open.

The other idea of mine to keep cars from flipping would be to place deployable flaps on the front of the car and on the sidepods. Under the nose of the car, a sensor will constantly measure the distance of the wing to the road and if the distance between the wing and the road exceeds a certain height then the hydraulically powered flaps will rise up and help push the car back down. It may not have a huge effect but it’s a way to keep downforce because as soon as the car rises, both the rear wing and front wing stop making downforce. Right now I’m in high school in Indiana and plan to go and study mechanical engineering and this mailbag has helped expand my knowledge about the DW12 and other vehicles on how they work. Thank you.
Hunter Smith

MP: Hi Hunter. Ferrari tried something like what you describe with its Formula 1 car in 1992 – a twin-floor to produce low pressure above its flat bottom – and it was a total disaster. Yes, Indy cars do have a massive underbody, but they aren’t alone; look at what’s beneath a Corvette C7.R GT Le Mans racer, but flipping isn’t really an issue. I do agree IndyCar could do more work on devising methods to shed downforce when the DW12 is in a serious state of yaw, but trying to have hydraulically actuated flaps manage a lifting car would be a bit tricky.

Ivan Capelli in the Ferrari F92A – nice idea, but…

Q: A vast majority of racing fans DO NOT want to watch fuel mileage racing. F1 needs to cut the technical crap, set an overall limit and give the teams so many liters/gallons each race, drop the green, and let’s get it on. The crap they are going through now is silly. Sounds like some engineer in the rulemaking department is trying to justify his salary!
John Miller

MP: Preach on, John! I’d understand the need for F1 drivers needing to conserve fuel at times if they had 1000 horsepower to work with during a race, but artificial flow restriction leading to 600hp F1 motors will go down as one of the sport’s most epically short-sighted conceptual failures. Anyone who’d go and buy a Renault, Mercedes-Benz or Ferrari because they’re impressed by the fuel economy of those respective F1 powerplants is A: an idiot, and B: likely to not exist.

Q1: The ACO introduced a “one air gun, two mechanics” rule a few years back (opposed to two air guns, two mechanics) to slow down the process of changing tires and/or allowing more time for a safe driver change. Teams pretty soon exploited that rule by doing some kind of “relay race” with up to three teams of “one air gun, two mechanics” playing with the out of bounds line. Where is the gain in safety and how is the rule justified as it’s contra dictionary to the cost saving measures – not for Audi, Toyota or Porsche, but the same rules apply to the GTE-Am cars or the Gentlemen Trophy in Blancpain Endurance.

Q2: What’s with the WEC’s lollipop man? Usually the chief mechanic waved the car in with some kind of board or simply his hands and a board was placed to mark the perfect stop. After the service, the chief mechanic then signaled the driver to start the engine and waved him out. With his hands free, he can also operate the radio. Again, I don’t see an increase in safety, as the chief mechanic now has no hands free to operate the radio. If he spots a car coming down pit road, all he can do is put the lollipop down again, but this creates a point of no return, while the old chief mechanic could still yell on the radio (Well, somebody else of the war wagon could yell…). What’s the point of having a F1-like lollipop man over a traditional chief mechanic like in the old days of Le Mans and IndyCar, where the RF tire changer was responsible to release the car (on ovals that is).

Q3: TUSCC allows servicing the car while the refueling takes place. We have many advances in safety, both on the technical side of the refueling system and on the safety rules for people in the pit lane. If there is one rule that should have been carried over from ALMS, then it is separate refueling and servicing, isn’t it? Why don’t they enforce this rule that is common in all sorts of endurance racing? Having worked as an accredited photographer from 2006-’09, before overalls became mandatory, I simply cannot understand this.
Thomas Roth, Germany

MP: Hi Thomas – great questions. 1: Every professional team will look for ways to exploit the rules to their advantage, and this is one of them. As for crew safety, this is what they do for a living. More injuries happen during a professional basketball game with 12 players on the court than a pit lane filled with dozens of crew members changing tires and refueling.

2: Radio communications to the drivers tend to come from the engineering stand, not the car controller, so those responsibilities have been split, in most endurance teams, for a while now. I’d rather have one person, in front of the car, with the sole responsibility of viewing the stop and deciding when to send the car than a tire changer looking up from a corner to try and assess what happened while he was looking down for most of the stop. WEC teams also use wheel torque monitors that give a green or red light indicator displaying correct/incorrect wheel tightening, and that’s also a job for the car controller to check before sending his driver. I’m happy with the current process and crew layout.

3: I’ll go back to my first point. Fueling and changing tires at the same time is done by professionals. There’s genuine safety – keeping people out of harm’s way, and then there’s implied safety, where we look at situations that could pose danger. Based on the percentages of things going wrong – fires, being hit by a car, flying tire, etc. – it’s hard to say that pit stops done in professional series come with a high incident rate. Facts, not fear, is where we should focus our energies to decide where improvements are needed.

Q: How do the IndyCar overboost penalties work? I understand that the wastegate serves as a regulator of turbine inlet pressure, so in theory the turbo compressor is limited in the amount of boost pressure that can be produced. So what circumstances lead to an overboost situation, and how is the penalty imposed? Is it a physical pressure relief valve or is there another performance reduction through the ECU?

And in a completely unrelated question, will we be seeing the visor cam on the ovals?
Brandon Clarke, Hebron, KY

MP: IndyCar’s spec McLaren ECU is tapped into the turbo plenum on each car, and when it sees an instance of overboost – a prolonged episode, not just a boost spike during an upshift, for example – it reacts by triggering an immediate penalty and lowers the available revs. In essence, it gives a penalty designed to balance out whatever power advantage was had until it’s a wash. Yes, we hope to have first examples of a newly configured visor cam filming method in place this weekend.

Q: I hope you pass on to Mr. Derrick Walker that switching to methanol will give Honda and Chevy 80-100 more horses. I don’t want to ever go back to gasoline after Indy 1964. I was there that day and the image of all that black smoke from the McDonald/Sachs inferno is permanently seared into my mind.

MP: It’s really up to the engine manufacturers on this one, John. The marketing benefits of E85 ethanol outweigh the desire to increase power through other, less eco-recognized fuels.

Q: My question is regarding the so called “slick intermediate” tires that Audi and Toyota were running at Le Mans last year. It sure seems like a contradiction, a slick wet weather tire. Is the compound just super soft, or is there a construction difference to the regular dry weather tires? Obviously the tires were not used when there was standing water, but how would they displace any moisture on the track?
Bill, Indianapolis

MP: It’s just a super gummy tire to use when the track’s too wet to go to more durable slicks and too dry to use grooved rain tires that will hurt lap times and quickly overheat. They have no sipes – nothing carved into the tread to disperse water. These tires are a perfect solution to a condition that has never had a proper answer, but will rarely see action.

Q: I wanted to ask a follow-up question asked in the last Tech Mailbag relating to IndyCar and fuel types. While Steve’s question last week referenced gasoline and you did a great job explaining what would happen with a theoretical switch back to methanol, I have another question about methanol and the smaller displacement engines with turbos that became the de facto standard after the switch.

Did the switch to methanol in the ’70s negate the need for turbo engine sizes above 3 liters as well as separate turbo intercoolers? Outside of the Mercedes 500I and the Menard Buick V6 for Indy allowed under the old USAC rules, I can’t recall any other CART-homologated engine that went higher than the old 2.65-liter displacement for the full-season turbo V8s or had dedicated intercoolers and I’ve always been curious about this. Also wanted to say thanks for the column and your awesome photos.
Humberto Saabedra, Ft. Worth, TX

MP: Moving to methanol was done to help what was going on in the combustion chamber – to better cool and increase power – than anything to impact the temperature of the air entering the chamber itself. You’re right about the use of intercoolers in that they were not a standardized solution across the 2.65-liter era, or with the bigger 3.4-liter motors. Those that did squeeze intercooler into place did see gains, but packaging was often the problem. The current IndyCar engine formula was written without the inclusion of intercoolers based on the manufacturers’ wishes – same packaging issues were cited.

Q: As a layman, can you explain just how insane the split turbo design is in the Mercedes F1 engine? Is this the most genius design in an engine in years?

MP: Great question following one about intercoolers, Ryan. I could write the answers for you, but frankly, there’s little I’d have to offer that isn’t covered in the video below. There’s only one downside to the Mercedes split-turbo arrangement, and that’s the added weight and inertia of the long shaft connecting the turbine and compressor, but based on the many other performance benefits the split-turbo setup offers, it clearly offsets the extra weight/inertia by a wide margin.

On a separate note, shortening intercooler piping and the piping from the turbo to the intake plenum was something I paid a lot of attention to while building a few different turbo-powered racecars. It makes a big difference.


Q: I’m a huge fan of DeltaWing car – the more I learn about it, the more fascinated I become. This is more pronounced after getting up close and personal at the Daytona 24 this year. I have a question about its performance both in the draft and for cars that are attempting to draft off of it.

Since the car has such a low drag coefficient, is there a notable increase in performance when following another, more traditional, car? Is the effect greater or lesser than one DP drafting off another DP? Is the handling of the DeltaWing more or less affected by dirty air compared to a more traditional car?

Does the way the DeltaWing generates downforce effect cars following? Is there a draft for trailing cars to try to utilize? Does it generate more, less, or about the same dirty air as more traditional cars?

Lastly, if in some alternate universe, the DeltaWing and the Nissan ZEOD were to be on the same track racing, could one beat the other?
Jack McCormack

MP: Hi Jack – lots of questions so let me bundle as many into some short responses: The DeltaWing definitely benefits from a tow and with its minimal frontal area, the car doesn’t need to be right on the bumper of another car to feel the effects. Think of a small boat in the wake of an ocean liner, then think of one ocean liner following another.

The ZEOD, with its more powerful 3-cylinder turbo engine, should walk the DeltaWing in any universe.

Q: With Ford already running its EcoBoost V6 in the TUDOR Championship (kicking butt, by the way) then why not take that motor and stuff it in an indycar?! I know you’ve said “Ford has no interest in open-wheel racing” but that motor that just won in LB is the SAME EXACT motor in a Ford Taurus that you can buy at your local dealership! With upgrades, obviously. I just can’t wrap my mind around the concept that the “all mighty” Ford likes to watch Chevy have all the fun in Indy.
Tory, Las Vegas, NV

MP: We get this question a lot, and it comes down to the EcoBoost V6 being a bigger and much heavier production-based engine that was never intended to fit into the back of a small open-wheel car. It could be made to fit, but the weight penalty alone would cause serious handling deficits without Ford spending a fair amount to make it more suitable to play with the smaller, lighter Chevy and Honda Indy car engines.

Q: Thank you for doing this mailbag. It’s awesome. During the last F1 race the guys were talking about something that connects the front and rear suspension. Could you explain what it is and what it does? I’m guessing it must be like an anti-roll bar or something.

The other question I have is I know how the “power unit” charges the battery and how it increases the horsepower. How do they choose when it increases power? Is there a button like push-to-pass or is it controlled from the pit? Thanks for RACER‘s great coverage of IndyCar racing, my first love.

MP: The first inter-linked F1 suspensions were tried in the ’60s and were done via mechanical systems. Today, it’s done hydraulically – in more than just F1 – to manage roll, pitch and heave. The ERS systems harvest energy under braking by using the spinning axles to charge the system – pretty much the same as any other shaft-driven electricity-generating system. No control from the pits – depending on the series – F1 or the LMP1 hybrids in the WEC – the power is either automatically dispersed, or used when activated by the driver.

Q: Marshall, thank you so much for taking time to connect to fans. This level of accessibility is exactly what will make motorsports so much more engaging to people like me.

I have a few very basic questions regarding IndyCar. In one response you said that teams use simulation software between races to plan setups, strategies, etc. Is this usually off-the-shelf software like ChassisSim or is it custom?

Second, I was reading in F1 Racing that a part of the weekend is not used tweaking the setup for that particular race but rather for testing and data gathering instead. Is that true for IndyCar as well, or is the DW12 so well understood now that most of the time is spent matching up the setup to the driver/conditions for that event?

Third, do you think when aero kits happen there will be any room for development by individuals like the ill-fated dihedral wings? Lastly, one thing has always puzzled me about the RC front wing. Why is the piece directly in front of the tires (at the trailing edge of the endplate) perpendicular to the flow of air? It seems like this would act as an air dam instead allowing the air to flow around the tire
Kyu Lee

MP: There are a few different sim packages out there that teams use, and each is based on individual preference. IndyCar teams are always working toward gathering data for the event they’re at. F1 teams are at such a rapid development pace, half their time is spent figuring out how the latest widget functions in the real world and interacts with the rest of the car.

IndyCar has yet to define if/what areas teams will be allowed to monkey with on aero kit pieces. That front wing piece is to prevent air fron hitting as much of the tire as possible – spinning tires cause huge amounts of drag, so like the rear sidepod bulges that block most of the rear tires to produce the same effect, the RC front wing endplate vertical pieces are there for the same purpose.

Q: 2008 F1 cars used this weird front wing. Formula Nippon also adopted the concept a year later with their Swift spec cars. Why? Is this a revolutionary aerodynamic thing? And why they were banned?
Giu Canbera, Sao Paulo, Brazil

MP: Open-wheel cars rarely have all the front downforce they need, so whether it’s through an opening in the F1 rulebook or an intentional design for a spec series like Formula Nippon, being able to run a second, full-width wing element (or something approximating an element that also helps route the downwash in desirable areas) is nothing but a good thing. As for why it isn’t used: rule changes to reduce downforce, plus, a new chassis manufacturer for FNippon.

Q: My rough draft for a new F1 pit procedure has been evolved and improved upon.

1) Get rid of the wheel nut entirely and negate the necessity to have wheel guns. That eliminates 4 people on the crew. Sorry I know those are people’s jobs but they are trying to save money in F1 (is that an oxymoron?).

2) A hydraulic/electric/air jacking system under the car. It is activated when the car is stationary in the pit box or by the driver. It has been suggested that automating the activation is a bad idea.

3) Attached to the activation of the jacking system is a release mechanism for the tires. You know the choke collar method of attaching something? Where you pull down the collar and the internal bearings relax allowing you to remove whatever? The jack goes up and the collar pulls back allowing the wheel to be removed without any wheel nut or gun. Reduces the issues with misthreaded wheel nuts as well and possibly the unsprung weight of the tire.

4) When the new tire is affixed to the car the process of putting it on causes the collar to return to position and secure the tire in place.

5) When all 4 tires have been placed the jack automatically releases and the car is released. This is an enhanced safety feature as theoretically cars can’t be released with loose wheels.

MP: 1) I’m guessing you’d have a different opinion if it was your job being eliminated. Firing people for the sake of sporting entertainment might be a door to crack open.

2) Making the sport less human and more automated. Surely we can get rid of those heavy, sniveling drivers, too. Are we then expecting toasters and vacuum cleaners to get up at 3:30 in the morning to watch other plug-in devices compete?

3) Interesting idea. That adds weight. And adds more cost to develop (see item No. 1 on reducing costs).

4) Surely this can be automated as well.

5) Theoretically, yes. A statistical anomaly has been solved. Unless, of course, something lodged in the exposed bearing/race while a wheel is being attached, or hydraulic pressure is lost to the lift system (how many retirements have been down to hydraulic failure in the past 25 years? A hundred? More?).

Q: Why is it so hard to put a racecar into reverse? Is it by design, or is it something that racecar engineers just don’t spend much time on. Sometimes you see someone trying to put a car into reverse (Patrick Dempsey comes to mind) and the chatter between the engineer and driver is more complex than from Mission Control to the Apollo Astronauts.
Ed Joras

MP: It’s usually the smallest gear in the ‘box that receives the least amount of use or practice to engage. If most open-wheel and sports cars continued to use manual ‘boxes, it would be less of an issue, although it was never easy then. With a sequential or paddle-shift arrangement, it usually involves pulling extra levers, lockouts and/or buttons and a multiple step process. For a guy like P-Diddy who isn’t in his Porsche that often, I wouldn’t expect the reverse gear engagement process to flow naturally.

Q: Can you discuss the kinds of things an engineer would change about an Indy car or sports car to optimize for performance in the rain? Springs, Dampers, Anti-roll bars, Ride height? Is it all to soften up the car? And if you go too far towards a wet set-up, are you screwed when the sun and wind dry out the track? Is that what happened to Will Power at Barber?

MP: Ride heights, cambers, springs and anti-roll bar are what’s usually changed – all to increase mechanical grip. Rain usually prevents high cornering loads, which means the suspension isn’t moving as much as usual, so you’ll soften the springs, possibly disconnect the bars, adjust the ride height to prevent aquaplaning, reduce camber, and pile on the downforce. You can go too far, or not far enough, and if you’re dealing with a drying track, a compromise of some sorts is what you’re aiming for.

Q: Has there has been some discussion about pursuing faster qualifying speeds/more horsepower, and what is the likelihood of IndyCar going back to the use of methanol? Correct me if I’m wrong, but my understanding is that alone would make for at least another 20-30hp right there. And personally, I miss that smell of methanol at the track.
Chris, Nashville, TN

MP: Yep, faster speeds for Indy were announced last year at Detroit. I’ll ask Derrick Walker about the exact engine allowances that might be utilized when I see him this weekend, provided he doesn’t run in the opposite direction…

Q: When a pit reporter says one driver had their crew put a teammate’s setup on their car, how many settings are there and what do they include?
Jeff Norris
Cicero, IN

MP: It could be a few things, based on what’s needed, or the whole thing. Ride height, rake, camber, toe, castor, springs, spring pre-load, shock canister pressure, J-damper weight, third spring rate, wing settings, Gurney heights/widths, center of pressure, tire pressures, and add-on/take-off aero pieces allowed by the series would all be standard areas to copy. On an oval, there’s more with cross weights, etc.

Q: Marshall, I’m a big fan of your mailbag and your great articles on After the thunderstorm passed on Sunday, I was wondering why they didn’t get the IndyCars out on track at Barber any sooner as it was just wet, albeit with a few rivers across the track. I’m glad they did get out as it was an interesting race and Bourdais and Montoya both impressed until their incidents.

In the postrace interview, RHR stated that the “wets” were like “intermediates.” Could you talk about the differences in the inclement weather tires between IndyCar and F1? I know we don’t have the budget to bring two levels of rain tires like in F1, but I thought that the rain tires in IndyCar were full wets?
See you at the GP of Indianapolis!
Gabe, Chicago, IL

MP: Hi Gabe. The rivers and areas of standing water would send the cars flying off the track, hence the delay. If it was just a case of rain falling from the sky, they would have been out earlier, but when that rain isn’t draining from the track, you get Extreme IndyCar Surfing instead of a proper motor race. The rain tires being used were, indeed, the less-aggressive option. I don’t know why teams weren’t on full wets, or if they were only given intermediates for the event. Indeed on the GP of Indy – I’m answering this from somewhere over Colorado on my way to Indiana…

Q: Do PCs us the same tires as P2’s and DP’s? If not, would P2s race better with PC tires?

MP: No, they use a different model and compound. The current 2014-spec Prototype tires from Continental have been surprisingly good on both DPs and P2s. Only issue, as I wrote about last weekend during the Monterey TUDOR Championship event, is the extra 300 pounds carried by the DPs brings their tires up to temp faster, giving a slight advantage at the start and on restarts.

Q: I know this is ancient history but perhaps you could hunt up an answer. I am currently reading the photo book Indy Cars 1911-1939 (Ludvigsen Series) and there are many close-up shots of the various engines used in those cars. There was certainly some wild engineering going on in those days!

The odd part is, nearly every carburetor appears to have a completely open air intake (perhaps 2-3 inches diameter) with no air filter in sight! They typically face backwards and are under the hood. Was it possible for those engines to run without any sort of air filter or am I seeing this wrong? Also, from what I understand the track conditions at IMS in those days were extremely dirty as it was sand that held the bricks together – about the worst possible thing for any engine to suck in!
Steve, Eden Prairie, MN

MP: Hi Steve, great question. This is far from scientific, and I welcome e-mails on the exact year/car, but as far as I remember, the first images I’ve seen of devices with the purpose of keeping klag out of the intakes came from the mid-’60s. They weren’t air filters, but simple aluminum plates that sat over the trumpets to block any sizeable objects from making their way in.

I asked IMS historian Donald Davidson for the second part of your question, and he says mortar was used to hold the bricks in place, not sand.