For a while now, the next big goal in the never-ending quest for speed has been to hit 300 mph in a road car. The race to break that barrier has been heating up lately, with Koenigsegg’s average 278 mph record-setting run in Nevada demonstrating just how close we are. Bugatti might have something to say about it too. But Texas car tuner John Hennessey is predicting that his latest supercar, the Venom F5, will hit 300 mph. There’s four important reasons why it may not: the tires.
Those are the car’s Michelin Pilot Sport Cup 2 tires, which were originally developed specifically for the Bugatti Chiron. They have been tested to withstand the 261 mph limited top speed of that car, and have seen documented speeds in excess of 280 mph for Koenigsegg’s run.
Right now, these Michelins are really the only tires you can buy that can even approach these sorts of insane speeds. Those tires have been specially developed for high-speed applications in mind, and use some non-traditional materials and construction methods to manage to be both drivable at normal speeds and capable of speeds decidedly abnormal.
Even so, that does not mean that these tires are capable of hitting a full 300 mph. Achieving those kinds of speeds on tires that are also usable for normal street driving has really not been accomplished so far; the significant and exponentially increasing forces acting on a tire at 300 mph, especially the high temperatures generated at such speeds, have made this a very difficult goal to reach.
But John Hennessey thinks that these tires can do the job. In an interview with Top Gear, Hennessey discussed his tire choice:
Hennessey will also use these Michelins (unless another manufacturer wants to make a bespoke tyre) but believes, because the F5 is a lot lighter than Chiron, they’re good for above and beyond 280mph. Possibly 300mph.
“Tyres are a limiting factor for Bugatti,” John says. “But I don’t believe they’re a limiting factor for us. When we do our math, we know that we are not overloading them. We’re not even close to the load specification of the tyres at our speeds.”
That’s a pretty bold statement. Let’s just be clear what Hennessey is saying: these Michelin tires will allow the Venom F5 to hit 300 mph, even though Bugatti—the flagship brand of the massive Volkswagen Group conglomerate—does not believe they will do so on their own car.
The reason Hennessey gives is that the F5 weighs less than the Chiron, and according to “[his] math,” the Venom is “not even close to the load specification of the tires at our speeds,” referring, presumably, to the only speed that matters here: 300 mph.
I’m not exactly sure why this statement has just passed through the automotive media without scrutiny, but we wanted to know a bit more. I reached out to Michelin about this, as well as to the CTO of Pirelli, Ian Coke, for a second opinion.
I also reached out to Hennessey himself to inquire about how exactly the company plans to achieve such speeds, but he has so far declined to respond.
The 300 MPH Cars, Maybe
Hennessey is a well-known car tuner. The Venom GT, Hennessey’s Lotus Elise-based predecessor to the F5, holds an unofficial speed record of 270 mph. The record is said to be unofficial because only one run was done; official Guinness rules demand two runs, in opposite directions. Of course, the rules for “fastest production car” are notoriously convoluted.
And even without the drama of the Guinness record, Hennessey manages to draw plenty of controversy. The company has come under fire—including from us—for having some very questionable business practices, and Hennessey’s reputation is checkered. In the early 2000s Hennessey was repeatedly sued by disgruntled customers over alleged shoddy work, cars that never got delivered, being slow to offer refunds and more issues.
And last year Jalopnik spoke to numerous ex-employees and former customers who said, among other things, that the shop had not delivered cars that foreign buyers had paid for.
Yet Hennessey has continued on despite the management issues alleged by former employees and former customers. And the Venom F5 certainly has impressive specs on paper. Powered by a 7.4-liter twin-turbo V8, it is claimed to have 1,600 horsepower while weighing 2,950 pounds—an extremely impressive power-to-weight combination, and far lighter than Bugatti’s Chiron. The Venom F5 has been teased for years, but only recently unveiled at SEMA this month.
It, along with the Chiron and Koenigsegg Agera RS, are the three most likely contenders for the crown, and all three cars have comparably impressive numbers:
Those Michelin Pilot Sport Cup 2 tires are the biggest question here, so it’s worth knowing a bit about where they came from. The tires were designed to be capable of handling the electronically-limited 261 mph top speed of the Chiron while at the same time being more affordable than the insane Michelin PAX tires used for the Veyron that came in at a spit-take-inducing $17,000 per set.
By comparison, Michelin Pilot Sport Cup 2 tires can be picked up for a much more reasonable $1,800 per set.
About Those Tires
Compared to the cheap, garbage tires you or I may put on our Hyundais or Nissans or whatever, these Pilot Sport Cup Tires are no joke. They’re able to achieve those 270+ mph speeds for all manner of reasons, including the use of two differing rubber compounds for the inside and the outside of the tire’s tread; exterior rubber is an elastomer with high molecular mass, hard and with good dry surface adhesion, while the interior is designed for more give.
The tires also don’t use standard steel belts, instead opting for a belt made of aramid fibers, which are strong and highly heat-tolerant.
Let’s start with what Michelin had to say, which really wasn’t that much. I tried to speak directly with an engineer, but was told engineers were too busy, and eventually I was simply informed I wouldn’t be able to speak to one, though no particular reason was specified.
Michelin did release this statement relating to the use of these tires on these speed record attempts:
With top speed initiatives such as this, tires are always an additional challenge to be fully analyzed. When Michelin is asked to participate, we work together with the manufacturer to guarantee the integrity of the tire at those very high speeds. Prior to any speed run, we validate the tires though analytical analysis as well as machine testing using the exact conditions the tires will encounter. We take into account vehicle weight, horsepower, camber & toe, aero loads at speed, road surface and more. Validating the tires are capable of reaching those speeds is critical.
Basically, Michelin works with automakers and tuners for stuff like this, but so as not to give away trade secrets, they’re coy about what they do exactly or what makes these tires special from a technical standpoint.
Significantly, Michelin also confirmed to me that they have not been approached by Hennessey or begun any direct work with Hennessey, which is notable because the tire company was a key part of Koenigsegg’s speed record attempt program.
In another email, Michelin’s PR rep made this statement:
But with these things—Chiron, Koenigsegg, etc.—it boils down to Michelin working with the automakers to deliver a tire that can reliably operate within the cars’ performance parameters, which can be extreme, as Koenigsegg just reminded everyone.
I think it’s important to point out that working directly with the carmakers is very important to Michelin, and something Hennessey is not currently doing.
Michelin didn’t comment on Hennessey’s assessment, so I reached out to a competing tire company, Pirelli, where I was able to talk to their Chief Technical Officer, Ian Coke.
I asked Coke specifically about Hennessey’s assessment that the Venom F5 could hit 300 mph when the Chiron can’t because of the Venom F5 is lighter, and this was his response:
“Weight has nothing to do with it. The car’s weight doesn’t matter when you have spoilers making massive amounts of downforce. It’s really not the load on the tire that’s the issue, when tires are rotating at those speeds, temperature is the killing factor.
As the temperature rises, the tire’s size actually grows. Again, load is not a problem. Running temperature is the issue, and that would be our main concern.”
Based on this response, whatever Hennessey’s “math” is about the tires’ ability to withstand 300 mph, it’s being used to solve the wrong problem.
Plus, he’s absolutely correct about the downforce; even if the Venom F5 weighs less, it’ll still need a comparable amount of downforce to keep from turning into a terrible and short-lived airplane. For reference, the Koenigsegg Agera RS makes 1069 lbs of downforce at 155 mph.
When I flat-out asked Coke if he felt that the Michelin Pilot Sport Cup 2 tires used on the Chiron, Agera RS, and the Venom F5 could actually hit 300 mph, his answer was pretty clear:
Obviously, Coke works for a rival manufacturer, so I don’t expect him to heap praise on Michelin’s product. He is not exactly an objective source. But he is someone who knows tires, so if it were technically possible in some way, I feel like we’d have a far less definitive statement.
Coke made it clear that he felt that Michelin would not allow a 300 mph attempt to be made on their off-the-shelf Pilot Sport Cup 2 tires, but would insist on some sort of bespoke tire being built that can withstand those speeds and temperatures. Again, Coke works for a Michelin competitor, but what he’s saying there speaks well of Michelin, in that he does not feel they would allow a 300 mph attempt to be made on tires that they do not feel were capable of such speeds.
Coke described the sorts of things such a tire would need, like replacing the metallic belts with more heat-tolerant textile belts, cold-running tread compounds, and materials that could flex and expand predictably as both temperatures and the tire’s physical size grew.
And Coke said that he did not believe there was currently a streetable tire that could withstand 300 mph speeds.
What Scientists Say
In the interest of objectivity, I reached out to many independent tire researchers as well, and got some very informative but ultimately inconclusive answers.
Professor Jon Gerhardt of the University of Akron (they’re very big in tire research), had this to say:
This is a indeed a complex question. Actually the major concern with high speed tires is the resonant frequency of the tire. As the speed increases the forcing frequency from the rolling of the tire increases. As the forcing frequency approaches the natural frequency of the tire, a standing wave appears on the tire. This causes large deformations all around the tire which is what causes the heating within the tire.
So to get a higher speed tire a couple of things need to happen. First the rubber must have a low hysteresis value to reduce the amount of heating. The second is a bit more complicated. The natural frequency of the tire needs to be increased. This is related to the structure of the tire and the components within it. The tire needs to be stiffer and at the same time must be made lighter. (These are usually opposing goals.) The first step usually used is to make the tread very thin whichever reduces weight. Metallic components need to be made very strong and light or replaced with other materials such as carbon fiber belts and reinforcements.
Are these things possible in order to make a 300 MPH tire? I think so. Will this resulting tire be acceptable for a production vehicle - even a very specialized one? I think maybe this might be even a more difficult one if it also has to survive potholes, curb scrubbing, and expected tread wear life.
This confirms what we heard from Pirelli, and is similarly inconclusive, though skeptical that such a tire would be the sort of thing you could drive normally on, like the Michelin Pilot Sport Cup 2 tires.
Professor Joe Walter, also from the University of Akron, broke down the challenges of such a tire:
1. Heat is the “Achilles heel” in all tires — especially high speed tires. If tire operating temperatures exceed the vulcanization temperature (usually 325-350 degrees F), the tire can be expected to fail in service.
2. Light weight tire constructions help, such as Kevlar belts, carcass and beads along with high inflation pressure. Not sure if this construction is being used in extant race tires, but major tire companies have built them for experimental studies.
3. As one of your respondents has surmised, its the aerodynamic down-force at high speeds that loads up the tires, not just the vehicle weight. This down-force on FI cars can be as great as 3-4 times the vehicle weight increasing vehicle drag due to increases in tire rolling resistance.
4. The centrifugal force causing the tire to stretch increases with the square of speed, while the power absorbed by the tire (causing heat build-up) increases with the cube of speed. While going from 280 to 300 mph is only a 7% increase in speed, it produces a larger increase in the centrifugal forces and greater build-up of heat generation due to hysteresis of the internal components (especially rubber) of the tire.
Walter confirms that Hennessey’s justification of lower weight as a reason why he could achieve speeds Bugatti can’t isn’t valid, and it’s also interesting to note that Walter describes the heat build-up as a “cube of speed” which means a pretty dramatic change in temperature between 280 mph and 300.
Why Street Cars Are Different
So what about other cars, like rocket cars or drag racers that do well over 300 mph? Well, it’s a different game there than with street cars.
Top fuel dragster tires routinely hit 300 mph+, but they’re massively oversized, low-pressure tires, and even they can only last for a minute or two at that speed.
This is not a slight to those Michelins—the tires have accomplished absolutely incredible things. Hitting speeds of 278 mph on a streetable tire like Koenigsegg did is a colossal achievement, and that should not be minimized.
The problem is that the difference from 278 to 300 is not trivial at all, and the forces that make engineering such a tire so difficult increase exponentially, making even that last 22 mph a massive hurdle.
As Bugatti test driver Andy Wallace told Popular Mechanics back in June:
“Even at 261 mph the wheel and tire has to withstand extreme forces. The valve cap on each wheel weighs 2.5 grams, but it equates to 16 pounds at 261 mph. As the speed moves even higher, the loads increase exponentially. Wallace says at the moment, there is no tire that can withstand the g-loading at 300 mph, but he predicts Michelin engineers will sign off on a top speed with the current production tire slightly north of 280 mph. Perhaps a future version of this car will be engineered to hit that magic 300 mph milestone.”
That statement has proven to be quite prophetic. Those Michelins have hit about 284.3 mph, as we saw in the video, and that could be close to their upper limit.
But 280 mph is definitely not 300 mph.
For what it’s worth, Hennessey himself seems like he’s going to see how Bugatti attempts it first. In a later interview with Top Gear, after the Koenigsegg run, Hennessey said:
“It all puts pressure on Bugatti, to step up and deliver the number that everybody expects them to do. Then we’ll let those guys duke it out for a little while, then, once we figure out which one of those guys [Koenigsegg and Bugatti] is going the fastest, then we’ll take the F5 out and lay down a number.”
I’m sure the Venom F5 is an incredibly fast car. I’m also sure that my past experiences with Hennessey have encouraged me to treat what they say with a healthy bit of skepticism, and I’m also sure I trust physics and tire engineers more than John Hennessey when it comes to what a tire is capable of.
We’ll see if Hennessey can put his money—and more importantly, his tires—where his mouth is.