Before NASA Mid-Atlantic Time Trial racer Ghais Khaleghi made an important switch in thinking, he’d found his track-day feet in a series of big, heavy, and consumable-hungry GT cars: a 911 Turbo, a Corvette Z06, and, finally, a high-power Nissan GT-R. He realized that he might have to take things other than horsepower into consideration when picking his next track car. Although his 700-horsepower Nissan could reach 165 miles per hour down VIR’s back straight, less powerful machines were still outpacing him. He’d realized that, beyond a certain point, more horsepower brought diminishing returns.
Increasingly aware that the more-is-better approach could only do so much at this stage in his development as a driver, he started to consider less. Less mass, coupled with real aerodynamic grip, might be the solution to his frustration.
The idea of downforce hadn’t yet piqued his interest, but when he chanced upon a classified for a Stohr 01D on his Facebook feed, its power-to-weight ratio intrigued him. Anything with that single-purpose shape would have, at the very least, a different sort of driving experience than the cars he had known.
He knew nothing of the car prior to reading the ad, but he was curious and the price was right. There was no reason not to pull the trigger.
The 01D is draped in fiberglass bodywork and incorporates a large, flat splitter as well as a single-element rear wing for over-body downforce. Under-body downforce comes from a flat floor and a half-tunnel arrangement starting halfway down the length of the car.
The sense of directness is what first catches an initiate’s attention after turning the wheel in 900-pound 01D, thanks to its low weight and high rigidity. These come courtesy of its carbon-steel hybrid composition. Essentially, the carbon cockpit provides much of the stiffness and safety needed, while the steel tube front and rear clips are meant to be easily repairable. Not that a crash is inexpensive in such a car due to the cost of body panels, but the clips do take the overall repair costs into consideration.
In the center of the rear clip, a small, transversely mounted motorcycle engine is mounted. There are several options available, and this example came with a 1,000-cc Suzuki motor plucked from a GSX-R 1000. The motor makes 150 horsepower and it’s at its strongest between 8,500 rpm and 10,500 rpm. Keeping it within its narrow powerband is made easier via a mechanical paddle-shifted transmission.
Wilwood billet aluminum brake calipers, lightweight aluminum hats, and ventilated floating rotors come standard. As fuel weight represents a large percentage of the vehicle weight, as the fuel load diminishes – a few gallons make a noticeable difference – the driver can adjust brake bias with a knob mounted in the cockpit.
But weight, as vital as it is, doesn’t define the car alone. That the Stohr is a wing on wheels has far more to do with how it must be managed on track. Understandably, this style of driving requires a special touch – one that Khaleghi had to wrap his head around before he could start extracting what this car had to offer. Unlike his GT-R, he couldn’t simply point, mat, pull a paddle, and expect to see much difference in lap time.
His first event in the new 01D was at VIR, where he yielded sub-par times – several seconds behind the best lap he’d set there in the Nissan, but Khaleghi was exhilarated by the spartan experience, if not a little confused.
“At slow speeds, it actually feels a little clumsy. I learned you need to get the tires up to temperature before you push. If they’re cold, once it goes, there’s no saving it,” he recalled.
Studying other drivers in similar machinery helped him get a sense of the timing, the braking distances, and the general limits of a car of this kind. Fortunately, the car had already been equipped with a data logger, and the previous owner was happy to review Khaleghi’s first and less-than-fruitful outing. His main takeaway: Brake later.
That spurred him on to understand just how differently a rolling wing like the Stohr will decelerate. After brushing up on the essentials of digressive braking before his second test, he realized that the tricky and all-important final phase of his braking zone — the one that requires a delicate release of the pedal — might get him into trouble if he bit off more than he could chew. Wisely, he chose to give himself the leeway needed to experience all these wings had to offer without locking up and sailing off the track.
Khaleghi knew to leave himself a lot of extra runway, so after reaching 130 miles per hour down VIR’s back straight, he tried to find threshold pressure well before his normal braking marker.
He was stunned. Stomping the brake pedal about as hard as his quads would allow threw him forward into his belts, and once he’d dropped below the aero threshold around 80 miles an hour, Khaleghi was given a clear demonstration of why the pedal must be released at a digressive rate. Locked Hoosiers R25 bias-plies aren’t cheap, but his planning allowed him to learn the right rate of release with just one squared-off set of slicks and without any off-track excursions.
Getting to terms with the car took time, but his growing confidence was only bolstered by the trophies he had started bringing home. TTU became his new playground, and there simply weren’t many in the region who could try to brake alongside a confident Khaleghi in his thousand-pound sports racer.
However, it doesn’t always go to plan. When running in TTU at the 2023 NASA Championships at PittRace, Khaleghi’s weekend went poorly. After his shifter broke, his brakes overheated, then his throttle stuck momentarily – without major consequence, thankfully. They replaced the pads, but the rotors were warped, so the car still shook like mad under braking. Ultimately, the shifter broke again, relegating him to take home third place. Not exactly a lousy weekend, but considering the way he’d been regularly setting records, it felt a little underwhelming.
Third at the NASA Championships might not have been the finale he wanted, but at least he had something to look forward to on his drive home. Khaleghi had already picked up the newer, shinier, stickier version of the 01D waiting in his garage. Over the winter, he beavered away, making sure the car would be sorted come the start of the season.
Mark Uhlmann, an accomplished Time Trial driver from Vancouver, British Columbia, had joined the exclusive group of Stohr owners a decade ago, and since moved from an 01D to their newer model, the WF1. Being a bit of a tinkerer, he made a few adjustments to his WF1 to sharpen control over its inputs, then promptly sold the machine to Khaleghi.
The WF1 claims LMP3 performance and lap times several seconds faster than the 01D, despite only weighing 30 pounds less. Of course, the aero package has seen serious improvements, and the powerplant in this particular example is much punchier than the Gixxer motor could hope of being.
The WF1’s powerplant is pulled from a 2015-2018 BMW S1000R, which, tuned on MoTeC M130 and E85, makes 170 horsepower at the rear wheels. When E85 isn’t available, a tank full of 93 will carry him roughly 25 miles. Because it revs to 14,200 rpm, he needs to keep an eye on the oil levels. It burns about a quart over the course of a hot day.
The BMW’s relatively cheap to service, too. Uhlmann was able to make his first motor last more than three years of competition without issue, After 40 hours, the motor is in for a rebuild, which costs somewhere between $2,500 and $4,000 — about twice as durable and one-third the cost of the Suzuki engine.
Stability is one of its greater strengths. The WF1 has a reasonably long wheelbase at 97 inches, which is roughly the same as the 01D’s, but it generates about 25 percent more downforce due revised bodywork with an improved upper body, rear wing, splitter, and, crucially, a vastly different floor with longer tunnels. Fortunately for those looking to retrofit their O1D, much of the WF1’s underbody aero, including the wing, splitter, and floor are modular and can be easily substituted.
Interestingly, the rear track (54 cm) is slightly narrower than the front track (56 cm). “This is because the overall body is a consistent width and the front wheels are narrower, so the track width is wider resulting in the same total width of outside of wheels,” Uhlmann added.
Standard equipment includes a WRD-designed chain-drive differential with lightened CV joints and hollow half-shafts, an aluminum radiator, and large oil cooler. The Stohr billet aluminum transaxle case is designed to take suspension loads while destressing the engine case.
Another Aero Challenge
“It’s a violent car to drive,” Khaleghi began. The spring rates, the additional power, and the difference in mechanical grip make the car harder to drive, bucking and unforgiving in the way the old car wasn’t.
The WF1 was designed with ultra-low rear suspension to lower the bodywork and clear out cross-sectional aerodynamic area in the hunt for maximum speed. The rear upper suspension is only a few inches higher than the axle half shaft, and the rear bodywork practically sits on the suspension. A knock-on effect of all this is the rear pushrod has to be laid over at a fairly extreme angle to get it to fit under the bodywork.
The salient difference between the two cars is the underfloor design. The tunnels run the full length of the body in the WF1, and the spring rates have been increased accordingly. “Spring rates are well north of 1,000 pounds per corner due to the extreme downforce even with 1:1 rockers. Considering the weight of the car that provides clues to how much downforce it truly makes,” Uhlmann added.
The added download from the WF1’S dual-element Hurley wing replacing the 01D’s single-element is factored into the reworking of the suspension. To better control the car at speed, Uhlmann opted to upgrade to a set of three-way Ohlins TTX36s, another improvement over the factory WF1’s factory Ohlins.
To put it simply, there is one way the WF1 fails to match the 01D’s performance, if driving ease is discounted. The WF1’s dihedral front wing from Zebulon/Hurley Racing Products covers roughly the same surface area, but unlike the 01D’s flat diffuser, this raises at the centerpoint to create an inlet to funnel air into the tunnels.
Uhlmann did all he could to maximize braking performance. In addition to replacing the Stohr-offered Wilwood package, he opted for PFC brakes and floating monobloc calipers, as well as a custom pedal box incorporating the Tilton 900 pedals. All these contribute to shorter distances and an increased sense of security and modulation — both good qualities when a longer trail braking phase is vital to getting the car rotated into slow and midspeed corners.
Beyond that, the differences in corner-entry are negligible. The WF1’s air-shifted transmission is as crisp as they come, and that’s the result of a custom integration of MME Motorsports’ air shifter with integrated valves, Geartronics compressor and accumulator, and M130 ECU to control everything. This transmission is easier to rush gears with, while the old cable linkage in the 01D was something that wouldn’t always cooperate if not properly forced into the desired gear. Reduced shift effort, even with a paddle arrangement, makes a difference in optimizing the braking performance.
In the middle of the corner, the two cars feel indistinguishable, but the WF1 allows some room for error at corner exit. “You had to be pretty much perfect with the old car,” Khaleghi began,” because you couldn’t power your way out. Any scrub at the exit would show up clearly in your terminal speed.
The WF1’s BMW engine comes on hard at around 10,000 revs — the engine speed which the 01D’s Suzuki begins to fall flat — and carries all the way to 14,200. The BMW’s powerband is roughly twice the width, and this helps it net an additional 11 miles per hour at the end of VIR’s front straight.
But it’s far more than just a straight-line advantage the WF1 offers. Khaleghi lapped Carolina Motorsports Park five seconds faster than he ever had in his 01D. A 1:29 is seriously quick — and that’s without using the curbs or the rumble strips. Anywhere between 3 and 5 seconds ahead of the bests he set in the 01D at his regular tracks, and the bulk of this improvement is made in the corners and the braking zones. “The most I saw in the 01D was around 1.7 g of lateral grip, whereas I saw around 2.65-2.75 g’s of sustained lateral grip in the WF1,” Uhlmann added.
Minimizing Mass
Weight is paramount, clearly. That design ethos rubbed off on the owner, who’s been adamant about bringing only the necessities onboard. “It’ll burn about 3.5 gallons a session, but I’ll go out with less than that when I’m trying to set a time. I get about three laps out of 1.5 gallons. The difference is noticeable,” Khaleghi said.
With that much of the balance and performance influenced by fuel, he couldn’t avoid considering the other flexible weight variable onboard. Khaleghi, a welterweight, recognized that he had to hold himself to the same standards as the Stohr’s designers had when building the car. He made the commendable commitment to a strict diet and cardio regimen to bring his weight down from 145 pounds to 128 pounds, where he’s remained over the last year.
The secondary consideration this fitness addresses is simply handling the g loads. His stamina was limiting his performance early on, and so jogging was intended, coupled with weight training, to work as effectively as he could within the car — work being the operative word. Enduring 20 minutes of the aforementioned cornering force, unassisted steering, and unassisted brakes would leave him panting early on, but now he’s able to last a full day and still feel fresh on the way home.
Though the car imposes serious strain on the body that a closed-top GT would not, there is one benefit to driving an open-topped prototype: being exposed to the elements helps keep the driver relatively cool.
Having air run through the cockpit is vital, but not as important as the air flowing under the car. Maintaining the aero platform is crucial. So much so, the curbs are worth avoiding entirely. The benefit from taking a longer line through curb-flanked corners – the kind which a softly sprung GT might benefit from hopping over, is that he can maintain the airflow underneath the car and maintain consistent aero grip.
“I tried raising the ride height and softening the spring rates once so I could use the curbs, but I still couldn’t go any faster,” he admitted.
Khaleghi even shies away from the rumble strips. “If you drive over the rumble strips at Oak Tree with your teeth clenched, you’ll need to go to a dentist afterwards. I might start wearing a mouth guard,” he joked.
Radical Shape, Pedestrian Operation
The operational procedure is far less demanding than its shape might suggest. “I check every nut and bolt after every weekend – they will come loose. At the end of the day, I check the chain tension, and I check oil throughout the weekend. The BMW motor does burn about a quart per day if the ambient temperature is high.”
“By far, it’s the most track-ready of all the cars I’ve owned. Nothing has been easier to take to the track and drive. You just change the oil, check the nuts and bolts, and go.”
“It’s very low maintenance,” Khaleghi said. “Compared to the Corvette, I get so much more seat time and use so much less fuel. Between the fuel and the tires, the running costs are very reasonable: “I would say I spend about $500 a weekend,” he noted.
“Once I tried the lightweight thing and recognized where it was better on track, then took a look at the running costs and the serviceability, I knew there was no going back. I haven’t driven another road car on the track since I got the Stohr,” he laughed.
“My Stohr WF1 is undoubtedly one of the fastest cars for setting blistering lap times on the racetrack. Its lightweight design and nimble handling make it an incredibly fun and rewarding car to drive,” Ghaleghi said. “If I decide to keep it, my future goals would include fine-tuning the suspension to enhance its handling even further, and exploring ways to add a bit more power for improved performance.”
