Introduction

The Thunder Roadster is one of the purest racecars in all of NASA’s racing classes. They are designed and built solely as racecars to adhere to a strict set of rules. The end result is an affordable racing class with competition that is as close as you can get anywhere.

They are rugged and durable, easy on consumables and affordable to buy, race and maintain. This class is about the driver, perhaps more demonstrably than many other NASA classes. Championships classes are growing and there’s close racing throughout the entire field no matter where you are. And isn’t that why we race?

Class Description

“The Thunder Roadster Series was created to meet the needs of competitors seeking a low-cost platform utilizing the purpose-built Thunder Roadster chassis and specified parts designed and manufactured by U.S. Legend Cars International. The series focus is on fun, safe, and affordable racing while encouraging driver development, close competition, and comradery between its competitors.”

Eligible Makes and Models

“The Thunder Roadster Series (TR) is one class with two competitive preparation levels. Eligible Manufacturer Models include the Thunder Roadster or Thunder Cup car manufactured by US Legend Cars International that are marketed and sold though USLCI authorized dealers. Replacement parts are supplied through USLCI dealers or aftermarket suppliers as permitted in these rules. No modifications may be made to any part or system unless specifically permitted by these rules.”

Donor Prices and Availability

One of the biggest appeals of the Thunder Roadster class is the low price of admission. There are no donors because these are not production automobiles converted to racing trim. They are designed and built by U.S. Legend Cars International as purpose-built racecars. Prices range from $6,000 to $20,000 for used, race ready NASA spec racecars.

Engine Specs

There are two preparation levels in Thunder Roadster: prep level 1 and prep level 2. Be aware that Prep level 1 is gradually being phased out in favor of the faster and more reliable Prep level 2.

Prep level 1 is Thunder Roadster TR, which uses Yamaha 1200 or 1250 with stock Mikuni BS36 carburetors and black ignition coils / box as delivered from US Legends Cars. Owners may convert air cooled to water-cooled, but the TR cars must run the 2:93:1 or 3:30:1 rear axle ratios.

Prep level 2 cars, known as GTR cars, use first- and second-generation Suzuki Hayabusa engines with the stock Mikuni BS36 carburetors and the spec manifold. Any performance modifications to the engine to alter the factory stock horsepower are strictly prohibited. However, oil pump gears, oil pans and oiling system components may be upgraded to maintain adequate oil pressure. The 3:58:1 rear axle ratio is mandatory.

Weight

Varies by preparation level, but both are weighed with driver.
Prep Level 1 1,500 lbs.
Prep Level 2 1,600 lbs.

Fuel Required

“Only petroleum-based unleaded gasoline as defined by the American Society of Testing and Materials is permitted with a maximum of 93 octane.”

Average Cost to Build Car

New cars are available from Toys by Tink for right around $32,000.

Average Cost to Buy Built Car

Prices on used cars range from $6,000 to $20,000.

Typical Modifications

The Thunder Roadster GTR rules are fairly well locked down, which means modifications are limited.

  • Adjustments to bump steer settings will only be permitted by placing spacers between the steering rack and the heim ends of the tie rods or between the front spindle pickup points and the heim ends of the tie rods.
  • Frame repairs may include only front clips forward of the A-arm mounts and rear clips (behind the main rail of the sub frame) may be replaced as long as they are replaced with the exact material that it is replacing, and all pickup points must remain in the stock locations as delivered new from U.S. Legend Cars International.
  • The stock front control arm clevis may be replaced with a double sheer control arm clevis as long as it does not change the geometry and pickup points.

Cost Analysis

Average cost to run a weekend — $750 to $1,000.

Consumables Prices

Tires, size, brand and prices
Hoosier 26.5/8.0-15 Roadster Edition, $130

Brakes, brands and prices

Carbotech, Hawk, Wilwood, $90 to $225

Available contingencies

Hawk Performance, Raybestos

Factory Participation

None.

Benefits

Stable rules package that is only modified for parts superseded by availability or safety.

Being a tube-chassis race car, its designed with added safety features and specific crush zones to absorb energy in a major impact.

Challenges

Some parts are specific to the car, so availability is limited to dealers.

With the conversion to the Hayabusa engine platform, used cars built to the GTR spec are limited, but original Yamaha cars are available for conversion and, depending upon the market, very reasonably priced.

Rulebook Highlights

8.2. Air Filters
Only stock and K&N air filters and Outerwears Pre-Filters coverings as delivered new by US Legend Cars are permitted. Velocity/ram stacks are not permitted. No components that direct airflow to the carburetors or increase airflow are permitted.

8.19.2. Metal Fatigue
It is highly recommended to have the frame checked periodically by an expert for metal fatigue. Cracked or broken frames are strictly prohibited from any NASA sanctioned events.

8.31. Radios are Permitted
Two-way radios will be permitted in competition.

8.37. Shocks
All cars must use spec Bilstein shocks as delivered new by U.S. Legend Cars International for use on a Thunder Roadster. Changing or altering the shock or fluid or pressure inside is illegal. Altering or tampering with the shocks or competing with the same, will result in a penalty from probation to an indefinite suspension. Shocks may be turned upside down. Shock bumpers are permitted (maximum 1/4” tall).

9.5. Exhaust System
The header, gaskets and muffler must remain within the stock dimensions, steel thickness, location and configurations of the original, as delivered by U.S. Legend Cars International. Stainless or standard steel headers allowed. The internal components of the header may not be altered. Header wrapping (tape) is acceptable. Ceramic or baked on coatings are not permitted.

10.10. Oil Catch Cans
Oil catch cans (maximum 1 quart capacity each) can be used. It must be securely fastened and remain within the engine compartment. It may only be plumbed in by hose from the stock crankcase breather opening and/or the oil fill cap. A return line may be run to the stock return fitting on the oil pan.

What Racers Say

Brian Bohlander, NASA Great Lakes

“The Thunder Roadster is a sleek, full-fledged race car. For the money, you can’t race anything like it in competitive road racing. The drivers in this class are some of the best in the country in any NASA class and everyone works hard to help grow the class. In club racing, my money is staying in Thunder Roadsters.”

John Spain, NASA Florida

“Safety and parity. The competition is close and fierce, but still gentlemanly. After 20 years of racing, I recognize the need to compete and a survivable platform, but even more importantly, I value the extremely close racing. I was in a qualifying session at Barber Motorsports Park a couple of years ago with 10 Roadsters who were all within 1 second of one another. That is really hard to achieve in club racing. With Thunder Roadsters, we do. It is truly about the driver.”

Jason Oehler, NASA Great Lakes

“I was drawn to TR/GTR for a few reasons. I had been allowed a test drive in one while a DE student. I was instantly in love with the dynamic driving style of this car. You have to wring its neck to get it fast. The Spec nature of the series and the fact that it is an affordable, purpose-built racecar was the hook.

“What keeps me coming back is that I’ve been wringing my car’s neck for four years and I’m still learning how to get even more speed from it! Plus, the cost of consumables is so low that I really don’t mind it! Front brake pads, for example, last an entire season, and cost $90. The cars have proven robust in keeping drivers safe when things do go wrong and the cost to repair is so reasonable with an entire new frame at $3,000.”

Lapping Videos

Brian Bohlander Explains the Thunder Roadster Class

Thunder Roadster Action at Sebring

Gary Tinker Interview at 2018 Championships

Reverse Grid Start at Autobahn Country Club

This video will show you how robust the Thunder Roadster car is because it shows a bad wreck from which the driver walked away.

2018 NASA Championships Race

Image courtesy of Downforce Media

1 COMMENT

  1. I started road racing in 1956 in a Singer SM1500, advanced to a Jaguar XK120, Lotus 7, Formula Ford and finished racing my Thunder Roadster for 11 years. The Thunder Roadster as a race car and the Roadster drivers equal the most fun possible on a race track and after over 60 years behind the wheel I miss it.

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