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Everything You Wanted to Know About NASA's Thunder Roadster Racing Series

The Thunder Roadster is one of the purest racecars in all of NASA’s racing series. They are designed and built solely as racecars to adhere to a strict set of rules. The end result is an affordable racing series 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 series is about the driver, perhaps more demonstrably than many other NASA series. Thunder Roadster championships fields are growing and there’s close racing throughout the entire field no matter where you are. And isn’t that why we race?

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.
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.

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 $7,500 to $30,000 for used, race ready NASA spec racecars.

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 secondgeneration 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.

Varies by preparation level, but both are weighed with driver.

Prep Level 1 1,500 lbs.

Prep Level 2 1,600 lbs.

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

New cars are available from Toys by Tink for right around $39,000.

Prices on used cars range from $7,500 to $30,000.

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

Tires, size, brand and prices

Hoosier 26.5/8.0-15 Roadster Edition, $130

Brakes, brands and prices

Carbotech, Hawk, Wilwood, $90 to $225

Check the NASA Contingencies page for the latest programs.

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.
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.

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.


Questions and Answers to Feed Your Curiosity

Yes. They generally sell for around $17-$21K. It’s best to ask on the California Legends and Thunder Roadsters Facebook page.
Yes, you can upgrade a standard open-wheel Yamaha powered Thunder Roadster (TR) to a closed-wheel Hayabusa powered GTR. The cost of parts to do the conversion is about $16,000 assuming you already have a TR.
It is most popular in the Great Lakes Region, the Florida Region, and the Northern California Region. However, there is growing interest in the other regions.
Yes, we have numerous drivers that are 6’4″ tall and over 260 lbs.
Yes, we have numerous drivers that are 6’4″ tall and over 260 lbs.
Absolutely safe. They have a full factory-built cage system that has proven multiple times to be very safe.
Parts are readily available from your local INEX dealer.


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Thunder Roadster Series Contacts

Thunder Roadster
Jason Oehler
Region: Great Lakes
Title(s): National Series Director
Series: Thunder Roadster
Doug Marshall
Region: California-Northern
Title(s): Regional Series Leader
Series: Thunder Roadster
Jason Oehler
Region: Great Lakes
Title(s): Regional Series Leader
Series: Thunder Roadster