AFT Acts to Level the Playing Field in Twins Racing

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American Flat Track instituted new rules for non-production-based engines in the SuperTwins class. What does this mean for the race-only Indian FTR750? (Indian Motorcycle/)

American Flat Track (AFT) 2022 dirt track racing officially begins in March, but in the meantime, the off-season has treated us to plenty of political fireworks.

By 2023, AFT’s goal is to field one all-inclusive Twins class instead of the two present classes: SuperTwins (bikes powered by 750cc engines designed specifically for racing) and Production Twins (production-based engines of up to 890cc, with essentially unlimited modifications).

In 2016, AFT instituted a five-year plan to aggressively build the series rather than leave it to its own devices, as in the past. The hands-off approach had led to decline, and AFT believes a key to success is to do as NASCAR does: to race multibrand, production-based equipment that spectators identify with.

Just as the plan was up and running, Indian showed up with the game-changing race-only non-production-based FTR750. The same rules that had made Harley-Davidson’s race-only XR750 legal for years meant the new FTR750 was also legal.

Indian’s FTR was very good, and soon dominated AFT Twins. The next step was to split the class as explained above: race-only bikes in the SuperTwins class and production-based bikes in a separate Production Twins class. Last year Production Twins was a popular success, with multiple brands winning. SuperTwins, with their race-only engines, became virtually an Indian spec class.

Then AFT stepped in. CEO Michael Lock said, “We intervened in Twins because the diversity was going away. We’d rather make parity than kill the Indian.”

New Restrictions

To that end, in July of 2021, AFT announced changes in an effort to “make parity” in the hoped-for single Twins class that was scheduled to debut in 2023. The following limits were imposed on race-only bikes:

• Minimum weight for SuperTwins entries increased by 20 pounds to 330, while production-based bikes remained at 310 pounds.
• Only the base flywheel may be run on SuperTwins engines, remaining at approved weight and dimensions, with no mass added or removed.
• The maximum weight for the rear wheels of bikes with race-only engines was set at 35 pounds, and that of bikes with production-based engines at 43 pounds.

Let’s take a look at what’s going on here. The weight change needs no explanation. Regarding the engine flywheel and rear wheel, the heavier they are the easier it becomes to keep the rear tire from spinning and losing hookup.

Indian dominance continued, so further SuperTwins limitations were announced for the 2022 season:

• Engine output to be reduced through the use of 32mm thin-plate intake restrictors.
• RPM limited to 11,500.

Gary Gray, Indian’s VP for racing, technology and service, told Cycle World, “We knew they were [going to do] something, looking at rpm, flywheel mass, and airflow. We thought they’d pick one. But they did them all.”

Restrictors placed in each intake must have a 32mm inside diameter for race-only engines for the 2022 season of SuperTwins. (Indian Motorcycle/)

Gray went on to reveal that, on Indian’s dyno, the 32mm restrictors (one for each cylinder) cut power by 22 percent.

On December 23, 2021, the changes were amended. Bike weights were equalized; the 11,500-rpm SuperTwins limit remained; intake restrictors were enlarged to 34mm; and rear-wheel weight maxima were set farther apart, at 28 pounds for race-only-powered bikes and 48 pounds for Production Twins.

Cycle World’s Dyno Test

In order to get a firsthand look at the state of performance before the new limits were imposed, as well as with two different-sized restrictors, Cycle World arranged to have a private Indian FTR750 trucked down from Sacramento to our dyno.This is what we learned:

Restrictor	Max Horsepower	% of Open HP	Max Torque	% of Open Torque
Open	92.47 hp @ 10,180	(100%)	53.96 lb.-ft. @ 8,750	(100%)
32mm	76.80 hp @ 9,620	(83%)	46.55 lb.-ft. @ 7,700	(86%)
34mm	83.29 hp @ 9,920	(90%)	49.14 lb.-ft. @ 7,800	(91%)

Dyno chart for an unrestricted privateer FTR750. (Robert Martin Jr./)
Dyno chart for a privateer FTR750 with 32mm intake restrictors. (Robert Martin Jr./)
Unrestricted and 32mm restrictor-equipped Indian FTR750 dyno runs. (Robert Martin Jr./)

Bear in mind that these figures are for a non-factory engine tested on a rear-wheel dyno.

Paddock insiders suggested that while the horsepower reduction will slow the SuperTwins on mile tracks, it may actually help TT lap times.

This coming season, the top four Production Twins finishers will be eligible to run in the SuperTwins finals. This may well provide performance comparisons that could help in achieving parity in 2023′s coming solitary Twins class. Stay tuned.

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