Sound of Singles®/Battle of Twins®/Sound of Thunder/Modern Roadracing Mission Statement

AHRMA’s mission is to showcase single-, twin- and three-cylinder motorcycles which historically have been under-represented in modern roadracing. The Battle of Twins concept was born in the late 1980s as modern Superbike racing became increasingly dominated by inline four-cylinder machines. BoT racing kept alive the thunderous roar of twin-cylinder machines from British, European and American manufacturers. Sound of Singles racing features modern interpretations of the classic single-cylinder racebike, encompassing everything from production bikes to one-off custom-built machines.

Refunds will be issued only to pre-entered riders who have filed a Refund/Credit Request Form with the AHRMA National office. A refund form is in the Handbook, may be obtained from the office, or can be downloaded here. The form may be filed by mail, email, fax, or the office may be telephoned with the relevant information. Please see AHRMA Handbook rule 4.7 for more details..

Racing Classes

The following classes are offered. Check the AHRMA Handbook for complete details of class requirements..

Sound of Singles®1: (SoS1) Unlimited-displacement single-cylinder four-strokes.

Sound of Singles®2: (SoS2) Liquid-cooled four-strokes to 450cc and air-cooled four-strokes to 610cc.

Sound of Singles®3: (SoS3) Certain single-cylinder 250-350cc machines with GP-style chassis and 300-400cc machines with Production chassis.

Sound of Thunder 1 (SoT1): Unlimited-displacement four-stroke single-, twin- or three-cylinder machines; twin-rotor rotary engines and any eligible Open Two-Stroke machine. Turbocharging or supercharging is permitted only on single-cylinder machines.

Sound of Thunder 2 (SoT2): Any AHRMA SoS or Motard machine, liquid-cooled twins to 850cc, unlimited air-cooled twins, and triples up to 675cc.

Sound of Thunder 3 (SoT3): Harley-Davidson XR1200, and pushrod OHV twins to 1000cc, OHC two- or three-valve to 805cc and OHC liquid-cooled four-valve to 650cc.

Motard: Motocross, off-road, dual-sport and Motard-specific single-cylinder machines of unlimited displacement.

Battle of Twins® (BoT): Open to unlimited-displacement air-cooled twins.

Thruxton Cup Challenge: Open to lightly-modified Triumph Thruxtons and Harley-Davidson XL883 and XL1200 Sportsters.

Formula Thunder: Open to all Next Gen Superbike, Sound of Singles, Sound of Thunder and Battle of Twins motorcycles.

Open Two-Stroke: Open to any two-stroke motorcycle, regardless of displacement, number of cylinders, frame type, cooling type, or date of manufacture.

Formula Lightning Open to zero emission motorcycles that are typically powered by electric motors, but may use other no-exhaust propulsion methods as well.