Scott Smallwood
on his little Honda RS125 in Sound of Singles
Two-Stroke.
Photo: Matt Benson
MODERN ROADRACE
CLASSES
Sound of Singles®
(SOS)
Super Mono 2:
Four-valve four-strokes to 510cc and two-valve
four-strokes to 610cc.
Super Mono™:
Unlimited displacement four-strokes.
Production Singles.
Single-cylinder four-stroke motorcycles that are or were
available for sale to the general public and intended
for street use in the U.S.
Two-Stroke Singles:
Two-stroke singles to 550cc.
Battle of Twins®
(BOT)
Formula 3 Twins:
Pushrod OHV twins to 1000cc, OHC 2- or 3-valve to 800cc
and OHC liquid-cooled 4-valve to 650cc.
Formula 2 Twins:
Pushrod OHV machines to 1250cc, liquid-cooled OHC to
750cc, air-cooled 2-valve to OHC to 1000cc and
air-cooled 4-valve to 1000cc.
Formula 1 Twins:
No displacement limits. Engine modifications are
unlimited, except on water-cooled 4-valve twins over
900cc.
Open Two-Stroke:
Air-cooled machines to 500cc, water-cooled motorcycles
with tubular frame to 400cc and modern 250cc GP type
machines.
Sound of Thunder®
Unlimited displacement
four-stroke singles; 4-valve demo twins to 1000cc, OHC
twins to 1100cc and pushrod twins to 1350cc;
three-cylinder machines to 1000cc; and twin-rotor rotary
engines.
Copyright 1987-2009 AHRMA, Ltd. ~ Site Design
by TRPro.com
Battle of Twins®, Sound of Thunder®, Sound of Singles®,
BEARS® and Battle of Legends®
are registered trademarks of the American Historic Racing Motorcycle
Association.