1948 Triumph Speed Twin

1948 TRIUMPH SPEED TWIN BACKGROUND
In a few short years, the 5T Speed Twin went from being one of the world’s premium performance motorcycles to be Triumph’s entry-level twin. It had been surpassed by the T100 Tiger with its higher compression and hotter cams. And soon it would be bumped down still further when the 650cc 6T Thunderbird came out in 1950. And of course, the rest of the British motorcycle industry were also pushing out bigger and faster machines each year, so the competition was growing fierce. But for now, the 1948 Triumph Speed Twin was a solid seller, and while not the fastest thing on the road, its performance was adequate for the day.

1948 TRIUMPH SPEED TWIN DESIGN
The 500cc twin retained its cast iron cylinder block and head, and was fed by a single Amal carburetor. It was of non-unit construction, with the timing gear on the right, and the primary chain and clutch on the left, as usual. The 4-speed gearbox shifted with the right foot. Triumph continued to use it’s tried-and-true rigid frame, but offered a sprung rear hub as an option. The sprung hub used radially-positioned springs inside it to cushion the bumps. It was fine in theory, but tended to move in unintended ways when worn out or under extreme loads (ie: hard acceleration). It was a poor compromise solution, but one that made sense to Triumph at the time. It was a way to get some rear suspension while retaining their rigid frame, a very expensive thing to replace. The front end now had Triumph’s own telescopic forks with hydraulic damping.


1948 Triumph Speed Twin SPECIFICATIONS

Model Designation

Engine Number prefix

Engine Type

Displacement

Bore & Stroke

Compression ratio

Carburetor

Engine output

Top Speed

Electrical system

Primary drive

Clutch

Gearbox

Final drive

Frame construction

Suspension, front

Suspension, rear

Brake, front

Brake, rear

Wheel, front

Wheel, rear

Wheelbase

Seat height

Ground clearance

Fuel capacity

Weight

Triumph 5T Speed Twin

47-5T

Air-cooled OHV vertical twin

498cc

63mm X 80mm

7.0:1

one- Amal 15/16"

28 bhp @ 6,000 rpm

85-90 mph

6-volt, Lucas magdyno, 40watt

Chain

Multi-plate, wet

4-speed constant mesh, right-foot shift

Chain

Steel tube, brazed lug

Telescopic

Rigid frame, sprung hub

7-inch SLS drum

7-inch SLS drum

3.25" X 19.0" Dunlop Universal

3.50" X 19.0" Dunlop Universal

54.0"

29.5"

6.0"

4 Imp gal

361 lbs, dry


MORE SPEED TWIN PAGES:
.....1938
.....1946
.....1947
.....1948
.....1956
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Triumph TR6
Triumph TR7
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Triumph 5T Speed Twin
Triumph T150 & T160 Trident
Triumph X-75 Hurricane


Check out these TRIUMPH BOOKS

COMPLETE BOOK OF CLASSIC & MODERN TRIUMPHS


TRIUMPH MOTORCYCLES IN AMERICA


TRIUMPH MOTORCYCLE RESTORATION


TRIUMPH MOTORCYCLE RESTORATION, PRE-UNIT


TRIUMPH BONNEVILLE & TR6 RESTORATION GUIDE: 1956-1983


TALES OF TRIUMPH MOTORCYCLES & THE MERIDEN FACTORY


TRIUMPH 650 & 750 TWINS OWNERS WORKSHOP MANUAL, 1963-1983


TRIUMPH BONNEVILLE: ESSENTIAL BUYER’S GUIDE


TRIUMPH BONNEVILLE: PORTRAIT OF A LEGEND


ILLUSTRATED TRIUMPH BUYER’S GUIDE, by Roy Bacon


TRIUMPH BONNEVILLE, 2001-2015


TRIUMPH: PRODUCTION TESTERS TALES FROM MERIDEN


TRIUMPH MOTORCYCLE RESTORATION GUIDE


TRIUMPH OWNERS HANDBOOK, UNIT-CONSTRUCTION 350 & 500, Kindle


TRIUMPH ILLUSTRATED WORKSHOP MANUAL 1945-1955, by Clymer


TRIUMPH TWINS & TRIPLES


FACTORY-ORIGINAL TRIUMPH TWINS, 1938-1962


TRIUMPH BONNEVILLE & TR6, by Timothy Remus


TRIUMPH MOTORCYCLES: FROM SPEED TWIN TO BONNEVILLE


TRIUMPH MOTORCYCLES: THEIR RENAISSANCE & THE HINKLEY FACTORY


TRIUMPH PRE-UNIT TWINS OWNERS WORKSHOP MANUAL


TRIUMPH THRUXTON BONNEVILLE 1959-1969


TRIUMPH MOTORCYCLES ILLUSTRATED WORKSHOP MANUAL 1937-1951, by Clymer


TURNER’S TRIUMPHS: EDWARD TURNER & HIS TRIUMPHS


TRIUMPH TWIN RESTORATION, by Roy Bacon


TRIUMPH TIGER CUB & TERRIER 1952-1968, Haynes Repair Manual


TRIUMPH 675 DAYTONA & SPEED TRIPLE REPAIR MANUAL 2006-2010, Haynes


CLASSIC MOTORCYCLES: TRIUMPH


TRIUMPH BONNEVILLE YEAR BY YEAR


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TRIUMPH RACING MOTORCYCLES IN AMERICA


TRIUMPH MOTORCYCLES


TRIUMPH, by Roy Bacon


TRIUMPH 750/900 TRIPLES & 1200 FOURS 1991-1999, Haynes Repair Manual


TRIUMPH TROPHY BIBLE


TRIUMPH DAYTONA, SPEED TRIPLE SPRINT & TIGER: 885/955 1997-2005, Haynes Repair Manual


BSA & TRIUMPH TRIPLES GOLD PORTFOLIO 1968-1976


TRIUMPH TRIDENT OWNERS WORKSHOP MANUAL, by Haynes


TRIUMPH: A CENTURY OF PASSION & POWER


TRIUMPH BONNEVILLE, by Osprey


TRIUMPH TIGER 100 & 110, 1939-1961, by Roy Bacon


TRIUMPH TIGER 100 & DAYTONA


TRIUMPH BONNEVILLE, by Crowood


TRIUMPH by Don Morley


TRIUMPH TRIPLES & FOURS 1991 & 2004


TRIUMPH 350 & 500 1957-1974 ESSENTIAL BUYERS GUIDE


BONNIE: THE DEVELOPMENT OF THE TRIUMPH BONNEVILLE


TRIUMPH SINGLES: EARLY DAYS TO 1974, by Roy Bacon


TRIUMPH: RETURN OF THE LEGEND


TRIUMPH FUEL INJECTED TRIPLES 1997-2000


BOOK OF TRIUMPH TWINS 1968-1969, by Floyd Clymer


THE TRIUMPH STORY: RACING & PRODUCTION MODELS 1902-PRESENT


TRIUMPH 350 & 500 TWINS 1958-1973, Haynes Repair Manual


TRIUMPH BONNEVILLE 2001-=2008 ROAD TEST PORTFOLIO


HINKLEY TRIPLES & FOURS


TRIUMPH PRE-UNIT TWINS


HINKLEY TRIUMPHS: THE FIRST GENERATION


TRIUMPH BONNEVILLE BIBLE: ALL MODELS 1959-1983


TRIUMPH TWENTY-ONE TO DAYTONA: C CLASS 350 & 500 TWINS


ORIGINAL TRIUMPH BONNEVILLE


TRIUMPH 650 & 750 TWINS


TRIUMPH MOTORCYCLES & CUSTOM BIKES


TRIUMPH MOTORCYCLES


TRIUMPH, THE LEGENDS SERIES


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TRIUMPH SPEED TWIN & THUNDERBIRD BIBLE


TRIUMPH BONNEVILLE T120/T140


TRIUMPH MOTORCYCLES FROM 1950-1983


TRIUMPH & BSA TRIPLES: THE COMPLETE STORY


TRIUMPH THUNDERBIRD, TROPHY & TIGER ESSENTIAL BUYERS GUIDE


TRIUMPH TIGER CUB BIBLE


ROAD RACING HISTORY OF THE TRIUMPH 500 UNIT TWIN


EDWARD TURNER: THE MAN BEHIND THE MOTORCYCLES


SAVE THE BONNEVILLE: THE INSIDE STORY OF THE MERIDEN WORKERS CO-OP


TRIUMPH DAYTONA 1991-2006 ROAD TEST PORTFOLIO


TRIUMPH DAYTONA 2003-2009 ROAD TEST PORTFOLIO


TRIUMPH TIGER 100 / DAYTONA: DEVELOPMENT HISTORY


TRIUMPH, by Daniel Gilpin


BOOK OF TRIUMPH MOTORCYCLES ILLUSTRATED SHOP MANUAL 1935-1939


TRIUMPH: THE RACING STORY


TRIUMPH BONNEVILLE T120 1959-1974, by Roy Bacon


TRIUMPH BONNEVILLE GOLD PORTFOLIO 1959-1983


TRIUMPH TRIDENT SUPER PROFILE


ILLUSTRATED TRIUMPH BUYERS GUIDE, by Roy Bacon






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