Triumph TR4 Commission Number Plate
Every TR4 and TR4A carries its identity on a small plate in the engine compartment: a commission number whose prefix tells the version and whose place in the series dates the car. How to read it, with the body and engine numbers, and what else tells a TR4 from a TR4A.
About the pictureThe TR4's bonnet badge, not a commission plate
Triumph called a car's chassis number its commission number. On a TR4 or TR4A it is stamped on a small plate under the bonnet (hood), together with codes for the car's specification, and it is the number to check first: against the registration papers, against the body and engine numbers, and against the factory's build records, which the British Motor Museum at Gaydon holds and from which it issues a Heritage Certificate giving a car's build date, colour and market. This page explains how to read the numbers and what they say about a car's version and year.source 1source 2source 3
Reading the plate
Every TR4 has the prefix CT, from CT1 to CT40304. The TR4A with independent rear suspension has CTC, from CTC50001; the live-axle TR4As built for North America have CT again, from CT50001, in the same run of numbers:
Rigid rear US cars still had the prefix 'CT' but were numbered in sequence with the 'CTC' cars.
| Mark | Where | Meaning |
|---|---|---|
| CT | Prefix of the commission number | A TR4; from CT50001, a live-axle TR4A |
| CTC | Prefix of the commission number | A TR4A with independent rear suspension |
| ICTC | Prefix of the commission number | A TR4A assembled from a kit in Belgium |
| L | Suffix of the commission number | Left-hand drive |
| O | Suffix of the commission number | Overdrive, by the Vintage Triumph Register's reading |
| Number then CT | Body number, as 15076CT | The body, on its own smaller plate |
| CT then number then E | Engine number | The engine |
| CTA | Prefix of the engine number | The 2-litre engine, with smaller liners, by the Vintage Triumph Register's reading |
| FRE | Suffix of the engine number | An engine rebuilt by the factory |
On a TR4 the commission plate is on the left of the engine compartment, in front of the bulkhead; on a TR4A it is riveted to the bulkhead on the side of the spark plugs. Besides the number, the Vintage Triumph Register says, it gives the car's gross laden weight in pounds and, from some time in 1963, its paint and trim codes. The body number, on a smaller plate on the right of the engine compartment, is usually within a hundred or so of the commission number, but rarely the same. The engine number, stamped on the left of the block near the coil, follows a series of its own, partly because the same engines went to Morgan and other makers.
In Britain the commission number appears on the registration document as the car's VIN. The TR Register advises checking that the two match, and then asking a club registrar to help authenticate the car from its engine and body numbers.source 2source 1source 4source 5source 6source 7source 8source 9
CT40304
- CTThe prefix: a TR4, or, from CT50001, a TR4A with the live axle
- 40304The serial: on this car, the last TR4 built
Year breaks
Rimmer's dates are calendar years, but the catalogue also heads each year with a model year, and the two can differ: a TR4 built in 1961 is filed under the 1962 model year, and a TR4A built in 1967 under the 1966 one. The Vintage Triumph Register, after Piggott, gives the first number of each calendar year, and Revington TR an approximate break. None of the three counts cars, only the numbers given out.
| Year of build | TR4, by Rimmer | First, by the Vintage Triumph Register | Revington TR, approximately |
|---|---|---|---|
| 1961 | CT1 (18 July) to CT2648 | CT1 | CT1 to about CT2470 |
| 1962 | CT2649 to CT18604 | CT2649 | About CT2471 to CT18403 |
| 1963 | CT18605 to CT28708 | CT18605, "not verifiable" | About CT18404 to CT28485 |
| 1964 | CT28709 to CT40192 | CT28709 | About CT28486 to CT40000 |
| 1965 | CT40193 to CT40304 (6 January) | CT40193 | About CT40001 to CT40304 |
| Year of build | TR4A, by Rimmer | First, by the Vintage Triumph Register | Revington TR, approximately |
|---|---|---|---|
| 1965 | CTC50006 (5 January) to CTC64147 | CTC50001 | CTC50001 to about CTC63736 |
| 1966 | CTC64148 to CTC75171 | CTC64148 | About CTC63737 to CTC75000 |
| 1967 | CTC75172 to CTC78687; CTC78684, built on 11 July, was the last | CTC75172 | About CTC75001 to CTC78684 |
Two points differ. The Vintage Triumph Register's own table dates CT1 to 7 July 1961, against 18 July in its text and in Rimmer's list; and Rimmer's first TR4A built is CTC50006, on 5 January 1965, where the Register and Revington TR start the TR4A at CTC50001.
In the United States many cars were titled in the year they were sold, not the year they were built, and some importers added a plate with the year of sale. The Vintage Triumph Register is firm about which counts:
Present-day Triumph enthusiasts agree that the 'model year' is the year in which the car was built – no matter what the license or title says.
Telling a TR4 from a TR4A
The lamps tell the two cars apart from a distance, and the table sets out the other points to check.
| Look at | TR4 | TR4A |
|---|---|---|
| Grille | Stamped, carrying the sidelamps and flashers | Extruded aluminium bars |
| Flanks | No chrome strip | A chrome strip along wing (fender) and door, led by the wing lamp |
| Badges | TR4 on the bonnet and the boot (trunk) | The Triumph globe on the bonnet; TR4A on the boot, and IRS on cars that have it |
| Dashboard | Painted on early cars, walnut on later ones | Walnut |
| Handbrake | A fly-off lever beside the transmission tunnel | On the tunnel, between the seats |
| Hood (soft top) | A frame built into the car, with many fasteners | Folds away behind the seats under a cover |
| Commission number | CT | CTC, or CT from 50001 on live-axle cars |
Parts move between cars, too: the Vintage Triumph Register has seen TR4A body panels on a TR4 frame, so the commission number, not the trim, decides.
Change points useful for dating
Within a version, some details date a car more closely; the TR4 page and the TR4A page give the full lists. On a TR4, the longer bulge on the bonnet arrived at CT6429, flat-glass instruments at CT11308, the level steering rack at CT16350 (CT16463 with wire wheels) and the definitive seats from body 15076CT. Zenith-Stromberg carburettors took over from the SUs during 1963, on a first batch from CT16801 and generally from CT23594, by the TR Drivers' Club's account, or from engine CT21471E, by the German TR Register's. On a TR4A, SUs returned from CTC62191 or CTC61291, as the sources differ, and live-axle cars had a single cross-box silencer from about CT70000.source 10source 8source 12source 4source 6
Production
Production: how far the sources agree
- 40253, home 2,592; export 37,661
- One good source.
Sources
Every source the site cites is on the sources page.
- Primarymade at the time, by the maker or by people who were there
- Referenceserious later work: clubs, specialists, magazines, books
- Arthur Kelly (the VTR's TR4 consultant), "TR4": "A Historical Overview of the TR4" and the TR4 commission-number page, Vintage Triumph Register, Production Dates and Numbers; the commission plate; the plate's position and contents; the suffixes; the body and engine numbers; FRE; engines for Morgan; the first numbers of each year, after Piggott; "Jul 7, 1961"; titling by year of sale; the STC plates; Kelly on the model year; the TR4's features; walnut fitted to earlier cars since. vintagetriumphregister.org/tr4 Reference
- Graham Robson (essay "15 Years of Evolution"), Triumph TR2 – TR3/3A, TR4/4A – TR5, TR250 1953–1968 Parts & Accessories Catalogue, Rimmer Bros, edn 2.1 (source code TR2512), Part 1, p. 7, "Vehicle Identification – All Models"; p. 7, CT40304 on 6 January 1965; p. 7, the dated number list, by calendar year with model-year labels; p. 6, "TR Production Figures: 1953 to 1968". rimmerbros.com/images/PDFs/TR2-5_Part1.pdf Reference
- British Motor Museum (BMIHT), "Heritage Certificates", Heritage Certificates from the build records. britishmotormuseum.co.uk/archive/heritage-certificates Primary
- Vintage Triumph Register, "TR4A" (history, change points and yearly output, buyer's and spotter's guides, numbering), the TR4A plate on the bulkhead; CTC; the CT cars "numbered in sequence"; ICTC; CTA; the TR4A's first numbers by year; spotter's guide; TR4A panels on a TR4 frame; CTC62191. vintagetriumphregister.org/tr4a Reference
- Goodwood Classic Solutions, "Buyer's guide: Triumph TR4", 1 Nov 2024, the L suffix; painted dashboards; walnut on converted cars. insurance.goodwood.com/buyers-guide/triumph-tr4-2 Reference
- Revington TR, "TR4A: Technical Specification Change Points", CT50001; approximate year breaks; CTC61291; the cross-box exhaust from about CT70000. revingtontr.com/the-tr-series/tr4a/technical-specification-change-points Reference
- TR Drivers Club, "Early Cars: The TR4A", the CT and CTC prefixes; the TR4A's grille, lamps, strip, badges, dashboard, handbrake and hood. trdrivers.com/earlycars/tr4A.html Reference
- TR Drivers Club, "Triumph TR4", body 15076CT; body 15076CT; the Stromberg change. trdrivers.com/articles21/triumphtr4.html Reference
- TR Register, "Buyer Beware: TR6" (2 pp. PDF leaflet), p. 2, the V5 and the club registrar. tr-register.co.uk/storage/Pages/tr6-buyer-beware.pdf Reference
- Revington TR, "TR4: Technical Specification Change Points", approximate year breaks; CT6429, CT11308, CT16350/CT16463, CT16801. revingtontr.com/the-tr-series/tr4/technical-specification-change-points Reference
- Aaron Severson, "Grandfather's Ax: The Many Evolutions of the Triumph TR4, Part 1: TR4 and TR4A", Ate Up With Motor, 22 Oct 2012, the TR4A's changes. ateupwithmotor.com/model-histories/triumph-tr4-tr4a/view-all Reference
- Bruno Dwinger, "Geschichte, Typenkunde und Kaufberatung: Standard-Triumph TR4, TR5/TR250 – 'die Michelotti Autos'", TR-Register Deutschland, 2009, 13 pp. (PDF), engine CT21471E. tr-register.de/wp-content/uploads/2025/08/Kaufberatung-TR4-und-TR5-und-TR250.pdf Reference
- TR Register, "Triumph TR4 / TR4A Buyers Guide", TR4 model summary. tr-register.co.uk/resources/buyers-guide/triumph-tr4-4a Reference