MG TB

Full reference

MG TB specification and identification

The TB is the rarest T-Series by a wide margin and the one most often described from assumption. It was in production for less than six months, 379 were built, and its significance is not the body, which is essentially the TA's, but the engine underneath it. The TB introduced the XPAG, the unit that would go on to power the TC, the TD, the TF 1250 and the Y-Type. Because so little TB-specific factory literature appears to have been printed, TC data has migrated into TB specification tables across the internet, including on club pages, and this page tries to separate what is recorded from what has been borrowed.

• Specification →
• Chassis & engine numbers →
• Production figures →
• What to check →
• Parts & running costs →
• Values →
• Common questions →

Factory specification

No period road test of a TB has been found, and that is a finding rather than a gap in the search. Motor Sport's own cumulative road test indexes of July 1939 and March 1942 both list its MG Midget tests and neither includes a TB, and a 1942 Motor Sport article records a reluctance among manufacturers to submit cars to the press in the preceding years. The car had roughly four months of peacetime with the press before rationing began. The archive was not able to reach the Autocar or The Motor indexes for 1939, so whether either tested a TB is not established, and a reader holding a 1939 Autocar or Motor is invited to say so. What circulates instead should be treated carefully. The MG Owners' Club's TB page gives 87 mph and 0 to 60 in 22.7 seconds, but the same club's TC page gives 78 mph and 27.25 seconds for a car with the same engine, the same gearbox ratios, the same axle and a slightly wider body, and the 22.7 second figure is the one Wikipedia attributes to the TC. That looks like cross-contamination between pages rather than a measurement. One genuine period figure does exist: Motor Sport in July 1942 recorded the TB running 3,130 rpm and 1,860 ft per minute piston speed at 50 mph, against 2,930 rpm and 1,970 ft per minute for the TA. That is a real contemporary comparison, and it says more about what the engine change achieved than any top speed claim. On the 54.4 bhp at 5,200 rpm figure in the table above: the TB figure and the TC figure are the same figure, no located source distinguishes them, and it is likely that the TB number in circulation is the TC's output applied backwards. It is probably right, because the engines are essentially the same unit, but the archive would rather say that than imply an independent TB measurement. These are in any case 1939 manufacturer's figures, quoted gross on the engine with no agreed test standard behind them, and not comparable with modern outputs.

Chassis and engine number identification

Full number formats for every T-Type are set out in Chassis & Engine Number Identification, and the lookup procedure in Production Records.

Production figures

The 379 figure is not an estimate. It comes from the MG factory production records by way of John James in Totally T-Type 2, and it includes the 60 Tickford drophead coupés, so the open two seater total is 319. Two club-primary sources disagree by exactly one car at each end of the chassis range, the T Register publishing TB0252 to TB0630 and James's reading of the records implying TB0251 to TB0629. Both give 379 cars. The archive records both and does not pick between them. The Tickford cars sit inside the same chassis sequence rather than in a series of their own, which is confirmed by several individually documented cars. One correction worth making: production did not stop when war was declared on 3 September 1939. Eighty-four TBs were built after that date and the works ran on for another seven weeks.

What to check on a MG TB

• Read the chassis number, then check it against the factory record

  The number must begin TB and must fall roughly within TB0251 to TB0630. The single decisive check available to a private buyer is the MG Car Club T Register's searchable factory production records, which return the chassis number, the Production Car number, the original engine number, the production date and the Register's notes on later changes. The Register points out that these are a digital copy of the original paper records and have not been amended in the light of later information.

• Read the engine number, and know what it does and does not prove

  An XPAG numbered above 883 is a post-war unit. That does not mean the car is not a TB. The factory itself recorded engine changes, and given that the TB went straight from a six month production run into a war, a great many have been re-engined. The chassis number and the factory record determine what the car is. The engine number tells you only what is in it now.

• Check the body width across the seats

  A TC tub is about four inches wider than a TB's. Measured against a known TC this is a reliable check, and it is the one that separates the two cars when the engine has been changed.

• Expect a car that has been apart

  The TB was in production for under six months and then went into a war and a post-war period of extreme scarcity. Documented survivors include a car converted to a four seater and supercharged for racing, found decades later with a chassis that had been rolled at least three times, and a car rescued from a Glasgow scrapyard for about £30. A wholly original TB should be treated as the exception rather than the expectation. That is a reasoned inference from the documented cases rather than a counted statistic.

• Be alert to the substitution in both directions

  The TB is worth more than either neighbour, is outwardly identical to a TA and is mechanically almost identical to a TC, so the incentive is obvious. The archive found no published survey of how often it happens and will not assert a frequency. What it can say is that the chassis number, the factory record and the body width settle it, and that all three are available to a buyer before any money changes hands.

• Understand what you are buying into on parts

  See the note on parts below. The short version is that the TB sits across a parts boundary in a fortunate way, and the 379 figure is not the parts problem it looks like.

MG TB parts supply and running costs

Current suppliers and restorers are listed in the Specialists directory, and cars currently offered for sale in On the Market.

What a MG TB is worth

Source: Author analysis of published auction records (2025). Indicative ranges, not valuations, see the Values & Price Guide for condition definitions and caveats.

Common MG TB questions

What engine does the MG TB have?

The XPAG, of 1,250 cc, 66.5 mm bore by 90 mm stroke, a pushrod overhead valve four. The TB introduced it, replacing the TA's MPJG. Counter-intuitively the XPAG is the smaller engine of the two, by 42 cc. It is shorter in the stroke, larger in the bore and counterbalanced, which is what let peak engine speed rise from 4,800 to 5,250 rpm.

How many MG TBs were built?

379, from the factory production records rather than an estimate. That total includes the 60 Tickford drophead coupés, so 319 were open two seaters. Production ran from 1 May to 20 October 1939.

Is the TB the rarest T-Series?

Yes, by a wide margin. 379 were built against about 3,003 TAs, 10,001 TCs, 29,664 TDs and roughly 9,600 TFs. The reason is simply that it was in production for less than six months before the war ended it.

Did the war stop TB production?

It ended it, but not on the day war was declared. Britain declared war on 3 September 1939 and 84 TBs were built after that date, with the works running on until 20 October. The commonly repeated claim that production stopped on 3 September is wrong.

What is the difference between an MG TA and an MG TB?

Outwardly almost nothing, and mechanically a great deal. The TB has the XPAG engine where the TA has the MPJG, a Borg and Beck dry plate clutch where the TA has a cork insert clutch running in oil, synchromesh on second and third, and a 5.125 to 1 axle against the TA's 4.875 to 1. Hydraulic brakes are not a difference: the TA already had them.

What is the difference between an MG TB and an MG TC?

Chiefly the body. The TC tub is about four inches wider across the seats, though the chassis, wings and running boards were unchanged, so the car is not four inches wider overall. Mechanically the two are almost the same, with the TC block gaining a timing chain tensioner from engine XPAG/883 and changing casting number from 24001 to 24142.

What are the MG TB chassis numbers?

The T Register publishes TB0252 to TB0630. John James's reading of the factory production records implies TB0251 to TB0629. Both give 379 cars, and the archive records both rather than picking between them. Engine numbers run from XPAG/501; the end of the range is not published and is only inferred from the TC beginning at XPAG/883.

What is a TB Tickford?

A drophead coupé with a proper folding hood and wind-up windows, bodied by Salmons and Sons of Newport Pagnell under the Tickford name. Sixty were built out of the 379, and they sit inside the same chassis sequence as the open cars rather than in a series of their own.

How many MG TBs survive?

About 208 worldwide, roughly 55 per cent of production, of which somewhere between 64 and 84 are in the United Kingdom. That figure comes from John James in Totally T-Type 2.

What is an MG TB worth?

The archive does not publish a value band for the TB and does not think one can honestly be drawn. The number of publicly recorded sales is very small, they are spread across nearly twenty years, and they mix open two seaters with the rarer Tickford dropheads. Any band built from that would be arithmetic dressed up as knowledge. For a sense of the market rather than a valuation, see the values page.