Thornycroft recognised the importance of good publicity from winning competitive events, and the firm's cars successfully took part in several. For instance a 20hp car won a gold medal in the 1904 Scottish Automobile Club Reliability Trials, and a 24hp car made the fastest time of any car entered in the 1905 Aston Hill Climb. Thornycroft cars were regular competitors in the TT races from 1905 to 1908, and the firm's TT cars are described below:
1905 TT car
A new 14hp car with a strikingly modern engine specification, introduced during the summer, was entered for the 1905 TT Race. Notable features of the car's water-cooled straight "four" included square cylinder dimensions (3.75 x 3.75ins/95.3 x 95.3mm), a one-piece cylinder block, a single overhead camshaft and a five-bearing crankshaft at a time when three bearings were considered reasonable. But there the sophistication ended, because an LT magneto ignition system was fitted, with the make-and-break mechanism operating inside the cylinder! Although crude by modern standards, LT ignition was commonly used at the time. An HT coil ignition system was optional with a camshaft-driven distributor. The 2,715cc 14hp engine was relatively small for its time and, surprisingly, ran at a normal speed of only 900rpm, no faster than Thornycroft's more prosaic side-valve engines.
The 14hp's crankshaft was machined from a steel billet and, with its machined finish and ground bearing surfaces, the crankshaft must have been a work of art. Con rods were of forged-steel, and, in keeping with contemporary practice before the days of aluminium pistons, cast iron pistons were used. A cooling-water circulation pump and a single gravity-fed carburettor were fitted. There was forced lubrication by a gear-driven oil pump, which was a major improvement over earlier cars' splash lubrication.
The three-speed gearbox had a direct-drive top, and, as usual with Thornycroft cars, a prop shaft took the drive to the back axle via an axle mounted differential. Back axle wind-up was controlled by two radius rods running from the chassis cross member to the top and bottom of the differential, respectively. The transmission brake, fitted just behind the gearbox, was operated by a foot pedal, while a hand brake operated the rear-wheel brake drums. True to its time, the car had no front-wheel brakes. Beam axles front and rear were attached to the pressed steel chassis through semi-elliptic springs.
The TT Race took place on 14 September. Course distance was 208.5 miles (335.5km), there were 48 entrants, and each competing car was allowed a limited and identical supply of petrol, enough, in the opinion of the judges, to cover the full course at a reasonable speed. Two 14hp Thornycrofts participated as cars no. 12 and 47 and were entered, respectively, by Tom Thornycroft and G V Baxendale. Speeds in each gear for the Thornycrofts were 7.5, 19.25 and 31.75mph (12.1, 31 and 51.1kph) respectively, at 900rpm. This put the Thornycrofts among the slower cars, the fastest of which were the two 20hp Rolls-Royces geared to do 45.5mph (73.2km) at 1,000rpm. John Napier won the race in his 18hp Arrol-Johnston.
The list of cars entered is a golden who's who of names from past and present, including Argyll, Cadillac, Clément, Daimler, Darracq, Dennis, Humber, Maudslay, Minerva, Napier, Rolls-Royce, Rover, Siddeley, Vauxhall, White and Wolseley, among others. Many of the cars entered were standard models, most had four cylinders, there we no "sixes" and the two Whites had double-acting compound steam engines!
1906 TT car
An sohc 14hp car similar to that introduced the previous year was entered for the 1906 TT Race, updated with HT magneto ignition instead of its predecessor's LT system. In addition, the car had an all-indirect four-speed gear box instead of 1905's three-speeder. Driven by Tom Thornycroft, the 1906 car was faster than the 1905 cars, and normal engine speed had risen to 1,000rpm, giving corresponding speeds in the gears of 9.95, 17.3, 27.7 and 38.8mph (16, 27.8, 44.6 and 62.4kph). However, the car suffered from pre-ignition problems, and no less than 14 spark plugs failed during the race! The race took place on 27 September and was won by C S Rolls driving a Rolls-Royce Light Twenty.
1907 TT car
Driven by Tom Thornycroft, a 14hp car was entered for the TT Race as car no. 10. Powered by the same 2,715cc sohc engine used in previous TT Races, this car was a small-engined participant and reportedly ran well during pre-race trials round the course. Changes from the previous year's car included dual ignition comprising an HT magneto and an HT coil, a lower compression ratio to combat pre-ignition problems of 1906, and a change of wheelbase to conform to revised regulations. Not much is known of the 14hp car's showing in the race, which was won by Ernest Courtis' Rover.
Thornycroft's other TT contender for 1907 was the new 30hp car driven by H Niblett, entered for the Heavy Touring Car Race. The car had a large 5,213cc four-cylinder, water-cooled, T-head engine. Cylinders were cast in pairs in the usual Thornycroft way, and ignition was by HT magneto. The transmission followed established Thornycroft practice, with drive taken from a three-speed gearbox to the back axle by a prop shaft and differential.
In common with the nine other entrants in the Heavy Touring Car Race, the 30hp car was fitted with a wooden airbrake of about 24ft2 (2.23m2) to give the equivalent air resistance of a limousine body! Internal expanding brakes, with cast iron blocks working in pressed steel drums, were fitted to the rear wheels and transmission, and suspension was by semi-elliptic springs at the front and three-quarter elliptics at the back. The 30hp car ran out of its petrol allowance before the finish, and the Heavy Touring Car Race was won by G P Mills driving a 30hp Beeston-Humber.
1908 four-inch TT car
In order to foster the design of realistic competitive cars with benefits which could be read across to production cars, the 1908 TT regulations limited the RAC rating to 25.6hp, resulting in a maximum cylinder bore of 4ins (101.6mm) for four-cylinder cars, hence the so-called four-inch cars. Other requirements were a minimum of four cylinders, a minimum weight of 1,600lb (725.8kg), and a crew of two comprising a driver and mechanic both of whom had to carry out all repairs using spares and tools carried on-board, as no outside help was allowed. Course distance was 337.5 miles (543km).
For the 1908 TT Race, Thornycroft dispensed with the advanced, but small-engined 14hp used in previous TT events and, instead, fielded a more powerful 4,119cc car, albeit with a less sophisticated ioe engine. The four cylinders were cast in pairs, valve diameter was 2.25ins (5.72cm), and bore and stroke were 4 and 5ins (101.6 and 127mm), respectively.
Where the 1908 engine differed markedly from previous Thornycroft practice was in its high 2,000rpm speed - about twice that of other Thornycroft engines, and the new engine developed 46bhp so it was relatively highly tuned. Other features of the car included dual ignition by a Simms HT magneto and HT coil, a cooling-water circulation pump, Rudge-Whitworth detachable wire wheels, Dunlop tyres, and the usual Thornycroft rear-wheel drive. Internal expanding metal-to-metal brakes were used, and petrol was supplied from a pressurised tank behind the driver's seat. An interesting feature was the interconnection between throttle and HT magneto timing gear; the parallel coil ignition system had manual timing control.
Three Thornycroft four-inch racing cars, all painted light green, were built to compete with 36 other entrants in the 1908 TT, one car had a four-speed all-indirect gearbox, and the other two cars had three-speed boxes with direct top. Tom Thornycroft entered the four-speed car no. 35, while the two three-speeders, nos. 9 and 22, were entered by G V Baxendale and D S Hodge, respectively.
One of the three cars was withdrawn from the TT after being involved in a collision before the event. According to post-race accounts, Baxendale took no part in the event, Tom Thornycroft came fifth at an average speed of 44.1mph (71kph) in car no. 9 (the car entered by Baxendale), and Hodge came tenth in car no. 22, the car he entered. Evidently, Tom Thornycroft took over Baxendale's car, so the car involved in the pre-race collision may have been Tom Thornycroft's car no. 35. The winner was W Watson in a Hutton entered by S F Edge, but just to finish the race was an achievement when no less than 24 of the 34 cars on the starting grid either failed to finish or were unclassified.
The Thornycroft sales register links Baxendale and Hodge with vehicle nos. 801 and 802, respectively. Although the TT was held on 24 September, the delivery date of both these cars is given in the register as the 30th! The other four-inch car in the register (vehicle no. 580) may have been car no. 35 entered by Tom Thornycroft, assumed to have been withdrawn from the race. The car is registered as having been delivered to an H G Pelissier on an unspecified date, so perhaps H G Pelissier bought the damaged, or repaired car from the Thornycroft company after the TT.