Theory of relativity

How would a 1906 Renault or a 1939 Mercedes fare against last year’s McLaren MP4-21? How would they relate to each other? Would a current car have as big a lap time advantage over the Merc as that car had over the Renault? This and similar questions about cars that never competed against each other can in fact be answered, with a reasonable degree of certainty, by the Pomeroy Index.

Devised by Laurence Pomeroy, engineer and motoring journalist, the index is a perspective device for comparing lap-time potential of grand prix cars from different eras. Starting with an index figure of 100 for the first grand prix-winning car, the 1906 Renault, he made comparisons only at tracks where grand prix cars ran on two consecutive years, to build the index figure for the next year. He repeated this process for each year. By the time we get to an index figure of 200 (the 1969 Lotus 49B) it means that in theory the Lotus could lap any given track in half the time of the ’06 Renault.

Pomeroy used his index to illustrate order-of-magnitude progress in the overall performance of the cars and it gave him a way of directly comparing performance of machines that never raced against each other.

The device cannot be 100 per cent scientific because it depends wholly on recorded lap time data and so takes no account of the subtler differences that could be at play other than car performance — such as differences in track surface, wind strength and direction, and driver performance. But the most obvious of these potential skewing factors — rain — can be discarded simply by not including any wet-weather data. Overall it does make for a very useful long-range device as long as you bear in mind that it is an approximation of the truth and don’t imbue each decimal point with undue significance.

Pomeroy took his index up to 1953, and in a continuation of Pomeroy’s work Leonard Setright extended it to 1966 in his book The Grand Prix Car 1954-66. Whereas Pomeroy had used race lap times, Setright preferred to use qualifying times. It’s relatively simple to continue the list to the present day, starting from where Setright left off. First work out the fastest car of any given year, using qualifying times to establish a super-grid where the pole time is assigned a value of 100 and where subsequent times are expressed as a percentage of that. For example, pole at the first championship race of ’67 was the Brabham BT20 at 1min 28.3sec. If we assign this time a value of 100, then the Honda RA273 at 1min 29.8sec gets a value of 101.699 for that race. Its time deficit of 1.5sec represents 1.699%. Do this for each car at each race, then average each car’s values out over a year to find the fastest.

Next, compile a list of tracks common to both this and the previous year (in this case 1966 and ’67) in unaltered form. Then compare the lap times of the overall fastest car of ’66 with that of ’67 at each track. In this case we would be comparing the times of the ’66 Ferrari 312 with the ’67 Lotus 49 at Monte Carlo, Spa, Zandvoort, Nürburgring, Monza, Watkins Glen and Mexico City. Using these stats we’d derive an average percentage difference between these two cars, and that would be added to the index figure of the ’66 car to give us a new index figure for the ’67 car. Repeat each year.

With a full up-to-date list, we can also rewind through time, giving a theoretical lap time of, say, a 1906 Renault or 1948 Alfetta around a current track. Using the Pomeroy Index, the fastest qualifying grand prix car to date is the Ferrari F2002 (because parc fermé qualifying rules in force since 2003 have effectively made the cars around 50kg heavier in qualifying, and aerodynamic restrictions in place since last year have further restricted things). That car qualified at Spa with a lap time of 1min 43.726sec. Using the Pomeroy Index we can say that theoretically the 1906 Renault would go around the same track in 4min 03.756sec.

Here then is the first 20-year instalment of the fastest cars of each year in a century of grand prix racing, with a ‘virtual’ lap time for the current Spa-Francorchamps circuit.

1906 Renault Index Figure:100 Virtual current Spa lap:4min 03.8sec

Its 13-litre, four-cylinder, side-valve engine gave 90bhp, enough for a maximum of 92 mph in third (top) gear. It was advanced in its use of shaft drive rather than the more commonplace chain. As with grand prix cars for the next eight years, there were brakes only on the rear wheels. Ferenc Szisz, the former riding mechanic of Louis Renault, used it to dominate the inaugural GP, at Le Mans.

1907 De Dietrich Index Figure:102 Virtual current Spa lap: 4min 01.7sec

Four-cylinder, side-valve, 17.3-litre engine produced 120bhp and drove through four gears. It complied with a regulated fuel-consumption limit of 30 litres/100km (9.41mpg). Even though Fiat won every major race in this year, the Lorraine-Dietrich was capable of lapping faster. Arthur Duray retired it from the lead of the French GP with gearbox failure.

1908 Mercedes index Figure:105.5 Virtual current Spa lap:3min 58.1sec

For the 1908 French GP, cars had to have a minimum weight of 1150kg, and four-cylinder engines such as this had a bore size limit of 155mm. The Merc’s 13.5-litre engine had side exhaust valves but overhead inlet valves, laying the groundwork for future full overhead valves and the resultant improvement in combustion chamber shape. It all made for 135bhp at 1400rpm. Christian Lautenschlager won the French GP with this car after a close fight with Victor Hemery’s Benz.

1912 Fiat S74 Index Figure:108 Virtual current Spa lap: 3mln 55.5sec

GP racing’s return saw an unrestricted formula. Fiat’s 14.1-litre, 190bhp motor featured an overhead cam and four valves for each of four cylinders, but the car was outmoded in retaining a big straight-profiled chassis and wooden fixed wheels with only the rims detachable, at a time when some rivals were saving pit time with fully detachable wire wheels. In the French GP David Bruce-Brown retired it from a close battle for victory with the more advanced but smaller twin-cam Peugeot.

1913 Peugeot Index Figure:109 Virtual current Spa lap: 3min 544sec

A stipulated regulation weight of 800-1100kg and a fuel consumption limit of 20 litres/100km (approx 14mpg) suited the previous year’s voiturette-inspired Peugeot double-overhead-cam 16-valve. Capacity was reduced from 7.6 to 5.6 litres. Despite 115bhp versus the previous year’s Fiat’s 190bhp, it was faster. Its lower weight and dropped chassis allowed for a lower C of G and less drag. It brought Georges Boillot a second consecutive French GP win.

1914 Mercedes Index Figure: 112 Virtual current Spa lap: 3min 51.3sec

This was built to comply with the first GP capacity limit, of 4.5 litres. Based on its aero-engine research, Mercedes built this four-cylinder, 16-valve, single OHC car (main picture) with an engine giving 115bhp at 2800rpm. It had a forged steel block encasing separate cast cylinders. Despite retaining just rear-wheel brakes at a time when the rival Peugeot featured four-wheel braking, the Mercedes had the edge in performance and handling and finished 1-2-3 in the French GP

1919 Ballot Index Figure:118.5 Virtual current Spa lap: 3min 44.6sec

Ballot’s very competitive 4.9-litre Indy car was used in road-racing trim in the Targa Florio, the only major European race of the year. Engine designer Ernest Henry, responsible for the GP-winning Peugeots, came up with a straight eight, still with his characteristic twin-cam, four-valves-per-cylinder head. The greater piston area of multi-cylinders had finally been exploited by resolving the strains imposed by the longer crankshaft. René Thomas lost the chance of winning the Targa when his Ballot broke its diff in the late stages; at Indy the car was on pole but suffered tyre troubles.

1920 Ballot Index Figure: 115 Virtual current Spa lap: 3min 48.2sec

A 3-litre version of the previous year’s DOHC, 32-valve straight eight, meeting the Indy regulations of that year. It had 107bhp at 3800rpm, aided by the innovation of light alloy pistons. There were no major European races. Ralph de Palma was denied a likely Indy victory by magneto failure.

1921 Duesenberg Index Figure: 116 Virtual current Spa lap: 3min 472sec

The relaunched grand prix series featured a 3-litre formula and 800kg minimum weight, in line with Indy. Accordingly Duesenberg travelled across the pond to compete — and won, courtesy of Jimmy Murphy. It was the first American victory in a GP, the first straight-eight-engined GP winner, and the first to feature hydraulically operated brakes. The high-revving 24-valve (two inlets per cylinder, one exhaust) engine developed its peak at around 4250rpm, aided by the innovation of high-tension coil ignition.

1922 Fiat 804 Index Figure: 111 Virtual current Spa lap: 3min 52.3sec

A further engine-size reduction to two litres meant performance had still not returned to 1919 levels. Fiat achieved the 2-litre capacity by taking two cylinders off the straight-eight 3-litre engine of the 801 that had appeared in the 1921 Italian GP. A twin-cam design but reversing the previous fashion for multi-valves, with just two widely splayed valves per cylinder, it produced 112 bhp at 5000rpm. The key was a very stiff forged steel block (rather than iron castings) and a multi-roller-bearing crank, the combination of which liberated high engine speeds. It was hugely influential. Felice Nazzaro took it to victory in France, while Pietro Bordino did the same in Italy.

1923 Fiat 805 Index Figure: 116 Virtual current Spa lap: 3min 47.2sec

The straight-six of the previous year had been a matter of expedience for Fiat. With time to do a more fully considered 2-litre they reverted to a straight-eight — and added a supercharger, the latter an idea copied from the 1922 Targa Florio Mercedes. The blower was not in constant engagement but was triggered by full throttle. The Fiats retired in France when their superchargers ingested stones. Carlo Salamano won with it at Monza.

1924 Sunbeam Index Figure: 121 Virtual current Spa lap: 3min 42.0sec

This was based on the GP-winning Fiat-copy Sunbeam design of the previous year (the first British car to win a GP, driven by Sir Henry Segrave). It was designed by ex-Fiat man Vincenzo Bertarione, but with the innovation of a supercharger after the carburettor, allowing lower intake temperatures into the cylinders and a considerable power boost. With some 138bhp at 5500rpm, this 2-litre straight-six was capable of almost 130mph. Electrical problems cost it victory in the French GP.

1925 Delage V12 Index Figure: 127.5 Virtual current Spa lap: 3min 35.2sec

The first successful V12-engined grand prix car, its 2-litre power unit was developed from that of its 1924 forebear by adding supercharging to produce 195bhp at 7000rpm — an almost astronomical rev figure for the time. Robert Benoist and Albert Divo shared victory in the 2LCV in France after Alfa-Romeo withdrew its P2s following Antonio Ascari’s fatal accident. Divo set the race’s fastest lap. Delages also finished 1-2-3 at San Sebastian.