The Performance of
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COMMER'S LATEST THREEJONNER
FOR several years the Commer three-tanner has been a wellknown medium-weight goods chassis. It is built 'on conventional lines and its four-cylindered engine has been designed to give a torque curve which makes it eminently suitable for goods transport, in that it will pull on main-road gradients without constant recourse to lower gears. At the end of last year Commer Cali, Ltd., of Luton, decided to extend the scope of this model by listing it in forward-control patterns, as well as in normal-control types, with different vvheelbases. This test report applies in particular to the GF3 model, which is the forwardcontrol machine, listed at £635 in chassis form with either an 11-ft. 11-in. or 12-ft. 11-in. wheelbase. At an extra charge, chassis can be supplied with wheelbases up to 15 ft. 6 ins. The body spaces on these 'chassis are 13 ft. 6 ins., 15 ft. and 20 ft. respectively ; therefore, it will be appreciated that a useful range of wheelbase lengths is offered.
' On the day of the test a brandnew chassis was handed over to us, , complete with metal weights to represent the pay-load and a normal body. The first step was to weigh the vehicle; the figures under the a26 various headings will be found in the accompanying panel. Making allowance for a body weighing 1 ton and a full recommended payload of 3 tons, it was found that there was a slight overload, but in order to keep the figures comparable with others in the seine class this overlOad has been segregated. The front axle weight was 2 tons 7i cwt., whilst that on the rear axle was 4 tons 18-.1cwt. This means_ that the load on the six tyres was, within reasonable limits, equaL The chassis in question was the 12-ft. 11-in, wheelbase model.
On the road the first 'test was for speedometer accuracy, and the average error was discovered to be 6 per cent. below the true reading; therefore, figures throughout this article have been duly amended.
Fuel consumption was the first specific trial. The setting of the Solex MOVL carburetter was: choke 28, main jet 130, pilot 75. The special test tank was filled with measured quantities of No. 3 commercial spirit, and the first run was taken over the Luton-Pedford road, against the wind. The distance covered on a measured gallon was 10.05 miles.. The top-gear ability of the COrnmer was sufficient to avoid any need for use of the indirect gears on this run, despite its overload. When the gallon of fuel had been' expended the main tank was connected to the carburetter and the vehicle driven to a convenient turning point, after which the float long rise when nearing Luton demanded third gear for .7 of a mile.
Taking the average of these two runs, the fuel consumption rate works out at 10.58 m.p.g., and the average speed for the two trips was 25.1 m.p.h. This result is a good average figure, particularly bearing in mind the high speed which the vehicle put up. Amplified details of this test will be found in t h e accompanying panel.
Sharpenhoe Hill
Was used for the climbing test. On the day in question it was in its most difficult condition, on account of an almost continuous . downpour of rain, which increased the tractive resistance of the gradient. • The start of the climb was on top gear, and it was on the lower reaches of this hill that the marked pulling power of the engine showed to 'its best advantage.
It is interesting to note the torque curve of this engine. At 2,000 r.p.m. it gives approximately 2,000 in.-lb.,' at 1,500 r.p.m. it has risen to about 2,200 in.-lb., and to 2,310 in.-lb. at 900 r.p.m.
The stiffer portions of this
gradient cover about half a mile, but it was necessary to use only first and second gears for .4 mile. With a brand-new engine running at fairly high speeds on the indirect.. gears it might be expected that the cooling Would suffer. At the beginning of the _climb the water temperature a s 128 degrees F.,. the radiator not being blanked off in any way. At the top of Sharpenhoe -Hill another check was made, and tile, temperature was found to be 172 degree F. If a new engine. can give such
a good result as this, there is no reason to doubt that, when fully run-in, the GE3 Commer would have a sufficient cooling margin to permit its use in any circumstances without risk of boiling the water.
As regards the choice of gear ratios, the 28.41-to-1 first gear proved more than ample to deal with the stop-and-restart test on 1 in 6. Normally, second gear (17.28 to 1) proved sufficiently low to enable starts to be made on a level road without undue slipping of the clutch. The ratios were well graded and either upward or downward changes were made easily. It is not easy accidentally to lift the
reverse catch, and the range of travel of the lever was convenient without being excessive. A light pressure on the pedal sufficed to free the clutch, and for smooth take-up, silence and freedom when changing gear it was satisfactory in every way.
As regards steering, the wheel was found to be of a convenient size. The reduction gear allowed 2.2/3 turns of the steering wheel from full right lock to full left lock. This amount was found to be satisfactory for a vehicle of the weight and size in question. Over bumpy roads there was no appreciable "kick" at the wheel, and the castor action was sufficient to relieve the driver of the need for the expenditure of much effort in straightening up after a corner, it merely being necessary to check the wheel. On the other hand, there was no pull on the wheel which might be regarded as disconcerting.
Reference to one of the accompanying graphs shows the accelera tive abilities of the Commer GF3 model. The acceleration on top gear from 10 m.p.h. to 30 m.p.h. in 25 seconds is a good indication of
the choice of a suitable rear-axle ratio. In the case of the vehicle tested, this was 6.4 to 1, but the
maker offers an optional figure of 5.8 to 1.
Acceleration from rest to 30 rn.p,h., using second, third and fourth gears, proved satisfactory. The actual figures comply with the average for vehicles of this class, but the engine gives a top-gear performance appreciably above the average for its size. It may be said, therefore, that, whilst the performance, using the gears, does not suffer, the ability of the vehicle on direct gear is better than the normal for a three-tonner. The fact that constant recourse to the lower gears can be avoided is appreciated by both operator and driver ; for the former it means reduced maintenance costs and for the latter reduced fatigue.
With regard to braking, trials were carried out on a first-class level road, the surface being of the tarmac order and sufficiently rough to ensure a good wheel-grip. The hand brake was smooth in action, safe on a gradient of 1 in 6 when used as a parking brake, and gave gradual retardation, when used alone to stop the vehicle from speeds up to 30 m.p.h. The foot brake, on the other hand, acting on the transmission, took effect rapidly, sad could be made to lock the wheels if sufficient power were applied. It was found advisable to use the hand brake on long descents, applying the foot brake momentarily for additional checking.
Tests were carried out with each brake independently and then using them in conjunction. It was found that the figures obtained with the two brakes were almost identical with those when using only the transmission brake; in other words, the standard of efficiency displayed by the foot brake was the limiting factor. Neither brake caused the vehicle to deviate from its true course, unless one of the rear wheels struck a patch of tar. So far as it is possible to make a vehicle free from skidding when braking, this has been done in the case of the Commer GF3. Both systems proved easy to adjust, free from noise and "grabbing."
A minor point is the grouping of the instruments upon an aluminium " board " below the steering wheel. It makes the dials and switches easily visible and avoids their connections being disturbed. Summarizing our impressions of the Commer GF3, we found that it had a good all-round performance, whilst the capabilities on top gear were considerably above the average. Its control was easy, its braking safe, cooling was good, the fuelconsumption return satisfactory and the weight was the average for a vehicle of its pay-load capacity.