Germany Facing a Tyre Famine
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Enforcement of Lower Speed Limits, Smaller Tyres and Twin Front-wheel Equipment Among Measures to Combat Rubber Shortage
HOW serious is the effect of our blockade on the German rubber position is shown by the drastic steps that are being taken to keep down tyre consumption. Private cars are allowed for only the most urgent needs, apart from military purposes. All other cars have to be jacked up, the tyres being the first item to be confiscated, and batteries and other accessories are likely to follow.
Commercial vehicles are converted to operate on producer gas or fluid or compressed gases and under these conditions are allowed to continue fulfilling their services. However, the tyre famine sets limits to speed and performance which, during the past few months, have become notably severe. These limits hinder the economical use DI the vehicles extremely.
Measures to Save Money The following account will give an impression of how badly off our enemy is in this respect, and the reader may learn from it and think how similar measures could be adopted in this country to save money, labour and shipping space for the requirements of war.
For tyres of sizes from 7.5-20 to 9.75-21 (usual for commercial vehicles), or tyres of similar load capacities, according to a new order, speeds exceeding 25 m.p.h. are not allowed. Vehicles with larger tyres are forbidden to travel above 17.5 m.p.h. Goods machines which are equipped with these tyres and cari attain higher speeds must be provided with devices which limit the speed, and they must bear on their sides speed-limit plates; the same applies to trailers. This regulation does not apply to buses and their trailers with tyres above the size of 9.75-24, if used exclusively on fixed routes and running to a time schedule that does not necessitate a higher continuous speed than 17.5 m.p.h.
According to tables published by leading tyre companies, the load capacity of a tyre can be increased with -reduced speed; a common factor is -10 per cent. for a 12.5 m.p.h. speed difference. On the other hand, for the same load, the stress on the tyre is reduced in the same ratio. For instance, a commercial vehicle, which used to run at 50 m.p.h. and is now compelled to travel at only 25 m.p.h., will obtain a saving in tyres of about 20 per cent. Against this the vehicle can make only half the journey in the same time; thus the economical use of the vehicle is considerably reduced.
Among devices allowed for speed -regulation are centrifugal governors, restrictions of the inlet pipe and locking devices in the gearbox to prevent theengagement of the highest gears. Circular white plates must be provided on both sides of the vehicle indicating its highest permissible speed.
A Cause of Premature Wear In a recently issued decree, relating to the saving of tyres, it is stated that wheels not running true will cause premature tyre wear. If this can be traced to bent discs or shafts, the defects must be immediately repaired. Retreading of worn tyres is recommended both in the interest of safety and on economic grounds. If the tyre tread be worn so that the canvas is visible, the oWner is asked by the police • to have the tyres retreaded. By these means the full utilization of the material (mostly of foreign origin) incorporated in the tyres should be guaranteed,
A new introduction, by HenschelWerke, is the application of twin tyres for the front wheels of commercial vehicles. Of course, the steering, as a result, becomes materially heavier, and, in the bigger classes a servo-mechanism is imperative. It is claimed that the scheme 'gives greater safety at high speeds, but -the real reason for advocating this measure seems again to be the tyre famine. Big tyres are difficult to obtain, so twin tyres of considerably smaller size are used instead. This is shown by the following comparison between alternative tyre-equipment for a 60-seater bus:—
What Twin Equipment Saves Six 12 by 22 tyres weigh 1,525 lb., whilst the weight of eight 8.25 by 20
• tyres is 850.1b. Using the latter, therefore, represents a gain of 44 per cent. In the two cases respectively, the rims weigh 906 lb. and 620 lb., so there is a saving here of 32 per cent. In terms of value, the advantage is 46 per cent., the total cost for the six large tyres being-about £310. and for the eight smaller one £168, Rt being taken as the equivalent of 12 R.M.
A further advantage claimed for twin front tyres is that the floor height of buses is reduced. With such equipment long trials—extending over four years—have been carried out, including strenuous and • rough driving. The vehicle in question had Bosch servosteering apparatus, which, when produced in larger series, would cost about 600 to 700 R.M. (£50 .to A57). This device has proved itself to be of advantage, but for vehicles below 41 tons pay-load, the auxiliary steering device can be dispensed with provided that the steering gear ratio be lowered.
. The result of other tests on a 13tanner, which was fully laden throughout the trials, was that one set of tyres was run on the outsides of the wheels for 31,000 miles and then lasted for another 22,000 miles On the insides.