MOTORS & MOTORING

Dominion, Volume 14, Issue 176, 21 April 1921, Page 9

MOTORS & MOTORING

(By

"Clutch.”)

Tendencies of Motor Cycle Design. The general tendencies of motor cycle design find the popularity of different features and fittings could be followed more or less accurately by noting the numbers of each which appeared at the recent Olympia Show in London. The "Overseas Daily Mail” states that the four-stroke engine still retain its pride of place toy being fitted to no less than 80 per cent, of the machines shown, but when small engines only are considered — i.e., up to 2i-h.p.—the two-stroke has crept up from 20 per cent, to 45 per cent. In spite of the excellent engines which can be bought by the trade no less than 62 per cent, of manufacturers fit engines of their own make. Nondetachable heads are still in the majority and number 76 per cent, of the whole. In the matter of crankshaft bearings 45 per cent, are plain, 36 per cent, ball, 13 per cent, roller, and 6 per cent, a combination of ball and plain. The valves are situated at the side in 68 per cent, of cases, overhead in 6 per cent., and inlet over exhaust in the same number, while the two-strokes numbering 20 per cent, are, of course, valveless. Only 2 per cent, of the pistons are constructed of (in aluminium alloy, the rest being of cast-iron, and 81 per - cent, of the gudgeon are fixed in the piston, 15 pcs cent, to the connecting rod, and 4 per ce>< are flouting—i.e., loose in both. Plate clutches number 95 per cent, of the whole, and 90 per cent, of these are lined with Fcrodo, 86 per cent, of them being controlled by the hand, 14 per cent, by the foot. The numta of different speeds are as follows: —1, 7 per cent.; 2, 32 per cent.; 3 or more, 54 per cent.; and variable pulleys, 7 per cent. In the matter of transmission the chain is gradually proving its worth, and is to be found entirely on 40 per cent, of the machines, chain and belt on 48 per cent., all-belt drive on 12 per cent. In spite of their great advantages spring frames are only found in 10 per cent, of cases. This shows that the springing problem is not so simple as some people think, and that an excellent compromise can be obtained by the use of large tyres and a * well sprung saddle. Interchangeable wheels are to be seen on 15 per cent, of machines. The front rim brake is dying very slowly, although it is hard to find any motor cyclist who has a good word for it, and 'it is still fitted to no less than 76 per cent, of modern motor cycles. In the rear the belt rim brake, which has amply justified its introduction, is still most popular, and it has a place on 50 pel - cent, of machines. The internal expanding brake is fitted in 25 per cent, of cases. ' • i

Undertyring a Bad Policy. It is bad policy to undertyre any motor vehicle, for unduly small tyres wear out with gnat rapidity; and replacements are too frequently necessary. As to the (■•'.st of ’imlertyri .g (ter- are two opinions. Tyre manufacturers sometimes maintain that chassis manufacturers are mainly to 'blame, but the chassis manufacturer is driven to adopt a certain policy by reason of the demands of his clients. If 'he has to cut down his total price to a figure which is really too low he, naturally skimps the fittings and accessories which he does not make rather than the portions of the vehicle for which he is immediately and beyond doubt responsible. Thus he is induced to fit irululv sma’l iyr s in some ca-es to advise that they should be large enough. Undertyring is bad enough in a country like England; it is infinitely worse In countries where the heat is greater and the roads of worse quality. A great deal of heat must always be generated where the tyre rubs upon the road. The smaller the tyre the higher ths temperature rises in a given set of conditions. When the temperature increases beyond a certain point the nature of the tyre begins to suffer. It is not only a matter of more rapid wear of tyres due to a higher intensity of load on that portion of a tyre of narrower section which is in contact with the road, but also of the additional fact that in respect of temperature the load is carried under less favourable conditions,

Steam, Electricity, or Petrol? The electiric, petrol, and steam-pro-pelled vehicles nre about to enter on a struggle for supremacy in the road transport world (says a writer in an English paper). As far as development has gone at present it would appear that the electric vehicle is the . one for short journeys where frequent stopping is necessary and where the load to be carried is of no great weight, say not more than 15cwt. to one. ton. Under similar conditions, but for heavier loads the steam vehicle is. the ideal and'before going further, a word may perhaps be devoted to the meaning of frequent stopping and starting. One is apt to look upon frequent stopping and starting as only necessary when one is making numerous calls on a given trip. 1 his attitude, however, is apt to be misleading, encouraging one, as it does, to ignore such considerations as the traffic that is to be negotiated in one’s usual round. From a point of via,w of the vehicle it does not matter whether a stop is to be for delivery or collection of a load or through a traffic block. Consequently, where the area to be tiaversed is one in which traffic is thick the electric and steam vehicles score to advantage over their internal combustion engined rivals. The latter is the only one of the three that normally wastes fuel or Its equivalent when standing still for a temporary stop. AVhere the internal combustion engine scores' over either of its rivals and whore, so far as present knowledge goes, it would appear likely to remain supreme, is in delivery over long distances where speed is ot consideration. The road vehicle ed bv steam or electricity, that can co pare' with a petrol vehicle for speed | )nfi vet to make its appearance. It Mt unfortunate that the parrying capacitj c f the petrol vehicle is somewhat 1 muted by constructional considerations, but there are sure signs that is likely to be overcome n the not very distant future.

Lighting-up time: To-day, 5.13 p.m Next Thursday, 5.3 p.m.