Wheels and Tyres

WHEELS are fitted to the hubs by various methods, but the most popular method consists of a ring of equally spaced studs set in the flange of the hub. These studs correspond with holes in the wheel plate and the wheel is secured to the studs by special nuts. The bevel edges of the nuts fit into the countersunk faces of the holes in the wheel thus preventing any movement of the wheel on the studs or slackening of the nuts. It is usual to bevel both end faces of the nuts as a safety measure against incorrect fitting, but as wheel nuts bevelled on one end face only are still in use, care should be taken to see that they are fitted correctly.

As an extra precaution against the wheel nuts slackening off, some manufacturers favour using left-hand threads on the studs fitted to the near side hubs, and right-hand threads on the off side hubs. The nuts are usually marked L for left-hand and R for right-hand, and this should always be borne in mind when struggling to remove a tight nut at any time.

The Rudge Whitworth single centre nut fitting is very popular with the sports type of car. The driving and braking strains are taken on serrations on both hub and wheel centre, and the wheel is pulled firmly on to a cone section of the hub by a large single nut. These nuts always undo in the same direction as the rotation of the wheel to which they are fitted, and will be left-hand threaded on the near-side wheels, and right-hand threaded on the off-side wheels. If the hubs are removed at any time care must be taken to see that they are not refitted to the wrong side, the wheels would tend to work loose and in all probability come off. These centre locking nuts are often fitted with ears so that they can be tightened or loosened with a hide or copper hammer.

With motor cycles it is usually the practice to mount the wheels on a non-rotating spindle mounted on bearings in the hub of the wheel and rigidly held in the fork ends of the frame.

When the nuts securing this spindle in the forks are undone the wheel can be removed. The chain sprocket of the rear wheel is generally integral with the hub, the driving or braking strains are transmitted from hub to wheel through suitable dowels or dogs.

Whenever wheels are removed, the wheel registers and studs should be greased before replacing, to prevent rust. The correct procedure to be observed when removing or remounting wheels is as follows:

Initially slacken each nut before jacking up; if the nuts are extra tight it is easier to start them with the weight on the wheel to prevent it turning. Then jack up and remove all nuts and finally the wheel. As already suggested, take the opportunity of greasing studs and registers, etc., before replacing. When remounting, each nut should be given a few turns only at a time. This should be done with the wheel clear of the ground, and nuts, diametrically opposite, should be tightened in turn. The object is to enable the wheels gradually to seat themselves evenly on the faces of the studs and nuts. It is very bad practice to finish tightening one nut before moving to the others. Finally, jack down the car, and with the weight of the vehicle on the wheel, tighten nuts right home.

Tyres

It is very important that the tyres should not be kept at less than their minimum recommended pressures for the type of vehicle on which they are being used. Slack tyres, besides being conducive to wheel wobble and skidding, will show early disintegration of the cord foundation due to abnormal flexing. Tyres are liable to lose pressure through diffusion, even though there is no abnormal porosity or leakage due to a puncture or faulty valve. This loss may vary between 1 and 3 lb. Per sq. in. per tyre per week, so one can judge how important it is to check over the pressures weekly with a reliable pressure gauge and to rectify any discrepancies. But a cursory glance should be given daily to see that none of the tyres is unduly slack. The instruction book issued by the car manufacturer will specify the correct pressures, but a short list of tyre pressures advocated by the Dunlop Rubber Co. Ltd. Is given below for general reference. It will be appreciated, of course, that this list is not comprehensive and where high pressure, low pressure and extra low pressure tyres are concerned the undermentioned pressure specifications are no: applicable.

It will be noted that the ur pressure for any given size of t/re will vary in accordance with the load imposed. The necessary inflation pressure may be deterrrined by weighing the vehicle (full normal load) and dividing the results by four.

The tyres should be examined occasionally for flints or other similar foreign matter which may have become embedded in the tread. If these are left in, they may eventually work through the cover and puncture the tube. Fill up any large cuts or gashes with a suitable filler, or if serious return for repair by specialists. Care should be taken to avoid getting oil on the covers, it should be cleaned off with petrol sparingly used. Should the front tyres at any time show signs of rapid wear, suspect mis-alinement of the front wheels. Provision is provided by the manufacturers for the adjustment of the track of the front wheels, which are given toe-in or toe-out according to design. Toe-in is most usual, but front wheel driven cars invariably have toe-out, and in many independent suspension models the wheels are parallel.

Refer to the instruction book before making any adjustment. The operation of adjustment, is performed in the following manner. The steering is set in the straight ahead position • and the distance between the two front rims is measured at a height approximately equal to the centre of the wheels. By means of a suitable gauge compare this measurement as taken in front of the axle with it taken behind the axle. The variation (if any) should conform to maker’s specification. Periodically change the wheels round from front O/S to rear N/S and vice versa. Use the spare wheel in turn with the others, and so equalize wear of all 5 wheels. Big discrepancies in tyre mileages may be apparent when comparing drivers, and these can invariably be traced to the driving methods employed. In an endeavour to get improved mileage the driver should avoid wheel spin due to rapid acceleration, and allow the engine to slow down the car in preference to driving on the brakes. The wear at 50 m.p.h. Is double that at 30 m.p.h. Avoid driving with the wheels in tram lines. Do not bump against curbs as this is liable to fracture the casing and to upset the wheel alignment.

To facilitate quick running repairs it is generally the practice to carry a spare wheel complete with tyre and tube inflated ready for use. A number of motor cycle sidecar combinations are also provided with a complete wheel ready for fitting in case of tyre trouble on the road. Some commercial vehicles and American makes of car carry tyres and tubes fitted to spare rims only.

Tyre Removal

First deflate the tyre by removing the valve components,. The wired type of tyre on well based section rims (a tyre and rim are shown in the illustration***************) is practically universally adopted today. With this combination it will be seen that the diameter of the wired bead of the tyre is smaller than the diameter of the rim flange. Therefore the tyre (when inflated) cannot blow oft’, neither can the edges be lifted over the rim as the wire is inextensible. So do not attempt to stretch the wire edges of the tyre over the rim. Force is entirely unnecessary, for if the beads of the tyre at a part diametrically opposite the valve are pushed down into the well of the rim, the cover edge near the valve can easily be levered over the rim edge.

To fit the tyre, push one edge of the cover over the edge of the rim. It will go quite easily if the part first put on is pushed right down into the well of the rim. Very slightly inflate the tube, not sufficiently to disturb it, but only so that it takes shape, and place it in the cover with the valve through the hole in the rim. Take care that the valve (which is off-set) is on the correct side of the rim. Also, it is the practice for some manufac- turers to mark their covers for balance. The Dunlop Rubber Co. Ltd. Use a red spot on the wall which should coincide with the valve position. Make sure the cover is in its correct position, and then fit the second edge of the cover, commencing at a point diametrically opposite the valve, pushing the edge down into the well of the rim. The small tyre levers in the kit may be used to ease the last few inches over the rim edge. Whilst inflating see that the edges of the cover are seated evenly on the shoulders of the rim; there is a line circle on the wall which should be concentric with the rim.

Repair of Punctures

If a tyre is losing pressure it is as well to test the valve before removing wheel cover, etc. This can be done with the wheel in position by turning it until the valve is at the top. Remove the valve cap, and immerse valve in a glass of water. If bubbles are visible fit a new valve core, reinflate and test again.

When cover and tube are removed for the repair of a puncture, inspect the inside of the cover for, and remove, any sharp object which may have penetrated the cover and caused the puncture. Take the opportunity of extracting any other matter embedded in the bead of the cover. Wherever possible it is advisable to have punctures repaired by vulcanized patches in preference to stick-on patches, which are liable to lift and leak in warm weather.

The reader is reminded that it is a legal offence for the motorist to run a vehicle on tyres with bald treads. It has sometimes been the practice in the past to have smooth tyres re-cut, provided there is sufficient rubber left.

The tread on a tyre is not only a means of improving the drive of the rear road wheels by increasing the grip between road surface and tyre; it also reduces the risk of skidding on wet.roads, etc.

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