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THE DIMENSIONS OF THE BODY.
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Some Important Details in the DeqiOn of a Vehicle and the Reasons for their Determination.
A S the body must fit the chassis, 11.several dimensions of the former are directly influenced by it. With the conventional form of steering, the position of the driving seat is dependent on the distance of the steering wheel from the dash and the height of the wheel above the chassis. An average dimension from the back of the steering wheel to the front of the driver's back rest or squab is 1 ft. 3 ins., whilst from under the wheel to the top of the cushion should not be less than 8 ins. The front partition or bulkhead of a bus or the back framework of a driver's cab can then be set out aftera suitable allowance of, say, 2 ins. has the thickness of the cushion, which board is located after plotting out is seldonr more than 3 ins, for the commercial type of vehicle. The been made for the thickness of the back rest.
cushion may be the same width as the distance from the steering wheel to the back rest, but it
is an advantage to let it project an inch or two under the steer In a similar manner, the seating wheel, in order that the cushion may give better support. It will be seen, therefore, that the length of chassis available f o r passenger seats, or the loading space of a lorry, is deterA side eleva mined after the passenger-s driving compart
ment has been set out. Two similar kinds of body may differ as much as 6 ins, in the length from the dash to the back of the cab. This may be owing to the difference in steering rake or the amount of space provided for the driver. As heavy lorries usually have a more upright form a steer c34 lag than light delivery vans, the former have the shorter cabs. The overall length of a driving compartment varies from 3 ft. 6 ins. to 4 ft. 2 ins.
Hind-wheel Clearances.
The height of the chassis from the ground, the distance from the dash to the centre of the hind wheel, the diameter and track of the hind wheels together determine the radius, width and position of the wheelarch, which, in their turn, affect the seating arrangement. If It be a lorry or van, the hind-wheel clearance decides the height of the floor if no wheelarch be used. Hindwheel clearance is usually stated by the motor manufacturer on the print supplied to the body builder. In theory it should be about an inch more than the distance from the top of the axle or its casing to the bottom
flange of the frame directly above it. This dimension varies from 5 ins. for a light van up to 9 ins. or 10 ins. for a six-ton lorry. This measurement is allowed above the top of the tyre to the underside of the wheelarch. As the deflection of the springs is more or less vertical, the clear ance may be decreased to 3 ins., measuring horizontally from the side of the tyre to the lower corner of the wheelarch. This dimension should not be reduced for the smaller or lighter type of vehicle.
Side roll of the chassis must also be considered. The allowance made is from 2 ins. to 3 ins, on each side, measuring from the inside face of the wheel to the side of the wheelarch, or if it be a low-mounted, narrow body, to the body side. A bus body which is 6 ft. 8 ins, wide inside at the waist will only be about 4 ft. wide across the floor inside the wheelarch faces; consequently, if the wheelarchbe more than a few inches high at the crown, longitudinal seats must be used. It is also important that the body builder
should know the actual size of the tyre and not merely the nominal size.
Overhang.
In the early days of the commercial motor vehicle the length of the body was apt to be decided ac
cording to the wishes of the owner. Nowadays, it is fully recognized that the length of the body should be controlled by the length of the chassis. A 1-ton chassis may be purchased either by a furniture dealer or a building contractor. The length of each body should be about the same ; consequently increased capacity must be provided by making the body wider, or with higher sides, and, if necessary, building over the cab as well.
Overhang is the length from the centre of the hind axle to the back of the body. The Ministry of Trans port has proposed that overhang shall not exceed 7-24ths of the overall length of the vehicle, a suggestion which has been adopted as a regulation by the Scotland Yard authorities. This amount of overhang is not unduly restrictive, and should be regarded as quite applicable to goods as well as to passenger vehicles.
Occasionally the body builder. wishing to adhere to the 7-24ths overhang, finds that it is a little awkward at times when an inch or two either way is of particular importance. It is found that the general arrangement of the front part of the chassis is the controlling factor, and it may help matters if the chassis can be lengthened a few inches by the addition of a front bumper, so that a little more overhang is permissible, although the chassis has not really been altered.
(The basic length of the vehicle is variously interpreted as "the overall length" and "the length from the forward end of the dumbirons.")
Seating Capacity and Body Space.
Usually a modem single-deck bus may overhang the end of the chassis about a foot and still be within the limit of the 7-24ths overhang. The overhang is greatest at the waistline, and is reduced at the bottom according to the amount of turnunder given to the back panel. If the chassis has the ordinary type of steering and it is 15 .ft. 8 ins, long behind the dash, then the length available for passenger seats will be the body space, plus 1 ft. for overhang, less, say, 3 ft. 8 ins, for the driving compartment, leaving a net length of 13 ft.
A front row of seats next to a partition takes up about 2 ft. 8 ins. of the body length and each succeeding row, say, 2 ft. 3 ins., this dimension being less because of the leg space under the seats not available for the front-seat passengers. The body length occupied by three rows of seats facing forwards is therefore 7 ft. 2 ins., by four rows 9 ft. 5 ins.; by five rows 11 ft. 8 ins., and so on, adding 2 ft.
3 ins, for each succeeding row of seats. This simple calculation can seldom be applied, because a high wheelarch necessitates a changeover to longitudinal seats directly the crown of the arch is reached. This alteration of the seating arrangement usually entails the loss of at least two seats when compared with a body which has crosswise seats throughout. The long seats must provide at least 1 ft. 4 ins. per — passenger. If these seats are not continued to the rear, then the seat spacing starts again as from a bulkhead.
The body, which has 13 ft. of passenger-seating space behind the front bulkhead, will probably have three rows of seats facing forwards, occupying 7 ft. 2 ins. of the body length. Then a long seat on each side will be provided, say, 2 ft. 10 ins, long, and accommodating two passengers. The end of these seats is 10 ft. from the partition, leaving 3 ft., less 2 ins., for the thickness of the back framework of the body, or 2 ft. 10 ins, for a single row of cross-seats at the rear. In a length of 13 ft., allowing for a clear gangway in front of the emergency door, 20 passengers are accommodated. If 13 ft. be divided by 20 it is found
that each passenger represents ins, of the body length behind the front bulkhead. The average length taken up by rows of seats facing forward is about 2 ft. 4 ins, per row. A row of seats holds four passengers ; therefore the length of body per passenger in this instance is 7 ins. If long seats be fitted throughout, the length per passenger is then not less than half the regulation length allowed, or 8 ins.
Therefore, if an average be struck between bodies having long seats, crosswise seats and a mixed seating arrangement, the result will be approximately 71 ins. Using this figure, the seating capacity of a front entrance bus is found by deducting 2 ft. 8 ins, from the length of the chassis behind the dash and dividing by 71. The ehassis mentioned above has a body space 15 ft.
8 ins. long. Deduct 2 ft. 8 ins. (the difference between the driving seat compartment and the overhang), which leaves 13 ft., or 156 ins., which., divided by 7.5, gives 20.8. From this result it may be assumed that the chassis will easily accommodate 20 passengers.
Deduction for Rear Entrance.
If a rear entrance be provided as well as one at the front, then two seats must be deducted from the above total, that is to say, a 15-ft. 8-in, body space will only accommodate 18 passengers if it be a doubleentrance bus. If the same length or body space be available, but the chassis has forward control. then 16 ft. 8 ins, is divided by 7.5 ins., giving a quotient of 26.0. But as the entrance is within the net body space two seats must be deducted, so that the forward-control chassis
measuring 15 ft. 8 ins, behind the dash would accommodate 24 passengers comfortably, 'Headroom.
'A public-service vehicle is built so that the passenger of average height may walk down the gangway in an upright position with his hat on. This requires a minimum height of 5 ft. 10 ins, from the floor-wearing slat to under the roof framework. It may be increased to 6 ft. 2 ins. or 6 ft. 3 ins, in a single-deck bus, so as to afford greater convenience for the tall passenger and to improve the ventilation. Less headroom is required when the passenger is seated. Advantage is taken of this fact when a large camber of, say, 10 ins, is given to the roof, but the passenger sitting nearest to the side of the body still has plenty of headroom, because the curve of the roof rises quickly from the cant rail.
Headroom for the seated Passenger may be safely decreased to a further extent, so as to give the opportunity for reducing the, overall height of a covered-top doubledecker. In a private saloon the height from the top of the cushion to underneath the roof may be only 3 ft., but this is often insufficient should the car encounter a sharp hump in the road, when the passenger's head is apt to be forced against the roof.
If the headroom above the cushion be 3 ft. 4 ins, at the sides of the -lower saloon of a coveredtop double-decker, the roof line may then rise gently for about half the length of the crosswise seat and then sharply to the full headroom of the central gangway so that the roof in section forms a return curve. s If the cushion be 1 ft. 5 ins. off the floor and the headroom above the cushion is 3 ft. 4 ins., the inside height of the bus from floor to roof at the sides is 4 ft. 9 ins. In the middle of the seat it may rise to 5 ft. and to 6 ft. in the central gangway. As the headroom is only 5 ft. at a distance of half the length of a cross-seat from the body side, a side gangway may be built above this part of the lower saloon roof, which will be about 10 ins. lower than had the conventional arrangement 'been adopted. The top deck is provided with seats arranged back to back down the centre with a gangway on each Side, or an off-side gangway only is used and cross-seats fill the remaining width of the upper saloon.