TEACTION OP WHEELS AND AXLES. 
287 
The relative advantages and disadvantages of the foregoing wheels 
and axles may briefly be summed up as follows:—In A , there not 
being any strut to the working spoke, the cone of the wheel is a 
maximum, while in C it is a minimum, or nil j giving the latter, there¬ 
fore, the advantage in ease of draught in this respect. Apart, however, 
from draught, such a large amount of strut is disadvantageous; causing, 
as we have seen, the line of pressure to cross the spoke when in its 
normal position, and so giving a tendency to break it, and also, for a 
given track, reducing the width between the wheels at the axle (in A 
this distance is 4 ft. l^ins., in 67 3 ft. 9 ins.), which curtails the room 
for axle-seats in the gun-carriage, and for ammuuition boxes—and 
therefore ammunition—in the wagon and limbers. 
In A and B the centre of pressure corresponds with, or approximates 
to, the centre of the pipe-box, but in C it does not; so that in the 
latter a cross action of the wheel upon its arm is produced, causing 
greater friction and tendency to heat at certain points, more particu¬ 
larly at the base of the arm on the upper side—being the furthest bearing 
from the centre. In this respect, therefore, the construction of the 
Madras wheel is contrary to all principle and radically defective. 
The wheel A, it will-be noticed, is a medium, as regards strut, between 
A and C; that is to say, as much strut is given in it to the working 
spoke (being advantageous in assisting the spoke when the wheels are 
not on the level, and in reducing the amount of cone necessary for the 
wheel) as can be given without prejudice, namely, in reducing the 
distance between the wheels, in misplacing the line of pressure, or in 
sloping the under side of the axle-arm the wrong way. The additional 
grease chamber, as already pointed out, is an advantage in giving more 
space for grease, and permitting the wheel to be greased without 
removal ; but in addition to this, as in the service wheel the grease 
always works towards the shoulder, it supplies the lubricant at the 
correct spot. The weight of B is also in its favour, not only, as already 
stated, on account of traction, but also in opposing less inertia to 
recoil in the gun-carriage, and therefore putting less strain upon the 
axletree. 
I .—Results of Experiments on Traction. 
Tractive force in lbs* 
Nature of ground. 
Mean. 
Maximum. 
A 
B 
C 
A 
B 
G 
Asphalt road, level, smooth ... 
26 
34 
70 
97 
Do. inclined 1^° to 2°, smooth. 
r d 
.2 
*3 
104 
111 
<D 
'Jj 
145 
150 
Do.,do., with obstacles 1 in. high, at regular intervals 
-*■3 
-4-3 
o 
£5 
107* 
113* 
-4-3 
-4-3 
O 
iZj 
166 
180 
Eoad of ashes, level, fairly smooth. 
76 
87 j 
143 
200 
* The mean tractive force required to surmount the obstacles was respectively 138 and 142 lbs. 
In the foregoing table we see the results, as anticipated, wholly in 
favour of the modified service wheel and axle. 
