Fig. #18: Overall view of the A-7M from the right with tracks.
Fig. #19: Overall view of the A-7M from the left with tracks.
"A-7M and A-7 trials.
- Trials goal: to discover the reliability of tires when the vehicle travels on wheels.
- Date and place: June 22nd, 1939. June 23rd, 1939, June 27th, 1939. A stretch of highway between Kharkov and Belgorod.
- Weather conditions: Dry, sunny. Air temperature ranged from 28 to 32 degrees.
- Trial conditions: the trials were held on a concrete and road tar or gravel covered highway with the speed matching the average speed in the A-7 manual. For the first 80 km, the tank was stopped every 20 km to check the temperature of the tires.
After 80 km, the wheels were cooled to the ambient temperature with buckets of water and the tank began a nonstop march, first until the rubber started to melt, and then until it was destroyed completely."
Here are the results of the trials.
Vehicle type and number
|
Tire type
|
Vehicle mass in kg
|
Side
|
Load on the wheels, kg
|
Distance before the tire started
showing damage
|
Notes
|
||||
Drive
|
Support
|
Drive
|
Support
|
|||||||
Inner
|
Outer
|
Inner
|
Outer
|
|||||||
A-7
610-42
|
NK, 110x830 production
|
13950
|
Left
|
2160
|
2045
|
246
|
215
|
-
|
-
|
No further trials of this vehicle
were peformed
|
Right
|
2126
|
2018
|
-
|
-
|
-
|
-
|
||||
A-7M
0890-3
|
NK
110x830
production
|
14360
|
Left
|
2205
|
2145
|
246
|
246
|
-
|
-
|
-//-
|
Right
|
2092
|
2143
|
246
|
211
|
-
|
-
|
||||
A-7M
0993-5
|
NK
110x830
with drilled openings
|
14425
|
Left
|
2270
|
2250
|
-
|
191
|
-
|
-
|
-//-
|
Right
|
2300
|
2265
|
-
|
172
|
-
|
-
|
||||
A-7M
442-55
|
NK
110x830
production
|
14680
|
Left
|
2255
|
2145
|
160
|
160
|
-
|
160
|
|
Right
|
2266
|
2143
|
158
|
160
|
-
|
160
|
||||
A-7M
442-55
|
NK
110x830
Filed down according to sketch #2
|
14680
|
Left
|
2255
|
2145
|
522
|
522
|
1265
|
1265
|
The left support wheel travelled 560
km on tracks before the trial
|
It's a lot of numbers, but you can see that the wheels in the last test (BT-7M, filed down tires) performed leaps and bounds better than the rest of them. Here's how it looked.
Fig. #56: Sketch of the drilled rubber tire.
Fig. #57: Sketch of the filed down rubber tire.
"Conclusions:
- Inner regular production tires on A-7 and A-7M vehicles begin to melt after 65 km of nonstop motion at a speed of 38-40 kph on a gravel of tarred concrete highway. This is explained by the inner tires being under more load than outer ones even with horizontal axles.
- Production tires with drilled openings (fig. #56) also begin melting after 65 km. This is explained by the inner tires still being under more pressure than outer. Additionally, the ventilation holes for improved cooling led to an increase of pressure on the foundation of the rubber, which did not give a reliability increase compared to regular rubber.
- Production tires filed down according to fig. #57 showed satisfactory performance. Melting began only after 500 km, and the destruction of inner and outer tires happened at the same time. Production tires on the same vehicles began melting at 158 km.
Trials of these tires with tracks on and off-road also showed satisfactory results.
Conclusions: tires filed according to fig. #57 are much more reliable than other tires subjected to the same conditions, and mass production of this type of tire is reasonable."
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