I am Rubber, You are Glue

"For rapid transfer of enemy experience of materials and designs in the field of rubber into domestic production, I propose that the People's Commissar of Rubber Production be given the following samples"

American Tank Tires

I've picked on Soviet tires a few times, and even German ones, and now the time has come for American tires. How do they stand up to long road marches and heated chases? Maintenance of Armor in World War II from the Fort Leavensworth library has the answer.

The experience with steel and rubber tracks mirrors Soviet experience in the hot Ukrainian steppes. Rubber tracks tended to melt and fall to pieces, while steel tracks performed much better. Since the terrain was not rocky or mountainous, the drawback of all metal tracks tearing off chunks of tires did not come up. 

Even without any rocks, heat and dust appear to have a negative effect on American vehicles, which is, unfortunately, not quantified.

The British also complained about American tanks blowing bogies, although their experience with steel tracks was poorer:

Replaceable Tires

"USSR NKTP
All-Union State Special Machine-building Trust
April 4th, 1935
#37-372-1232s
To the director of the Voroshilov factory, comrade Dufur
Copy: director of the Kirov factory, director of factory #185, RKKA ABTU

Despite the quite obvious necessity of switching to T-26 tanks with removable road wheel tires in 1935, the issue is still not resolved. The necessity of using removable tires is confirmed by both trials (in a 3000 km run, only two road wheels broke for reasons not connected to their tires) and the unsatisfactory robustness of the enlarged road wheels on that same vehicle, SU-5, and other vehicles on the T-26 chassis.

The claim that the production will be too costly is countered by the necessity to restore the old casting molds, which will be more expensive than making new casting molds for the simpler removable tires.

Finally, the cost of use will not increase if one considers the significant gain in reliability and decrease in rejections of manufactured components. The tire will be molded on a separate simple mold, as opposed to a complicated combination mold.

Considering the aforementioned points, I consider it necessary to immediately switch to removable tires for the T-26, for which:

1. The director of the Voroshilov factory, comrade Dufur, in cooperation with the Kirov factory, must develop a plan to produce production together with the aim of switching to production of removable tires in the fourth quarter of 1935.
2. The directory of factory #185 comrade Barykov must sign a contract with the Kirov factory to supply road wheels for the production of the SU-5 and other experimental vehicles on the T-26 chassis.

The full plan of shifting production to road wheels with removable tires and the cost of this transition should be given to me for approval no later than April 15th of 1935.

Director of the Special Machine-building Trust, Neimann"

V. Lehn Collection

SU-76I Trials

"To the State Committee of Defense, comrade V.M. Molotov

I report on the results of the proving grounds trials of the experimental SPG that uses a 76 mm tank gun mod. 1940 (F-34) on the chassis of a captured German medium tank PzIII (or StuG) produced by factory #37 according to the GOKO decree issued on January 19th, 1943, #2758ss.

Trials were held at the Sofrino proving grounds from March 13th to March 20th of this year in the amount of 434 shots and 280 kilometers, supervised by the commission led by Lieutenant-General of Artillery, comrade Tikhonov.

The prototype supplied for trials satisfies tactical-technical requirements.

The major characteristics of the 76 mm SU-76 SPG are as follows:

1. Armour:
1. Front: 45 mm at 45 degrees
2. Side: 25 mm at 20 degrees
3. Rear: 25 mm at 20 degrees
4. Roof: 10 mm
2. Ammunition capacity: 95 shells
3. Vertical gun angles: -5 to +15 degrees
4. Horizontal gun angles: +/- 10 degrees
5. Height of the fighting compartment: 1760 mm
6. Bore axis height: 1870 mm
7. Crew: 4

The design of the SPG is very good. The stability when firing is good. The SPG is easy to service. The accuracy is satisfactory. The performance of the vehicle matches that of the PzIII, recorded in the service manual of the latter, and are characterized by insufficient traction of tracks with a slippery frozen road, which results in drifting and slipping. The reliability of rubber tires and drive sprocket is insufficient. This deficiency requires the speed to be limited at 25 kph. When moving on icy or frozen terrain, it is necessary to install V-shaped German spurs. The commission decrees that the SU-76 SPG is adequate for tasks delegated to this type of self propelled artillery, has passed trials, can be recommended for adoption by the Red Army, and must be produced immediately, provided that satisfactory tires can be found or produced domestically, spurs, spare road wheels and sprockets, and careful quality control and re-checking of all PzIII and StuG tanks used in production. 

I consider the tested SU-76 76 mm SPG to be ready for adoption by the artillery branch and mass production.

GAU KA Chief, Colonel-General of Artillery, Yakovlev"

CAMD RF 81-12063-10

Note that the SU-76I weighed only 22.5 tons, compared to 22 tons of a mid-production StuG or 20 tons of a late production PzIII, so excess weight can't be blamed for this fragility of the suspension. 

T-34 Tires

"To member of the State Committee of Defense, comrade Beria

At this time, the T-34 has rubber tires with ventilation openings (made from rubber gr.80). These tires do not provide reliable service due to the destruction of the rubber, and limit the top speed of the tank.

From August 1st to September 10th, the NIBT proving grounds and NII of tire manufacturing tested T-34 tires made from various types of rubber. As a result of the trials, it was shown that 210 km of runtime with production tires caused damage to 43% of the tires, while tires without ventilation openings made from 120s rubber did not have damage after 2000 kilometers. The average speed of movement was 25.5 kph and the external air temperature reached 33.5 degrees.

Wheels with smooth tires made of 120s type rubber without ventilation openings easily last the warranty period of the T-34. In connection to this, I ask for your order to the People's Commissariat of Rubber Production (comrade Mitrokhin) to supply tank factories with 120s rubber tires without ventilation openings starting from November 1st, 1943. Attached are the summary of trials and the conclusions made by the NIBT proving grounds and NII of tire production.

Malyshev.
Fedorenko
October 12, 1943

Summary and Conclusions on the trials of T-34 tank tires, conducted by the NIBT proving grounds.

1. The following is data on trials of tire damage as a result of motion with the average speeds of 25-35 kph.

Rubber type	With ventilation openings			Without ventilation openings
	Distance (km)	Air temperature	Percent damaged	Distance (km)	Air temperature	Percent damaged
gr.80	210	20-22	43%	2001	15-27.5	30.8%
gr.81	525	14-22	25%	2034	14-33.5	17.7%
120s	502	14-22	10%	2001	14-33.5	0%

The presence of openings weakens the rubber mass, as a result of which it is deformed more easily, generates more heat, and, as a result, damages the rubber wheel due to the rubber melting (gr.80 and gr.81) or cracking (120s). 

2. The most heat resistant tires are ventless tires made from 120s rubber.

3. Tires without openings suffer from damage at speeds 40-45 kph, more so tires made from gr.80 and gr.81 rubber than tires made from 120s rubber.

Conclusions:

1. Rubber tires for T-34 road wheels (size 830x150) without ventilation openings are much more robust compared to tires with ventilation openings. Tires without openings survived trials 2315 km long with the average movement speed of 25.5 kph with external temperature ranging from 14 to 33.5 degrees.
2. Out of the trialled rubbers, gr.80, gr.81, and 120s, 120s type rubber demonstrated the greatest heat resistance and lowest heat generation properties.
3. Tires with 120s rubber, without ventilation openings, and with a smooth surface are recommended for production.

Lieutenant-General of Tank Forces, Vershinin.

October 11th, 1943"

CAMD RF 38-11355-1660

BT-7M Tires

The slanted tires weren't the first attempt to help with the BT-7's tire problem. Turns out, when a tank goes really fast in really hot weather, its road wheels aren't going to last long. One of the comparative trials between the BT-7 and BT-7M involved measuring how the tires heat up and how long it takes before they are destroyed.

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.

1. Trials goal: to discover the reliability of tires when the vehicle travels on wheels.
2. Date and place: June 22nd, 1939. June 23rd, 1939, June 27th, 1939. A stretch of highway between Kharkov and Belgorod.
3. Weather conditions: Dry, sunny. Air temperature ranged from 28 to 32 degrees.
4. 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:

1. 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.
2. 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.
3. 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."

RGVA 31811-3-1681

Burning Rubber

A method of improving rubber life.

"To Deputy Chief of ABTU, comrade Panfilov

According to your recommendation, tilted wheels will be installed on the production A-7M vehicle. This modification leads to improvements when moving on wheels, as it significantly increases the lifetime of the rubber (see report #061 on field trials of A-7M tanks model 1939, pages 185-191 and 208). When driving on tracks, this modification leads to no changes.

Using tilted wheels will decrease parts commonality and introduce the possibility of confusion when using spare wheels in the field. Please confirm the necessity of using tilted wheels.

Senior Military Representative of ABTU, Military Engineer 2nd grade, Kozyrev."

"To the Chief of the Red Army ABTU, Army Commander 2nd grade, comrade Pavlov
Copy to: factory #183 director comrade Maksarev

Factory #183 notified you with letter #S01271 on March 5th that the replacement of wheels with tilted ones on A-7 and A-7M vehicles is not suggested. In a telegram from April 18th of this year, the factory reports that there was no answer to its letter from ABTU.

GlavSpetsMash asks you to confirm that replacing wheels with tilted ones is not recommended due to the reduction of parts commonality.

I propose to the factory #183 director that he should not make any changes to the production process without prior agreement from GlavSpetsMash.

GlavSpetsMash Chief, Surenyan"

Despite the arguments, handwritten comments on the page order tilted wheels to be put into production. There seems to be no record of this modification actually making it into production, though.