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Tire designs for mobility—USSR
Journal of Terramechanies, 1975, Vol. 12, No. 3/4, pp. 247 to 253. Pergamon Press Printed in Great Britain.
TIRE DESIGNS FOR MOBILITY--USSR D. R. WARNER*
Summary--The Soviet Union has developed many types of tires to increase the mobility of wheeled vehicles. Five design types are described with characteristics, models, sizes, and construction details noted. This information is primarily the result of searching Soviet publications. The five design types will be discussed in their order of development. The focus of this report is on tires for use on military transport vehicles. INTRODUCTION TIRE design strongly affects vehicle mobility. Vehicle mobility can be radically changed simply by changing tire design or size. Soviet tire designs to improve ground vehicle mobility are described here. This survey presents tire designs investigated by the Soviets in chronological order. Five tire designs were considered: high pressure, adjustable inflation pressure, low profile, arched, and air roller tires. HIGH PRESSURE OR HIGHWAY TIRES In the Soviet Union, high inflation pressure or highway truck tires were used on mass-produced military transport vehicles up through the late 1950's. Examples are shown in Fig. 1. High pressure tires have been modified with a variety of tread patterns to increase their mobility. Three groupings are shown in Fig. 2. The use of large tread lugs in generally open, directional patterns such as those on the left, provided increases in cross-country mobility, particularly over wet loam soils, as compared to the same tires with highway tread patterns. These, however, have poor highway performance. The center grouping of tread patterns provides improved highway performance with the exception of lateral stability but have poor crosscountry performance compared to those on the left. Those on the right provide the best balance of highway and cross-country performance. Problems encountered with the use of high inflation pressure tires on military trucks included: inherently low mobility due to high tire-to-ground contact pressures, which are in the order ot 70-100 lb/in 2, tire inflation pressures which cannot be lowered below 40 lb/in 2, and tires of this type are often grouped in pairs on rear axles which leads to further decreases in mobility. Soviet investigations also revealed that if tire tread lug heights were increased to any great extent over those of normal highway tires, problems with lateral stability, highway ride, and performance on ice were encountered. The Soviets had realized the shortcomings of these tires by the end of World War II, but development and mass production of new designs required time. This type of tire is included in this report because the terminology is pertinent to the tires used on some current U.S. military vehicles. It should be noted that Fig. 1 includes radial cord high inflation pressure tires. *AMXST-GEI, USAFSTC, 220 Seventh Street NE, Charlottesville, VA 22901, U.S.A.
247
248
D.R. WARNER $17[
' PROF!tF •,F;I,~<:
~ NUMBER Or ot!F~
I
STATIC !OADED
I CAPACITY ' [OADIINFLATION
RAft iN
E~BS ~pRES_StPSI
STANDARD 240-508 260-508
19oo 2o I
300-508
;i
(N.O0_~O RADtA~ 200-~L,'I ~' [7.50- 20 260-508
i
.
.
.
.
.
.
5,;(Jli
90
{ 00{
6b
I00 i i2 i iS.i i4•00 FTG. I. High inflation pressure tires.
i
95
h(;. 2. 3 groups of tread patterns. Soviet efforts in the development of radial cord rites started in the early 1960's. To date, designs have been for highway use, but there are indications that research in high mobility radial cord designs is being considered. The Soviets have devoted considerable effort toward reducing radial tire manufacturing processes, and matching tires to vehicle suspensions. The quality of their radial tires appears high. Expanded application of radial cord tires is expected because of their long life and improved traction. ADJUSTABLE INFLATION PRESSURE TIRES Adjustable inflation pressure tires were developed specifically for vehicles equipped with Central Tire Inflation Systems (CTIS). These first appeared on Soviet Military transport vehicles in 1958 with the introduction of the 2½-ton, ZIL-157, 26 ×6. The Soviets had been most impressed with the mobility advantages of the tire inflation system on the World War iI U.S. Army, 2½-ton amphibious truck, the DUKW. However, they noted that the full advantage of this system could not be achieved using conventional high pressure or highway type tires because of their inherently rigid sidewalls. The 1200 x 18 size adjustable inflation pressure tires used on the ZIL-517 replaced the conventional high pressure dual tires used on the ZIL-151, predecessor to the ZIL-157. The mobility gain by this replacement is approximated in the comparison of the ZIL-157 to the U.S. M35A2 with dual rear wheels, Fig. 3. Today adjustable inflation pressure tires are the most common high mobility tires in the Soviet Union. All Soviet heightened mobility transport vehicles now in production are equipped with central tire inflation systems and tires designed specifically for these systems, with the exception of their jeep and one model of their tank transporter. Characteristics of these tires as compared to highway types include: similar profile series, decreased number of cord plies, softer rubber, and an effective inflation pressure range between 7 lb/in 2 (0-49 kg/cm 2) and 50 lb/in '~ (3.52 kg/cm2). While these tires
TIRE DESIGNS FOR MOBILITY--USSR
249
FI6.3. Drawbar pull/wt--slip curves for U.S. M35A2 and Soviet ZIL-157 trucks. can be tube type or tubeless, to date only tube types have been observed. Tire bead locks are used to prevent movement of the tire relative to the rim at lower pressures. Tire tread designs are usually of the heavily segmented herringbone directional lug style with a lug height of up to 1.2 in. On newer models, the tread pattern is denser to improve highway ride, and the segmented herringbone tread extends up the sidewall to improve traction at low inflation pressure. Typical examples of adjustable inflation pressure tires and their model characteristics are given in Fig. 4. Adjustable inflation pressure tires are intended for use on vehicles designed for a wide range of road and cross-country soil conditions. The ability of these tires to vary ground contact area accounts in part for this. Gross ground contact area can be increased about 130% by reducing the inflation pressure from 50 lb/in ~ (3.52 kg/cm 2) to 7 lb/in 2 (0.49 kg/cm2). This system relies on the driver to select the tire inflation pressure which will provide optimum performance for a given road or soil condition. Examples of suggested inflation pressures are given in Fig. 5. It should be noted that while mobility is increased with reductions in inflation pressures, the vehicles speed must also be reduced to prevent tire damage. In general, as compared with contentional highway tires, adjustable inflation pressure tires provide increased off-road mobility, drawbar pull is increased in low bearing strength soils,
FIG. 4. Adjustable inflation pressure tires.
250
D.R. WARNER
FIG. 5. Operating recommendations for adjustable inflation pressure tires. over-snow performance is improved, ride over rough terrain is improved slightly, and it is possible to maintain movement when tires are damaged if the vehicle is equipped with a CTIS. These tires normally have a ground contact pressure of between 12 and 15 lb/in ~ (0.84-1.05 kg/cm 2) when the tire inflation pressure is 7 lb/in ~ (0.49 kg/ c m 2).
The useful life expectancy of adjustable inflaticn pressure tires is lower than that of highway types. Soviet literature indicates a life expectancy of between 9,000 and 15,000 miles (9,620-16,000 kin). LOW PROFILE TIRES Low profile tires were developed after adjustable inflation pressure tires in the Soviet Union. Tires falling in this category have section height to width ratios between 0-8 and 0.5 low profile or wide profile tires (to use the Soviet terminology) are divided into two groups: those designed to replace dual high-pressure highway tires and those designed for use as adjustab!e inflation pressure tires. Low profile tires designed to replace dual highway tires were developed for the following reasons: a saving of between 15 and 30% in construction materials is possible, the tires have a lower and more evenly distributed ground contact pressure, the design reduces total unsprung weight, and improves soft soil mobility, hard surface maneuverability and drawbar pull. However, low profile tires have the shortcomings of reduced life and decreased lateral stability as compared to dual highway tires. Examples of low profile Soviet tires are given in Fig. 6. All of the special vehicle grouping of tires in Fig. 6 are assumed to be for vehicles with Central Tire Inflation Systems. The 1300 × 530-533 series tire is used on the 6 × 6, 8-ton, KRAZ-255B, which is the Soviet ground forces standard general purpose heavy truck. Low profile tires have been in use on the KRAZ-255B since its introduction in 1969, and is currently the only known Soviet application of a low profile tire on a general purpose military truck. ARCHED TIRES The remaining two tire designs described are not standard equipment for any massproduced Soviet vehicles. Tires included in these designs should be considered "limited production" rather than "mass production" items. The first design is that of arched tires, a Soviet development which was an offshoot from the English lipsoid design. Soviet arched tires differ from English lipsoid tires in that the Soviet arched tire
TIRE DESIGNS FOR MOBILITY----USSR
251
FIG. 6. Low profile tire characteristics. design has a very short sidewall. Lipsoid tires have no sidewall as shown in Fig. 7. Soviet development of arched tires started in 1956 only two years after the English lipsoid design was developed. Arched tires are of tubeless design and have a profile height-to-width ratio of between 0.42 and 0-31. The inflation pressure of Soviet arched tires can be varied between 4 and 30 lb/in ~ (0.28-2.1 kg/cm2), and it is possible to achieve ground contact pressures of between 8.5 and 13 lb/in 2 (0.6-0.9 kg/cm2). Limited characteristics of selected Soviet arched tires are given in Fig. 8. Because arched tires are designed primarily for cross-country operation, tread lug heights o f between 1.2 and 2.4 inches (3.05-6.1 cm) are employed. Arched tire models with the extremely high lugs and open tread patterns are not intended for use on paved roads. However, these are models produced for use both on and off roads and these designs have demonstrated a useful life as great as 37,000 miles (59,500 kin). This gives them an advantage over some of the adjustable inflation pressure and low profile tires described earlier. Replacement of dual highway tires was one of the original goals set for arched tire development. Toward this goal, the arched tire has been successful in improving the mobility of non-all-wheel-drive vehicles. The arched tire enjoys an unsprung weight saving of about 25 % over a standard dual wheel assembly. Also, when used on low mobility vehicles, the payload capacity for cross-country operation can usually be increased. The application of arched tires to all-wheel-drive vehicles has begun and it is possible that mass-produced military heightened mobility trucks may receive such tires in the future. In general, the arched tire can be considered superior in mobility to all tires previously described.
TIRE CONSTRUCTION COMPARISON
Lipsoid
Arched
Fro. 7. Tire construction comparison.
D. R. W A R N E R
252
S 7F
N,Rnr
mPrrl~
NO or
Trpl
N n~n
F~.PACITY
,J.[, :,
1000
×
iNFLAT ~RESS
: :
61}i
7D! 1140
~
',
6OO Fie,. 8.
Arched tire characteristics.
AIR ROLLERS--ROLLIGGN
TYRES
Soviet development of air rollers or rolligon type tires started in the late 1950's, well after development originated in the U.S. The Soviets consider this design a further development of super-balloon tires, a development program which the Soviets began work on in 1932. The Soviets divide the super-balloon tire concept into two developmental trends : that of drastically increasing tire diameters, and development through increasing tire width, the latter being the air roll tire. To date, their efforts in air roll tire designs have not equalled that in the U.S., but two programs have paralleled each other. Shown in Fig. 9 are the characteristics for several models of Soviet air roll tires. Air roll tires are extremely flexible, low profile, low inflation pressure tires which are mounted on relatively small diameter, extremely wide wheel rims. Their width to overall diameter ratios vary between 1 and 1.5 which relates to corresponding profile series of between 37 and 25. These are the lowest or widest profile tires described in this paper. Inflation pressures between 1 and 20 lb/in 2 (0.07-1.4 kg/cm ~) are used by the Soviets for air roll tires. Pressures between 14 and 20 lb/in z (0.98-1.4 kg/cm ~) are
Yo-194
FIG. 9.
Air roll tire characteristics.
TIRE DESIGNS FOR MOBILITY--USSR
253
required for pavement and high speed-operation. Tread patterns for air roll tires are usually open, direction bar types but with lugs of lower height than other crosscountry tire designs. Typical lug heights are from 0.4 to 0.8 in (1.0-2-0 cm). While no information on ground contact pressures was found for Soviet air roll tires, ground contact pressures for equivalent U.S. rolligon tires are between 2 and 5 lb/in 2 (0.40.35 kg/cm2). Ground contact pressures for the Soviet tires are assumed to be similar. Air roll tires give the greatest overall mobility of any Soviet tires, but are probably the least developed. CONCLUSION In conclusion, two general comments can be made concerning Soviet tire development. First, that the Soviets feel the introduction of adjustable inflation pressure, lowprofile and arched tire designs solve the problems of transport vehicle movement under "medium difficulty" cross-country conditions. This is significant because, so far as can be determined, the term "medium difficulty" is their mobility requirement or mobility standard for wheeled heightened mobility military transport vehicles. Based on this, it is anticipated that in the future Central Tire Inflation Systems and adjustable inflation pressure tires will continue to be the backbone of the Soviet solution to mobility. The use of the low profile adjustable inflation pressure tire will expand to cover most of their general purpose military transport fleet. These tires may include designs using radial cord construction. Arched tires may also be employed on military transporters. The second comment concerns the problem of wheeled vehicle movement under especially difficult cross-country conditions. The Soviets apparently feel this has not been solved for wheeled vehicles; in fact, their position is that it has not been solved for any category of land vehicle. Air roll tires used in various configurations hold promise for this second problem. Their use in the roadless far North and Eastern portions of the U.S.S.R. has already started. Mobility is a major problem in these areas and the Soviets look to air roll vehicles as part of the solution to development of these regions.
TIRE DESIGNS FOR MOBILITY--USSR D. R. WARNER*
Summary--The Soviet Union has developed many types of tires to increase the mobility of wheeled vehicles. Five design types are described with characteristics, models, sizes, and construction details noted. This information is primarily the result of searching Soviet publications. The five design types will be discussed in their order of development. The focus of this report is on tires for use on military transport vehicles. INTRODUCTION TIRE design strongly affects vehicle mobility. Vehicle mobility can be radically changed simply by changing tire design or size. Soviet tire designs to improve ground vehicle mobility are described here. This survey presents tire designs investigated by the Soviets in chronological order. Five tire designs were considered: high pressure, adjustable inflation pressure, low profile, arched, and air roller tires. HIGH PRESSURE OR HIGHWAY TIRES In the Soviet Union, high inflation pressure or highway truck tires were used on mass-produced military transport vehicles up through the late 1950's. Examples are shown in Fig. 1. High pressure tires have been modified with a variety of tread patterns to increase their mobility. Three groupings are shown in Fig. 2. The use of large tread lugs in generally open, directional patterns such as those on the left, provided increases in cross-country mobility, particularly over wet loam soils, as compared to the same tires with highway tread patterns. These, however, have poor highway performance. The center grouping of tread patterns provides improved highway performance with the exception of lateral stability but have poor crosscountry performance compared to those on the left. Those on the right provide the best balance of highway and cross-country performance. Problems encountered with the use of high inflation pressure tires on military trucks included: inherently low mobility due to high tire-to-ground contact pressures, which are in the order ot 70-100 lb/in 2, tire inflation pressures which cannot be lowered below 40 lb/in 2, and tires of this type are often grouped in pairs on rear axles which leads to further decreases in mobility. Soviet investigations also revealed that if tire tread lug heights were increased to any great extent over those of normal highway tires, problems with lateral stability, highway ride, and performance on ice were encountered. The Soviets had realized the shortcomings of these tires by the end of World War II, but development and mass production of new designs required time. This type of tire is included in this report because the terminology is pertinent to the tires used on some current U.S. military vehicles. It should be noted that Fig. 1 includes radial cord high inflation pressure tires. *AMXST-GEI, USAFSTC, 220 Seventh Street NE, Charlottesville, VA 22901, U.S.A.
247
248
D.R. WARNER $17[
' PROF!tF •,F;I,~<:
~ NUMBER Or ot!F~
I
STATIC !OADED
I CAPACITY ' [OADIINFLATION
RAft iN
E~BS ~pRES_StPSI
STANDARD 240-508 260-508
19oo 2o I
300-508
;i
(N.O0_~O RADtA~ 200-~L,'I ~' [7.50- 20 260-508
i
.
.
.
.
.
.
5,;(Jli
90
{ 00{
6b
I00 i i2 i iS.i i4•00 FTG. I. High inflation pressure tires.
i
95
h(;. 2. 3 groups of tread patterns. Soviet efforts in the development of radial cord rites started in the early 1960's. To date, designs have been for highway use, but there are indications that research in high mobility radial cord designs is being considered. The Soviets have devoted considerable effort toward reducing radial tire manufacturing processes, and matching tires to vehicle suspensions. The quality of their radial tires appears high. Expanded application of radial cord tires is expected because of their long life and improved traction. ADJUSTABLE INFLATION PRESSURE TIRES Adjustable inflation pressure tires were developed specifically for vehicles equipped with Central Tire Inflation Systems (CTIS). These first appeared on Soviet Military transport vehicles in 1958 with the introduction of the 2½-ton, ZIL-157, 26 ×6. The Soviets had been most impressed with the mobility advantages of the tire inflation system on the World War iI U.S. Army, 2½-ton amphibious truck, the DUKW. However, they noted that the full advantage of this system could not be achieved using conventional high pressure or highway type tires because of their inherently rigid sidewalls. The 1200 x 18 size adjustable inflation pressure tires used on the ZIL-517 replaced the conventional high pressure dual tires used on the ZIL-151, predecessor to the ZIL-157. The mobility gain by this replacement is approximated in the comparison of the ZIL-157 to the U.S. M35A2 with dual rear wheels, Fig. 3. Today adjustable inflation pressure tires are the most common high mobility tires in the Soviet Union. All Soviet heightened mobility transport vehicles now in production are equipped with central tire inflation systems and tires designed specifically for these systems, with the exception of their jeep and one model of their tank transporter. Characteristics of these tires as compared to highway types include: similar profile series, decreased number of cord plies, softer rubber, and an effective inflation pressure range between 7 lb/in 2 (0-49 kg/cm 2) and 50 lb/in '~ (3.52 kg/cm2). While these tires
TIRE DESIGNS FOR MOBILITY--USSR
249
FI6.3. Drawbar pull/wt--slip curves for U.S. M35A2 and Soviet ZIL-157 trucks. can be tube type or tubeless, to date only tube types have been observed. Tire bead locks are used to prevent movement of the tire relative to the rim at lower pressures. Tire tread designs are usually of the heavily segmented herringbone directional lug style with a lug height of up to 1.2 in. On newer models, the tread pattern is denser to improve highway ride, and the segmented herringbone tread extends up the sidewall to improve traction at low inflation pressure. Typical examples of adjustable inflation pressure tires and their model characteristics are given in Fig. 4. Adjustable inflation pressure tires are intended for use on vehicles designed for a wide range of road and cross-country soil conditions. The ability of these tires to vary ground contact area accounts in part for this. Gross ground contact area can be increased about 130% by reducing the inflation pressure from 50 lb/in ~ (3.52 kg/cm 2) to 7 lb/in 2 (0.49 kg/cm2). This system relies on the driver to select the tire inflation pressure which will provide optimum performance for a given road or soil condition. Examples of suggested inflation pressures are given in Fig. 5. It should be noted that while mobility is increased with reductions in inflation pressures, the vehicles speed must also be reduced to prevent tire damage. In general, as compared with contentional highway tires, adjustable inflation pressure tires provide increased off-road mobility, drawbar pull is increased in low bearing strength soils,
FIG. 4. Adjustable inflation pressure tires.
250
D.R. WARNER
FIG. 5. Operating recommendations for adjustable inflation pressure tires. over-snow performance is improved, ride over rough terrain is improved slightly, and it is possible to maintain movement when tires are damaged if the vehicle is equipped with a CTIS. These tires normally have a ground contact pressure of between 12 and 15 lb/in ~ (0.84-1.05 kg/cm 2) when the tire inflation pressure is 7 lb/in ~ (0.49 kg/ c m 2).
The useful life expectancy of adjustable inflaticn pressure tires is lower than that of highway types. Soviet literature indicates a life expectancy of between 9,000 and 15,000 miles (9,620-16,000 kin). LOW PROFILE TIRES Low profile tires were developed after adjustable inflation pressure tires in the Soviet Union. Tires falling in this category have section height to width ratios between 0-8 and 0.5 low profile or wide profile tires (to use the Soviet terminology) are divided into two groups: those designed to replace dual high-pressure highway tires and those designed for use as adjustab!e inflation pressure tires. Low profile tires designed to replace dual highway tires were developed for the following reasons: a saving of between 15 and 30% in construction materials is possible, the tires have a lower and more evenly distributed ground contact pressure, the design reduces total unsprung weight, and improves soft soil mobility, hard surface maneuverability and drawbar pull. However, low profile tires have the shortcomings of reduced life and decreased lateral stability as compared to dual highway tires. Examples of low profile Soviet tires are given in Fig. 6. All of the special vehicle grouping of tires in Fig. 6 are assumed to be for vehicles with Central Tire Inflation Systems. The 1300 × 530-533 series tire is used on the 6 × 6, 8-ton, KRAZ-255B, which is the Soviet ground forces standard general purpose heavy truck. Low profile tires have been in use on the KRAZ-255B since its introduction in 1969, and is currently the only known Soviet application of a low profile tire on a general purpose military truck. ARCHED TIRES The remaining two tire designs described are not standard equipment for any massproduced Soviet vehicles. Tires included in these designs should be considered "limited production" rather than "mass production" items. The first design is that of arched tires, a Soviet development which was an offshoot from the English lipsoid design. Soviet arched tires differ from English lipsoid tires in that the Soviet arched tire
TIRE DESIGNS FOR MOBILITY----USSR
251
FIG. 6. Low profile tire characteristics. design has a very short sidewall. Lipsoid tires have no sidewall as shown in Fig. 7. Soviet development of arched tires started in 1956 only two years after the English lipsoid design was developed. Arched tires are of tubeless design and have a profile height-to-width ratio of between 0.42 and 0-31. The inflation pressure of Soviet arched tires can be varied between 4 and 30 lb/in ~ (0.28-2.1 kg/cm2), and it is possible to achieve ground contact pressures of between 8.5 and 13 lb/in 2 (0.6-0.9 kg/cm2). Limited characteristics of selected Soviet arched tires are given in Fig. 8. Because arched tires are designed primarily for cross-country operation, tread lug heights o f between 1.2 and 2.4 inches (3.05-6.1 cm) are employed. Arched tire models with the extremely high lugs and open tread patterns are not intended for use on paved roads. However, these are models produced for use both on and off roads and these designs have demonstrated a useful life as great as 37,000 miles (59,500 kin). This gives them an advantage over some of the adjustable inflation pressure and low profile tires described earlier. Replacement of dual highway tires was one of the original goals set for arched tire development. Toward this goal, the arched tire has been successful in improving the mobility of non-all-wheel-drive vehicles. The arched tire enjoys an unsprung weight saving of about 25 % over a standard dual wheel assembly. Also, when used on low mobility vehicles, the payload capacity for cross-country operation can usually be increased. The application of arched tires to all-wheel-drive vehicles has begun and it is possible that mass-produced military heightened mobility trucks may receive such tires in the future. In general, the arched tire can be considered superior in mobility to all tires previously described.
TIRE CONSTRUCTION COMPARISON
Lipsoid
Arched
Fro. 7. Tire construction comparison.
D. R. W A R N E R
252
S 7F
N,Rnr
mPrrl~
NO or
Trpl
N n~n
F~.PACITY
,J.[, :,
1000
×
iNFLAT ~RESS
: :
61}i
7D! 1140
~
',
6OO Fie,. 8.
Arched tire characteristics.
AIR ROLLERS--ROLLIGGN
TYRES
Soviet development of air rollers or rolligon type tires started in the late 1950's, well after development originated in the U.S. The Soviets consider this design a further development of super-balloon tires, a development program which the Soviets began work on in 1932. The Soviets divide the super-balloon tire concept into two developmental trends : that of drastically increasing tire diameters, and development through increasing tire width, the latter being the air roll tire. To date, their efforts in air roll tire designs have not equalled that in the U.S., but two programs have paralleled each other. Shown in Fig. 9 are the characteristics for several models of Soviet air roll tires. Air roll tires are extremely flexible, low profile, low inflation pressure tires which are mounted on relatively small diameter, extremely wide wheel rims. Their width to overall diameter ratios vary between 1 and 1.5 which relates to corresponding profile series of between 37 and 25. These are the lowest or widest profile tires described in this paper. Inflation pressures between 1 and 20 lb/in 2 (0.07-1.4 kg/cm ~) are used by the Soviets for air roll tires. Pressures between 14 and 20 lb/in z (0.98-1.4 kg/cm ~) are
Yo-194
FIG. 9.
Air roll tire characteristics.
TIRE DESIGNS FOR MOBILITY--USSR
253
required for pavement and high speed-operation. Tread patterns for air roll tires are usually open, direction bar types but with lugs of lower height than other crosscountry tire designs. Typical lug heights are from 0.4 to 0.8 in (1.0-2-0 cm). While no information on ground contact pressures was found for Soviet air roll tires, ground contact pressures for equivalent U.S. rolligon tires are between 2 and 5 lb/in 2 (0.40.35 kg/cm2). Ground contact pressures for the Soviet tires are assumed to be similar. Air roll tires give the greatest overall mobility of any Soviet tires, but are probably the least developed. CONCLUSION In conclusion, two general comments can be made concerning Soviet tire development. First, that the Soviets feel the introduction of adjustable inflation pressure, lowprofile and arched tire designs solve the problems of transport vehicle movement under "medium difficulty" cross-country conditions. This is significant because, so far as can be determined, the term "medium difficulty" is their mobility requirement or mobility standard for wheeled heightened mobility military transport vehicles. Based on this, it is anticipated that in the future Central Tire Inflation Systems and adjustable inflation pressure tires will continue to be the backbone of the Soviet solution to mobility. The use of the low profile adjustable inflation pressure tire will expand to cover most of their general purpose military transport fleet. These tires may include designs using radial cord construction. Arched tires may also be employed on military transporters. The second comment concerns the problem of wheeled vehicle movement under especially difficult cross-country conditions. The Soviets apparently feel this has not been solved for wheeled vehicles; in fact, their position is that it has not been solved for any category of land vehicle. Air roll tires used in various configurations hold promise for this second problem. Their use in the roadless far North and Eastern portions of the U.S.S.R. has already started. Mobility is a major problem in these areas and the Soviets look to air roll vehicles as part of the solution to development of these regions.