Tire aspect ratio is described as tire section height divided by section width (figure 1). Aspect ratios are also known by series. For example, a 0.50 aspect ratio tire (say for example a P265/ 50VR15) is alleged to be 50-series.
FIGURE 1 OMITTED
Passenger car tire aspect ratios historically have decreased and attempt to decrease further. The aspect ratio of the very first pneumatic tires, manufactured for passenger cars (1905-1915), was ready 1.10. Until the 1930s, aspect ratios remained at approximately 1.0. In 1984, the aspect ratio of 60% of produced tires was 80%. In 1996, this amount was reduced to 10%, and quite a few of produced tires aspect ratios were between 50% and 65% (refs. 1-4).
Effects of aspect ratio on stresses and deformations of tires Distribution of stresses and deformation in tires is one with the primary properties which could determine several tire properties and gratification, which is greatly suffering from aspect ratio.
Studies demonstrate that when the aspect ratio is decreased, the stresses in belt cords increase, while stresses down the carcass cords and circumferential stresses inside bead wires decrease. Also, the distribution of stresses seems being more during lower aspect ratio tires. According to your new tire design theories (for instance TCOT, D SOC), the stresses from the belt cord increase, plus the tension on the carcass cords decreases simultaneously, which ends up in a marked improvement in tire properties. Decreasing aspect ratio also results in decrease of normal displacement in sidewalls and radial displacement on the crown center (ref. 5).
Handling performance
In lower aspect ratio tires, lowering of flexible sidewall height adds to the structural integrity in the tire and increases radial, lateral and circumferential stiffness. Increased lateral stiffness improves cornering performance. Increased circumferential stiffness improves handling during acceleration and deceleration, particularly combination with cornering. Shorter sidewalls, in low aspect ratio tires, be able to increase rim diameter without increasing tire outer diameter. Higher rim diameter is desirable for anti-lock braking systems (ABS). However, it ought to be considered that you have a greater potential for damaging the wheel when driving over deep chuckholes or another objects. Also, forces related to irregularities in road surface will likely be transmitted more completely from the tire to your suspension system with the vehicle on account of the reduced radial flexibility (refs. 4 and 8-10).
Hydroplaning resistance
Accumulation of water being a film beneath the footprint, which in turn causes a tire to lift in the road surface and lose traction, is referred to as hydroplaning. As the aspect ratio of any tire is lowered, or width from the tire is increased, the tire footprint area increases. The larger footprint area lessens the average pressure on the contact patch. Since footprint pressure is closely relevant to hydroplaning resistance, lower aspect ratio tire hydroplaning resistance isn't as high as that regarding high aspect ratio tires. Tread void could be increased to further improve hydroplaning resistance, but this reduces dry cornering capability (ref. 4).
Rolling resistance
Intuitively, you'll accept that lowering aspect ratio would increase a tire's radial stiffness and dimensional stability. This lessens the deflection of the tire and decreases rolling resistance, thereby improves fuel economy and reduces polluting exhaust emissions.
Lowering the aspect ratio also increases circumferential stiffness; hence energy loss at high speeds is reduced. At low speed, reducing the radial tire section height is less powerful on rolling loss, with respect to bias tires. But, at high speeds the section height has considerable relation to rolling resistance (refs. 7-10).
Tread wear As mentioned before, decreasing the aspect ratio cuts down on the average pressure from the contact area. It also reduces deflection from the tire because of more dimensional stability. These could bring about improving the tread wear.
Figure 2 shows the issue of aspect ratio on tread wear. The effect of aspect ratio on tread wear is a bit more obvious in bias tires than radial ones. Aspect ratio is a bit more important if the tread pattern has higher void volume or if the tire will be used in higher severity conditions (ref. 6).
FIGURE 2 OMITTED
High speed performance
Experiments demonstrate that a tire's chance to sustain high speeds is primarily related for the following two factors:
A relatively low level of heat generation; and
a tread compound with good hot tear strength.
Naturally, period of time tear strength yields lower broadband test results; however, the fall off in broadband performance could possibly be academic. Tread compound tear strength is related towards the tread compound's hardness. As the compound becomes harder, the tear strength increases. However, its traction is reduced. Figure 3 shows their bond between traction and indoor high-speed test performance.
FIGURE 3 OMITTED
From the top speed capability viewpoint at least, lower aspect ratio tires can successfully use softer tread compounds. It seems that is due to the greater uniform stress distribution of such tires as compared with high aspect ratio tires. The use of the softer compound improves the traction in the tire for the track. At high speeds, that is very desirable for vehicle handling (ref. 4).
Run flat performance
When normal inflation air pressure is lost, like when a tire is punctured, the relatively thin and flexible sidewall of any tire can collapse and buckle in this particular manner which the sidewall doesn't provide its normal functions. These include radial flexibility, distribution in the weight from the vehicle, and transmission from the forces of acceleration, deceleration or cornering in the wheel towards the road.
In lower aspect ratio tires, due to improved tire structural integrity and shorter drop height (the space a wheel drops during air loss), the chance from the tire beads un-seating from your wheel is reduced. And it enables better control to get maintained in bringing the auto to a safe stop (refs. 4 and 9).
Production
Production of low aspect ratio tires is much more complicated and difficult than high aspect ratio tires.
Low aspect ratio tires are prone with a problem called 'reverse curvature,' on account of the increased width with the tire. The term reverse curvature refers for the tendency of carcass cords from the crown region to dip radially inward in the equatorial plane. This deformation creates points of inflection which could lead to premature failure. So, the right design and assembling of belt and carcass plies of low aspect ratio tires is critical (ref. 11).
The condition from the sidewall is strongly interrelated towards the value from the aspect ratio. In a decreased aspect ratio tire, as a consequence of shortening the sidewall height, these parts play a critical role. This is shown in figure 4 (ref. 8).
FIGURE 4 OMITTED
The tendency of considerably raising the peak importance of tension strain is definitely an unavoidable fact remarkably appearing as the price of aspect ratio becomes small. This causes the occurrence of cracking as well as growth to get considerably higher when aspect ratio is lowered. So, lower aspect ratio tires must use sidewall compounds with optimized properties (refs. 8 and 9).
The role on the bead section in low aspect ratio tires is a lot more prominent too. Due towards the shorter distance relating to the rim plus the road surface, it is hard to produce high rigidity and stiffness, instructed to provide greater support for carcass and sidewall of the tires, as well as build up the strain smoothly. To achieve these goals, the construction in the bead section is quite a bit different than high aspect ratio tires. For example, the complete height from the apex is increased approximately 100% and much more stiff compounds can be used for various parts on the bead zone. Also, a thick rubber part that is referred to as a pad or rim cushion is utilized in low aspect ratio tires. The pad is really a relatively hard and high modulus rubber strip located below the sidewall, and give more stiffness and rigidity on the bead section on the tire. Therefore, it assists the tire being fitted about the wheel rim. It also serves to guard the sidewall from being damaged with the rim flange if the tire is subjected to some large flexing deformation (refs. 7 and 9).
Softer compounds for that tread and much more stiff compounds inside the bead division of low aspect ratio tires need more precautions to get taken into account during mixing and extrusion processes.
Also, assembling on the tire's components and building the green tire is a lot more difficult and requires better precision. This could lessen the productivity of low aspect ratio tires in comparison with high aspect ratio tires (refs. 8-12).
Other considerations
In addition to your above mentioned subjects, lower aspect ratio tires have a far more cosmetic appearance and sleek contour around match the aerodynamic style of new modern automobiles. For these reasons, the trends to decreasing the aspect ratio of tires, to meet top rated tire requirements, is continued. Today, a tire without sidewall, through an aspect ratio of 0.2, has become invented (refs. 9 and 10).
This trend is just not limited to passenger car tires (refs. 13-15). In a new and patented work, Bridgestone is promoting an ultra-low aspect ratio tire for bus and truck use containing the technology for traditional dual-mounted drive tires to get replaced with one particular tire. A number of benefits is reported, for instance greater durability, low level of noise, improved ride and comfort, decrease in rolling resistance (around 10%), weight savings which is between 80-110 kg around the drive axle, and much less width (175 mm) than equivalent dual tires (ref. 16).
References
(1.) D. Beach, J. Schroeder; "An breakdown of tire technology, " Rubber World, vol. 222, no. 6, pp. 44-53 (Sept. 2000).
(2.) "The tire industry: A new perspective to 2005, " The Tire Industry, Dec. 1997.
(3.) R.A. Ridha and W.W. Curtiss, "Development in tire technology, " in Rubber Products' Manufacturing Technology, ed. by M.M. Hall, A.K. Bhowmick and H.A. Benewey, Marcel Dekker Inc.
(4.) J.T. Warchol and R.C. Schroeder, "Ultra low aspect ratio, high end tire development, " SAE Technical Paper Series, No. 841290.
(5.) G.Z. Wu and X.M. He, "Effects' of aspect ratio on stress and deformation of radial passenger tires," Tire Science and Technology, TSTCA, vol. 20, no. 2, April-June 1992, pp. 74-82.
(6.) A.G. Veith; "Tire treadwear-a comprehensive evaluation of factors: Generic type, aspect ratio, tread pattern, tread composition. Part II, outcomes of primary treadwear test series," Tire Science and Technology, TSTCA, vol. 14, no. 4, Oct.-Dec. 1986, pp. 219-234.
(7.) M.H.R. Ghoreishy, M. Karrabi and M. Razavi, "Development of optimized compounds with the components on the bead section of an low aspect ratio steel-belted radial tire," Iranian Polymer Journal, vol. 10, no. 2, pp. 115-123 (2001).
(8.) United States Patent, No. 5, 746,860.
(9.) United States Patent, No. 6,499,521 B2.
(10.) United States Patent, No. 4,811,771.
(11.) United States Patent, No. 4, 967, 817.
(12.) United States Patent, No. 5,693,160.
(13.) United States Patent, No. 4,082,132.
(14.) United States Patent, No. 5,634,995.
(15.) United States Patent, No. 4,112, 994.
(16.) "Ultra-wide bus and truck tire by Bridgestone," Tires and Accessories; no. 7, Aug. 2001, p. 56.
Vahdat Vahedy and Mir Hamid Reza Ghoreishi, Iran Polymer Institute
FIGURE 1 OMITTED
Passenger car tire aspect ratios historically have decreased and attempt to decrease further. The aspect ratio of the very first pneumatic tires, manufactured for passenger cars (1905-1915), was ready 1.10. Until the 1930s, aspect ratios remained at approximately 1.0. In 1984, the aspect ratio of 60% of produced tires was 80%. In 1996, this amount was reduced to 10%, and quite a few of produced tires aspect ratios were between 50% and 65% (refs. 1-4).
Effects of aspect ratio on stresses and deformations of tires Distribution of stresses and deformation in tires is one with the primary properties which could determine several tire properties and gratification, which is greatly suffering from aspect ratio.
Studies demonstrate that when the aspect ratio is decreased, the stresses in belt cords increase, while stresses down the carcass cords and circumferential stresses inside bead wires decrease. Also, the distribution of stresses seems being more during lower aspect ratio tires. According to your new tire design theories (for instance TCOT, D SOC), the stresses from the belt cord increase, plus the tension on the carcass cords decreases simultaneously, which ends up in a marked improvement in tire properties. Decreasing aspect ratio also results in decrease of normal displacement in sidewalls and radial displacement on the crown center (ref. 5).
Handling performance
In lower aspect ratio tires, lowering of flexible sidewall height adds to the structural integrity in the tire and increases radial, lateral and circumferential stiffness. Increased lateral stiffness improves cornering performance. Increased circumferential stiffness improves handling during acceleration and deceleration, particularly combination with cornering. Shorter sidewalls, in low aspect ratio tires, be able to increase rim diameter without increasing tire outer diameter. Higher rim diameter is desirable for anti-lock braking systems (ABS). However, it ought to be considered that you have a greater potential for damaging the wheel when driving over deep chuckholes or another objects. Also, forces related to irregularities in road surface will likely be transmitted more completely from the tire to your suspension system with the vehicle on account of the reduced radial flexibility (refs. 4 and 8-10).
Hydroplaning resistance
Accumulation of water being a film beneath the footprint, which in turn causes a tire to lift in the road surface and lose traction, is referred to as hydroplaning. As the aspect ratio of any tire is lowered, or width from the tire is increased, the tire footprint area increases. The larger footprint area lessens the average pressure on the contact patch. Since footprint pressure is closely relevant to hydroplaning resistance, lower aspect ratio tire hydroplaning resistance isn't as high as that regarding high aspect ratio tires. Tread void could be increased to further improve hydroplaning resistance, but this reduces dry cornering capability (ref. 4).
Rolling resistance
Intuitively, you'll accept that lowering aspect ratio would increase a tire's radial stiffness and dimensional stability. This lessens the deflection of the tire and decreases rolling resistance, thereby improves fuel economy and reduces polluting exhaust emissions.
Lowering the aspect ratio also increases circumferential stiffness; hence energy loss at high speeds is reduced. At low speed, reducing the radial tire section height is less powerful on rolling loss, with respect to bias tires. But, at high speeds the section height has considerable relation to rolling resistance (refs. 7-10).
Tread wear As mentioned before, decreasing the aspect ratio cuts down on the average pressure from the contact area. It also reduces deflection from the tire because of more dimensional stability. These could bring about improving the tread wear.
Figure 2 shows the issue of aspect ratio on tread wear. The effect of aspect ratio on tread wear is a bit more obvious in bias tires than radial ones. Aspect ratio is a bit more important if the tread pattern has higher void volume or if the tire will be used in higher severity conditions (ref. 6).
FIGURE 2 OMITTED
High speed performance
Experiments demonstrate that a tire's chance to sustain high speeds is primarily related for the following two factors:
A relatively low level of heat generation; and
a tread compound with good hot tear strength.
Naturally, period of time tear strength yields lower broadband test results; however, the fall off in broadband performance could possibly be academic. Tread compound tear strength is related towards the tread compound's hardness. As the compound becomes harder, the tear strength increases. However, its traction is reduced. Figure 3 shows their bond between traction and indoor high-speed test performance.
FIGURE 3 OMITTED
From the top speed capability viewpoint at least, lower aspect ratio tires can successfully use softer tread compounds. It seems that is due to the greater uniform stress distribution of such tires as compared with high aspect ratio tires. The use of the softer compound improves the traction in the tire for the track. At high speeds, that is very desirable for vehicle handling (ref. 4).
Run flat performance
When normal inflation air pressure is lost, like when a tire is punctured, the relatively thin and flexible sidewall of any tire can collapse and buckle in this particular manner which the sidewall doesn't provide its normal functions. These include radial flexibility, distribution in the weight from the vehicle, and transmission from the forces of acceleration, deceleration or cornering in the wheel towards the road.
In lower aspect ratio tires, due to improved tire structural integrity and shorter drop height (the space a wheel drops during air loss), the chance from the tire beads un-seating from your wheel is reduced. And it enables better control to get maintained in bringing the auto to a safe stop (refs. 4 and 9).
Production
Production of low aspect ratio tires is much more complicated and difficult than high aspect ratio tires.
Low aspect ratio tires are prone with a problem called 'reverse curvature,' on account of the increased width with the tire. The term reverse curvature refers for the tendency of carcass cords from the crown region to dip radially inward in the equatorial plane. This deformation creates points of inflection which could lead to premature failure. So, the right design and assembling of belt and carcass plies of low aspect ratio tires is critical (ref. 11).
The condition from the sidewall is strongly interrelated towards the value from the aspect ratio. In a decreased aspect ratio tire, as a consequence of shortening the sidewall height, these parts play a critical role. This is shown in figure 4 (ref. 8).
FIGURE 4 OMITTED
The tendency of considerably raising the peak importance of tension strain is definitely an unavoidable fact remarkably appearing as the price of aspect ratio becomes small. This causes the occurrence of cracking as well as growth to get considerably higher when aspect ratio is lowered. So, lower aspect ratio tires must use sidewall compounds with optimized properties (refs. 8 and 9).
The role on the bead section in low aspect ratio tires is a lot more prominent too. Due towards the shorter distance relating to the rim plus the road surface, it is hard to produce high rigidity and stiffness, instructed to provide greater support for carcass and sidewall of the tires, as well as build up the strain smoothly. To achieve these goals, the construction in the bead section is quite a bit different than high aspect ratio tires. For example, the complete height from the apex is increased approximately 100% and much more stiff compounds can be used for various parts on the bead zone. Also, a thick rubber part that is referred to as a pad or rim cushion is utilized in low aspect ratio tires. The pad is really a relatively hard and high modulus rubber strip located below the sidewall, and give more stiffness and rigidity on the bead section on the tire. Therefore, it assists the tire being fitted about the wheel rim. It also serves to guard the sidewall from being damaged with the rim flange if the tire is subjected to some large flexing deformation (refs. 7 and 9).
Softer compounds for that tread and much more stiff compounds inside the bead division of low aspect ratio tires need more precautions to get taken into account during mixing and extrusion processes.
Also, assembling on the tire's components and building the green tire is a lot more difficult and requires better precision. This could lessen the productivity of low aspect ratio tires in comparison with high aspect ratio tires (refs. 8-12).
Other considerations
In addition to your above mentioned subjects, lower aspect ratio tires have a far more cosmetic appearance and sleek contour around match the aerodynamic style of new modern automobiles. For these reasons, the trends to decreasing the aspect ratio of tires, to meet top rated tire requirements, is continued. Today, a tire without sidewall, through an aspect ratio of 0.2, has become invented (refs. 9 and 10).
This trend is just not limited to passenger car tires (refs. 13-15). In a new and patented work, Bridgestone is promoting an ultra-low aspect ratio tire for bus and truck use containing the technology for traditional dual-mounted drive tires to get replaced with one particular tire. A number of benefits is reported, for instance greater durability, low level of noise, improved ride and comfort, decrease in rolling resistance (around 10%), weight savings which is between 80-110 kg around the drive axle, and much less width (175 mm) than equivalent dual tires (ref. 16).
References
(1.) D. Beach, J. Schroeder; "An breakdown of tire technology, " Rubber World, vol. 222, no. 6, pp. 44-53 (Sept. 2000).
(2.) "The tire industry: A new perspective to 2005, " The Tire Industry, Dec. 1997.
(3.) R.A. Ridha and W.W. Curtiss, "Development in tire technology, " in Rubber Products' Manufacturing Technology, ed. by M.M. Hall, A.K. Bhowmick and H.A. Benewey, Marcel Dekker Inc.
(4.) J.T. Warchol and R.C. Schroeder, "Ultra low aspect ratio, high end tire development, " SAE Technical Paper Series, No. 841290.
(5.) G.Z. Wu and X.M. He, "Effects' of aspect ratio on stress and deformation of radial passenger tires," Tire Science and Technology, TSTCA, vol. 20, no. 2, April-June 1992, pp. 74-82.
(6.) A.G. Veith; "Tire treadwear-a comprehensive evaluation of factors: Generic type, aspect ratio, tread pattern, tread composition. Part II, outcomes of primary treadwear test series," Tire Science and Technology, TSTCA, vol. 14, no. 4, Oct.-Dec. 1986, pp. 219-234.
(7.) M.H.R. Ghoreishy, M. Karrabi and M. Razavi, "Development of optimized compounds with the components on the bead section of an low aspect ratio steel-belted radial tire," Iranian Polymer Journal, vol. 10, no. 2, pp. 115-123 (2001).
(8.) United States Patent, No. 5, 746,860.
(9.) United States Patent, No. 6,499,521 B2.
(10.) United States Patent, No. 4,811,771.
(11.) United States Patent, No. 4, 967, 817.
(12.) United States Patent, No. 5,693,160.
(13.) United States Patent, No. 4,082,132.
(14.) United States Patent, No. 5,634,995.
(15.) United States Patent, No. 4,112, 994.
(16.) "Ultra-wide bus and truck tire by Bridgestone," Tires and Accessories; no. 7, Aug. 2001, p. 56.
Vahdat Vahedy and Mir Hamid Reza Ghoreishi, Iran Polymer Institute