Spare tires, often smaller and lighter than standard tires, are inflated to a greater pressure than those typically used on a vehicle. This elevated pressure compensates for their reduced size and construction, ensuring they can adequately support the vehicle’s weight and maintain proper handling characteristics, albeit for a limited time and distance.
Maintaining the recommended higher inflation pressure is critical for the temporary tire’s structural integrity and performance. Insufficient inflation can lead to premature wear, potential tire failure, and compromised vehicle stability. Historically, the need for increased pressure arose from the inherent limitations of these compact spares, which were designed as a space-saving solution, necessitating a trade-off in load-bearing capacity.
Understanding the reasons behind this specific pressure requirement is important for safe and effective use. The following sections will delve further into the design considerations, safety implications, and practical aspects of managing the pressure of these specialized tires.
1. Load-bearing capacity
The fundamental reason for increased pressure in temporary spare tires lies in their reduced load-bearing capacity compared to standard tires. These spares are designed to be smaller and lighter, a design that inherently limits the amount of weight they can safely support. To compensate, manufacturers prescribe a higher inflation pressure, which effectively increases the tire’s stiffness and its ability to carry the vehicle’s load without experiencing excessive deformation or failure.
Consider a typical scenario where a full-size tire is replaced by a temporary spare. The vehicle’s weight, previously distributed across four standard tires, is now unevenly distributed, with the spare tire bearing a significant portion of the load relative to its size. Insufficient pressure in the spare would lead to rapid wear, overheating, and an elevated risk of tire blowout. For example, a spare tire intended for 60 PSI but operated at 35 PSI under load would experience significantly increased sidewall flexing, leading to premature degradation and potential catastrophic failure. This principle also applies to vehicles with heavier curb weights; these require a higher pressure in the spare to compensate for the increased load demands.
In summary, the increased pressure in temporary spare tires directly addresses their limited load-bearing capacity. By maintaining the recommended inflation level, the tire’s structural integrity is preserved, reducing the risks associated with overloading. Awareness of this relationship is vital for safe vehicle operation when utilizing a temporary spare tire, reminding drivers to adhere to the manufacturer’s pressure specifications and to replace the spare as soon as practical with a standard tire.
2. Smaller tire volume
The reduced dimensions of temporary spare tires significantly influence the need for increased inflation pressure. This diminished volume directly impacts the tire’s ability to support vehicle weight and maintain stability.
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Reduced Air Capacity
The smaller internal volume of the spare tire means it contains less air overall. To achieve the same load-bearing capacity as a larger tire with more air, the pressure within the spare must be increased. This compensates for the reduced volume and ensures the tire can support the vehicle’s weight without excessive deformation.
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Increased Pressure per Unit Area
With a smaller contact patch, the pressure exerted on the road surface is more concentrated. A higher internal pressure helps distribute the load more evenly across this smaller area, preventing localized stress and premature wear. The increased pressure provides a more rigid structure, allowing the tire to maintain its shape under load.
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Impact on Rolling Resistance
Although counterintuitive, the higher pressure mitigates excessive rolling resistance that would result from a significantly underinflated, smaller tire. The increased stiffness reduces sidewall flex, minimizing energy loss as the tire rotates. This becomes especially crucial for a temporary spare designed for limited use.
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Thermal Considerations
A smaller tire volume is more susceptible to temperature increases due to friction and flexing. The higher inflation pressure helps to minimize this flexing, thereby reducing heat buildup. This is vital for preventing tire damage and potential failure, particularly during longer trips or at higher speeds.
In conclusion, the limited air capacity inherent in a smaller tire volume necessitates increased inflation pressure to ensure adequate load support, optimized rolling resistance, and minimized thermal stress. These factors underscore the importance of adhering to the manufacturer’s recommended pressure for temporary spare tires to maintain vehicle safety and handling.
3. Sidewall stiffness compromise
Temporary spare tires often exhibit a reduced sidewall stiffness compared to standard tires to achieve a smaller overall size and weight. This design compromise directly influences the need for a higher inflation pressure. A less rigid sidewall deforms more readily under load, increasing the risk of tire damage and compromised handling. Higher inflation pressure effectively stiffens the sidewall, mitigating this inherent weakness and enabling the tire to bear the vehicle’s weight safely. For example, a compact spare might have a significantly thinner sidewall profile than a standard radial tire, leading to excessive flexing under load if not properly inflated. This flexing generates heat, accelerating wear and potentially leading to a blowout. The elevated pressure counteracts this by providing additional support and reducing the degree of sidewall deformation.
The impact of sidewall stiffness compromise is particularly evident in vehicle handling. A softer sidewall leads to increased body roll during cornering and a less precise steering response. By increasing the inflation pressure, the spare tire’s sidewall becomes more resistant to lateral forces, improving stability and control. In practice, this means a vehicle equipped with a properly inflated spare tire will exhibit less noticeable handling differences compared to when a standard tire is in place. Conversely, a spare tire with insufficient pressure will exacerbate the handling issues, making the vehicle feel unstable and less responsive, especially at higher speeds or during emergency maneuvers. Adhering to the recommended pressure specification effectively minimizes the negative effects of the reduced sidewall stiffness.
In summary, the reduced sidewall stiffness in temporary spare tires necessitates a higher inflation pressure to compensate for this design compromise. The increased pressure enhances load-bearing capacity, minimizes sidewall flexing, and improves handling stability. Understanding this relationship is critical for ensuring safe vehicle operation when using a temporary spare. Regular pressure checks are essential to mitigate risks associated with under-inflation, reinforcing the importance of adhering to manufacturer recommendations for temporary spare tires.
4. Fuel efficiency optimization
While not the primary design goal, the increased inflation pressure in temporary spare tires contributes indirectly to fuel efficiency optimization, even during their limited usage period. This effect arises from minimizing energy loss due to rolling resistance.
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Reduced Rolling Resistance
Higher inflation pressure decreases the contact patch between the tire and the road surface. This reduction minimizes the energy lost to friction as the tire rolls, thereby improving fuel economy. While the improvement is marginal during the brief lifespan of a spare tire’s use, it is a tangible benefit.
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Minimized Sidewall Flex
Insufficient tire pressure leads to increased sidewall flexing. This flexing absorbs energy, which is then dissipated as heat, reducing fuel efficiency. Higher pressure reduces sidewall deformation, preserving energy that would otherwise be lost, translating to a slight improvement in miles per gallon during the spare’s use.
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Optimal Tire Shape Maintenance
Maintaining the correct tire shape through proper inflation helps the tire roll more efficiently. Underinflated tires deform more easily, leading to increased drag and reduced fuel economy. The higher pressure in a temporary spare ensures it maintains a more circular profile, reducing energy waste.
Although fuel savings are secondary to safety and load-bearing considerations, the increased inflation pressure in temporary spare tires does contribute to fuel efficiency optimization by minimizing rolling resistance and sidewall flexing. This underscores the multifaceted benefits of adhering to recommended inflation pressures, even for short-term tire usage.
5. Preventing sidewall flexing
The elevated inflation pressure in temporary spare tires is intrinsically linked to the necessity of preventing excessive sidewall flexing. The design characteristics of these spares, which prioritize compactness and reduced weight, often result in less robust sidewalls compared to standard tires. These thinner sidewalls are inherently more susceptible to deformation under load, particularly when subjected to the weight of a vehicle. Insufficient inflation exacerbates this susceptibility, leading to significant sidewall flex, which has detrimental consequences for tire performance, durability, and vehicle safety. A real-world example includes a spare tire deflecting visibly inwards under load, especially during cornering, due to inadequate pressure. This flexing concentrates stress within the sidewall structure, promoting premature wear and increasing the likelihood of catastrophic failure. The higher prescribed pressure mitigates this risk by stiffening the sidewall, reducing the degree of deformation under load, and distributing stress more evenly across the tire structure.
The practical significance of understanding this connection lies in the ability to proactively manage the risks associated with using a temporary spare. Regularly checking and maintaining the recommended inflation pressure is crucial for ensuring that the sidewall retains its structural integrity and can effectively support the vehicle’s weight. Ignoring this aspect can lead to compromised handling, increased stopping distances, and a heightened risk of tire blowout, particularly at higher speeds or during abrupt maneuvers. Moreover, excessive sidewall flexing generates heat within the tire, further accelerating wear and potentially leading to thermal degradation of the rubber compound. The elevated pressure helps to minimize heat buildup by reducing the amount of flexing and deformation, thereby extending the lifespan of the spare tire and enhancing its overall reliability.
In summary, preventing sidewall flexing is a primary driver for the higher inflation pressure specified for temporary spare tires. The increased pressure compensates for the inherent weaknesses in the tire’s construction, enhancing its load-bearing capacity, improving handling stability, and mitigating the risks associated with premature wear and tire failure. Understanding this cause-and-effect relationship underscores the importance of adhering to manufacturer recommendations for inflation pressure, thereby ensuring safe and effective utilization of temporary spare tires. The challenge remains in consistently educating drivers about this critical aspect of vehicle maintenance and safety.
6. Minimizing heat buildup
Elevated inflation pressure in temporary spare tires plays a crucial role in mitigating heat generation during operation. This consideration is paramount due to the inherent design limitations of these tires, which can make them more susceptible to overheating under stress.
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Reduced Sidewall Flexing
Higher inflation pressure minimizes sidewall deflection as the tire rotates under load. Excessive flexing generates internal friction within the tire’s materials, converting mechanical energy into heat. By reducing this flexing, the higher pressure significantly curtails heat buildup. A tire inflated to its recommended pressure will exhibit less sidewall deformation, thus reducing the amount of heat generated during use. Conversely, an underinflated tire will flex significantly more, leading to rapid heat accumulation and potentially compromising the tire’s structural integrity.
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Optimized Rolling Resistance
Increased pressure optimizes the tire’s rolling resistance. Underinflated tires present a larger contact patch with the road surface, increasing friction and consequently generating more heat. The higher pressure reduces the contact area, minimizing friction and the associated heat generation. This effect is critical, especially during extended use or at higher speeds, where heat buildup can become a significant concern. Maintaining correct pressure ensures the tire rolls more efficiently, preventing excessive energy loss in the form of heat.
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Enhanced Structural Stability
Proper inflation pressure contributes to overall tire structural stability, which is essential for preventing localized stress concentrations. When a tire is underinflated, certain areas of the tire, particularly the shoulders, bear a disproportionate share of the load, leading to increased stress and heat generation. Maintaining higher inflation pressure helps to distribute the load more evenly across the tire, preventing localized overheating and prolonging tire life. This is particularly relevant for temporary spares, which are often used in emergency situations and may be subjected to higher than normal stresses.
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Improved Heat Dissipation
While higher pressure does not directly improve heat dissipation, it does contribute to minimizing the sources of heat generation within the tire. By reducing flexing and optimizing rolling resistance, the tire operates at a lower overall temperature, which facilitates more effective heat dissipation to the surrounding environment. This is vital for preventing thermal degradation of the tire’s materials, particularly the rubber compounds, which can become brittle and prone to failure at elevated temperatures. Maintaining correct pressure ensures the tire operates within its design temperature limits, enhancing safety and reliability.
These facets collectively underscore the importance of maintaining higher inflation pressure in temporary spare tires to minimize heat buildup. The reduction in sidewall flexing, optimized rolling resistance, enhanced structural stability, and improved heat dissipation all contribute to a safer and more reliable tire performance, especially during temporary use. Ignoring this requirement increases the risk of tire failure due to overheating, underscoring the need for diligent pressure monitoring and maintenance.
7. Enhanced rolling resistance
Temporary spare tires necessitate careful management of rolling resistance to ensure adequate performance and safety despite their smaller size and temporary nature. Inflation pressure plays a significant role in optimizing this characteristic.
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Reduced Contact Patch
Higher inflation pressure decreases the contact area between the tire and the road surface. This minimized contact area reduces friction and, consequently, the force required to roll the tire. Standard tires benefit from a larger contact patch for grip, but for temporary spares, minimizing rolling resistance becomes more critical to offset inherent performance limitations. A smaller contact patch translates to less energy expenditure and lower fuel consumption during the limited time the spare is in use.
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Decreased Hysteresis Losses
Hysteresis refers to the energy lost as a tire deforms and recovers during each revolution. Underinflated tires exhibit greater deformation and, therefore, higher hysteresis losses, resulting in increased rolling resistance. Elevating the inflation pressure reduces the degree of deformation, minimizing these losses and contributing to lower rolling resistance. For instance, a tire inflated to 60 PSI will deform less than the same tire at 30 PSI, requiring less energy to maintain its rolling motion.
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Optimized Tire Shape
Proper inflation pressure helps maintain the tire’s optimal shape, which minimizes rolling resistance. Underinflated tires tend to bulge, increasing the contact area and causing greater deformation. By maintaining the recommended higher pressure, the spare tire retains a more circular profile, reducing drag and improving its rolling efficiency. This optimized shape is particularly important for temporary spares, as it helps to compensate for their reduced size and load-bearing capacity.
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Heat Buildup Mitigation
Rolling resistance directly correlates with heat generation within the tire. Increased rolling resistance leads to higher heat buildup due to internal friction. The elevated inflation pressure, by reducing rolling resistance, also mitigates heat accumulation within the tire, helping to prevent premature wear and potential tire failure. This relationship is crucial for temporary spares, as they are often used under emergency conditions and may be subjected to higher stress levels.
In summary, the higher inflation pressure in temporary spare tires is a key factor in enhancing rolling resistance, thereby improving fuel efficiency, minimizing heat buildup, and compensating for performance limitations. By reducing the contact patch, decreasing hysteresis losses, optimizing tire shape, and mitigating heat generation, the elevated pressure ensures that the spare tire operates as efficiently and safely as possible during its temporary deployment. Understanding this connection is essential for ensuring proper tire maintenance and safe vehicle operation.
8. Vehicle handling stability
Vehicle handling stability is a critical safety aspect directly influenced by tire characteristics, including inflation pressure. When a temporary spare tire is deployed, its design differences from standard tires necessitate specific adjustments to maintain acceptable handling performance. Elevated inflation pressure is a key factor in mitigating the negative impacts of these design compromises on vehicle stability.
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Compensating for Reduced Sidewall Stiffness
Temporary spare tires often feature less rigid sidewalls to minimize size and weight. This reduced stiffness allows for greater sidewall flex, compromising handling precision and increasing body roll during cornering. Higher inflation pressure effectively stiffens the sidewall, reducing flex and improving responsiveness, thereby enhancing vehicle stability. The pressure counteracts the inherent weakness in the spare tire’s construction, providing a more stable platform for maneuvering.
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Maintaining Load Distribution
Uneven tire pressures can lead to unpredictable handling behavior. When a standard tire is replaced with a smaller spare, the load distribution across the vehicle changes. Higher inflation pressure in the spare helps to ensure that the load is adequately supported, preventing excessive weight transfer and maintaining a more balanced distribution. This improved load support stabilizes the vehicle, particularly during braking and cornering maneuvers.
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Mitigating Oversteer/Understeer
Differences in tire characteristics between the spare and standard tires can induce oversteer or understeer tendencies, making the vehicle more challenging to control. The higher inflation pressure in the spare helps to minimize these imbalances by providing a more predictable and consistent response. This can be critical in emergency situations, where maintaining control is paramount. By promoting a more neutral handling profile, the spare tire contributes to safer vehicle operation.
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Enhancing Steering Response
Underinflated tires exhibit sluggish steering response, making the vehicle feel less connected to the road. The higher inflation pressure in the temporary spare enhances steering responsiveness, allowing for quicker and more precise corrections. This improvement is particularly important in avoiding obstacles and navigating challenging road conditions. The enhanced steering feel provides the driver with greater confidence and control, even with the limitations of a temporary spare.
The elevated inflation pressure in temporary spare tires directly addresses the challenges posed to vehicle handling stability by their design differences. By compensating for reduced sidewall stiffness, maintaining load distribution, mitigating oversteer/understeer tendencies, and enhancing steering response, the higher pressure contributes to a safer and more predictable driving experience. Regular monitoring and maintenance of the recommended inflation pressure are essential for ensuring that the spare tire performs its intended function without compromising vehicle stability.
9. Compact storage design
Compact storage design is a primary driver in the development and implementation of temporary spare tires, influencing the necessity for elevated inflation pressures. The requirement for a smaller, lighter spare necessitates compromises in tire construction, directly impacting load-bearing capacity and handling characteristics. Manufacturers prioritize space efficiency; therefore, the spare tire volume is significantly reduced compared to standard tires. This reduction, in turn, demands increased pressure to compensate for the diminished air volume and maintain adequate support for the vehicle’s weight. The higher pressure becomes a critical design element, ensuring the compact spare can fulfill its intended function safely and effectively.
For instance, consider a vehicle originally equipped with 225/65R17 tires. A temporary spare designed for the same vehicle might be a T135/80D16, a significantly smaller tire. The reduced diameter and width necessitate a higher inflation pressure, often around 60 PSI, compared to the standard tire’s recommended 35 PSI. This pressure differential is crucial for maintaining a comparable load-bearing capacity despite the reduced dimensions. The compact design, therefore, dictates the need for this higher pressure as a compensatory measure, safeguarding against tire failure and ensuring the vehicle can be driven safely, albeit at reduced speeds and for limited distances. The practical application of this design is evident in modern vehicles where trunk space is at a premium, necessitating the use of these smaller, high-pressure spares.
In summary, the compact storage design of temporary spare tires is inextricably linked to the requirement for higher inflation pressures. This design trade-off necessitates increased pressure to compensate for reduced size and maintain adequate load-bearing capacity and handling stability. Understanding this relationship is paramount for ensuring safe and effective use of temporary spares, highlighting the importance of adhering to manufacturer-specified inflation recommendations. The challenge remains in effectively communicating this critical information to drivers, promoting responsible tire maintenance and safe vehicle operation.
Frequently Asked Questions
The following addresses common inquiries regarding the specific pressure requirements of temporary spare tires, designed for limited use and distinct from standard vehicle tires.
Question 1: Why do spare tires require significantly higher pressure compared to standard tires?
Temporary spare tires are engineered with a smaller volume and lighter construction than standard tires. To compensate for these design limitations and maintain adequate load-bearing capacity, a higher inflation pressure is mandated. This elevated pressure enables the spare tire to support the vehicle’s weight safely, albeit for a limited duration and at reduced speeds.
Question 2: What are the potential consequences of underinflating a spare tire?
Underinflating a temporary spare tire can lead to several adverse outcomes, including premature wear, increased risk of tire failure, compromised handling stability, and diminished fuel efficiency. Insufficient pressure increases sidewall flexing, leading to heat buildup and potential tire blowout. Vehicle handling can become unpredictable, particularly during cornering or emergency maneuvers.
Question 3: Is it permissible to inflate a spare tire beyond the maximum pressure indicated on the sidewall?
Exceeding the maximum pressure specified on the tire sidewall is strictly prohibited. Overinflation can compromise the tire’s structural integrity, increasing the risk of blowout and diminishing ride quality. Adhering to the manufacturer’s recommended pressure is crucial for safe operation.
Question 4: How often should the pressure in a spare tire be checked?
The pressure in a spare tire should be inspected regularly, ideally at least once a month and before any extended road trips. Pressure loss can occur over time due to permeation, temperature fluctuations, and minor leaks. Maintaining the correct pressure ensures the spare tire is ready for use when needed.
Question 5: Can a standard tire be used as a spare tire, and what pressure should it be inflated to?
While a standard tire can be used as a spare, it must meet or exceed the vehicle manufacturer’s specifications for tire size and load rating. The inflation pressure should correspond to the recommended pressure for standard tires, as indicated on the vehicle’s tire placard or in the owner’s manual. Do not inflate a standard tire to the higher pressure specified for temporary spares.
Question 6: Are there any specific precautions to observe when driving with a spare tire?
When driving with a temporary spare tire, adherence to the manufacturer’s speed and distance limitations is paramount. Typically, these tires are intended for speeds no greater than 50 mph (80 km/h) and distances no longer than 70 miles (110 km). Avoid abrupt maneuvers, such as hard braking or sharp turns, as the handling characteristics may be compromised. Replace the spare tire with a standard tire as soon as feasible.
Proper maintenance and adherence to manufacturer recommendations are paramount for safe and effective utilization of temporary spare tires. Regular pressure checks and prompt replacement with a standard tire are essential for optimal vehicle performance and safety.
The following section will transition to a discussion of alternative tire solutions and their implications for vehicle safety and performance.
Tips for Managing Spare Tires and Inflation Pressure
This section provides essential guidelines for maintaining spare tires and understanding the importance of correct inflation pressure. Adherence to these tips promotes safety and prolongs the lifespan of the spare tire.
Tip 1: Verify Recommended Inflation Pressure. The vehicle’s owner’s manual or the tire placard on the doorjamb specifies the correct inflation pressure for the spare tire. This value must be adhered to for optimal performance and safety. Failure to verify this value could lead to tire failure.
Tip 2: Use a Calibrated Tire Pressure Gauge. Employ a reliable and calibrated tire pressure gauge when checking and adjusting inflation pressure. Inaccurate gauges can lead to over or underinflation, both detrimental to tire performance. Consider digital gauges for enhanced precision.
Tip 3: Inspect the Spare Tire Regularly. Conduct routine inspections of the spare tire for signs of damage, such as cuts, bulges, or uneven wear. Any signs of damage necessitate replacement of the tire to ensure safe operation. Neglecting regular inspections may lead to unforeseen tire failures.
Tip 4: Adjust Pressure When the Tire is Cold. Check and adjust inflation pressure when the tire is cold, ideally before the vehicle has been driven. Driving causes the tire to heat up, artificially inflating the pressure reading. Cold inflation ensures accuracy.
Tip 5: Understand Temporary Speed and Distance Limitations. Temporary spare tires are designed for limited use. Always adhere to the manufacturer’s recommended speed and distance limitations, typically 50 mph and 70 miles, respectively. Exceeding these limits can compromise tire integrity.
Tip 6: Reinstall the Standard Tire Promptly. Replace the spare tire with a standard tire as soon as possible. Prolonged use of the temporary spare can negatively impact handling and stability. Returning to a full-size tire configuration is the safest course of action.
Tip 7: Consider Tire Pressure Monitoring Systems (TPMS). Certain aftermarket TPMS systems can monitor the pressure in the spare tire, providing real-time alerts of any pressure loss. This technology promotes proactive maintenance and prevents unforeseen issues.
These guidelines emphasize the importance of diligent maintenance and a thorough understanding of temporary spare tire limitations. Adhering to these tips promotes vehicle safety and prolongs the lifespan of the spare tire. Regular pressure checks, adherence to speed and distance limitations, and prompt replacement with a standard tire are critical components of responsible vehicle ownership.
The following section will transition to a summary of key considerations discussed in this article.
Why Do Spare Tires Have Higher PSI
This exploration addressed why temporary spare tires are inflated to a greater pressure. The analysis detailed the design compromises inherent in compact spares, necessitating increased pressure to compensate for reduced size and load-bearing capacity. Factors such as minimized sidewall flexing, enhanced rolling resistance, and vehicle handling stability were identified as key drivers behind this specific pressure requirement. The consequences of neglecting proper inflation, including premature tire failure and compromised vehicle safety, were also examined.
Understanding the rationale behind the elevated pressure in spare tires is critical for responsible vehicle maintenance. Adherence to manufacturer-specified inflation pressures is paramount for ensuring safe and effective utilization of these temporary solutions. Neglecting this fundamental aspect can undermine the vehicle’s handling characteristics and increase the risk of catastrophic tire failure, emphasizing the importance of informed and proactive maintenance practices.
