Why Is Using the Spare Tire Risky for Subaru Drivetrains?

Are you aware that relying on your spare tire for too long could pose a risk to your Subaru's drivetrain? While it is a great temporary solution, using the spare tire beyond its intended purpose can lead to unexpected complications for your vehicle's drivetrain system. But why is this practice risky, and how does it impact Subaru drivetrains?

The Subaru's All-Wheel Drive System

Subaru is renowned for its Symmetrical All-Wheel Drive (AWD) system, which offers superior handling, stability, and traction. This system distributes power evenly to all four wheels, ensuring optimal performance in various driving conditions. However, the AWD system's precision also means it's sensitive to differences in tire size and wear.

The Importance of Tire Matching

One of the critical aspects of maintaining a Subaru's AWD system is ensuring all four tires are matched in size and tread. Even slight differences can cause significant problems. The AWD system constantly monitors and adjusts the power sent to each wheel. If one tire is a different size, it rotates at a different speed, confusing the AWD system and potentially causing it to overcompensate.

Using a spare tire that doesn't match the other tires' size and wear can lead to differential stress. The differentials in a Subaru's drivetrain allow the wheels to rotate at different speeds, which is crucial when turning. A mismatched tire can cause these differentials to work harder, leading to increased wear and even failure.

Why Spare Tires Pose a Risk

Spare tires, especially the compact "donut" spares that come with many vehicles, are intended for temporary use only. They are designed to get you to a service station, not for prolonged driving. Using a spare tire for an extended period can create imbalances in the AWD system, leading to potential damage.

Even if the spare tire is the same size as the other tires, it's likely that the tread wear is different. Over time, your tires wear down, and if the spare has been sitting in your trunk for a while, it probably has more tread than your regular tires. This discrepancy can still cause issues with the AWD system, similar to having a different sized tire.

Potential Damage from Using a Spare Tire

Differential Wear and Tear

The differentials in your Subaru are designed to handle small variations in tire rotation speeds, but a spare tire with a different size or tread can cause excessive wear. This can lead to costly repairs and even the need to replace the differentials entirely.

Transmission and Differential Strain

An imbalanced AWD system affects the differentials and can strain the transmission. The transmission in a Subaru is finely tuned to work with the AWD system, and any discrepancies can cause it to work harder, potentially leading to overheating and premature wear.

Best Practices When You Have a Flat Tire

Use the Spare Tire Temporarily

If you get a flat tire, it's okay to use your spare to get to a safe place or a repair shop. However, minimize the distance you drive on the spare and avoid high speeds or rough terrain.

Replace the Tire Promptly

As soon as possible, replace the damaged tire with one that matches the size and tread depth of your other tires. If your tires are significantly worn, you might need to replace all four to ensure they are properly matched.

Consider a Full-Size Spare

Consider carrying a full spare tire if you frequently drive long distances or in remote areas. This will more closely match your existing tires, reducing the risk of damage to your drivetrain.

Drive safely and keep your Subaru's AWD system in top condition with Mountain Tech Inc. Schedule a tire check today!

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Why Does My Car Have a Burning Smell on The Long Downhills?

September 26, 2025

Driving downhill for an extended period puts unique demands on your vehicle, especially when it comes to braking and engine performance. If you’ve ever noticed a burning smell while descending a steep grade, it can be concerning. Sometimes the odor is harmless, but in other cases, it signals that your brakes, transmission, or other components are overheating. Knowing what causes these smells and how to address them can help you prevent damage and drive more safely. Brakes Overheating on Long Descents The most common source of a burning smell during downhill driving is overheated brakes. When you ride the brakes continuously, friction builds up between the brake pads and rotors, producing intense heat. This heat can cause the pads to emit a sharp, acrid odor as the material begins to break down. In extreme cases, overheated brakes can lead to brake fade — a condition where your braking power is reduced because the pads and rotors are too hot to function properly. If you notice a burning smell accompanied by reduced stopping ability, pull over safely and allow the brakes to cool before continuing. To prevent this, use engine braking whenever possible. Downshift to a lower gear to let your engine help control speed rather than relying entirely on the brake pedal. This reduces stress on your braking system and keeps temperatures in check. Transmission Fluid Overheating If your car has an automatic transmission, long downhill drives can sometimes overwork the transmission and cause its fluid to overheat. Transmission fluid helps cool and lubricate internal parts, but when it gets too hot, it can produce a distinctive burnt odor. This is more likely if you’re carrying a heavy load or towing while descending a steep grade. An overheating transmission can lead to significant wear if ignored, so if you notice a persistent burning smell combined with gear slipping or delayed shifting, have the system inspected as soon as possible. Burning Smells From the Clutch For vehicles with manual transmissions, a burning smell on downhills may come from an overheated clutch. This happens if you ride the clutch pedal or keep partial pressure on it while trying to control your speed. The friction between the clutch disc and flywheel generates heat, which produces a noticeable odor. To avoid clutch overheating, fully engage or fully release the pedal rather than “feathering” it. Downshifting properly and letting the engine handle more of the braking can also help reduce stress on the clutch. Engine Oil or Coolant Leaks Sometimes the burning smell isn’t related to the brakes or transmission at all. Engine oil or coolant can leak onto hot engine components, such as the exhaust manifold, where it burns and produces strong odors. An oil leak typically creates a thick, bitter smell, while burning coolant produces a sweet, syrupy scent. If the smell continues even after normal driving, or if you see smoke under the hood, it’s important to have your vehicle inspected. Ignoring leaks can lead to overheating, reduced engine performance, and costly repairs. Worn or Contaminated Brake Pads Even when you’re braking properly, worn or low-quality brake pads can overheat more easily on steep descents. Some pads use materials that produce stronger odors when hot, especially if they’ve absorbed contaminants like oil or grease. Replacing them with high-quality pads designed for your driving needs can minimize these smells and improve braking performance. How to Prevent Burning Smells on Downhills A few simple driving habits can make a big difference when it comes to avoiding overheating and burning odors: Use lower gears to take advantage of engine braking and reduce reliance on your brakes. Avoid riding the brakes for long stretches; apply firm, short braking instead. Check your brake system regularly to ensure pads, rotors, and fluid are in good condition. Inspect for leaks if burning smells persist after normal driving conditions. These steps reduce strain on critical systems and help maintain control during extended downhill driving. Expert Brake and Transmission Care at Mountain Tech Inc. If you’ve noticed a burning smell while driving downhill, let the team at Mountain Tech Inc. in Oregon City, OR, inspect your vehicle. Our technicians can determine whether the odor comes from overheated brakes, transmission fluid, the clutch, or leaking engine fluids, and we’ll address the issue before it leads to bigger problems. Schedule an appointment with Mountain Tech Inc. today and enjoy peace of mind knowing your vehicle is ready for every climb and descent.