Brake pads are one of the most important safety components in your vehicle. They provide the friction required to slow down and stop your car. But how many brake pads actually come in a set? Do you need to replace all of them at once or just certain ones? This article will explain everything you need to know about brake pads and how they are sold and replaced.
1. A set of brake pads contains 4 pads – 2 pads per wheel to pinch the rotor evenly.
2. Front and rear pads are different sizes to match caliper design. Always use the correct pads for each axle.
3. Only replace the worn front or rear axle set, not necessarily all wheels at once.
4. Replacing single pads can cause uneven braking and loss of control. Always install new pads in pairs.
5. Rotors don’t always need replacement if pads are changed before excessive wear. But resurfacing may be needed if rotors are scored.
What Are Brake Pads?
Brake pads are friction material that presses against the brake rotor to slow down your wheels and stop the vehicle. There are separate brake pads for the front and rear wheels.
Front brake pads are larger and thicker since the front brakes handle 70% of the braking force. They experience more heat and wear than the rear.
Rear brake pads are smaller and thinner since the back wheels are responsible for only 30% of braking power. The rear pads provide stability and prevent the back end from skidding out under heavy braking.
Disc brake diagram showing brake pads
Each wheel has an inboard pad (closest to the vehicle center) and an outboard pad (farthest from the center). Pads work in pairs to squeeze the rotor evenly from both sides.
Why Are 4 Pads Needed Per Axle?
So why does each axle need 4 pads – 2 per wheel? Because when you hit the brakes, the brake caliper squeezes both pads against the rotor to create friction. Using just one pad would cause uneven and inefficient braking.
The two pads work together to slow each wheel down smoothly. If one pad wears out faster, you’ll get vibrations and pulling when braking. That’s why pads must be replaced in pairs.
How Many Pads Are In a Box?
Brake pads are sold in sets of 4 – enough for the front or rear axle. Here’s what’s in a typical box:
- 2 front inboard pads
- 2 front outboard pads
- 2 rear inboard pads
- 2 rear outboard pads
So one box contains the 4 pads needed for just the front or rear wheels.
To replace all pads on a vehicle with disc brakes, you’ll need two boxes – one for the front axle and one for the rear.
Some vehicles have rear drum brakes with shoes instead of pads. But the front discs still use pads.
Do Front and Rear Pads Look Different?
Yes, front and rear brake pads usually look different because of their different sizes and friction material:
- Front pads are much thicker and bulkier to handle the higher braking forces. They may have grooves or slots for heat dissipation.
- Rear pads are thinner and smaller in surface area since less friction is needed. The friction material also varies to optimize stability.
You cannot interchange front and rear pads since they are designed specifically to fit their brake caliper. Always check your owner’s manual for the right part numbers.
When Should Brake Pads Be Replaced?
Brake pads wear down over time and need replacement every 40,000-70,000 miles depending on driving conditions. Here are signs that your brake pads need changing:
- High-pitched squealing or grinding noises when braking
- Vibration in the steering wheel or brake pedal
- Longer stopping distances
- Brake fluid leaks as pads wear down
Look for pad material thickness of 2-3 mm or less – then it’s time for new pads.
Do I Need to Replace All 4 Brake Pads at Once?
You don’t need to replace all four wheel pads at the same time – just the front or rear axle set.
Since the front brakes wear faster, the front pads typically need replacement more often than the rear. If you only hear grinding or feel vibration when braking, then likely just the front pads need changing.
However, if the rears are also worn out, you can do all four wheels together. Replacing pads in axle sets is crucial to prevent uneven braking.
Staggering front and rear changes is fine. But each axle must be done together for safety.
What If Pads Aren’t Replaced in Pairs?
Replacing just one brake pad instead of both on each wheel can be extremely hazardous and compromise braking ability. When you press the brake pedal, a single new pad gripping the rotor will cause uneven braking forces between the left and right wheels.
This imbalance makes the vehicle pull sharply to one side when braking. The driver can lose control of steering as one side slows down faster than the other. Sudden swerving or spinning out could occur under hard braking, increasing the risk of an accident.
Uneven pad wear also leads to accelerated damage on the new pad and rotor. The fresh pad takes the brunt of braking force and gets hotter than the worn opposing pad. This concentrated heat causes glazing and cracks in the friction material. The thinner worn pad allows the rotor to overheat and warp on that side. Replacing pads in pairs distributes wear and heat evenly to prevent premature failure.
Always replace worn brake pads in complete axle sets, even if it’s more expensive than just replacing one pad. Compromising safety to save money is never worth the risk of brake failure. Following the manufacturer’s replacement schedule maintains the brake system at peak performance.
Do Rotors Need Replacement With Pads?
Not necessarily. If you replace pads on time before they wear down too far, the rotors may not need replacement.
However, if pads are worn to the metal backing, they can score and damage the rotor surface. Then the rotors will need resurfacing or replacement.
Look for deep grooves, pits, or thickness variation in the rotor. If damage is minor, the rotor can be machined to a smooth surface again and reused.
Step-by-Step Guide to Installing New Brake Pads
Replacing your brake pads is easy to do yourself and can save on labor costs. Follow these steps closely for proper installation:
- Clean the brake carrier and caliper where the pads sit. Use brake cleaner spray and a rag to thoroughly remove any debris, rust or old pad material from the caliper and brake carrier plate. This ensures the new pads seat cleanly with maximum contact.
- Check that new pads are seated properly without rubbing. The pads should fit snugly in the caliper without touching the rotor surface. Spin the wheel and make sure there is no friction. Adjust pad placement if needed. Improper seating can reduce braking ability.
- Avoid oil or grease on the pads which can damage friction material. Brake fluid, lubricants or spilled oil will contaminate the pads. Use brake cleaner if needed to remove any fluids from the caliper or rotor. Oil-contaminated pads must be replaced.
- “Bed-in” pads with light braking pressure for the first 200 miles. New pads require this break-in period to transfer pad material evenly across the rotor surface. Make repeated stops from 40-5 mph, avoiding hard braking. This allows the pads to adjust to the rotor shape and seat perfectly.
Proper pad installation optimizes braking performance. Always consult your vehicle repair manual for the exact pad replacement procedure. Taking care during initial bed-in stops prevents glazing and extends pad and rotor life. Maintaining your brake system keeps you safe on the road.
Frequently Asked Questions
How many brake pads are on a car?
There are 8 total brake pads on a typical car – 4 pads per axle (2 per wheel). Each wheel has an inboard and outboard pad.
Do you have to change all 4 brake pads?
No, you only need to change the front or rear axle set. But always replace in pairs within each axle.
Can you mix front and rear brake pads?
No. Front and rear pads are different in size, friction material, and design to fit their brake caliper.
How much does a brake pad replacement cost?
Front pad replacement costs $150-$250 for parts and labor. Rear pads cost $125-$200. So all 4 pads could be $300-$450.
How long do brake pads last?
Around 40,000-70,000 miles depending on driving style. Aggressive driving wears pads faster.