Can you drive a car with bad brake rotors?


 Short answer, I don’t recommend it! We have discussed the basics of brake physics and operation in a couple of previous blogs to which I will leave links at the end of this article, But in a nut shell your brakes convert kinetic energy into heat through friction and dissipate this heat in order to slow the vehicle.

In an extreme example like in the picture below it is obvious that not only is all of the brake friction material gone but so is half of the rotor. Worn down to the cooling fins, there is no rotor surface to act as a friction surface. This also leads to over extending the brake caliper piston to the point of having it come out of its bore causing caliper failure as well. At this point things can quickly escalate from poor or noisy braking to a vehicle that will not stop.



How do you know when you need new brake rotors?

As a driver it’s a little more difficult to know the answer to this question. There are some signs that at the minimum, indicate that it’s time to go in for a brake inspection. These include brake pedal pulsation when braking, brake noise or “squeal” or having a shake in the steering wheel when braking.

The true indicator of knowing that a brake rotor needs to be replaced is measurements. These include parallelism, run out and minimum thickness. Ok, sometimes it’s obvious as indicated in the previous pic! Let’s go over these quickly.

Parallelism; the state of being parallel or of corresponding in some way. The easiest way to explain this is to say that as the overall thickness as measured in various locations around the rotor is uneven. Often caused by a “hard” spot or spots in the metal of the rotor. This condition is best cured by replacement of the rotor.

Run out; this condition is best described as “wavy” with the thickness being consistent but not flat. This condition can often be caused by overheating the brakes and can be resolve by “turning” or machining the rotors on a brake lathe as pictured below. Assuming there is sufficient thickness left to the rotor.

Minimum thickness; all brake rotors have tolerances. These being “Nominal” thickness, “Machine to” thickness and “Discard” thickness. Nominal can be thought of as normal or the beginning thickness of a new rotor.  The machine to thickness is a measurement that allows us to “turn” a rotor, which removes material and reduces its ability to absorb and dissipate heat, but keeps the rotor at a safe thickness for normal operation. Finally the discard thickness is pretty obvious, the rotor is too thin to effectively and safely stop the car and needs to be discarded.





How much does it cost to replace rotors?

Cost of replacing your brake rotors can vary a bit depending on a number of things. This brings up a couple of other things we might want to look at. Specifically, ability to do the job of bringing your car to a safe stop and survive, or more simply put – lifespan.

Here’s a quick overview of how cars and trucks have changed. As we have moved forward in time manufactures have made vehicles lighter in an effort to be more fuel efficient and meet constantly changing EPA requirements. This has led to many changes in all of the vehicles systems. For example radiators are not only made of aluminum to reduce weight but also have reduced capacity compared to previous models, further reducing weight. The side effect of this is that radiators are less expensive but have a shorter lifespan and with reduced coolant capacity have a narrow margin of error. Meaning that a small leak or a loose radiator cap can quickly lead to overheating when compared to an older model with a significantly greater amount of coolant which would take longer to reach a point of overheating.

OK, what does the cooling system have to do with braking? It is the same principle of being lighter in weight and closer to its minimum tolerances. What does this mean for you the vehicles owner/driver? While newer cars and trucks in most cases still have the same set of tolerances, nominal, machine to and discard, the rotors are often not as efficient as earlier models if machined. This means that if we do a brake job on your car and machine the rotors within specifications you might just be back in the shop with warped rotors that have been overheated in normal driving or a trip over the mountains.

Some models of light trucks and SUVs have even had problems right out of the factory with rotors that are too light for the job and require premature replacement while the brake pads have very little wear. So, tying all this back into the question of “How much does it cost to get new rotors?” We also have to consider these type of factors as well as condition and wear.


What kind of rotors are best?

I will try to make this as quick and easy as I can, considering how many factors there are to consider. There are a couple of rotor types to look at, OE replacement, Premium replacement, Drilled rotors, Slotted rotors and in some cases Drilled and slotted.

OE replacement – Factory or an equivalent aftermarket replacement made to factory specs.

Premium replacement – Aftermarket rotors engineered to be thicker and allow for better heat absorption and dissipation. Sometimes they are also coated for better heat and wear characteristics.

Drilled rotors – These are like the premium rotors but also have a pattern of small holes drilled in them which helps to cool and will shed water quicker for better braking. Down side? In some cases, overheating may lead to cracking.

Slotted rotors – these are also like the premium rotors but instead of holes drilled in them they will have machined groves that help with cooling and moving water but may increase pad wear – meaning shorter life for pads.

Drilled and slotted – simply put, they’ve got it all! 



Left to right – Drilled, Slotted, Drilled and slotted


Choosing the right brake rotor for your needs is best done based on the knowledge of whether or not your specific vehicle has any known rotor issues, the type of driving you do and the load you common carry. In most cases a good quality premium type aftermarket rotor is the best choice and a good balance between cost and quality.


Tying it all together

Actual cost for replacing your brake rotors will depend on the make and model of your vehicle, the cost of the rotor depending on which rotor type is chosen plus the cost of additional brake components that may have been damaged and the resulting labor based on the level of services needed. As a general range you could spend between $175 and $700 dollars when all is said and done.


We are always happy to perform a brake inspection and counsel with you our customer to create a balance between cost and performance as to which brake rotors, pads and services will best suit your driving and braking needs. Call London’s Automotive, Inc. anytime for assistance 541-753-4444
For more information on brakes, how they work and serviciong them see our other blog posts, How to Stop Safer and Faster, How Much Does It Cost To Get A Brake Job?, Is It Necessary To Flush Brake Fluid?

Written by London's Automotive