When to swap Rotors

[deeldoo]

Hell yall,

If my rotor has around a millimetre lip on it but i have more than 60% brake pad material left do i have to switch rotors out and pads.

Are rotors swapped only when under the limit and the pad is gone or anytime the rotor goes under regardless how much pad you have they come of?

I genuinely don't know how i ate up a rotor but have so much pad left

[hC1001]

Measure the thickness of the rotor. Replace if below minimum thickness, its etched onto the rotor.

I normally like to use new pads but used pads may have some odd wear/grooves in them and you dont want to introduce it to the new rotor. You can sand the pads flat if you want to reuse them though. Some coarse sandpaper on a glass or stone countertop(flat surface). Circular motions, CW and CCW. You just want to level the pad material.

[deeldoo]

No i don't care to use old pads, if I'm paying 2k+ for rotors of course i would toss new pads.

I have just got conflicting information, some people have said it doesn't matter if the rotor is under minimum thickness if the pad as a ton of meat on it.

Others say doesn't matter how much pad is left if the rotor is dead you replace everything.

[hC1001]

Originally Posted by deeldoo

No i don't care to use old pads, if I'm paying 2k+ for rotors of course i would toss new pads.

I have just got conflicting information, some people have said it doesn't matter if the rotor is under minimum thickness if the pad as a ton of meat on it.

Others say doesn't matter how much pad is left if the rotor is dead you replace everything.

Steel rotors are around $250 each corner. So around $1K US dollars for a full set.

The first statement about under minimum thickness and tons of meat on pads is wrong. The thickness of the rotors(or mass) has direct correlation to the rotors heat capacity. Pad life make no difference. Rotors can begin to glaze or crack if it goes over their heat capacity.

If you do not drive aggressive or use the brakes hard, you can certainly run the rotors below minimum thickness because you will probably never exceed the heat capacity but life is not always that simple and unexpected things can happen. For safety and probably liability, the minimum thickness is there.

Used pads wont be flat and level. This decreases the surface area of the pad that touches the new flat rotor. It may also create grooves into your new rotor causing premature wear. Nowadays, rotors and pads are cheap and companies just replace. In the past they resurfaced rotors but its no longer cost effective. At some point the auto industry shifted from charging for a resurface job into charging for time. It use to be $15-$20 per rotor but now most garages dont have brake lathes because they want to charge 1 hour of labor @$120/hour.

[robbo mcs]

Originally Posted by deeldoo

Hell yall,

If my rotor has around a millimetre lip on it but i have more than 60% brake pad material left do i have to switch rotors out and pads.

Are rotors swapped only when under the limit and the pad is gone or anytime the rotor goes under regardless how much pad you have they come of?

I genuinely don't know how i ate up a rotor but have so much pad left

The accepted convention is that you measure a rotor when you change the pads, and if it is under you replace it as well.

They are engineered so that under normal use, as long as it is over minimum thickness when you install a set of pads, it should be good for the life of the pads. That means it may go under at some stage, but still be ok. They are designed that way, so that you only ever need to measure them when you change pads. It would be crazy if people had to go around and measure them every month etc

Note, this means "normal" use, ie standard pads and rotors, street use etc.

[deeldoo]

Originally Posted by hC1001

Steel rotors are around $250 each corner. So around $1K US dollars for a full set.

The first statement about under minimum thickness and tons of meat on pads is wrong. The thickness of the rotors(or mass) has direct correlation to the rotors heat capacity. Pad life make no difference. Rotors can begin to glaze or crack if it goes over their heat capacity.

If you do not drive aggressive or use the brakes hard, you can certainly run the rotors below minimum thickness because you will probably never exceed the heat capacity but life is not always that simple and unexpected things can happen. For safety and probably liability, the minimum thickness is there.

Used pads wont be flat and level. This decreases the surface area of the pad that touches the new flat rotor. It may also create grooves into your new rotor causing premature wear. Nowadays, rotors and pads are cheap and companies just replace. In the past they resurfaced rotors but its no longer cost effective. At some point the auto industry shifted from charging for a resurface job into charging for time. It use to be $15-$20 per rotor but now most garages dont have brake lathes because they want to charge 1 hour of labor @$120/hour.

Thank you this is what i needed.

No i would never put used pads on brand new rotors, no use cheaping out.

Everything you said makes much more sense.