How can I tell when I need to have my rear rotors replaced?

I had my front rotors replaced in September (I think), and I know that there is a pulsing feeling in the brakes when the front rotors need to be replaced. But I don't know what to listen/feel for - in terms of the rear rotors.

As far as I know, the rear rotors are stock.

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'02 Pontiac Bonneville SE 108,539 miles, N/A, SSEi exhaust system, boat roller mount. Gone, but not forgotten.
'13 Buick Regal GS 102k miles, 270 hp, 295 lb/ft, ZZP intake.
(yes, there is a story behind my avatar.)

The "correct" method is to measure the thickness. Rotors will have a discard thickness cast into them and anything less than that number (after machining) must be replaced. The idea is to generally measure each one in several places.

According to the service manual, the minimum is 9.0mm or 0.354" (for rear rotors on the 2002). Again, if the number cast into the rotor is different, use that value instead. I expect the numbers are the same for others in this body style, but I didn't check so I'm being specific to your car.

Personally, I replace rotors every time I replace pads because they just aren't that expensive anymore. If you reuse rotors, they "should" be machined and with this cost, it's the same or less expensive to just buy new (although many people don't do this). Machining of course takes precious metal off and the thinner they get, the sooner they'll start to warp. Rear brakes provide a fraction of your overall braking and won't typically wear or warp as fast (unless you have a stuck caliper).

I'm sure there will be several others chime in as well, but this is my two cents worth. There are three things on a car I decided many years ago never to "cheap out" on... Brakes, tires and suspension/steering components.

Further to your post, "pulsing" is not an accurate or industry accepted means to determine if rotors are worn to the point of needing replacement. This simply means they have heated and cooled to such an excess that they have warped. I've seen almost brand new, low end rotors warp very quickly even though by measurement, they are well within tolerance. Warped rotors can be machined and re-used as long as the final thickness meets/exceeds the specification. Again, for the reasons above, I buy quality and replace every time.

I'm not a crazy driver, but I never have problems (pulsating, squealing, etc) with my brakes.

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I agree with Darcy. The only thing that I would add is that a visual inspection is limited, as you can only see the front of the rotor. The dust shield prevents this on the back of the rotor, which often can be quite pitted. As you believe that yours are original, that's likely to be the case. The only real way to check is to pull the rotors. If you're going to do that, may as well replace the pads and rotors at the same time.

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*Gone, but not forgotten* - Black 2000 SSEi, HIR Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, 180 degree thermostat, HS 1.9 rockers, LSx yellow springs, Intense FWI, PCM, shift kit, push rods, and 3.4 Pulley. ZZP Power Log.

Grab some centric or ACDelco rear rotors and pads off Amazon and send it. So inexpensive and quick to do.

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-Car Guy Carl
"Penelope" - 2003 SLE - 247k Miles
"Sydney" - 2000 Honda S2000 - 98k miles