So I just ordered new tires Friday, and knew my rear brake pads are getting thin, but wanted to check the rotors. Manual shows 4.5 mm as min thickness, and both fronts are running in the 4.6 range, so I figured thats close enough, since I will have both wheels off anyway.

Question, what is new thickness? My rear rotor is like 6.xx on average, so that seems like quite a bit of wear on the fronts.

Looking at HD rotors, and I see the "raw" rotor for $135. Since this is a wear item, I really am not looking for anything fancy, all I want is for them to stop like they should. Are the raw ones, what HD puts on from the factory. These have gone 70K.

 

Your HD parts dept could help with OEM part numbers, I would think...

 

Don't know what the "raw" rotors are, but...

Your OEM front rotors are #41500017 showing an MSRP of $155.78 on the online parts finder. It shows them available online or at the dealer...

Your OEM rear rotor is #41810-08B showing an MSRP of $155.78 on the online parts finder. It shows them available online or at the dealer...

Check with your factory service manual. I seem to remember they recommended new screw bushings and/or springs, maybe even new screws with new front rotor installs.... The rear rotor just takes screws..

I changed rotors back in 2020, on my 2016 Ultra Classic. I measured the new ones and was surprised they weren't thicker... They certainly weren't as thick as the rear rotor... I want to say they were only 5.0mm thick right out of the box, but I can't seem to find where I put those measurements...

 

Question, what is new thickness?
Do you have a way to measure the unused parts of the rotor, like the very outside edge or the inner part where the pads don't touch? That should be the OEM thickness.

My rear rotor is like 6.xx on average, so that seems like quite a bit of wear on the fronts.
I believe the front brakes do like 75%(?) of the stopping power and then if you use them even more often, they will wear at an even greater rate than the rears, like mine do.

 

Can't check the dealer, cause local shop is closed Sun-mon around here.

Hattitude
Good points. Will consult the manual to see what else they recommend to replace. Well, after looking at my service manual (HD factory) it says zip about replacing the rotors. It tells when, but not how.
Looking at section 1-42. Great detail on replacing pads. Anyone know where the info is? I know I must be missing it somewhere.

Ok found it. Section 2-14, a small mention. This manual seems all over the place. They DO recommend new screws, bushings and spring washers. Thanks for the heads up.

 

I'm curious to know what they are new as well. Rotors shouldn't wear much... What did you measure them with to get your 4.6 mm measurement? (machinist by trade) The minimum size of 4.5 mm is only .004" smaller. I'd personally replace them if they are grooved or warped.

 

I have my stock take-offs in the garage, I can mic a non-contact area when I get home tonight...

 

Don't hate, but I have a cheap harbor freight digital micrometer. I used the metric measurement because there is less math involved, lol. Mine are due for replacement, no doubt. Not just because of thickness, but they are not worn smoothly, and there is a definite "lip" on the outer ring of the rotor. Didn't measure that, but is s good idea for comparison, and a base thickness.

I got the micrometer because I only will use it for these rotors. Never needed one before that, and probably not after. I went digital because even with reading glasses, I could not read the little numbers on reg one. I'm old, what can I say.

 

It might not be the best mic for accuracy if we were going down to microns, but they are for sure close enough for measuring rotors. I'd plan on replacing them for sure.

 

Do the current rotors stop as they should? Any chattering, pulsing or fading? If not, I'd save my money and continue to run the current rotors.

The main reason for a minimum thickness has nothing to do with stopping power under normal conditions. It is mainly for temperature control and heat dissipation. Depending on your riding style, brake temperature may not be a concern. If you never experience any brake fade with your riding style and brake usage, your rotors are probably fine regardless of any thickness measurements.

Where rotor thickness really comes onto play is during high-performance riding where you are frequently and repeatedly using aggressive braking... Like at a track day or racing through the canyons. In such cases the rotors can become hot enough that you'll experience some brake fade.

Short of that, or other performance issues such as chattering or pulsing, I wouldn't be concerned about rotor thickness measurements (within reason). I would place a higher priority on performance than thickness measurements when deciding to replace or not replace.

Of course, your own peace-of-mind plays into the decision process as well. But for me, performance, or lack thereof, would be the primary determining factor.