[bavarianride]

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Most shops recommend pads + rotors together, but one indy said they will measure rotor thickness and check if it is still above min. spec. If it is above min. spec, they will do pads-only.

But should rotors be way above min. spec for pads-only to work?

[Stubok]

I'd like to know this too. My SA gave me a estimate for my brakes all round of $2k. Cars only done 40k miles.

I've heard a few others say you only do rotors every second set of pads. So it would seem doing rotors every time pads are changed seems overkill. Unless of course he rotors are below minimum thickness.

[McQueen2014]

It is not a simple answer but here is my thought process.

I check the specs for a "new" rotor and then check my current rotors. If they are over 50% worn to the minimum then I need new ones.

Also note that if there are ridges or uneven wear on the rotors your new pads will likely not bed in properly.

Putting new pads on a rotor that is close to but not below the minimum is fine initially but 6, 12, or even 24 months down the road could present a safety concern to you, your passengers, and everyone you share the roads with.

[bavarianride]

What I collected so far is this:

1. dealer service now uses a mobile brake lathe to resurface/turn rotors for rotor issues on new car warranty work.

2. my local dealer says they can turn rear rotors, but usually not for front rotors, as rear rotors do not wear as much as front ones.

3. resurfaced rotor needs to be above min. thickness threshold. One poster said rotor should be at least 1mm above min. thickness to use brake lathe.

If the above is true, then it will mean there is margin below the min. thickness to allow the new pads to wear 100% down.

There is one youtube video that says going below min. thickness can lead to hydraulic failure, but that does not make sense to me given the caliper should also have margin/play built in.

My leaning is that new rotors at $150-$200 a pair may not too bad, esp. additional labor is paid for resurfacing anyway(not sure how much).

[khj24]

When I got my car CPO they didn't put new front rotors on, but they did install new pads. I found at the hard way that my front left rotor(assuming both sides) was at 28.7mm after only a few thousand miles which in total is less than 25k on the car. Min thickness is 28.4mm.

[Billfitz]

Minimum rotor thickness is what it measures after being turned. There is no allowance made for any wear that might occur in use. There's a very simple and obvious reason why they don't do that: How would they know? Crystal ball?

[khj24]

If thats in response to me, my experience is just a data point with how my dealer treated a pad change for OP- in which they kept the stock rotors even with my rotors probably being under 29mm (extrapolating a bit) which I am sure they measured with a caliper tool for CPO cert.

[Stubok]

Just pulled out my Bentley manual. Here is what they say.

[bavarianride]

Originally Posted by Billfitz

Minimum rotor thickness is what it measures after being turned. There is no allowance made for any wear that might occur in use. There's a very simple and obvious reason why they don't do that: How would they know? Crystal ball?

So the prudent thing to do is, even if turned rotor can be right at min. thickness, it is still preferred in that case to replace rotors.

In other words, rotors turned or not cannot absolutely drop below min. thickness with old/new pads, correct?

[Billfitz]

If the rotor is 22.4mm after turning it's fine and there's nothing to be gained by replacing the rotors other than a higher repair bill.

[bavarianride]

Originally Posted by Billfitz

If the rotor is 22.4mm after turning it's fine and there's nothing to be gained by replacing the rotors other than a higher repair bill.

Hmm BMW rotors are $80-90 per axle online, that's less than 30 minutes of labor rate at local indies. Maybe easiest is to just replace then.

[oceanview]

When the pads are worn (pad sensor gives the alert), so are the rotors (or at least closed to).

I drive the pads down until it at least scratches the pad sensor and then I change pads/rotor at the same time.
Beding in process is much quicker and easier.

If you change the pads and then a few thousand miles later you need to change the rotor, where is the saving? It's even more expensive because touching it twice.

[Billfitz]

Originally Posted by oceanview

If you change the pads and then a few thousand miles later you need to change the rotor, where is the saving? It's even more expensive because touching it twice.

In forty plus years I've never seen a turned rotor wear out before the new pads wore out. They seldom can be used with a third set of pads, but only because turning them again usually takes them below minimum thickness.

BMW rotors are $80-90 per axle online, that's less than 30 minutes of labor rate at local indies. Maybe easiest is to just replace then.

Easiest, for sure. Least expensive, that depends. I doubt turning by a dealer will be any better than new rotors installed by an Indy, but turning by an Indy will be less than new rotors by an Indy. You might find a brake shop like Meineke is very competitive. I wouldn't trust a chain with much, but brakes aren't rocket science. The least expensive way is to do it yourself, most local auto parts stores can turn rotors for like $20. The PITA is needing a second car to schlep them to and from. I do my own resurfacing, but not many of us have a metal lathe in their shop.

[bavarianride]

Originally Posted by Billfitz

Easiest, for sure. Least expensive, that depends. I doubt turning by a dealer will be any better than new rotors installed by an Indy, but turning by an Indy will be less than new rotors by an Indy. You might find a brake shop like Meineke is very competitive. I wouldn't trust a chain with much, but brakes aren't rocket science. The least expensive way is to do it yourself, most local auto parts stores can turn rotors for like $20. The PITA is needing a second car to schlep them to and from. I do my own resurfacing, but not many of us have a metal lathe in their shop.

Wow your garage is well equipped!

That is true brakes should be straightforward, may be those $160-$225/hour labor cost should be reserved for complicated repairs.

My local indy is ok with customers bringing parts, it looks like BMW pads + rotors + sensor(one) + clips + bolts is less than $150 + tax/shipping, and labor is around $200, so $360-370 can be doable.

[bavarianride]

Originally Posted by oceanview

When the pads are worn (pad sensor gives the alert), so are the rotors (or at least closed to).

I drive the pads down until it at least scratches the pad sensor and then I change pads/rotor at the same time.
Beding in process is much quicker and easier.

If you change the pads and then a few thousand miles later you need to change the rotor, where is the saving? It's even more expensive because touching it twice.

From other poster's replies, it looks like rotor has margin below min. thickness for new pads to wear. As long as the resurfacing is done right and the machined rotor is still above min. thickness then it should be OK for the life of the new pads.

Now the choice of new pads can be a factor too, BMW standard non-sport pads versus aftermarket sporty pads can be quite different.

[oceanview]

Originally Posted by bavarianride

From other poster's replies, it looks like rotor has margin below min. thickness for new pads to wear. As long as the resurfacing is done right and the machined rotor is still above min. thickness then it should be OK for the life of the new pads.

Now the choice of new pads can be a factor too, BMW standard non-sport pads versus aftermarket sporty pads can be quite different.

Well, where I live, it's not allowed to go below minimum thickness of rotor. Every 2 years a car has to be taken to the DMV and if they measure it, you would need to change rotors.

Also with dimpled slotted rotors re-surfacing makes no sense.

However on all my last BMW I saw that rotors where worn almost to min. thickness when first set of pads where worn.

I don't turn the penny on that, and just replace the rotors as well instead of re-surfacing.

[celsdogg]

Originally Posted by Stubok

Just pulled out my Bentley manual. Here is what they say.

I just wanted to update this old thread with some information concerning the rear rotors for reference for the future as I came upon this thread after searching for the minimum thickness for the rears.

My wife's F30 335i has the standard (for the 335i in the US) unpainted, grey Brembo dual piston front and single piston rears. The photo above from a Bentley says the minimum thickness is 22.4. This seems to be incorrect. The size of the rear rotors when new is 330x20 as shown below and TMS' guide:




Turner's F30 Brake guide: https://www.turnermotorsport.com/t-b...ke-Differences

A reasonable guess is that allowable rear wear for the rear is also 1.6mm like the front, thus 18.4mm or below in the rear requires rotor replacement.

[Carlman3]

I usually get a new set of rotors per axle when I change brakes. I'm doing this now on an X1. I check the old rotors and if they're fine (which they will be with only 40,k miles, no grooves, etc.)
I get the new ones installed, then I can get the old ones resurfaced at my convenience at a local shop. Used to be $20/rotor.. not sure what is now post covid/inflation.
Next time I need new pads, I do the same thing, with my resurfaced rotors ready to go.