[jgoens]

Was wondering if anyone knows what the minimum front disk rotor size might be for an Msport 335. I've been trying to figure it out and it seems that there are different numbers.

I have found that there is a number stamped on the rotor somewhere but I am trying to avoid pulling the wheel off if anyone already knows the answer. I just did my rears yesterday and the fronts look as if I should do them in the next month--figuring I would do them before the sensor clicks and save changing that like I did on the rears.

My rear pads (changed under warranty with the rotors) only lasted 20k miles so I did not change them but now my car has 46k miles on original front brakes. Since those rotors are not cheap if they are still spec I would prefer to not change them.

[bavarianride]

The min. rotor thickness is stamped on the hub part of the rotor, usually next to the part#. Just keep looking around the hub(it can be on the side facing down). Also since both rotors per axle are identical, do search on both rotors.

[jgoens]

Originally Posted by bavarianride

The min. rotor thickness is stamped on the hub part of the rotor, usually next to the part#. Just keep looking around the hub(it can be on the side facing down). Also since both rotors per axle are identical, do search on both rotors.

I have not been able to find it. I found the numbers on the rear, but the front discs are a different design. I'm wondering if the stamp might be on the inside.

[Billfitz]

It should be listed here: https://www.newtis.info/

[jgoens]

Originally Posted by Billfitz

It should be listed here: https://www.newtis.info/

Yes, I have been looking here, but don't know which spec I need. There are several different numbers and I'm a bit confused as to which one I need. I think you have to know the diameter of your rotor to know the spec, but how do you measure that without taking the wheel and caliper off. I tried to eye it with a tape measure, but that is pretty inaccurate. I think it is either 340 or 370.


https://www.newtis.info/tisv2/a/en/f...kes/1VnXN0TRAm

[jgoens]

So, in cross referencing realoem to see what disk I have it seems like I have this:

https://www.realoem.com/bmw/enUS/sho...49#34116792223


Though mine is not blue or ventilated--but the picture of the non-ventilated one looks like mine. In which case this would be a 340mm. I used a tape measure on my rotor and am getting 29-29.5 mm thickness which based on the TIS chart would be above spec as far as I can tell.

[Billfitz]

If you haven't had the rotors turned before it's likely they have enough meat on them to do it, assuming they're not badly scored.

[khj24]

28.4mm is the minimum on the 340mm, mine are unfortunately really close to that.

[oceanview]

Normally when the pads are worn down (and I mean down to touching the pad sensor) the rotor is due to be replaced as well.
Mostly it makes no sense to put new pads to old rotors as you would have to change the rotors just a few thousand miles later anyway.

Most shops recommend to change the pads far before they are even close to the pad sensor. Which is completely out of sense for normal street use.

I have 35 tsd miles now still 1st pads/rotors on my 2013 335i.
I know I will have to change pads in about 3tsd miles. Sure I will change rotors as well and I won't have to touch the brakes for the next 35-40 tsd miles.

[Billfitz]

Originally Posted by oceanview

Normally when the pads are worn down (and I mean down to touching the pad sensor) the rotor is due to be replaced as well.

I wouldn't say that's normal with BMW. I could not turn the rotors on my Japanese cars because the rotors were too thin to begin with, to save weight. They didn't even have a specified minimum thickness, because they were at that thickness when new, and the repair manuals specified that they were not to be resurfaced. If you do your own brakes new rotors are the norm, as few home mechanics have a rotor resurfacing lathe. Current BMW shop procedure is to resurface, as they have a resurfacing lathe that does the job on the car.

28.4mm is the minimum on the 340mm, mine are unfortunately really close to that.

With normal wear you need at least 1mm, preferably 1.5mm, thickness in excess of the minimum before resurfacing, to be sure that after resurfacing the minimum still remains.

[jgoens]

Originally Posted by oceanview

Normally when the pads are worn down (and I mean down to touching the pad sensor) the rotor is due to be replaced as well.
Mostly it makes no sense to put new pads to old rotors as you would have to change the rotors just a few thousand miles later anyway.

Most shops recommend to change the pads far before they are even close to the pad sensor. Which is completely out of sense for normal street use.

I have 35 tsd miles now still 1st pads/rotors on my 2013 335i.
I know I will have to change pads in about 3tsd miles. Sure I will change rotors as well and I won't have to touch the brakes for the next 35-40 tsd miles.

Originally Posted by Billfitz

I wouldn't say that's normal with BMW. I could not turn the rotors on my Japanese cars because the rotors were too thin to begin with, to save weight. They didn't even have a specified minimum thickness, because they were at that thickness when new, and the repair manuals specified that they were not to be resurfaced. If you do your own brakes new rotors are the norm, as few home mechanics have a rotor resurfacing lathe. Current BMW shop procedure is to resurface, as they have a resurfacing lathe that does the job on the car.
With normal wear you need at least 1mm, preferably 1.5mm, thickness in excess of the minimum before resurfacing, to be sure that after resurfacing the minimum still remains.

I have now changed the pads on front and rear but did not change or resurface the rotors. The rotors were above spec so my only concern is whether I would get squealing.

I was getting some squealing from the rears which I did last week and yesterday did a bed in process which so far has taken the squeal out.

Despite the fact that I drive very light on the brakes, my pads wear out fast due to the constant stop and go driving I do. It it is very rare I do a hard stop or heat things up and this is why I think my rotors are in such good shape yet the pads wear out quickly (20k).

[oceanview]

Originally Posted by Billfitz

With normal wear you need at least 1mm, preferably 1.5mm, thickness in excess of the minimum before resurfacing, to be sure that after resurfacing the minimum still remains.

"Minimum" defines the point when you have to replace the rotor, not where it should be after resurfacing and putting new pads on!

[Billfitz]

If it's below minimum before or after resurfacing it should be replaced. The point of being sure the rotor measures at least 1mm more than minimum before resurfacing is so you won't waste time and money on a resurfacing job that would probably take the rotor below minimum. If you want to be cheap you could not bother to resurface rotors that don't have enough material to resurface them, or replace them either, but that leads to the next scenario:

I have now changed the pads on front and rear but did not change or resurface the rotors. The rotors were above spec so my only concern is whether I would get squealing.

The purpose of resurfacing is to provide the new pads with a perfect rotor surface. If you don't then the break in period for the surface of the pads and rotors to perfectly mate will be measured in the thousands of miles, and braking will suffer in the meantime.

[oceanview]

Billfitz Even if you still have 1mm left to minimal thickness after resurfacing, this will be gone in a few thousand miles. For me it is wasted money to resurface a rotor that has 40k miles or more and is close to it's end.
I think resurfacing makes sense, where one would (for whatever reason) change the pads in use, with other new pads. I.E. after 15k miles and you decide to go for a more agressive pad.

Let's say, I'll keep my 5 year old car for another 5 years. I have to change the rotors anyway sooner or later. So I change them the same time the pads are down and fine I am for another 5 years not wasting money on resurfacing.

(dimpled / slotted rotors, as I have, should have enough deep dimples and slots anyway. Therefore I wont resurface them anyway. But that's another story than flat surface rotors)

[Billfitz]

Originally Posted by oceanview

Even if you still have 1mm left to minimal thickness after resurfacing, this will be gone in a few thousand miles.

No way. At least not in my 50 years of experience doing my own brakes, including turning my own on my metal lathe.

[khj24]

Originally Posted by Billfitz

No way. At least not in my 50 years of experience doing my own brakes, including turning my own on my metal lathe.

Considering these rotors stock have a 1.6mm delta between New and min thickness I sure hope not!! Imagine changing rotors every 5k miles