[aakash.shah235]

Please share!

[aturk]

I just put new pads/rotors on my 2014 M235i with 25k miles or so.

My car has had factory rotors, but several different sets of pads on it (OEM, Power Stop Carbon Ceramic Street Pads, Power Stop Track Pads) and it was getting tough to get pads to bed back into the surface.

I went with StopTech Slotted/Coated rotors from Jeff@TopGearSolutions

I was pricing out a lot of options, including some Centric blanks from Rock Auto, but they ended up being close in price to the premium Stop Techs. Only went with slotted simply for the looks.

Once again I HIGHLY recommend the Power Stop Carbon Ceramic pads for street use. Basically no dust, stop fine, ultra quiet. If you are doing some spirited driving and get some heat into them, they work very good as well.

Note:
BMW must use some factory thread sealant/locker on the caliper bolts. Mine took everything my impact had and then some before they even budged. Even turned up the compressor to 150psi. The fronts were easy as I could rotate the hubs so I didn't have to use swivel sockets or extensions.

Total cost of rotors + pads + shipping was probably $625 or so, plus 2-3 hours of my time.

[Maynard]

fcpEuro has a lifetime replacement, so you only pay once. And I think quality brands, so you don't have to weed out the bargain basement crap. And Zeckhausen racing has this tech article on bedding in brakes, and how to clean off past layers of material.

https://www.zeckhausen.com/catalog/i...Path=6446_6444

[SerenVoX]

Originally Posted by aturk

I just put new pads/rotors on my 2014 M235i with 25k miles or so.

My car has had factory rotors, but several different sets of pads on it (OEM, Power Stop Carbon Ceramic Street Pads, Power Stop Track Pads) and it was getting tough to get pads to bed back into the surface.

I went with StopTech Slotted/Coated rotors from [Jeff@TopGearSolutions](contact:50880)

I was pricing out a lot of options, including some Centric blanks from Rock Auto, but they ended up being close in price to the premium Stop Techs. Only went with slotted simply for the looks.

Once again I HIGHLY recommend the Power Stop Carbon Ceramic pads for street use. Basically no dust, stop fine, ultra quiet. If you are doing some spirited driving and get some heat into them, they work very good as well.

Note:
BMW must use some factory thread sealant/locker on the caliper bolts. Mine took everything my impact had and then some before they even budged. Even turned up the compressor to 150psi. The fronts were easy as I could rotate the hubs so I didn't have to use swivel sockets or extensions.

Total cost of rotors + pads + shipping was probably $625 or so, plus 2-3 hours of my time.

ATURK, did you buy everything from Jeff@TopGearSolutions or just the rotors? On the website I see the Stoptech rotors(SLOTTED) listed for $569 but it states rear wheel drive only.. So I guess these dont come in variant for my 2015 M235i x-drive Do you have a link for the Powerstop Carbon cermic pads? These pads are an upgrade from the OEM correct? I do alot of high speed spirited pulls with upgraded turbo and would like better stopping power. Thanks for the input!

[dradernh]

Originally Posted by aturk

Note:
BMW must use some factory thread sealant/locker on the caliper bolts. Mine took everything my impact had and then some before they even budged. Even turned up the compressor to 150psi. The fronts were easy as I could rotate the hubs so I didn't have to use swivel sockets or extensions.

Just curious - if you recall offhand, what's the torque spec for those bolts?

Did you see any sign of sealant on the threads after you removed them?

[aturk]

Originally Posted by SerenVoX

ATURK, did you buy everything from Jeff@TopGearSolutions or just the rotors? On the website I see the Stoptech rotors(SLOTTED) listed for $569 but it states rear wheel drive only.. So I guess these dont come in variant for my 2015 M235i x-drive Do you have a link for the Powerstop Carbon cermic pads? These pads are an upgrade from the OEM correct? I do alot of high speed spirited pulls with upgraded turbo and would like better stopping power. Thanks for the input!

I bought the Stoptech slotted rotors from Jeff. I bought the pads from Amazon. The pads are Power Stop Z23, you can look up the part numbers on Power Stop's site, and then cross reference to Amazon.

I have not had OEM pads on my car in a long time. I hate the amount of dust they give off. I went with the Powerstop's to keep my wheels cleaner longer. Once these Powerstop ceramics get a little heat in them, they stop very well. I've had them in the mountains of North Carolina (Tail of the Dragon) and they were plenty for street driving.

I've also used the Powerstop track day pads, which are great. The downside is they give off lots of dust and make some noise. The dust will etch into your wheels if you let it sit for too long.

[aturk]

Originally Posted by dradernh

Just curious - if you recall offhand, what's the torque spec for those bolts?

Did you see any sign of sealant on the threads after you removed them?

I did not see any signs of sealant on the rear caliper bolts at all, which is why it was so weird. It seriously felt like they were cross threaded, but once they were out they were in perfect shape... I did clean them before re-installing in my ultra sonic cleaner to be sure, then a quick spray with brake cleaner. I did not re-apply any thread lock or other compound.

I could only find reference to the front caliper bolt, which is a 18mm. I went with 85ft/lbs up front (seems like a lot).

The rears were a 16mm bolt I believe, and I went with 65ft/lbs.

I have ~600 miles on everything, and the car needs an oil change, so I will check torque values in a few weeks to make sure nothing has loosened.

[aerobod]

Originally Posted by aturk

I did not see any signs of sealant on the rear caliper bolts at all, which is why it was so weird. It seriously felt like they were cross threaded, but once they were out they were in perfect shape... I did clean them before re-installing in my ultra sonic cleaner to be sure, then a quick spray with brake cleaner. I did not re-apply any thread lock or other compound.

I could only find reference to the front caliper bolt, which is a 18mm. I went with 85ft/lbs up front (seems like a lot).

The rears were a 16mm bolt I believe, and I went with 65ft/lbs.

I have ~600 miles on everything, and the car needs an oil change, so I will check torque values in a few weeks to make sure nothing has loosened.

Front brake torques: https://www.newtis.info/tisv2/a/en/f...rakes/GfqyNpyB
Front caliper to stub axle is 110Nm (which is 81ft-lb, so 85ft-lb is within a reasonable tolerance).

Rear brake torques: https://www.newtis.info/tisv2/a/en/f...rakes/GfyH0Hrd
Rear caliper to stub axle is 50Nm +60 degrees rotation, with replacement of the bolts required, as they are stretch-to-yield bolts.

[dradernh]

Originally Posted by aerobod

Rear caliper to stub axle is 50Nm +60 degrees rotation, with replacement of the bolts required, as they are stretch-to-yield bolts.

I've seen this type of spec before, and I suspect you're just the person to explain it in plain English.

Can you do that for us?

TIA.

[aerobod]

Originally Posted by dradernh

I've seen this type of spec before, and I suspect you're just the person to explain it in plain English.

Can you do that for us?

TIA.

The bolts are first tightened to a value that gives a consistent clamping force on the bolt head (the force tensioning the bolt along it’s length), but not enough torque that variability in the thread friction becomes a big factor in what the final clamping force is - this value is the jointing torque and provides about 1/3 to 1/2 of the final clamping force.

The final bolt tightening angle is then applied. As the jointing torque has ensured there is no gap between the bolt head and the components being clamped together by the bolt, this final angle only stretches the bolt. In the case of a 60 degree angle, that would mean a stretch of one-sixth of the bolt thread pitch. Most of this stretch will occur from between where the bolt enters the threaded component and the bolt head.

To make the bolt stretch apply the most consistent clamping force, the amount of stretch for a given bolt size is calculated to stretch the bolt into it’s plastic deformation range as opposed to it’s elastic range. Where the stretch in a material changes from elastic to plastic is the material yield point, hence “stretch to yield”.

Reusing a stretch-to-yield / torque-to-yield fastener is problematic, as it is never the same in properties after it has been deformed in this controlled manner and will certainly have less than the design safety factor if stretched again. In best case for reuse if it absolutely has to be done, the bolt has to be rotated to exactly the same position as when it was undone, as applying the same jointing torque and angle again will just stretch it more, lengthening it beyond what the design envisioned. It is also important to use a bolt with exactly the right grade, head and thread length of the original to ensure designed clamping force and safety margin is achieved.

Sorry this is a lengthy explanation, but hopefully I made it as non-technical as I could. I can throw around some sample calculations for typical bolts to show how the basic maths works

[dradernh]

Originally Posted by aerobod

The bolts are first tightened to a value that gives a consistent clamping force on the bolt head (the force tensioning the bolt along it’s length), but not enough torque that variability in the thread friction becomes a big factor in what the final clamping force is - this value is the jointing torque and provides about 1/3 to 1/2 of the final clamping force.

The final bolt tightening angle is then applied. As the jointing torque has ensured there is no gap between the bolt head and the components being clamped together by the bolt, this final angle only stretches the bolt. In the case of a 60 degree angle, that would mean a stretch of one-sixth of the bolt thread pitch. Most of this stretch will occur from between where the bolt enters the threaded component and the bolt head.

To make the bolt stretch apply the most consistent clamping force, the amount of stretch for a given bolt size is calculated to stretch the bolt into it’s plastic deformation range as opposed to it’s elastic range. Where the stretch in a material changes from elastic to plastic is the material yield point, hence “stretch to yield”.

Reusing a stretch-to-yield / torque-to-yield fastener is problematic, as it is never the same in properties after it has been deformed in this controlled manner and will certainly have less than the design safety factor if stretched again. In best case for reuse if it absolutely has to be done, the bolt has to be rotated to exactly the same position as when it was undone, as applying the same jointing torque and angle again will just stretch it more, lengthening it beyond what the design envisioned. It is also important to use a bolt with exactly the right grade, head and thread length of the original to ensure designed clamping force and safety margin is achieved.

Sorry this is a lengthy explanation, but hopefully I made it as non-technical as I could. I can throw around some sample calculations for typical bolts to show how the basic maths works

Thank you very much - I think that was very clear.

If you know of any bolts on our cars that are clamped in this fashion and can offer examples, whether accurate for those applications or not, I think that might further our understanding of this subject.

[aerobod]

Originally Posted by dradernh

Thank you very much - I think that was very clear.

If you know of any bolts on our cars that are clamped in this fashion and can offer examples, whether accurate for those applications or not, I think that might further our understanding of this subject.

The rear caliper bolts are a good example, they are M12x1.5 32mm long. About 16mm of the bolt seems to be exposed between the head and thread engagement when in use. The 60 degree turn of the bolt in the 50Nm +60 degree tightening spec will stretch the bolt 0.25mm, or about 1.5% of the exposed shank (this is the strain value). 8.8 spec bolts will yield at 800MPa of stress at about 1% strain so from a bolt calculator the required torque will be in the range of 120 to 200Nm, depending on thread and bolt head friction / lubrication.

Another example is the M12 aluminium bolts attaching the gearbox to the transmission. A typical high strength aluminium alloy will yield at about 400 MPa and 2% strain. The tightening spec on these bolts is 25Nm +130 degrees. I think about 20mm of the shank is exposed, so when tightened to 130 degrees beyond jointing torque a stretch of about 2.7% is induced in the exposed shank, again into the bolt plastic / stretch range. The torque required to do that in this case is in the range of 60 to 100Nm.

Stretch bolts are now used by BMW in many areas, they provide accurate clamping without having to deal with the wide range torque required due to thread and friction variability.

[Maynard]

Very good info - I had my rear pads changed and they did not replace the bolts; since then I've swapped out those brakes for MPerf models so the bolts should be good, but this is fairly crucial info - would have prompted me to remove and replace the original bolts. Wonder why they don't include those bolts in rotor/pad swap kits like they do w/ crush washers and o rings for oil changes?

[BEM-S4]

I upgraded my F31 to OEM BBK and damn they are noisy. Not squeaky but the dimples make a ticking noise from wind. I'd advise slotted but not drilled or dimpled for street use.

[lieb923]

I have had good success with Zimmerman rotors. They are made in Germany and are available in plain or dimpled/slotted. FCP carries them.
I am presently using Cool Carbon ST+ pads. I am happy with them.

[Luftwaffe1O1]

Originally Posted by BEM-S4

I upgraded my F31 to OEM BBK and damn they are noisy. Not squeaky but the dimples make a ticking noise from wind. I'd advise slotted but not drilled or dimpled for street use.

All the M performance dimpled rotors do this... I wish there was a thread on it somewhere. I got Pilenga 2pc Dimpled rotors (which are OEM manufacturer I believe), and man... it makes a ticking noise. I thought something was loose, was thinking maybe it is the EBC yellows, but searches didn't yield anything. Finally, when I checked on F30 post... all the F30 guys with M perf rotors seem to be having these ticking noises with dimpled rotors.

Kind of embarrassing.

[BEM-S4]

Originally Posted by Luftwaffe1O1

All the M performance dimpled rotors do this... I wish there was a thread on it somewhere. I got Pilenga 2pc Dimpled rotors (which are OEM manufacturer I believe), and man... it makes a ticking noise. I thought something was loose, was thinking maybe it is the EBC yellows, but searches didn't yield anything. Finally, when I checked on F30 post... all the F30 guys with M perf rotors seem to be having these ticking noises with dimpled rotors.

Kind of embarrassing.

Well I upgraded to VFF105 19" and I haven't done extensive testing just drive the car a bit but it seemed like the extra breathing room helped. Fingers crossed.

At least we know it's not something wrong which is what I originally thought.

[WolfGTI]

How's the Philly roads with 19's?

Originally Posted by BEM-S4

Well I upgraded to VFF105 19" and I haven't done extensive testing just drive the car a bit but it seemed like the extra breathing room helped. Fingers crossed.

At least we know it's not something wrong which is what I originally thought.

[BEM-S4]

Originally Posted by WolfGTI

How's the Philly roads with 19's?

I wouldn't tempt fate in the F23 with 19" wheels around here. I did the BBK on the F31 which came from the factory with the optional upgrade 18" wheels. The BBK looked silly on the 18" there was virtually no room, and the wheels were due for replaced soon anyway mom did a number on them. So I went up to 19" and I also went up a tire size so I am slightly above spec. Filled out the wheel well nicely and kept the sidewall basically the same so I don't worry too much.

When F23 needs brakes I am going to stick with blue calipers, upgrade rotors and pads (thinking StopTech but who knows). Would stick with 18" wheels been happy with Apex on that car, would do VFF-108 in 18" if they ever need to be replaced.

Cars will be side-by-side at Radnor Hunt Concours Motorsport Park in a few weeks if you're in the area. Nice event.

[WolfGTI]

I've been going to the Radnor Hunt for the last several years. I'll definitely check out your cars.
I know what you mean - I run around on the 18's BBS RF's for the summer - going to change to 17's with taller sidewall for the winter.

Originally Posted by BEM-S4

Cars will be side-by-side at Radnor Hunt Concours Motorsport Park in a few weeks if you're in the area. Nice event.

[kthor703]

Just to note, the OE 2 piece option is lighter than most of the other options from stoptech, Zimmermann, etc (1 piece cast). Just something to keep in mind. I don't know the exact weight, but at least a pound per rotor.

[teinesina]

Originally Posted by aerobod

The rear caliper bolts are a good example, they are M12x1.5 32mm long. About 16mm of the bolt seems to be exposed between the head and thread engagement when in use. The 60 degree turn of the bolt in the 50Nm +60 degree tightening spec will stretch the bolt 0.25mm, or about 1.5% of the exposed shank (this is the strain value). 8.8 spec bolts will yield at 800MPa of stress at about 1% strain so from a bolt calculator the required torque will be in the range of 120 to 200Nm, depending on thread and bolt head friction / lubrication.

Another example is the M12 aluminium bolts attaching the gearbox to the transmission. A typical high strength aluminium alloy will yield at about 400 MPa and 2% strain. The tightening spec on these bolts is 25Nm +130 degrees. I think about 20mm of the shank is exposed, so when tightened to 130 degrees beyond jointing torque a stretch of about 2.7% is induced in the exposed shank, again into the bolt plastic / stretch range. The torque required to do that in this case is in the range of 60 to 100Nm.

Stretch bolts are now used by BMW in many areas, they provide accurate clamping without having to deal with the wide range torque required due to thread and friction variability.

This is such amazing info, but how do people who work on their own cars ever know if BMW has decided to use a stretch bolt in a particular application? Or are some unfortunate folks not replacing bolts and being unsafe without even knowing it? Or does bmw assume no one works on their own cars anymore?