[Ennoch]

Originally Posted by danarino

Why not save a couple pounds directly over the hub and match what the bmw engineers designed? I get your argument if it’s $200 but for $50 it’s such a no brainer to get the lighter weight and avoid the need to put paint on a brand new part. In my case I’m waiting on wheels/tires that save 11lb per corner and wanted to keep as much of that savings as I could given I’m getting larger heavier parts all around. My brake set up is 10lb total less than a Zimmerman 1 piece set up for $100 more. Given it’s unsprung weight and matches oem construction I think it’s worth it.

I'm all for weight saving and in climbing kit I go for as light as practically possible (rather than absolute at the cost of practicality/ergonomics), and on bikes have spent thousands on titanium springs and bolts over the years along with other lightweight stuff (because you're shifting it around with your body). But with all else being equal, shaving less than 0.5kg per rotor (I don't have an actual weight, nobody seems to quote weights and nobody on a forum seems to have weighed a one piece rotor and two piece side by side) on a car weighing 1800kg is just never going to make a difference. So by all means do it for looks, but don't kid yourself that it's for performance. Iron is heavier than aluminium but the overall product has a greater volume of material because of the two piece setup; big steel rivets to hold it together, a bell perimeter/handbrake surface that is basically the same as a one piece rotor and then an aluminium hat on the top too. Yes you save on the bit at the end but then you've doubled up elsewhere. The 380mm M3/4 rotors on the other hand are a very different discussion as their design is actually focused on increased performance through reduced unsprung weight and better ventilation/thermal properties. The two piece 340mm and 370mm are a standard rotor with a pretty little piece of aluminium riveted over the top so it looks cool in the showroom. Have I got the two piece rotors on mine? Yeah, sure, but I'm honest with myself about why I've got them...

[danarino]

Originally Posted by Ennoch

I'm all for weight saving and in climbing kit I go for as light as practically possible (rather than absolute at the cost of practicality/ergonomics), and on bikes have spent thousands on titanium springs and bolts over the years along with other lightweight stuff (because you're shifting it around with your body). But with all else being equal, shaving less than 0.5kg per rotor (I don't have an actual weight, nobody seems to quote weights and nobody on a forum seems to have weighed a one piece rotor and two piece side by side) on a car weighing 1800kg is just never going to make a difference. So by all means do it for looks, but don't kid yourself that it's for performance. Iron is heavier than aluminium but the overall product has a greater volume of material because of the two piece setup; big steel rivets to hold it together, a bell perimeter/handbrake surface that is basically the same as a one piece rotor and then an aluminium hat on the top too. Yes you save on the bit at the end but then you've doubled up elsewhere. The 380mm M3/4 rotors on the other hand are a very different discussion as their design is actually focused on increased performance through reduced unsprung weight and better ventilation/thermal properties. The two piece 340mm and 370mm are a standard rotor with a pretty little piece of aluminium riveted over the top so it looks cool in the showroom. Have I got the two piece rotors on mine? Yeah, sure, but I'm honest with myself about why I've got them...

Any time you can reduce unsprung weight and it’s cheap to do so, you should always do it. You can look up the specs directly from the manufacturers, but it’s a legitimate 10lb total weight I’ve reduced at a cost of about $100 extra. And on top of that to your point, it looks cool. It’s tough to find that kind of benefit for so cheap. It’s a fact that reducing weight anywhere is a benefit, especially over the hub. It’s just a matter of cost benefit analysis, and at this price it is worth it in my opinion. Even if it was 5lb I’d do it because I like the way it looks. As enthusiasts, sweating the details for the slightest of benefits is part of the fun.

[Ennoch]

Originally Posted by danarino

You can look up the specs directly from the manufacturers, but it’s a legitimate 10lb total weight I’ve reduced at a cost of about $100 extra.

Where are the weights for the stock 370mm two piece BMW rotors, and the single piece alternatives? The only weight I've seen mentioned for the 370mm two piece was an anecdotal 26lb against 22.5 for the 340mm but nothing for the single piece other than people saying they think they're going to be wildly heavier.

There is not a single chance that the weight difference between the single and two piece discs is 2.5kg each, there isn't enough material for that to be the case. A basic calculation assuming the disc end is 10mm thick (it's thinner) and is 200mm diameter (it's smaller) and the bore is about 70mm then even without the relieving of the corners and the wheel stud holes a plain steel disc would be 2.1kg vs 0.8kg for the aluminium. Except that would only be the saving made if it was bonded straight onto the steel disc. Instead you've got the normal diameter steel hat, and more aluminium as an additional layer, plus rivets. It might be a few hundred grams or so lighter but that's bugger all in the grand scheme of the unsprung mass involved in these cars. Even if you were saving 2.5kg on a total unsprung mass of 10kg then that's dramatic but we're talking sprung mass of 50kg upwards, and as a rotational mass it's negligible too as it's such a small diameter. I mean it'll have an impact but unless you do lots of other stuff to reduce mass too it's just not going to be discernible.

If someone puts a brand new two piece stock rotor on a scale and does the same with a one piece and it shows a big difference (or shows manufacturers tech specs) then I'll happily believe it but until then I will continue to believe that these rotors are simply for looks and not performance.

To save 2.5kg by going to aluminium from steel you would need to replace the equivalent of a 25cm diameter by 1cm thick piece of solid steel, and not add any more material on anywhere else. Clearly this isn't the case with these rotors. I'm not trying to personally go at anyone here, it's just some people seem to be arguing against basic maths and physics because 'aluminium is lighter than steel', which while vaguely true in that it's less dense, also needs greater volume for equivalent strength which also complicates things in these *** paper calculations. Start adding on bits of aluminium AND steel and those potential savings become moot very quickly. Like I say, show me numbers and I'll believe it.

[danarino]

Originally Posted by Ennoch

Where are the weights for the stock 370mm two piece BMW rotors, and the single piece alternatives? The only weight I've seen mentioned for the 370mm two piece was an anecdotal 26lb against 22.5 for the 340mm but nothing for the single piece other than people saying they think they're going to be wildly heavier.

There is not a single chance that the weight difference between the single and two piece discs is 2.5kg each, there isn't enough material for that to be the case. A basic calculation assuming the disc end is 10mm thick (it's thinner) and is 200mm diameter (it's smaller) and the bore is about 70mm then even without the relieving of the corners and the wheel stud holes a plain steel disc would be 2.1kg vs 0.8kg for the aluminium. Except that would only be the saving made if it was bonded straight onto the steel disc. Instead you've got the normal diameter steel hat, and more aluminium as an additional layer, plus rivets. It might be a few hundred grams or so lighter but that's bugger all in the grand scheme of the unsprung mass involved in these cars. Even if you were saving 2.5kg on a total unsprung mass of 10kg then that's dramatic but we're talking sprung mass of 50kg upwards, and as a rotational mass it's negligible too as it's such a small diameter. I mean it'll have an impact but unless you do lots of other stuff to reduce mass too it's just not going to be discernible.

If someone puts a brand new two piece stock rotor on a scale and does the same with a one piece and it shows a big difference (or shows manufacturers tech specs) then I'll happily believe it but until then I will continue to believe that these rotors are simply for looks and not performance.

To save 2.5kg by going to aluminium from steel you would need to replace the equivalent of a 25cm diameter by 1cm thick piece of solid steel, and not add any more material on anywhere else. Clearly this isn't the case with these rotors. I'm not trying to personally go at anyone here, it's just some people seem to be arguing against basic maths and physics because 'aluminium is lighter than steel', which while vaguely true in that it's less dense, also needs greater volume for equivalent strength which also complicates things in these *** paper calculations. Start adding on bits of aluminium AND steel and those potential savings become moot very quickly. Like I say, show me numbers and I'll believe it.

Here are the pagid 2 piece front 370mm rotors, which you'll see from the spec sheet weigh 11.9kg

https://brakeguide.com/hpa/en_US/8DD...atasheet.xhtml

Here are the zimmerman 1 piece front 370mm rotors, which per the spec sheet weigh 13.2kg

https://web.tecalliance.net/otto-zim...eNumber:113409

Therefore, 1.3kg savings per wheel or 2.6kg for the front rotors only vs going 1 piece. The rears are .9kg lighter per rotor vs zimmerman which you can find on both sites. Total savings of 4.4kg.

[Ennoch]

Originally Posted by danarino

Here are the pagid 2 piece front 370mm rotors, which you'll see from the spec sheet weigh 11.9kg

https://brakeguide.com/hpa/en_US/8DD...atasheet.xhtml

Here are the zimmerman 1 piece front 370mm rotors, which per the spec sheet weigh 13.2kg

https://web.tecalliance.net/otto-zim...eNumber:113409

Therefore, 1.3kg savings per wheel or 2.6kg for the front rotors only vs going 1 piece. The rears are .9kg lighter per rotor vs zimmerman which you can find on both sites. Total savings of 4.4kg.

Thanks for the links, I'd not found anywhere actually quoting comparable weights before. I'm surprised the differences are as much as they are at 1.3kg per front rotor (although ironically what I roughly calculated based on the end dimensions) but I will also say that I still don't believe it's worth any additional cost for the unsprung mass benefit.

The amount of mass in the suspension system of an F30 is sizeable, and even though not all of it counts as unsprung, the weight of a wheel, tyre, hub, caliper, driveshaft end etc add up very significantly. If you're saving 1kg here, 2kg there off each and every part and going to the point of milling down uprights then you're likely to detect something at the wheel even on a heavy car, but saving 1.3kg on such a mass as a stock F30 just isn't going to make a difference, especially when the mass of the car is so great and the unsprung mass therefore has a heavier opposing mass to work against (unsprung:sprung mass ratios are also a key factor, more so in many instances than just unsprung mass itself). Personally I like the look of the aluminium centres, but if I was wanting to actually make a meaningful difference then I'd look at pukka 2 piece rotors with a full aluminium bell and a racing style disc with much thinner braking surfaces and larger venting slots.

[danarino]

Originally Posted by Ennoch

Thanks for the links, I'd not found anywhere actually quoting comparable weights before. I'm surprised the differences are as much as they are at 1.3kg per front rotor (although ironically what I roughly calculated based on the end dimensions) but I will also say that I still don't believe it's worth any additional cost for the unsprung mass benefit.

The amount of mass in the suspension system of an F30 is sizeable, and even though not all of it counts as unsprung, the weight of a wheel, tyre, hub, caliper, driveshaft end etc add up very significantly. If you're saving 1kg here, 2kg there off each and every part and going to the point of milling down uprights then you're likely to detect something at the wheel even on a heavy car, but saving 1.3kg on such a mass as a stock F30 just isn't going to make a difference, especially when the mass of the car is so great and the unsprung mass therefore has a heavier opposing mass to work against (unsprung:sprung mass ratios are also a key factor, more so in many instances than just unsprung mass itself). Personally I like the look of the aluminium centres, but if I was wanting to actually make a meaningful difference then I'd look at pukka 2 piece rotors with a full aluminium bell and a racing style disc with much thinner braking surfaces and larger venting slots.

If you don't think saving 10lb over the hubs with a more premium design is worth $100 then that's your opinion. I strongly disagree but to each their own.

[Ennoch]

Originally Posted by danarino

If you don't think saving 10lb over the hubs with a more premium design is worth $100 then that's your opinion. I strongly disagree but to each their own.

Hey, I've got them, I'm not against them, I just think that anyone putting them on and believing they can feel the difference is kidding themselves. On a Caterham a 10lb saving in rotational/unsprung mass is sizeable, but on a large and heavy saloon/estate I think it's pissing into the wind unless you've got a large chequebook out and made some other fairly large chunks so you get a reasonable cumulative effect. Even then you've got a lot of mass elsewhere which is difficult to overcome. Maybe I'm just more pragmatic than some having already pissed much money on tweaking road cars, or just have lower expectations of a daily, but on public roads I just don't see that you will ever notice the difference of what is in essence the square root of bugger all and I'd say I'm at the upper end of what people would consider (un)reasonable behaviour on tight and twisty public roads, most of which are rough enough to definitely highlight any improvements.

[johnung]

Originally Posted by Ennoch

Hey, I've got them, I'm not against them, I just think that anyone putting them on and believing they can feel the difference is kidding themselves. On a Caterham a 10lb saving in rotational/unsprung mass is sizeable, but on a large and heavy saloon/estate I think it's pissing into the wind unless you've got a large chequebook out and made some other fairly large chunks so you get a reasonable cumulative effect. Even then you've got a lot of mass elsewhere which is difficult to overcome. Maybe I'm just more pragmatic than some having already pissed much money on tweaking road cars, or just have lower expectations of a daily, but on public roads I just don't see that you will ever notice the difference of what is in essence the square root of bugger all and I'd say I'm at the upper end of what people would consider (un)reasonable behaviour on tight and twisty public roads, most of which are rough enough to definitely highlight any improvements.

I've been reading through this thread and I agree with you. Very unlikely to be able to feel the weight savings of 2.6 lbs from a riveted aluminum hat.

I would much prefer a StopTech full crossdrilled with directional left/right vanes for optimal cooling. That's a difference that can definitely be felt in bite and in stopping power in the rain.

Heck, if one could feel a sizable difference, then people would be refusing Brembo 370's for Brembo 340's. There's a weight savings of 5.1 lbs per rotor alone, and more from the smaller caliper.

The front StopTech 370x30 full floating 2-piece that I have now weigh 10.5kg (23.2 lbs)

If someone was really targeting weight savings, I'd be looking at forged wheels at 18 lbs each vs stock 400M wheels at 26 lbs each. 8 lbs per corner is probably something that could actually be felt.

[Ennoch]

Yep. I actually just did a quick google as I suddenly wondered what my 403M's weigh and it's 29.5lb apparently, according t'tinternet. Whether that's front or back is anyone's guess, but it's heavy. Throw on a 22lb Michelin PS4S front, or 23.8lb for the rear, and you have a 50lb+ tyre setup on each corner. It's certainly noticeable how heavy they are compared to my Impreza's 17's. Of course there's then another however many kg/lb's from all the other unsprung mass and it's just such an inconsequential amount, I mean just disc plus wheels on the front is 78lbs a corner. The calipers are 10.8lb each, so say a round 90lbs a corner, but then you've still got a portion of the control arms, the strut lowers, a portion of the springs, a portion of the driveshafts and the wheelnuts...I reckon you're probably looking at another 50lb or more so say 150lb a corner unsprung mass. Against that backdrop the couple of pounds saving is just so tiny.

[johnung]

Originally Posted by Ennoch

Yep. I actually just did a quick google as I suddenly wondered what my 403M's weigh and it's 29.5lb apparently, according t'tinternet. Whether that's front or back is anyone's guess, but it's heavy. Throw on a 22lb Michelin PS4S front, or 23.8lb for the rear, and you have a 50lb+ tyre setup on each corner. It's certainly noticeable how heavy they are compared to my Impreza's 17's. Of course there's then another however many kg/lb's from all the other unsprung mass and it's just such an inconsequential amount, I mean just disc plus wheels on the front is 78lbs a corner. The calipers are 10.8lb each, so say a round 90lbs a corner, but then you've still got a portion of the control arms, the strut lowers, a portion of the springs, a portion of the driveshafts and the wheelnuts...I reckon you're probably looking at another 50lb or more so say 150lb a corner unsprung mass. Against that backdrop the couple of pounds saving is just so tiny.

Yup, a race car team would look to trim every ounce of unsprung weight that they could because they are trying to push the car to its limits in a highly competitive environment against other teams. That's really where most unsprung weight comments/conversations originate. Most of it just doesn't apply/wouldn't be noticeable in a daily driver environment.

[danarino]

I'm actually waiting on a set of backordered fl-5 wheels with dws06+ tires that weight 11lb less per corner while having 255 square vs 225. By going to the larger brakes, I'm negating some of those savings, but this route at least makes it a bit better (gaining 4lb vs 7lb with 1 piece as it pertains to the fronts, gaining 1.8lb vs 3.8lb for the rears). I've felt a significant difference going with a 5lb lighter per corner wheel set up in a past car, so I'm really excited for the lighter wheels and want to keep as much of those weight savings as I can. Will anyone feel the difference with these rotors vs 1 piece? Highly unlikely, but to me the looks and weight savings are worth such a tiny investment.

[danarino]

Originally Posted by johnung

I've been reading through this thread and I agree with you. Very unlikely to be able to feel the weight savings of 2.6 lbs from a riveted aluminum hat.

I would much prefer a StopTech full crossdrilled with directional left/right vanes for optimal cooling. That's a difference that can definitely be felt in bite and in stopping power in the rain.

Heck, if one could feel a sizable difference, then people would be refusing Brembo 370's for Brembo 340's. There's a weight savings of 5.1 lbs per rotor alone, and more from the smaller caliper.

The front StopTech 370x30 full floating 2-piece that I have now weigh 10.5kg (23.2 lbs)

If someone was really targeting weight savings, I'd be looking at forged wheels at 18 lbs each vs stock 400M wheels at 26 lbs each. 8 lbs per corner is probably something that could actually be felt.

I would have got the stoptech drilled one piece rotors in a heartbeat for the same price over the pagid rotors. They cost 3 times as much as the rotors I got. I was strongly considering the the slotted 1 piece variant just for the looks and black painted hub since they cost less than drilled, but it came to around $900 and I couldn't justify the cost, especially since they were 1 piece. The pagid route was my compromise of getting something better than heavy 1 piece rotors, while still spending less for all 4 than a set of OEM front rotors would cost.

[johnung]

Originally Posted by danarino

I would have got the stoptech drilled one piece rotors in a heartbeat for the same price over the pagid rotors. They cost 3 times as much as the rotors I got. I was strongly considering the the slotted 1 piece variant just for the looks and black painted hub since they cost less than drilled, but it came to around $900 and I couldn't justify the cost, especially since they were 1 piece. The pagid route was my compromise of getting something better than heavy 1 piece rotors, while still spending less for all 4 than a set of OEM front rotors would cost.

Prices have gone crazy which I assume is raw material and supply chain cost increases due to the pandemic. Raw material metals are about 3x-4x more than they were just two years ago.

[snipagang]

So, I have a 320i (stg2 fbo) with base brakes. 312 front 300 rear. 2017 xdrive. I am looking to do this exact same converstion (I believe its warranted given how I drive on backroads, ive destroyed 2.5 sets of rotors in 50k miles). I am very confused on whether or not this will fit my car (assuming I throw in 18inch rims). Can anybody speak to whether or not this works in an F30 320ix? edit: I do not care at all about looks, only performance. If the calipers are unpainted then so be it. Suggestions?

[danarino]

Originally Posted by snipagang

So, I have a 320i (stg2 fbo) with base brakes. 312 front 300 rear. 2017 xdrive. I am looking to do this exact same converstion (I believe its warranted given how I drive on backroads, ive destroyed 2.5 sets of rotors in 50k miles). I am very confused on whether or not this will fit my car (assuming I throw in 18inch rims). Can anybody speak to whether or not this works in an F30 320ix? edit: I do not care at all about looks, only performance. If the calipers are unpainted then so be it. Suggestions?

If you only care about performance and are cost conscious, you may want to consider upgrading to the 340mm front 330mm rear brakes from the 328 m sport and all 340 models. You can typically find the full caliper set around $500 then you can buy new rotors and pads. Both this option and the option i went with will definitely fit on your car, but you may need some additional parts such as the dust shields. Also, I came across something about some base brakes having a different parking brake size which may affect the rear rotors. I didn't do a deep dive into upgrading from the base size so someone else may know more. These cars are very modular so its pretty straight forward either way. If you get the full m performance kit, it comes with the dust shields so you may want to consider that if going with the largest size.

[danarino]

Got the brakes put on. They feel great and look amazing. I appreciate the smooth nature of the akebono pads. The initial bite is very smooth which helps when your wife gets car sick easily. Still more stopping power than i had before but buttery smooth. No additional parts needed and smooth sailing. Due to a miscommunication with the install shop, they did not code for the brakes but offered to do so free of charge whenever I'd like. Going to live with them as is for a bit to determine if its necessary. If anything, i'll just get it done at my next oil change. 1 pic pre install and the rest taken 40 miles after getting them on.

[snipagang]

Originally Posted by danarino

If you only care about performance and are cost conscious, you may want to consider upgrading to the 340mm front 330mm rear brakes from the 328 m sport and all 340 models. You can typically find the full caliper set around $500 then you can buy new rotors and pads. Both this option and the option i went with will definitely fit on your car, but you may need some additional parts such as the dust shields. Also, I came across something about some base brakes having a different parking brake size which may affect the rear rotors. I didn't do a deep dive into upgrading from the base size so someone else may know more. These cars are very modular so its pretty straight forward either way. If you get the full m performance kit, it comes with the dust shields so you may want to consider that if going with the largest size.

If I was going this route I would do the 340mm rotors in the front with 345mm rotors in the rear. Im wondering where I could even buy those unpainted brembos for my car though, and whether or not this setup would fit over my 17” rims which would be way more cost effective since as of now I need to source 18”ers to fit m perf kit

[danarino]

Originally Posted by snipagang

If I was going this route I would do the 340mm rotors in the front with 345mm rotors in the rear. Im wondering where I could even buy those unpainted brembos for my car though, and whether or not this setup would fit over my 17” rims which would be way more cost effective since as of now I need to source 18”ers to fit m perf kit

I actually have a nice minty set of the 340mm grey brembo calipers with pins, retainer clips, and brake lines off my 2018 with 42k miles on them. I see that you are located in NJ like me, so we could avoid the hassle of shipping. If your interested, shoot me a PM. I'm looking to get $500 for the complete set, but perhaps we could figure something out if you just want the fronts. They will fit under 17s in the front, but the 345mm in the rear may cause an issue. I'd imagine it depends on the exact wheel chosen.

[quixotemi]

Originally Posted by danarino

Got the brakes put on. They feel great and look amazing. I appreciate the smooth nature of the akebono pads. The initial bite is very smooth which helps when your wife gets car sick easily. Still more stopping power than i had before but buttery smooth. No additional parts needed and smooth sailing. Due to a miscommunication with the install shop, they did not code for the brakes but offered to do so free of charge whenever I'd like. Going to live with them as is for a bit to determine if its necessary. If anything, i'll just get it done at my next oil change. 1 pic pre install and the rest taken 40 miles after getting them on.

Looks clean. I just ordered the MPerf kit from FCP over labor day. They had it on sale for $2250. Also got the genuine BMW 345 rears (blanks). Figured going with FCP is a bit better than GetBMWParts as FCP will warranty all the parts and I'd get another set of rotors pads for free when I'm due again.

[danarino]

Originally Posted by quixotemi

Looks clean. I just ordered the MPerf kit from FCP over labor day. They had it on sale for $2250. Also got the genuine BMW 345 rears (blanks). Figured going with FCP is a bit better than GetBMWParts as FCP will warranty all the parts and I'd get another set of rotors pads for free when I'm due again.

Can't go wrong with all new calipers. I'd have probably done the same had they offered them in blue. Good luck with the install