04-25-2024, 02:16 PM | #1 |
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Downsizing Rear Calipers from F30 to fit 17" Wheels
Hi all
I'm looking to downsize my rear calipers to F30 calipers so I can run a 17" wheel in the rear. I've had this confirmed by many, but no one can confirm what calipers to run. I see the 340i M-Sport (same calipers as F80) can run 17" wheels, so why exactly can't I run these? I'm aware the rear rotors are smaller, but downsizing the rotor doesn't make the caliper go in more. Is it that the hub has the caliper spaced farther away from the hub? Does this mean my only options are to use 330i base calipers with a 330i rotor? I'm looking for a cheaper alternative than running the vargas setup. Thank you! |
04-25-2024, 05:06 PM | #2 |
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The caliper mounting locations on the hub are different so the same caliper can be used on different rotor OD but the same pad radial depth. Most aftermarket custom caliper adapter brackets are designed to move the caliper more outboard so a larger diameter rotor can be used. I’m not sure if anyone makes a caliper bracket that moves the caliper inboard. Also, the rear brake rotor has an integral barrel for the drum parking brake which may/may not be the same diameter for the f8x and f3x.
The oem blue two-piston rear caliper should be identical between the f8x and f3x. Like I said above, a caliper adapter bracket that moves the caliper inward to work with the f3x 330i smaller rotor OD. I’d use realoem.com to verify whether the drum parking brakes have the same barrel/drum and shoe diameters. |
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04-28-2024, 12:34 PM | #3 | |
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So, I'm looking at 330x20 (actually 330x24 from EBC) spec'd from a 2016 335i. I feel like the answer in this case is to also use calipers and pads from this same car, but you have me thinking about the outward spacing on the hub. If I bolted these calipers to replace my M caliper, wouldn't the pad sit farther away from the rotor then? Does this make sense? Perhaps the solution would be to use 340mm rotors from the 340 m sport? Trying to find this stuff out without buying and having to return parts. EDIT: I identified F30 330 M-Sport, 335i w/o M-Sport, 340 w/o M-Sport all share the same rear 330x20 rotors, calipers, and pads. Autozone P/N's #73046 (rotor) #19-B7217 (R caliper) # 19-B7216 (L caliper) #DG1610 (Pads). So any of these above applications are good for the parts search. However I am still concerned of caliper/pad alignment on the rotor if they are indeed spaced farther from the hub. I have a buddy who's last 7 of the VIN on realoem.com pointed to the 185mm rear ebrake, which means he should have 330x20 rotors and an M-Sport brake package. I'll see if he will let me borrow a brake setup for test fitting. Last edited by tftimbn; 04-28-2024 at 12:43 PM.. |
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04-28-2024, 01:16 PM | #4 | |
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You need someone like Seems Legit Garage to make a caliper mounting bracket that shifts the caliper 20 mm closer to the center of the hub. Whether you go with 330 mm or 340 mm OD rotors, you have the same problem relocating the caliper closer to the hub by 20 mm and 15 mm, respectively. Doing this is going to shift the brake bias forward by 7-8% to 69% forward bias (assuming same pad CoF is used on the front and rear) which is significant. Dynamic brake bias shifts braking farther forward. For the f8x wheelbase, track widths, weight, etc. will see another dynamic 9-10% forward shift so that would make your proposed setup to have 79% of the braking done by the front brakes. |
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04-28-2024, 08:31 PM | #5 | |
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Just stumbled across this too https://f80.bimmerpost.com/forums/sh....php?t=2022801 Any thoughts on that? |
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04-28-2024, 10:20 PM | #6 | |
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300 mm e46 (?) 328i brake rotors and a single-piston sliding caliper from an e46 M3? Good luck finding pads that will fit the caliper and use the full radial depth of the rotor. |
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05-04-2024, 02:17 PM | #7 |
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So I did go ahead and try out E46 rotors with F30 300mm pads and calipers, here is the pad depth. I reached out via PM to the guy who suggested that if that’s what he ran before I bolt these up.
View post on imgur.com View post on imgur.com Although looking at the VS kit, it looks like theres full pad depth. So I’m not sure what rotors are being used here. I might go grab some rotors from autozone for testing and just return if anything. View post on imgur.com |
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05-04-2024, 03:55 PM | #8 | |
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The rotors used in the other kit appear to be M-drive (alum mounting hat with steel pins cast into the alum hat and iron disc) rotor machined down to a smaller OD. You can clearly see the steel pins and only two rows of venting holes in the rotor face. Stock M-drive rotors have three rows of venting holes. |
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05-04-2024, 08:42 PM | #9 | |
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Interesting now that you mention that, the outer ring of holes is REALLY close to the edge of the rotor. Hmm. I ordered rear rotors for a 2003 M3. My buddy with the 330 came by today, I verified he has 300mm rotors which means he does not have m sport. Coincidentally, he needs pads and rotors on his car so I’m going to use his garbage ones for fitment testing anyway. I will also take measurements of the rotor and get back tomorrow. |
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05-05-2024, 06:03 AM | #10 | |
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I’ll look to see if I can find the e46 M3 rear pad profile and its radial depth. You’d think I’d know because I took delivery of 03.5 in August ‘03 but added an AP Racing brake kit within the first 8 months of ownership. |
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05-05-2024, 07:42 AM | #11 |
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Here’s the major dimensions of the e46 M3 rear pad. It has a 61 mm radial depth actually, it’s the pad full depth, radial depth I’d probably 58 mm). I also found the rear f30 rear pad which has a 46-47 mm radial depth so at least 11-12 mm (as much as 14-15 mm) too short for the e46 M3 rotor.
Last edited by M3SQRD; 05-05-2024 at 11:49 AM.. |
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05-05-2024, 11:58 AM | #12 |
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tftimbn
Why didn’t you use the e46 M3 rear sliding caliper? Is it a problem with mounting it to the f8x rear assembly? You’ll need to have someone like Carbotech make a custom version of the f30 46-47 mm radial depth with an increased radial depth of 58-60 mm. The top half of the pad and mounting tabs/guides would remain unchanged but an extended tapered lower half of the pad with the correct IR that matched the e46 M3 pad/rotor IR. I’ve had plenty of custom pads made by Carbotech over the past almost 35 years and I’ve used Cobalt a couple of times as well. |
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05-05-2024, 03:55 PM | #13 | |
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So to make sure I’m getting this right, utilize the E46 rotors, 330 caliper, with custom made pads that are essentially longer? I still haven’t measured anything as it’s been pouring rain all day, and the F30 300mm calipers are coming in on wednesday, so I’ll likely test fit and do some measurements on the car just to make sure the outer edge lines up to begin with. Let’s figure this out and sell these kits lol, maybe cheaper than vargas and safer than the VS setup |
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05-05-2024, 04:13 PM | #14 | |
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The pad would look something like the upper pad with the added blue lines representing the additional brake pad material (with a radius on the horizontal line). |
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05-08-2024, 06:29 PM | #15 | |
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Alright, calipers came in today. Ran out to the car with them and got mounting. Here's the photos: View post on imgur.com So, everything lines up great, and there is what appears to be exactly 5/8" (sorry nothing to measure mm in ) gap between the hat and the pad. So, it would seem to me, along with your idea of a pad that's 5/8" (approx 16mm) longer would do the trick. 47+16 = 63mm. As it turns out, 2014 Audi S3 pads (DP42173R) are 123 x 61 x 16mm. It seems to be an extremely similar pad, both with the caliper piston inner springs and the mounting tabs. The only issue I see is that one of the pads is drastically smaller. Both of my pads appear to be the same exact size when lining up the same direction, despite the picture saying one is 47 and one is 46, but I'm sure my eyes and touch can't tell a 1mm difference. As well, perhaps I'm measuring wrong, and doesn't help I'm using a 25ft measuring tape, this pad I ordered appears to be closer to 42/43mm rather than 46 or 47mm. Here are actual pics of the F30 330 pads: View post on imgur.com This is the same style diagram but for the 2014 Audi S3: View post on imgur.com Thus, making the setup 2003 M3 Rotors, 2017 330i 300mm Calipers, 2014 Audi S3 pads (FMSI Number 1761). Might be better sacrificing only a few MM for something that's available off the shelf. What do you think? |
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05-08-2024, 07:02 PM | #16 |
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Well, I ran over to the nearest auto parts store. They let me test fit without buying any since I brought the rotor and caliper with me...
View post on imgur.com Think we found our answer! |
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05-08-2024, 07:25 PM | #17 |
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tftimbn
The two stacked pads in one picture are showing two different pads with different pad guides. You’ll receive two identical pads when ordered. Your pads are the ones that have a sideways “T” shape. The BMW and Audi “T” pad caliper and anti-rattle guides are different. I’ve included an image with the two pads stacked together which clearly shows the guides are not the same. Pad guides have a relatively tight clearances to ensure the pads remain easily to slide forward (out of the screen) as pad material wears. You cannot use the 56 mm pad radial depth (PRD) in your BMW F30 single-piston sliding caliper, only the 47 mm PRD is the correct pad. Does the f30 single-piston sliding caliper used with the 315 mm rotor OD? If not, you’re still stuck with having a custom 47 mm PRD 123 mm wide pad extended by 15 mm (0.59”/15 mm or 13-14 mm so there’s clearance for thermal growth of the various parts). |
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05-08-2024, 08:10 PM | #18 | |
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I'm a bit confused, why exactly wouldn't this work? It was a snug fit and the "T" shape guides on the side, I'd argue are extremely identical when I put the F30 and Audi pads side by side. Of course this is the one thing I didn't take a picture of. The only thing that was obvious to me was the pad wear sensor won't fit, but I don't really care about that. If you look at the picture of my EBC pads, you'll see one has the T shape and one only has a nub that points down. The audi pads do the same for the front and back side respectively. To answer your question, the F30 caliper I am using is designed for 300mm rotors on the F30. The E46 rotor I believe is 325 or 328mm. |
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05-08-2024, 08:40 PM | #19 | |
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05-08-2024, 08:58 PM | #20 | |
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I’ll take a video of a comparison. |
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05-08-2024, 10:48 PM | #21 |
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05-10-2024, 08:31 PM | #22 |
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M3SQRD
Alright, here's the comparison. I noticed that if I line up the side tabs, the Audi pad is also taller. You can see in my excellent tracing, the top comparison is by lining up the tops of the pads, and the bottom comparison is by lining up the mounting pads. The Audi pad is longer in the direction we want, but also a few mm in the direction we don't. This does create an issue on the caliper only for the piston side, where the pad does not fully go in due to this. I see 2 options, 1) trim the top of the pad, or 2) what I would likely prefer to do, is grind down part of the caliper bracket with a die grinder to allow the pad room. You can see the obstruction in the video around the 3:37 mark. I would likely grind up to the visible seam on the caliper. My thoughts are this would likely have to be done even with a custom pad, and at that rate, the size of the pad would be about the same as this Audi pad, and for simplicity sake, we have off-the-shelf replacement parts and a one-time caliper modification. The pad play opposite of the piston side appears to be the same (granted theres no rotor installed nor is this on a vehicle at the moment, it's pouring rain today and tomorrow). The piston pad no longer has the springs either. I'm not sure if I would consider this an issue or not. As well, the pad wear sensor is supposed to go on the outer pad, where this outer pad does not have a spot. It may fit on the inner pad, but at this point, I wouldn't lose sleep over trying to get the pad wear sensor in. I'd rather just plug it in and tie it up somewhere and not worry about the idiot light. View post on imgur.com |
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