Hi Folks,
I hope this is helpful for anyone considering upgrading their brakes, as I am just finishing off this very straightforward and economical conversion. I'm amazed its not more common, given it should deliver similar performance to the GT 8 piston swap, while being 1/4 of the price.
As an intro, I'm a bit of a track junkie, after seeing how well the X3m went after a custom E70 tune (10.5 sec 1/4 mile @ 131mph), I was very keen to take it to the circuit.
While a lot of fun, it was obvious that brakes are a huge limiting factor. Before heading to the track I changed my fluid to Castrol SRF and upgraded my pads to EBC Blue. if you aren't familiar with these in the U.S, they are a decent street / track pad, designed to handle a bit of abuse.
Regardless of these mods, I baked my brakes after about 10 minutes. 700hp and 2000kg does take its toll.
I did manage to keep going through the day doing quick sprints, 1-2 warm up laps followed by 2 laps at full speed, then a full cool down.
Not the easiest way to get a lap time in, but the best I could manage giving the circumstances.
Anyway, I'm due out again in 2 weeks and wanted to ensure my brakes were up to the task. What's the point in dusting young guys in sports cars if you can only handle a few laps at speed?
I looked into the GT 8 piston upgrade, but it seemed very costly. It provides a bigger disk (which is usually good) but it does limit you to a 21 inch wheel, not ideal for many. If you want to read more about that, a few members discuss it here:
https://x3.xbimmers.com/forums/showthread.php?t=1723703
Prices here:
https://www.vividracing.com/brembo-4...153125573.html
It's clear when looking at the stock X3M brakes the discs aren't the issue, it is the tiny caliper / pad combination - which at first glance looks decent.
A 60% increase in swept area from M5 to X3M pads is absolutely massive.
You will see pics below of both pad specs, but please note the actual contact area for each is as follows. See pics of measuring tape of stock X3M pads.
Stock X3M: 92x90mm = 8280mm2
Stock M5: 180x75mm = 13,500mm2
The M5 calipers are 100% bolt on using standard X3m discs, you just have to make sure you get calipers
with brackets.
This is essential as the X3M brakes have different brackets, so you can't swap them over.
I paid about $1300 USD for my M5 calipers which had done 2000km, so virtually brand new pads. Best of all they come in BMW blue, matching the rears, so no need to respray anything (which is necessary with the GT kit).
On top of that, I have also made up some brake ducts using 2.5 inch high temp silicone hose. I have added some brackets (which can be sprayed black). At the front they just poke through the standard bumper vents.
They connect to the standard brake heat shields with hose clamps, with holes drilled there for 2.5 inch flanges.
I will be trimming the inside edge where these hoses come out in the wheel well to avoid them fouling the wheels on lock. Regardless, this isn't much of an issue as I plan to remove them for street use.
I have located some track compound pads to suit these and the stock rear calipers, but if push comes to shove I'll try them out first time with stock pads.
I'll update the post once that day happens, I'm heading out this time with Cup 2 tyres (275/35 21 all round) as well as the brake mods so expect to knock a bit off my lap times.