Minimum brake pad thickness & track day prep

[e82n54]

After my last track day my pads have been squealing really loud. It's only when approaching a stop. I don't know if it's from the sensor causing a squeal or if the rotors have been glazed. I have stock pads.

The outer front pads are 4-5 mm thick. I can't see the inside pad thickness. My iDrive says I should replace the front pads in about 3,500 miles.

I have a track day coming up, and I want my brakes to work.

What should I look for when checking the pads to make sure they're okay for a single track day?

What's the minimum pad thickness for a single track day?

Thanks!

[Lubo]

Originally Posted by e82n54

What's the minimum pad thickness for a single track day?

Thanks!

It really depends on the driver, car setup (tires), and the course.

With 4mm left some organizations may no let you run. I would come with extra set of pads and tools to do the swap. You don't want to be coming home with no brakes or cut the track day early.........

Also don't forget to cool the brakes if you need to change the pads.

[e82n54]

Thanks Lubo. I've never changed brake pads before so I don't think I want to tackle that at the track for the first time. I think I may just keep an eye on them. Is it possible that the inner pads are worn much more than the outer pads?

[Kgolf31]

Originally Posted by e82n54

Thanks Lubo. I've never changed brake pads before so I don't think I want to tackle that at the track for the first time. I think I may just keep an eye on them. Is it possible that the inner pads are worn much more than the outer pads?

yes, if your guide pins are sticking it can wear more.

stick you head inside the wheel well with the wheel off and check it out

[Ginger_Extract]

I had the same question as well. Ultimately, like many things, the answer is "depends". My car is still on OEM pads, at 7.x mm, inside and out, at all four corners. I'm going to measure how much pad I have left after my next DE this weekend.
I'll be running a single-day event at Chuckwalla Valley Raceway, a 2.7mi long track. I'm not sure how hard this particular track is on brakes, as I haven't run there before, but none-the-less, I'll keep you posted on brake wear.

[jordantii]

On a single piston caliper it is likely that the inside pad is more worn than the outer. On an opposing piston caliper, like the six piston it is less common. Either way, you should measure them. Also on a single piston sometimes the leading or trailing edge will wear more than the other. So it's best to check both top and bottom.

[MMisencik157]

Dont forget that the pads will wear faster the thinner they get (on a track). This is because of the reduced thermal capacity. If you are going to be using your car on track you may want to consider going to a slightly more aggressive "hybrid" pad... especially as you start becoming faster. How old are your pads? How many track days have you done on them? Have you faded them?

[Ginger_Extract]

Originally Posted by MMisencik157

Dont forget that the pads will wear faster the thinner they get (on a track). This is because of the reduced thermal capacity. If you are going to be using your car on track you may want to consider going to a slightly more aggressive "hybrid" pad... especially as you start becoming faster. How old are your pads? How many track days have you done on them? Have you faded them?

Completely agree.

Big thing to note: fresh front pads for the 135i are 11mm

Alright, bumping this up, as I have returned from my previously-mentioned 1 day DE at Chuckwalla Vallet Raceway. Before the event, the pads were at 7mm all around, with even wear. CVR is not a braking intensive track, peak speed was 110mph, average speed was ~70, with two "big" braking zones, both of which were relatively flat.
I burned through 0.5mm of pad from 5 sessions, at approximately 15 minutes each, 98 total on-track miles, bringing me down to 6.5mm up front. More than that, after checking the pads, I found that the material had begun to crack. After my last DE, the pads exhibited scoring, and a slight sheen associated with being glazed over. A month of street driving sorted them out.
To be honest, if your pads are at 4-5mm, and the track you're going to is hard on brakes, buy new pads. As mentioned by the poster above, the thinner the pads the faster they wear, and ultimately, have the propensity to fail. I pulled mine off and am shelving them as spares. Replaced them with EBC Yellowstuff, which is supposed to be a hybrid-Clubsport/Street pad. We shall see.

[MMisencik157]

I think the "safe" amount of pad thickness is dependent on the friction material, track, driver, and of course supporting mods such as a BBK, aftermarket rotors and/or brake ducting.

Pads for the stock 135 front caliper come at 17mm total thickness (this measurement includes the backplate which is typically 5mm thick for most pads. That leaves roughly 12mm of friction material. Street pads or OEM pads will vaporize on most tracks even with a more entry level driver behind the wheel. Fade will set in quickly when the pad is at full thickness but obviously gets worse as they wear. Since no experienced drivers use OEM pads on the track (as they shouldn't) you cant really put a safe minimum on them.

Real race pads can be run very thin. I try to run my pads to within 1mm of the backing plate just to squeeze all the life out of them. Even with only 1 or 2mm of actual friction material my XP10s felt fine in a 15-20 minute session.