Necessary pad thickness for track event?

[iPhoneEngineer]

Hey guys,

I'm going to Thunderhill Raceway in Northern California for a two-day event in mid July. I have a touch over 5mm of pad left, though the rotors are pretty worn, and there's a bit less clearance (maybe 4mm) at the edge. I expect about 4x 20 minute runs each of the two days (maybe 3).

BMW has refused to replace the brakes yet, though I have the extended main't plan which will cover the rotors and pads, because they aren't less than 3mm yet. I'm really impressed by how long they have lasted, and think they may well hold up through the track weekend, after which would be a perfect time to replace them--but it would suck to have to sit out some runs if they get too low.

What would you guys do in this situation? How long can you run with the wear indicators exposed, knowing that these rotors are about to be trashed and replaced anyway? Thanks!

[SmartBastard]

If you don't overcook them, then you should be fine for the event. Only when you put too much heat into the brakes without cooling them off, you will see extrem pad wear.

[iPhoneEngineer]

Cool, great advice! Indeed I've had the car since the mid 20's (k-miles) and it's now turning 45k, on the same set of brakes. In that period there was a year where my commute involved descending 2,500ft daily, and though I made use of engine braking to a certain degree, I really am impressed they are still serviceable.

Important auxiliary note: this car has the VT2-500 kit and dyno'd at 410RWHP, which will obviously create additional braking demands on the track. However, it will be only my 3rd time on-track, and I'll be driving for fun and experience--not to push to the limit.

[Finnegan]

IIRC front OEM pads are 14MM new and rear 12MM new. You're past what I consider the cutoff points for track use (50% remaining). I don't like to go too far past that since the pad itself provides a barrier to heat getting into the caliper/piston/fluid. You're be putting the pads to a good amount of use, especially going into 10, 14, and 1 (given your power levels assuming you're not going to restrain your right foot).

Pads aside, I'd be more concerned with how old your brake fluid is. If it's over 6 months old flush the system and get new fluid. You don't have to be Speed Racer to boil old fluid and end up having issues.

Given that you're doing 2 days plus lodging and etc. which aren't cheap, I would replace the both the fluid and pads. Swap back your old pads after your track days if you want new wear out the stock BMW pads. A nice set of Stoptech Street Performance pads isn't that expensive. These are great dual use pads for those of us starting out on the track. Just bed them per the Zeckhausen recommendations and you'll be good to go both days.

1 x StopTech Street Performance brake pads - front (D394) [1 box required] (63-309-0394) = $85.00
1 x StopTech Street Performance brake pads - rear (D683) [1 box required] (63-309-0683) = $61.00

Have fun!

[seank]

I would only if had a spare set in the trunk. I would not want you to ruin your weekend. Maybe, you could buy some and return them if you don't use them. I think your going to need them. It will cheaper than the damaged caused by going off in turn 1.

I also agree with everything Finnegan said, although if your going to be tracking regularly, get good track pads. They are great because they STOP.

2 questions:
- where's la honda california
- What club is running 2 days at Thunderhill in July? I don't know of anyone

[mfanatic325]

Scott, you will cook your brakes easily. Try to do some highway 9 runs and get the stealer to give you new pads and rotors before the event.

Btw Sean, La Honda is near Atherton and Los Altos, but I don't think Scott lives there anymore :P

If you need spare OEM pads, I've got some that I can sell you for cheap. They've got plenty of life left, almost new.

[iPhoneEngineer]

Thanks all! I've never swapped the pads myself (done the headers twice tho), and it looks involved enough to be quite a pain to do while at the track. I guess it might be possible after the first day, but the brakes would have to be completely cooled down. If I do swap the pads I'd have to swap them back as well to get BMW to replace the rotors, as these rotors won't last through a fresh pad.

I my brake fluid was flushed a year ago; not sure if that's passible, though clearly not ideal. If the pads were fresh, perhaps there would be enough heat isolation.

Perhaps I should bring my '12 911 Turbo S instead, since it's definitely ready to go. I've been looking forward to the first VT2-500 experience on-track though!

As for the questions:
- The event is done by the Porsche Club. One of my friends is going, though I've been planning to bring the M instead of the Turbo S. http://www.motorsportreg.com/index.c...8BEBD2E333B1D9
- La Honda is in the hills above Palo Alto, though I'm now in Redwood City.

[mfanatic325]

Just bring the Turbo S instead Scott
Much less hassle.

And in the meantime, wear out the Z4M's pads and rotors some more and then take her into the stealer for replacements. I'm sure you'll have no problem rompin' on them if you go up 9 and stuff

[iPhoneEngineer]

Thanks Lon, I might just do that . It has just 1,300 miles right now, though, so I'm going to investigate a way to trailer it up there instead of subjecting it to ~6hrs of highway driving. A track day is a pretty nice way to wrap-up the break in period! That said, taking the 911 will at least double the cost of the event, as it will compel me to get track insurance + the trailering + more expensive component wear (damn PCCB's & wide tires, lol).

Lon, we should go on a drive with the M's soon! The S/C kit was retuned by ESS after I shipped it to them in AZ, and is dramatically more powerful at the high end.

[iPhoneEngineer]

Scratch that, I'll be taking the M. Geico doesn't cover track events, I just found out, though my friend's plan with Farmers does. The PCA's recommended track insurance for this event is over $500 for a $60k car, and that's probably just for one of the two days--and they probably won't even insure $165k.

I wonder, do the track pads eat the rotors more quickly? If so, I think OEM is fine for me.

[mfanatic325]

Yeah, track pads do eat up rotors more in comparison to OEM pads, since the friction material is more abrasive and thus bites harder.

Swapping pads is pretty easy. I'm 110% sure you can do it yourself no problem. Just go in with a newer set of pads, and use your existing rotors. Then after the track day, swap your other ones back in, or use up whatever is left after track day. Win-win

[iPhoneEngineer]

So my new electronic brake fluid tester says 1% water content (next step is 2%, goes up to 4%), and my new bleeder equipment won't arrive until next Monday with the fastest available shipping. That blows my last weekend before the two track days.

Is ~1% too much to be confident in the fluid? I'm not sure what type of fluid was used by the mechanic who changed it last, but it was a reputable shop that knew I was going racing, so hopefully something like the ATE stuff I just purchased for the next flush.

[mfanatic325]

I just bought ATE Super Blue in preparation for my Brembo install. Are you going to use Super Blue as well? You should definitely rebleed before the event, just in case; since you haven't had it done in a while.

[iPhoneEngineer]

Yes, I bought both the Super Blue and the "TYP 200", which is the same formula with an amber color. However, I'd have to take a day off of work to bleed the brakes since my pressure bleeder won't be here by the weekend...so that would be a pain. It's been only a month over a year, and 1% water content doesn't sound too bad, though I would prefer fresh of course.

[The HACK]

Originally Posted by iPhoneEngineer

I have a touch over 5mm of pad left, though the rotors are pretty worn, and there's a bit less clearance (maybe 4mm) at the edge.

I'd be far more concerned with the rotors being "pretty worn" than the pads having a touch over 5mm left. The rotors are the primary heat dissipator, and the less material is left on the rotor, the more likely you'll experience heat related fade since the system can't hold and evacuate heat fast enough.

Take a micrometer and measure the rotors and see if they're below spec. If they are, replace them. IF this is your first time at the track, 5mm of pad material may suffice, although I'd bite the bullet and go ahead and replace both if I were you.

Safety on track is not something to skimp out on or procrastinate with. When in doubt, error on the side of caution.