997.1 GT3 - how much brake disc wear on track days? - Page 1 - 911/Carrera GT - PistonHeads UK

Hopefully not too much of a how-long-is-a-piece-of-string question... For a 997.1 standard braking setup, does anyone know how much thickness discs might lose on track days? My front discs have been measured recently at 32.36mm when the minimum recommended thickness is 32mm. I'm wondering if a single track day is going to reduce that thickness noticeably. For what it's worth, the car is on Pirelli road tyres (Rossos?), the track is likely to be the Rockingham ISCC circuit and it will be my first track day in a GT3 (so I'll be getting to know the car rather than banging around at 10/10ths all day). Cheers.

braddo said: Hopefully not too much of a how-long-is-a-piece-of-string question... For a 997.1 standard braking setup, does anyone know how much thickness discs might lose on track days? My front discs have been measured recently at 32.36mm when the minimum recommended thickness is 32mm. I'm wondering if a single track day is going to reduce that thickness noticeably. For what it's worth, the car is on Pirelli road tyres (Rossos?), the track is likely to be the Rockingham ISCC circuit and it will be my first track day in a GT3 (so I'll be getting to know the car rather than banging around at 10/10ths all day). Cheers. When considering friction material wear (that's pads and discs, not fluid) you are primarily concerned with heat. The more wear on your discs and pad friction material, the more heat will be generated in your brake system (with a given amount of braking), as there is less material for that heat to be transferred across and dissipated. So the brakes will still work fine with worn discs, as long as there is no scoring etc (which you should check thoroughly when using such old discs on track) and this holds true even below tolerance levels for discs. The problem you have, is that you will be generating more heat, so the pads operating temp will be higher and the fluid temp will go higher. If you are going to take it relatively easy, I would suggest new (higher temp if possible) fluid and I would make sure your pads have at least 60-80% life left when using these older discs. If you have a combination of worn discs, worn pads, and old fluid, you will most probably boil your fluid relatively quickly or get brake fade from going above the operating temp of your pads. So it is a "how long is a piece of string" question. If you are going to use them, I would make sure the fluid and pads are relatively new to counter the extra heat the discs will create/retain. Best case: everything should be in tip top shape to minimise any problems and maximise your time on track. Disc wear estimate is something that can't be estimated and doesn't really matter when you consider the more pressing effects of using worn discs above. HTH Edited by S1MMA on Tuesday 20th May 19:38

I get 2-3 days out of a set of fronts. If you change to Alcons/brembos you will get 12-15 days

Thanks. In the other road cars I've used on track I have never had a problem with brake fade so I expect I will be OK as far as heat management goes, but as far as wear is concerned it sounds likely that a single track day will have these discs down to their minimum allowed thickness (assuming useable wear on standard discs is 2mm and they typically last 2-5 track days).

braddo said: Thanks. In the other road cars I've used on track I have never had a problem with brake fade so I expect I will be OK as far as heat management goes, but as far as wear is concerned it sounds likely that a single track day will have these discs down to their minimum allowed thickness (assuming useable wear on standard discs is 2mm and they typically last 2-5 track days). Your concern should not be whether you are below the minimum recommended tolerance for the disc - or will you reach that on one trackday, as I said above your discs will still work below this level. The advisory tolerance is just that. Your braking system will not suddenly be massively less effective going below 2mm. The small difference of disc wear pre and post trackday will really make little overall difference to the effectiveness of your braking system. If you will be 0.01mm above tolerance after the trackday, or 0.01mm below, what difference will this make? If I was you, I would be worried about your brakes lasting the day and take steps to ensure they do, as I outlined above.

Just FYI - Steve Rance is an experienced racing driver - you are not going to be anywhere near his level of pace or have anywhere near the wear levels he will get from consumables on track. You would probably get 10 or more trackdays out of a set of front discs on sessioned trackdays, if your PSM is on and regularly active then your rear discs can see quite hefty wear, so keep an eye on them also.

Thanks and I realise who Steve is (having read some of his posts on driving styles/methods for the various GT3s with great interest). I mentioned 2-5 track days as the JZM website suggests 4-5 track days from standard discs in contrast to Steve's 2-3. The front pads are only 20% worn; the rear pads about 40% worn and the rear discs about 60% worn. The brake fluid is due for a change which I intend to have done before the track day (although would that new fluid be wasted if front discs/pads get replaced in a few months?). I need to inspect the front discs in more detail but a cursory look suggested they are in very good condition (other than being worn). Your comments lead me to my next question: If discs are down to their recommended minimums but are otherwise in good condition, what are potential consequences of using them for a little longer (on the road)? If the answer is, "they continue to work fine until they have a catastrophic failure that will spit you off the road," that is not terribly appealing.

How do these discs look (photo taken when cold)? Are the small cracks cause for any concern?

Are they light cracks?

>sucksairthroughteeth<

They are very minor cracks and would not concern me personally in the slightest. Most drilled discs that have been used hard will look like this.

Actually, the cracking is the main reason most people who track GT3s switch to Alcon/Brembo/PF discs. Porsche say that if the cracks extend beyond 5mm, or meet up, or go to the edge of the disc you need to change discs; often it's the size of the cracks & not actual disc wear that forces the change. Keep a very close eye on the rear pad wear if you leave the nannies switched on (I wouldn't) because that's where you can kill a set of pads in a day on the 997.1

Looking at JZM's website, it suggests that an Alcon/RS29 combination on the front is only about £500 more than the OEM Porsche setup - does that sound right? £500 for 5x the disc durability seems like a no brainer.

I may be talking out of my bum here but here goes.... <is_this_true?> When tracking the 997.1 GT3 make sure you put the gen 2 rear brake cooling ducts on. The car will use the rear brakes as a form of traction control and that could cause excessive heat being built up as well as increased wear. </is_this_true?>

The cracks in this post look quite small still - but they will grow with track day use. This happened on mine and so I switched to the Alcon / RS 29 set-up and also had the brake cooling ducts fitted to the rear brakes - as thes are still OEM discs. The Alcon setup has a high initial cost - not sure of the term but you need to buy the disc and bell assembly - total was around 2 to 2.5K all in. However, I can completely recommend the Alcon / RS29 set-up, they are excellent and with low wear rates on both discs and pads. Re the comment on stablity control eating the rears - I dont think this applies to the 997.1 GT3 as it only has "basic" traction control which appears to cut power rather than stability control using the rear brakes. I have never had a problem with this on mine and I leave the TC on as a safety net - its pretty tolerant and only seems to intervene when things a going wrong.

With the standard drilled discs you should clear the holes of brake dust after each track day and periodically otherwise. The holes get blocked up and cause cracks to form and grow more quickly.

I've noticed a few holes with brake dust in them so I'll certainly be clearing those out in advance of a track day, thanks. I'll keep a close eye on all the brakes on the day including rear pad wear; the aim is to run with TC off but I will be starting with it on as I get to know the car a bit. Can't wait!