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04-19-2009, 01:20 PM | #1 |
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Limerock with BFG R1s in the dry = not so Fail!
I took another shot at Limerock yesterday, and this time the weather cooperated, and we had a dry track the whole day, so I got the chance to try out the BFG R1s on the TE37s. I must say the tires rocked! So much grip and friendly at the limit.
More info on the tire/wheel setup here: http://www.m3post.com/forums/showthread.php?t=243432 Some specific observations: 1. I was in group 3A. Track/race prepped cars/drivers were mainly in 4, and I guess the slower intermediate cars/drivers were in 3B. I ended up chasing a few Corvettes all day long. The E92 M3 seems to be a pretty good match for the C6 base Corvette. I would sneak up on the Vettes around the twisties and come up to their bumpers turning into the straight, but then they would gradually pull away from me on the straight. 2. This is my second time at Lime Rock; first real dry track experience there. So, I don't really have a baseline to compare how much of an improvement the R1s yielded, but compared to the dry track experience I had with PSCs at NHMS, they are a significant improvement. My girlfriend was informally timed me out of curiousity (this was an HPDE, so not a timed or competitive event), and she said I put in several 1:03 laps in 3 of the sessions. (I took her out as passanger in one of the sessions, and she didn't puke although she is complaining her right arm is sore from grabbing the door handle). I don't know what 1:03 means for this car. (My car is stock except for the tires and the Vorsteiner exhaust/muffler.) 3. The extra grip brings up some other issues. The stock seats simply don't cut it. Although I had the side bolsters as tight as possible, I was still fighting to stay in position the entire time. 4. The need for more negative camber on the front is obvious. I ordered the Dinan camber plates, and hope they will help. 5. The gearing was kind of problematic for this particular course. Keep in mind that the BFGs I am running have 25.0" rolling diameter front and back, and stock is 26.3" in the back, so the gearing is affected. I was catching the rev limiter in 3rd right before braking for the uphill, which translates to 102 mph for this setup, so I ended upshifting past the mid-point of Noname, and downshifting shortly after. I felt this was faster than riding the limiter in that case. The same thing happened down the main straight. I was catching the limiter in 4th past the start/finish line, which translates to 135 mph with this setup, so went up to 5th. I wasn't sure if that was the faster option in that case; riding the limiter seemed to be just as fast. A similar issue down the hill. I found that riding the limiter rather than grabbing 4th there was faster since I could accelerate faster onto the straight. 6. This is the first track that let me test the brakes at 140 mph. Last year, I did NHMS, where top speeds there are significantly lower. Everything was fine at NHMS, but I must say I have mixed feelings after the Lime Rock experience. It's not as if I had a serious problem stopping the car or anything, but in the last session, the pedal feel was not good at all, and I "felt" like I had to plant it lower. I also "felt" my braking distance was reduced. After the last session in the paddock, I measured front brake rotor temp of 460C (280C in the rear). So, the rotor probably had a little over 5 minutes to cool down a bit. The CoF vs temp data for RS19s indicate that CoF starts to drop right around 500C. Also, the 4 sessions were only 40 minutes apart from each other, and there probably was some residual temp at the beginning of the 4th session. The numbers indicate that I might have indeed experienced real brake fade toward the end of the 4th session. I don't know about why I felt like the pedal dropped though. I do have proper fluid in there, and Turner told me steel lines would not make a difference, so I didn't mess with the lines. Any advice/insights on the gearing/shifting and brake fade/feel issues would be appreciated.
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04-19-2009, 01:29 PM | #2 |
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Great report Lucid.
What fluid do you have in it? I boiled the stock fluid at a TT I did, which gave a long and soft brake pedal. I've got SRF and RBF600 ready for when PFC gets their pads to market. |
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04-19-2009, 01:38 PM | #3 |
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ATE Type 200. The system was flushed 1 month ago. Maybe SRF is indeed necessary for some tracks then to preserve pedal feel/travel?
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04-19-2009, 01:59 PM | #4 |
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[QUOTE=lucid;
I don't know what 1:03 means for this car. (My car is stock except for the tires and the Vorsteiner exhaust/muffler.) 5. The gearing was kind of problematic for this particular course. Keep in mind that the BFGs I am running have 25.0" rolling diameter front and back, and stock is 26.3" in the back, so the gearing is affected. I was catching the rev limiter in 3rd right before braking for the uphill, which translates to 102 mph for this setup, so I ended upshifting past the mid-point of Noname, and downshifting shortly after. I felt this was faster than riding the limiter in that case. .[/QUOTE] I did 1:05.75 with stock setup last year. great report btw. hope to see you at the track. |
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04-19-2009, 08:15 PM | #5 | |
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just trying to help |
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04-19-2009, 08:25 PM | #6 | |
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People recommend tricking the upper part of the stock 3-point system to locking as well. I am not sure if that is a good idea as the airbag system is designed to account for your body moving around in a crash. Would the front airbag function as designed for instance if all 3-points were locked in place at the time of impact? There is nothing restraining your head, so wouldn't your neck flex even more if your shoulder was locked in? These types of questions concern me...
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04-20-2009, 01:21 AM | #7 |
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Thanks (got your PM too). Interesting. There is defintiely cooling as soon as you let off the brakes from the radiation but even more so from the forced convection down the center vanes. I do not doubt you exceeded 500C, maybe 600C. I don't recall do the RS19's really start to decline in friction above 500C
As you know unless you get substantially bigger (heavier, specifically) rotors or higher temp pads the BBK is not a sure fire win to get rid of the fade. It sounds like the best option would be an after market brake cooling duct set up. Other have certainly inquired about whether one exists here on the forum and AFAIK, there is not one. It's kind of funny how maybe the most important thing for getting the car totally sorted on a high speed/hard on the brakes track is still not available... Oh well, says a lot about how folks are using their cars I guess... |
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04-20-2009, 02:24 AM | #8 | ||
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http://rennstore.com/page/z72k/Home.html And the CoF vs Temp chart is here: http://rennstore.com/page/z72k/Home.html RS-14 looks more appropiate at these temps, but I don't know what that''ll do the stock rotors. I can only assume things will run hotter on a faster track like Watkins Glen. Quote:
The other reason for thinking about aftermarket rotors would be material characteristics. I haven't done any research in this area, but one would think the better systems would be more durable than the stock rotors when used with more aggresive pads. And then there is the pedal feel issue. I supposed a more advanced caliper design would help with that. I've thought of cooling ducts as well. I might have something to report on that front later this summer. A friend of mine does CFD for a living. He's run simulations for Nascar teams. We are thinking about a redesigned bumper that does cooling and more...
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04-20-2009, 07:15 AM | #9 |
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First, 1:03 is pretty fast. I can't tell you how fast you SHOULD be running with your car though, sorry.
SS lines will MOST CERTAINLY help with your pedal feel. Surprised that Turner would tell you not to bother. You might experience fade which is a different issue but lines will definitely help your pedal feel |
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04-20-2009, 09:00 AM | #10 | |
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Yes, fade is mainly a function of pad material, thermal capacity of the rotor, and convective brake cooling.
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04-20-2009, 10:16 AM | #11 | |
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04-20-2009, 11:01 AM | #12 | |
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I had a little trouble getting the stock belt to lock. After a number of tries I did it, I had to push the seat all the way back, lock the belt and then move the seat fairly far forward (luckily I sit fairly far forward) and it would just stay. Since the belt is designed to lock in a crash I don't think you would sacrifice your safety but I had not really thought about it. In my old E36 I would lock the rear belts to secure the kids car seats and both belt mechanisms wound up breaking (wouldn't retract anymore) and I had to replace both rear belts. It didn't seem to be a safety issue because of how they failed but after they failed they obviously couldn't be used anymore and that wasn't safe. Anyway, the belts might not be designed to be constantly locked and under load. |
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04-20-2009, 12:55 PM | #13 | |
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As for SS lines, I'd definitely do it. I have them on my track car and love them. I'm putting them on my street cars as well as a more aggressive street pad for a little better initial bite as well as overall feel. |
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04-20-2009, 04:57 PM | #15 |
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Motul and SRF seem to be popular choices.
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04-22-2009, 09:57 AM | #16 |
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Lucid, I would suspect you're probably braking too much as opposed to having equipment issues. Those are pretty good times, at least from prior to the repaving (I don't know how old and new times compare), but with race tires and pads you shouldn't have the kind of issues you did, as Lime Rock isn't that tough on brakes. The stock brakes are great on these cars. I think ducting is always a good idea, as it helps extend the life of your pads and rotors in addition to keeping fade at bay, but one of the things I see with students is an over dependence on the brakes. Braking harder and later can help a lot. Most folks tend to get on the brakes too early, and not engage the brakes hard enough, and that extra time on the brakes tends to get them overheating more easily. It's certainly cheaper, and I suspect it will be fruitful, to modify how you brake before spending more money.
I ran the Glen the past two days on street pads, and would get two good laps out of them before the pads started to fade. They were half worn to begin with, but taking it easy for a turn or two brought them back to life for another couple laps. That is with stock fluid, stock rear pads, and HP+ front pads. I was running street tires and had respectable times (sub 2:20s in the dry, with a best of 2:17.0). I was amazed though at the plinking sounds the stock rotors make when you pit in, they were popping for about 20 minutes as they cooled when I got into the garage. My student, who had a Z4MC, was also getting the 'plinking', so I think it's a characteristic of the stock rotors as his are similar. Sign up for COM @ Mt. Tremblant in June, and I'll go out with you and see if you're using too much brake or are really in need of some more wallet lightening |
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04-22-2009, 09:09 PM | #17 | |
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That said, I must say your explanation about how the rate at which one brakes might affect rotor temps is incorrect. The simple thermal model is that whatever kinetic energy you end up depleting during braking will mainly end up in the rotors as heat by the end of the braking zone (as per the conservation of energy principle). How rapidly that energy transfer process takes place can have an effect but not as you describe. Braking later and harder--assuming the speeds at which you start and end braking are the same--would actually result in higher peak rotor temps (at the rotor surface) as there would be less time during the braking event for conduction of heat away from the rotor surface to the rest of the rotor and for convection out of the rotors (you would have a higher temperature gradient across the rotor). If you set those aside, the only relevant figures are the speed at which you started to brake and the speed you ended up after braking, and what happens in between is irrelevant. It would be great to get your feedback on my driving if we ever get the chance to be in the same car. One issue is my track insurance does not cover COM, so we'd have to meet up in a BMW or NASA event.
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04-22-2009, 09:29 PM | #18 |
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Lucid, I get the conservation of energy aspect, but the take away is, if you brake later (and harder) you're going to wind up with fewer brake issues.
I was guilty of overusing my brakes at the Glen, which I think made my pad fade more acute, as I wasn't confident in them 'being there' so I got on them a bit early just to reassure myself I would have some brakes going into the turn. That slowed me down a bit more than I needed but I'd rather go a wee bit slower than slow down in the armco Yeah, I was thinking about doing the track insurance thing, but I have two friends who attended this event that paid for coverage so you can definitely get it for a COM event. What insurance provider are you using? One of the guys used this company: https://hpdeins.locktonaffinity.com/ but I am not sure of the one the other guy used. And anyways, just don't crash If you want me to get some more info on the insurance shoot me a PM and I'll ping my buddies to get the specifics. I know it was about $100 for my friend in an E36 M3 for the entire event, and it covers everything but the actual 3 time trial laps. |
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04-22-2009, 09:42 PM | #19 |
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Ryan, there are two scenarios:
1. Brake later and harder (same set of speeds before and after braking) 2. Brake more (to the extent that you bleed more speed than you need to) 1 will absolutely not result in lower brake temps for the reason I explained. However, 2 can, but that should also result in poor lap times. Meaning, if my speed before the braking zone on the straight was 140, but in one case, I dove into the corner at 50 and in another at 30 (and I could have gotten away with 50), then sure, I overused the brakes when I went down to 30, and heated them up more than necessary. But again, if in both cases I went down to 50, how hard and when I was braking is not a factor from a temp perspective (if you set the two issues I mentioned aside). I have an annual HPDE policy with wsib. I'll check with them, but I didn't see COM on the list. If they see time trials on there, the whole thing is out I think. That's probably why. And, yeah, the "plinking" sounds from the rotors freak people out as they walk by!
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04-23-2009, 01:42 AM | #20 |
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Nice write up.
What size tires are you running?
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04-23-2009, 07:04 AM | #21 |
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04-23-2009, 08:07 AM | #22 |
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Sounds like you had a great time. I look forward to getting to LRP this season after i take delivery of my E90 (I just ordered yesterday). Sounds like some good times considering your car is mostly stock. I was running around 2 minutes flat in my E46 (it had a lot of suspension work + rcomps)
As for the seats, I completely agree with you - Not enough support. With my E46 M3 I just had to replace the seats with Recaros. I might have to do the same with the E90. There is way too much movement when pushing the car on the track. I really wish the M3 came equiped with Recaro's from the factory. |
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