Wiggle under high speed braking?
08-21-2011, 09:44 PM
#17
Instructor
Join Date: Jan 2011
Location: Wellington, South Florida
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
Hi, I was at PBIR yesterday and braking hard from 150ish for turn 10, I noticed the same thing, (PCCBs too) a slight wiggle. This was under super hard braking with the ABS tripping in and out. Nothing too fightening, but some definite wiggle. I had the wheels totally straight ahead. I have 4K miles and 7 track days.
Can somebody explain why this could be a symptom of an LSD problem (LOL - not drugs)? I can understand why an LSD issue would affect lap times but not sure why it would cause wiggle under hard braking.
Thanks,
Carl.
Can somebody explain why this could be a symptom of an LSD problem (LOL - not drugs)? I can understand why an LSD issue would affect lap times but not sure why it would cause wiggle under hard braking.
Thanks,
Carl.
08-21-2011, 10:03 PM
#18
Race Director
I just wanted to get a survey from those braking from high speeds at the track. It seems the gt3rs will "wiggle" when under heavy braking from 130 to 60. I have PCCB and have bed them in properly. The pads are not cold as this was in the middle of the day, after 3 runs.
First track event with the rs. No visible rotor defects, although the inspection was with the wheels still on.
First track event with the rs. No visible rotor defects, although the inspection was with the wheels still on.
Sincerely,
Macster.
08-21-2011, 11:03 PM
#19
Rennlist Member
Join Date: May 2008
Location: Somewhere in a galaxy far, far away....
Posts: 17,107
Likes: 0
Received 258 Likes
on
172 Posts
Hi, I was at PBIR yesterday and braking hard from 150ish for turn 10, I noticed the same thing, (PCCBs too) a slight wiggle. This was under super hard braking with the ABS tripping in and out. Nothing too fightening, but some definite wiggle. I had the wheels totally straight ahead. I have 4K miles and 7 track days.
Can somebody explain why this could be a symptom of an LSD problem (LOL - not drugs)? I can understand why an LSD issue would affect lap times but not sure why it would cause wiggle under hard braking.
Thanks,
Carl.
Can somebody explain why this could be a symptom of an LSD problem (LOL - not drugs)? I can understand why an LSD issue would affect lap times but not sure why it would cause wiggle under hard braking.
Thanks,
Carl.
I had the same problem and recall it being explained that once the LSD drops below a certain percent of grip only one side has power and both sides fight each other due to the ratio. When on the brakes/off the gas one side has backdrag whereas the other rolls freely...
Im not 100% sure of the scientific wording or explanation and i cant really recall the mumbo jumbo. But once i got the LSD beefed up the problem was solved.
Magic!
08-22-2011, 10:51 PM
#21
Burning Brakes
Had the same issue with my 2011 GT3, had the alignment checked and rear toe was out. Had the shop realigned the car to the correct toe and the car is now very stable under hard braking.
08-23-2011, 06:29 PM
#22
Rennlist Member
Doing so on Sunday! I wasn't planning on tracking the car before October (too hot here) but I figured the diff wouldn't bed in right unless it had seen track duty. So I dutifully pounded away last night at Yas Marina F1 circuit until I ran out of fuel. :-)
Oh, tried the PSS out for the first time too. They are really not a track tire - definitely better than PS2, but do not compare to P-Trofeo's or MPSC. Had a guy ahead of me on Trofeos in a 997.2 gt3 and it was ridiculous the kind of corner speeds he was managing.
Oh, tried the PSS out for the first time too. They are really not a track tire - definitely better than PS2, but do not compare to P-Trofeo's or MPSC. Had a guy ahead of me on Trofeos in a 997.2 gt3 and it was ridiculous the kind of corner speeds he was managing.
08-23-2011, 07:02 PM
#23
The Trofeos are basically Hoosiers with treads - unfortunately they appear to only last as long as the Hoosiers. Your experience following a GT3 on Trofeos is correct - you are not going to hang with it with a PSS - neither will the OE MPSCs - ive seen in car data showing 1.5G corner loads consistently with the Trofeos. I think the true wear rating for those tires is 40-50 - by contrast the PSS is 300 - but it appears to put down times below it's wear rating - but not in the Trofeo range.
08-24-2011, 03:13 AM
#24
The Trofeos are basically Hoosiers with treads - unfortunately they appear to only last as long as the Hoosiers. Your experience following a GT3 on Trofeos is correct - you are not going to hang with it with a PSS - neither will the OE MPSCs - ive seen in car data showing 1.5G corner loads consistently with the Trofeos. I think the true wear rating for those tires is 40-50 - by contrast the PSS is 300 - but it appears to put down times below it's wear rating - but not in the Trofeo range.
I would have thought that MPSC would be comparable to the Trofeo. Maybe slightly slower, but not considerably.
I thought about buying a set of the Pirellis, but a) you can't find them and b) they cost $3k a set (here)
08-24-2011, 09:28 AM
#25
Three Wheelin'
I say the wiggle is from the MPSC.
Most professional drivers that I know blame the MPSC.
Which is so much more noticeable when you are used to driving on slicks.
Most professional drivers that I know blame the MPSC.
Which is so much more noticeable when you are used to driving on slicks.
08-24-2011, 10:53 AM
#26
Why do the pro's hate the MPSC so much? I thought they were the industry standard in DOT-R compounds, until Hoosiers and Trofeo showed up..
08-24-2011, 12:01 PM
#27
Race Director
08-24-2011, 02:22 PM
#29
Instructor
Yorkshireman asked why a "wiggle" is a sign of a worn LSD. Matt can explain it in great detail I am sure, but the simple answer is that the LSD provides assistance under both hard acceleration and hard deceleration. It essentially locks both rear wheels together when ever there is significant torque being applied to the rear axles, either in a positive or negative direction. So, under hard braking, the rear wheels are locked together through the friction disks in the differential which will help to keep the rear end stable. If one tire provides more friction due to surface irregularities it cannot pull the rear of the car to one side like it can with an open diff. This is the big reason a friction disk LSD is more desirable than a torque vectoring LSD in a track driven car.
08-25-2011, 09:25 AM
#30
Nordschleife Master
Yorkshireman asked why a "wiggle" is a sign of a worn LSD. Matt can explain it in great detail I am sure, but the simple answer is that the LSD provides assistance under both hard acceleration and hard deceleration. It essentially locks both rear wheels together when ever there is significant torque being applied to the rear axles, either in a positive or negative direction. So, under hard braking, the rear wheels are locked together through the friction disks in the differential which will help to keep the rear end stable. If one tire provides more friction due to surface irregularities it cannot pull the rear of the car to one side like it can with an open diff. This is the big reason a friction disk LSD is more desirable than a torque vectoring LSD in a track driven car.
Either 11 cup LSD or guard
Is there a pro or con to either