Rear Lateral Movement During Heavy Breaking

Discussion in 'Road Racing Forum' started by ScottyD_GT, Oct 15, 2018.

  1. TymeSlayer

    TymeSlayer Tramps like us, Baby we were born to run...

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    Sorta like when you took my Boss out in Hastings and we didn't turn the nannies off. You hated the car and couldn't get the car off t5rack fast enough.
     
  2. Bill Pemberton

    Bill Pemberton TMO Addict

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    Oh, did get them off, that was why I was concerned why you had such weird brake bias. Felt like an old Vette I raced with brakes that had caliper issues. Heck, must of worked anyway, got you running 2 seconds quicker, ha.
     
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  3. TymeSlayer

    TymeSlayer Tramps like us, Baby we were born to run...

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    Must be something wrong with me. I had one session where I didn't get them shut down and other than that, I thought the car ran exceptionally well all three days. Other than staying on them too long, I thought the brakes did well. I think you're just used to better equipment. I have to get away from the Hawk Street/Track pads to something better next season. And you got me running better because, well you're a good instructor. (There, I said it!) - The good news is, I did not feel any shimmying of the back side while breaking in my Boss like the OP has in his GT350.
     
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  4. Bill Pemberton

    Bill Pemberton TMO Addict

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    My first thought with your car was something to do with your rotors or pads and it could have been just weird buildup. I changed where and how I was braking with the Blue Beast, after that first hit slowing from 120. Now we know it was wacky street/track pads and you are too fast to be running Adolescent Hawk pads - they are not really track, more like puberty race pads. You are mature man and you can whine about being slow , but it was way too easy to overpower those things. Get some new rotors and some serious pads for next year and we will shave another 2 seconds off your time - minimum!! PS -it is a tyme honored tradition to get pure race pads once you get fast and you are there!
     
  5. TymeSlayer

    TymeSlayer Tramps like us, Baby we were born to run...

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    Duly noted. With all I already have to do on the car this winter, I'll add brakes to the ever growing list. I'm thinking about a hans device as well.
     
  6. TMSBOSS

    TMSBOSS TMO Addict

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    Stop thinking about the device, buy one. I have one and need to wear it.
    I have a few sets of pagid pads which are 50% worn if you want to give them a try.
    And as much as it pains me to say it, “Bill May be right”. You need to move up to serious brakes before you have serious breaks.
     
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  7. Bill Pemberton

    Bill Pemberton TMO Addict

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    Tyme to get a Hans Device, since you are no longer as slow as you try to tell everyone you are!
     
  8. Drlee50

    Drlee50 TMO Advanced

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    I have had that problem before too but only at Road America where they have a real long front straight. The car I ran at that time was a twin turbo gen 2 viper. At 160 the whole car would get very light ( not enough aero). And my speed approaching turn 1 was 180 to 185mph. It was
    REALLY light by then! When I would get on the brakes the front would nose over and the rear still super light and it would wobble the rear bad! It was scary but predictable. I did find that tightening up the single adjustables did help by still there was an aero problem. Had a front splitter and no rear wing. Bought one and never got it on prior to selling the car. Lowering your ride height may help from an aero perspective but wouldnt do much from a shock strut /compression rebound stand point.
     
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  9. Bill Pemberton

    Bill Pemberton TMO Addict

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    Can imagine , as ran my Gen II there also and destroyed rotors and pads. Yours more have been more speed related and old technology than the ABS situation folks are seeing on some of the new machines.
     
  10. fpGT350

    fpGT350 TMO Intermediate

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    180 MPH going into turn 1? That's flying! Never saw more than 160 in my Competition Coupe. Even with the original 2003 flimsy rear wing, very stable under high speed braking with Hoosiers. When we were required to run those crappy undersized Toyos for World Challenge, very scary braking into Turns 1,5, Canada corner. Larger downforce and bigger tires may be the solution. Also make sure you have toe-in on the rear wheels. By the way, Hello Bill. Guess who!
     
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  11. Bill Pemberton

    Bill Pemberton TMO Addict

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    Hmmm....pretty sure it is one pretty fast Italian, how u doin Fast Franco?!
     
  12. fpGT350

    fpGT350 TMO Intermediate

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    Couldn't be better Billy P, that is unless I could have more low end torque on my GT350 :D
     
  13. fpGT350

    fpGT350 TMO Intermediate

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    By the way, another thing occurs to me about rear end wobble under heavy braking. Under heavy braking the rear tire contact patches become way small due to weight transfer from the rear tires to the front tires. if you happen to be running lots of negative camber in the rear, your rear tire patches are even smaller. I would probably try less rear camber and also soften up the compression settings on the rear shocks. Compare lap times after the change, then adjust back to original if that doesn't work.
     
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  14. Bill Pemberton

    Bill Pemberton TMO Addict

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    Franco........you will do fine, just keep it wound up and don't be afraid to buzz that 8250 redline, plenty!
     
    Last edited: Oct 18, 2018
  15. Drlee50

    Drlee50 TMO Advanced

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    180 into 1, 155 into 5 and 150 to Canada corner. I ran 335 square Hoosier slicks so the front really gripped on braking .

    The boss only gets 145 on 1, 140 on 5 and 135 CC. It's all shes got captian !!

    Sent from my LG-H932 using Tapatalk
     
  16. ScottyD_GT

    ScottyD_GT TMO Intermediate

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    I found some interesting info from Steeda.

    “The S550's subframe mounting holes are very large compared to the subframe mounting bolts. Since there is a large difference in bolt and hole size, the subframe can be mis-aligned from the factory up to 1/2" left to right. These voids between the stock bolts and subframe can have up to a quarter inch of movement in most cases in any direction.
    Our Alignment dowel kit fills the factory bolt hole voids with CNC machined delrin inserts that will square up the rear subframe to the chassis. By filling these voids we are also limiting the side to side and front to back movement of the subframe that is present under hard acceleration and braking.”

    This aligns with a few folks comments. I think it’s a combination of multiple things, but for $40 the Steeda IRS Subframe Alignment Kit seems like a great option to try first.

     
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  17. rwleonard

    rwleonard TMO Beginner

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    FWIW: My GT500 would wag its tail under hard, straight-line braking until I had a Griggs torque arm installed. It has not done it since.
     
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  18. OPMustang Tim

    OPMustang Tim TMO Race

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    @ScottyD_GT if you do not plan to go all in Replace the Lower Control Arm Bushings with bearings, add the cradle support bushings, alignment kit and possibly the braces. This will remove 95% of the compliance with a minimal penalty increase in NVH, if any. Big sticky tires overwhelms the rubber bushings and causes massive geometry changes. The stock tires overwhelm the factory bushings on track. If this is a track toy just replace the cradle bushings with solid ones.
     
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  19. ScottyD_GT

    ScottyD_GT TMO Intermediate

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    Thanks, Tim. This looks like solid advice! Sounds like a fun winter project.
     

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