Car is bouncy

Discussion in 'Suspension, Brakes & Chassis' started by donmcgowen, Sep 14, 2018.

  1. donmcgowen

    donmcgowen Well-Known Member

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    I have a 2015 GT Premium with D1 Procharger on e85 making 750whp. I have BMR handling springs and Koni struts and shocks with BMR cradle lockouts. The car sits very low but does not rub. I'm having two issues. First, the car seems bouncy. It doesn't bounce like an old Lincoln, it rebounds quickly. But just very springy. Hard to explain. I'm thinking that some roads are just not smooth and with tight suspension is follows the road because it doesn't happen everywhere. Maybe it's normal. The second issue is the car seems loose on the expressway. I do have Mickey Thompson ET Streets in the rear so that might be causing it. But sometimes I feel if I'm on a exit ramp turning and I hit a bump, I'm scared the car will kick out on me. Maybe it's just the car is now really tied to the road so it feels all the imperfections. But I know what you are going to say, but I have not had an alignment yet after installing the suspension. Is that a possibility for these symptoms? I want to feel safe at 140+ at the track. I guess the overall thing is the car doesn't seem planted like I feel it should. I almost feel like the IRS is disconnected from the car. I don't know. If anyone has any ideas I would like to hear them. Alignment is coming this weekend, maybe that will help. Maybe I should change the Koni's from firm to medium? Maybe the car is sitting too low? But not sure how I would adjust that. But I have also seen other lowered sports cars look like they are bouncing going down the road so maybe it's normal.



    Thanks. Low_small.jpg
     
  2. BmacIL

    BmacIL Enginerd

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    Couple questions:
    1. Which Koni struts (I assume yellow)?
    2. If Koni yellows, what do you them adjusted to?
    3. Tire pressures?
    4. Alignment sheet, can you post it if you have a prior one? If you haven't had one, that's almost certainly the source of the loose feeling.

    Drag radials are not known for their confidence-inspiring handling. So that's definitely part of your wiggly-at-speed issue, but it could be any of the above items too. Where are you in the metro area? I have a pretty sensitive butt for this kind of thing.
     
  3. Norm Peterson

    Norm Peterson corner barstool sitter

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    Width of the ET streets vs rear wheel width probably has something to do with it as well.


    Norm
     
  4. OP
    OP
    donmcgowen

    donmcgowen Well-Known Member

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    Thanks for the responses. I'm thinking it normal. When I see real track cars from behind, the rear is always bouncing with the road.

    Anyway, Koni Yellow on firm settings
    305/35/20 ET Street @ 34 psi
    I will be getting an alignment this weekend
     
  5. BmacIL

    BmacIL Enginerd

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    What is firm? # of turns from soft? I would run 1 full turn up from soft in the back based on my experience with those shocks and same springs.
     
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