First full track day - front end push!

Discussion in 'Corner Carver Racing Tech Discussion' started by RJdude3, Aug 13, 2017.

  1. RJdude3

    RJdude3 Junior Member

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    Well, just completed my first full track day in the car ( I've done many motorcycle track days at this track) and what a blast it was! Very different feeling going around this track in a car versus a track bike.

    Car ran really well and felt like I was in the top half of the intermediate group as far as lap times go. However my biggest complaint was the front end push, besides the high RPM shift lockout trying to downshift. No matter what kind of throttle I gave it in the middle of the corner, the front end just wanted to go straight. The faster the corner, the worse it was. At least around some of the slower corners, I would be in 2nd and give some throttle to get the rear end to rotate more. However around the sweepers, the harder I pushed the front end the worse it got. When I was chasing a Camaro ZL1, I could tell I started to abuse the front tires too much to the point I overheated them and made the push even worse. I would have to back down my pace to cool the tires down and regain some grip. I am also running the billet grill and the NMD ducktail spoiler, witch could also be adding to my problem. I did notice quite a lot of hood movement at 120mph, I could imagine that spoiler giving me a lot more rear downforce over stock.

    My current setup:

    255/45/18 BFG sport comp 2's (front/rear)
    2007 OEM GT500 wheels 18x9.5
    Ford Racing Struts
    Eibach sportline springs
    GT500 front brembo's
    Rear Tubular control arms (upper and lowers) and aftermarket UCA mount
    Adjustable panard bar
    Stock front/rear sway bars

    To me it felt like the car was falling over too much on that outside tire which was attributing to the push. some of the guys at the track were telling me that stiffening the front way would make my car push worse and that I needed to stiffen rear bar. I thought I would ask you guys that have these cars before I spend the money on new front/rear bars. I also saw a lot of guys running strut tower bars and thought that might need to be on my buy list as well.

    This was my fastest lap of the day. Let me know what you guys think.
    https://www.youtube.com/watch?v=HBKPkiiWeTc
     
  2. Sky Render

    Sky Render Stig's Retarded Cousin

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    You can always start with sway bars, because some good adjustable units let you fine tune the handling.

    I think the first thing you need, though, are some good wide tires.
     
  3. RJdude3

    RJdude3 Junior Member

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    What tire size are most people running on the track? 275/40/18?

    These tires are still pretty new so I got time to spec out my next set.
     
  4. kerrynzl

    kerrynzl Junior Member

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    Do you know the rating of those Eibach sportline springs? [Do they know?]

    Mid corner understeer is too much weight transfer onto the outside front, And a common problem when putting stiffer front springs in without addressing the issue of the rear roll stiffness.

    Adding stiffer front springs increases understeer

    You'll always get weight transfer during cornering, but what is happening is the soft rear end is "falling over more" causing the outside front to support more weight transfer.
    Everything is usually great until you get to the limit of adhesion, then these flaws show up.
    You could always slow down a bit [but we don't want to do that ,do we?]

    First thing I'd do is try and get some negative camber into the front.[neg 3 degrees]
    This helps the tyre footprint during body-roll


    Then a stiffer rear sway bar [or stiffer rear springs] to tune the roll couple
     
  5. 85258

    85258 Junior Member

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    Does the panhard bar have Height adjustment on both ends? Wouldn't lowering the Panhrd bar effectively stiffen the rear and loosen the car up?

    While I had a watts link on my road racing stock car, lowing the watts link would loosen it up. On my circle track car when we lowered the panhard it would loosen up as well. We also ran split height in the panhard in circle track but I would think it should be level in road race.
     
  6. kerrynzl

    kerrynzl Junior Member

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    Because most vehicles have a higher CGH than the roll centre, raising the RC stiffens the rear roll stiffness.

    Think if it like a lever [eg:a Torque wrench with the square drive in a vice]
    The pivot [square drive] is the RC, and the length of the handle is the force applied at the CGH.

    With a car there is always weight transfer due to lateral acceleration [even with no suspension]
    What we're trying to control here is... Weight transfer through "overturning moment" [Bodyroll]
     
  7. nawagner

    nawagner forum member

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    With this in mind could a person adjust the rear shocks, with adjustable shocks of course, to be stiffer and the front to be less stiff? Without adjustable shocks can tire pressure be adjusted to achieve similar results?
     
  8. kerrynzl

    kerrynzl Junior Member

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    Please understand, The shocks DON'T support the weight of the vehicle.
    So Generally NO!

    [but there are exceptions]
    Firstly you need to be a very aggressive driver on corner entry.
    A diamond pattern "double" Apex type driver on short tracks, and a real leadfoot on corner exit.

    What we do here is start off with a good handling car, and change to a locked rear-end to suit the drivers style.
    We then stiffen the shock on rebound and soften the shock on compression.
    When the driver enters the corner the stiff rebound unloads the inside rear [helping the locked rear corner]
    On Corner exit, when the driver floors it, the soft compression shocks help the car squat along with the locked rear there is a lot of forward bite.

    It is a good setup for dirt drivers switching over to road racing on tight tracks,
    Or drivers that like doing Banzai type "slide job" passing manoeuvres



    Please get your car sorted first before trying this crazy shit!
     
  9. RJdude3

    RJdude3 Junior Member

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    Yeah i know there were a couple corners where the line i was running, was not the preferred one. The long sweeper definitely benefits from a diamond pattern after talking with some of the other drivers and watching other videos.
     
  10. Sky Render

    Sky Render Stig's Retarded Cousin

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    Holy shit, there's some bad info in this thread.

    The only panhard bar that is height adjustable is the "race" unit made by Steeda. Most are only adjustable for length. The only way to adjust rear roll center is either the aforementioned Steeda unit or an adjustable Watts Link. I don't think the OP needs either of those yet.

    S197s have McPherson struts up front, so the front shocks DO support the weight of the car.

    And anyone who runs a locked rear on this chassis for anything other than straight drag racing or drifting is a moron.

    While it is generally true that increasing front stiffness increases understeer, the design of the S197's front suspension can lead to rolling outside of the camber curve. In other words, the front rolls so much under hard cornering that it can roll onto the outside of the tires and thus understeer. The solution to this, believe it or not, is a stiffer front bar.

    255s are TINY for track use. 275s are barely sufficient. You really want some 18x10s (or 11s) with 285 or even 305 width.

    OP, if your tires are new, don't sweat it. Use them up before you get some new ones. Until then, get some more seat time in. Make sure that the car is what's causing the understeer and not your driving. If you're confident it's the car, I would seriously consider a big, adjustable front bar and a rear bar to match.
     
  11. slackinoff

    slackinoff Member

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    I just wanted to chime in in your high rpm lock out. I tried a braided line - didn't work. What ended up working, (and working very well) was replacing the clutch matercylinder with the gt500 part....I will dig up the part number when I get to work. But basically it has a better ratio and will give your clutch more "disengagement". It completely fixed my problem.

    Sent from my LG-H910 using Tapatalk
     
  12. Norm Peterson

    Norm Peterson corner barstool sitter

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    18x9.5 is about the best you can do for 255/45-18 tires - your tire treads are about as well supported as reasonably do-able. But you need better tires. I used to run those exact sizes (different tires), and understeer was never so heavy that throttle-steering in 3rd gear on a long sweeper needed any more than a touch more throttle.

    I doubt that the FRPP struts & shocks are up to what the Sportlines' firm rates really need. Best information I have puts the firm rate of the Sportlines way up there (300-ish & 240 or so), but the initial rate is way low. If you're getting into the low rate on the inside corners, the inside is going to lift more than the outside will drop and you're effectively getting "extra" roll - and more loss of camber on the outside front. Sportlines are somewhat front-biased, while the Ford OE springs are slightly rear-biased, meaning that the Sportlines in addition to reducing roll (increasing front grip) also increase the amount of front lateral load transfer (decreasing front grip). IOW, it's kind of a three steps forward/two steps back situation. Most "lowering springs" are in the same boat to some degree.

    Separately for cases of extreme lowering is the possibility that you're riding the outside front suspension on its bump stop most of the way through the corner (extremely high rate and a lowered amount of average mechanical grip). You might have gained some unwanted bumpsteer as well.

    I'm guessing your car only has stockish camber, -0.75° or so. It'll work better on track with something like a degree more negative as long as you're running on true street tires rather than R-compounds or autocross specials (RE-71R, Rival S), which demand still more. If toe is OK and you tend to drive somewhat "enthusiastically" all the time, you won't necessarily end up wearing the front tires enough unevenly to matter. It is at least possible that max-suggested-width wheels for any given tire size (like what you have) actually demand a bit more static negative camber because of the greater stiffnesses that result.

    It's the kind of pivots those rear control arms have that really matters. Though if they're all polyurethane I'd expect their individual contribution to reduce understeer slightly rather than increasing it.

    I would strongly consider getting adjustable sta-bars, with both bars being adjustable. I happen to be running Sam Strano's bars (Hellwig, IIRC).

    The STB won't improve the cornering much (if any), but it might improve your ability to use all of what you do have via improved driver confidence. I don't have one of those.


    Norm
     
    Last edited: Aug 14, 2017
  13. Sky Render

    Sky Render Stig's Retarded Cousin

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    I've tested three (3), yes THREE strut tower braces.

    They don't do squat, at least on a coupe.

    They sure look pretty under the hood, though!
     
  14. RJdude3

    RJdude3 Junior Member

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    Thanks Sky Render and Norm! That is great information. Everyone at the track (none driving S197's) was saying that I needed to tighten my rear bar and soften the front, but that is not what the car or my butt was telling me. I really felt like the front end was falling over still too much on the more demanding corners. I got some pictures of mar car and you can see some good amounts of lean around the corner.

    As far as camber, i am running -1° btw.

    That kind of sucks about the stut tower bar being a waste Sky Render, i also think they look really good under the hood. I was looking forward to picking one out! lol

    I know of plenty adjustable front bars, but haven't seen many adjustable rear bars. The ones I see on AM or LMR look to be just beefed up over stock.
     
  15. RJdude3

    RJdude3 Junior Member

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    That would be fantastic! The lockout was really bothering me, especially going into Turn 1 at about 90. I really had to wait until the RPM's were low enough to get the car back into gear. I was giving up a lot of time during the braking zones, messing around with down shifting. A few corners i decided to just stay in 3rd and try not to scrub off speed. The only problem was i was getting my ass kicked out of the corner because the car would only be at 2,000rpm and had no power in 3rd.
     
  16. RJdude3

    RJdude3 Junior Member

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    These were the few pictures showing some lean in the car. Both of these corners were lower speed, about 50mph, but they were sharp and
    "high load" situations.
     

    Attached Files:

  17. Sky Render

    Sky Render Stig's Retarded Cousin

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    BMR's biggest bar is the one I'd use up front; start out on full soft.

    For an adjustable rear bar, you can either use BMR's (which may or may not fit depending on what exhaust you have), or you can look at Eibach, Steeda, or even Whiteline.

    Adjustable bars let you fine tune the balance very quickly and easily.
     
  18. kerrynzl

    kerrynzl Junior Member

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    You really need about -3° camber on the track. But with a street compromise you can back of the negative and add in a lot more positive caster [which becomes dynamic camber by turning the steering]

    The roll couple needs to be sorted on a Mustang because they're front heavy and naturally understeer [the rear needs stiffening]

    All cars are set up from the factory to understeer [The average Soccer Mom doesn't know how to apply opposite lock]
     
  19. kerrynzl

    kerrynzl Junior Member

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    Everybody at the track is correct.
    What you are feeling is driver feedback through the steering.
    When you have -1° camber but the car leans over 3-5° the front end washes out mid corner [ but it will turn in OK because the car isn't leaning over yet]

    I'll try and explain it easier .
    Go going back to newton's laws of equal & opposite reactions. Moving mass will continue in a straight line until it is met with an equal and opposite force.
    So Weight needs to overcome by Steering [traction]
    So at the LIMIT of traction the heaviest end want's to continue in a straight line [understeer in a front heavy car, or oversteer in a rear heavy car]

    Most vehicles have stiffer suspension to support more weight, hence the wheel rate on the front suspension is stiffer than the rear.

    Now here is the Trick.
    When the front end of the car bodyrolls 5°, the rear end of the car also bodyrolls 5° [unless the chassis is soft]

    So if you stiffen up the rear end so at the same G's of weight transfer it will only bodyroll eg: 4° , the rear end will support more of the total weight transfer.
    In simple terms you are tricking the TYRES into "thinking the car has more rear weight"
    So it will over load the rear tyres Before the front tyres reach the limit.
    [the opposite to what you have now]

    A lot of people misunderstand this concept because they only think about roll centres when both front and rear RC's are actually a roll axis [the whole chassis rolls together the same amount along this axis]

    The Stiffest end will always slide out first.

    If you cant get an adjustable rear bar, install stiffer rear springs.
    ---------------------------------------------------------------------------
    A note to Sky Render , about using locked rears being a moron comment.

    All Australian V8 Supercars, and NZV8 Supertourers have a locked rear mandated by the rules.
    Most space frame TransAm cars also run them.

    A locked rear doesn't cause understeer, it only aggravates an already understeering car.
    Even with racing tyres, the slip angle of the tyres will overcome the differential difference on the tightest corners
    The only thing is, a locked rear will natural want to straighten up when everything is relaxed [so there is some forward/aft loads on the tyres]

    I've even used a locked rear in a Vintage Lotus Cortina [with correct roll couple] and it is very predictable. You could only tell it was locked when driving around in the paddock.

    If you are driving at the limit of adhesion, it makes no difference with a locked rear.
     
  20. Thenorm

    Thenorm Autocrosser

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    more camber.
     

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