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Post by JasonMurphy on Tue Jun 12, 2012 9:41 pm

I've got a single tuning question, but if this turns into a sort of troubleshooting thread, great. Smile

I have this happen on a couple of my cars: when under heavy braking, the car tends to slide around involuntarily. Usually, it's the front end swinging left or right, though sometimes it also feels like it's the rear getting a little bit fishy too.

When it happens, I'm not turning the wheel at all except to try to counteract the drift. The drifting begins before I start downshifting as well.

My initial guess is that there's something going wrong with the weight transfer under braking and it's just pushing the car in weird directions, and that my springs might be a little too stiff, but I'm open to many suggestions.

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Post by beefsupreme42 on Tue Jun 12, 2012 10:04 pm

I would say that you need to adjust the brake balance, probably more toward the rear. I don't know the first thing about tuning, but I think this might help

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Post by MFKR RAMBO on Tue Jun 12, 2012 10:46 pm

Go into test drive mode. Do a lap and get your tires warm. Switch to the far outside view of your car. Make sure you are on a track with a long straight and hit it full bore. Turn the camera angle with the stick to view the side of the car and stand on the brakes full on. Your looking to see which locks first fronts or rears. To me it sounds like your rears are locking up way early. If so, adjust more brake bias to the front and retest. You want to get it to lock all four at the same time.

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Post by beefsupreme42 on Tue Jun 12, 2012 11:56 pm

MFKR RAMBO wrote:Go into test drive mode. Do a lap and get your tires warm. Switch to the far outside view of your car. Make sure you are on a track with a long straight and hit it full bore. Turn the camera angle with the stick to view the side of the car and stand on the brakes full on. Your looking to see which locks first fronts or rears. To me it sounds like your rears are locking up way early. If so, adjust more brake bias to the front and retest. You want to get it to lock all four at the same time.
good tip, I should use this to tune some of my cars.

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Post by BiggLou55 on Wed Jun 13, 2012 12:08 pm

Beef is correct (he gets a cookie)... It's your brake balance...

This is an excerpt from VVV Worms tuning guide, which I still reference today when tuning (AWESOME tuning resource)... You can find it on the FM4 Forums HERE

VVV Worm Tuning Guide (on FM4 Forums) wrote:
Straight Line Instability
  • Too much rear wheel toe-out.
  • Not enough rear downforce.
  • Too much front downforce.
  • Not enough rear toe-in (under hard acceleration) –presumably for RWD.
  • Too much front toe (either in or out) – car darts over bumps.
  • Front ARB is way too stiff – car darts over bumps.

Instability Under Brakes
  • Front end darts or wanders – too much front brake bias.
  • Car wants to spin – too much rear brake bias.


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Post by beefsupreme42 on Wed Jun 13, 2012 12:13 pm

BiggLou55 wrote:Beef is correct (he gets a cookie)... It's your brake balance...
I did something right!!!! Very Happy

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Post by BiggLou55 on Wed Jun 13, 2012 12:14 pm

Actually... One REALLY good tip to start from is something I use for myself when tuning... Take the % of weight subract from 50 and cut in half... Move you brake bias that number....

Example 1:
    Front weight bias = 43%
    Diff from 50 = -7 / 2 = -3.5
    Remove 3% to 4% brake bias (basically set it to 47% or 46%)... You are moving more brakes to the rear of the car...


Example 2:
    Front weight bias = 62% (obviously a FWD car Very Happy )
    Diff from 50 = 12 / 2 = 6
    Add 6% to the brake bias (basically set it to 56%)... You are adding brake bias to the front of the car....

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Post by beefsupreme42 on Wed Jun 13, 2012 12:18 pm

by the way, thanks for posting that there, lou. I finally have a decent collection of useful info about tuning Very Happy

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Post by BiggLou55 on Wed Jun 13, 2012 12:41 pm

Just remember.... That calc is a STARTING point... You'll still need to fine tune it through testing... No calc will get your the "perfect" set-up. Once you have a really solid base tune, tuning becomes subjective.... The tunes I run for myself are not always the tunes I provide to others or on my SF. I like my tunes to be much grippier than most, and I do A LOT of trans tuning to get the acceleration shift points I want... That also helps to counter the drag from increased down-force and/or reduced HP/Tq....

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Post by beefsupreme42 on Wed Jun 13, 2012 12:44 pm

BiggLou55 wrote:Just remember.... That calc is a STARTING point...
yeah, I would never even dream of starting a tune from nothing.... Very Happy

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