The "Pedal Dance" testing

[autoXracer]

Originally Posted by Element Tuning

So if you transition from throttle to brake fast enough, you will be greated with that rock hard pedal and no vacuum assist momentarily. The brake booster is a mechanical device so you can't trick it.

This could explain what I experience with pedal dance. Transiting from throttle to brake during the turn, messing up my braking, hence causing the car understeer.

[7thgear]

Originally Posted by autoXracer

Anyone experience understeer with pedal dance? Oh and let me add I'm no pro, so it could be just my driving.

understeer is when you have more grip in the rear than in the front

analyze your inputs and you fill find a solution

pedal dance removes all nannies so you're free to control your car

although I can see how CGS Mike's brake booster explanation could affect your perception if driver inputs.

[Godzilla35]

Mike... the problem is DURING the spinout... the pedal goes almost to the floor making a grinding sound / vibration noise... and almost no braking force... not so bad when you're in the middle of the skidpad... but I was almost going to roll backwards into a wall once... really annoying.

[CSG Mike]

Originally Posted by Godzilla35

Mike... the problem is DURING the spinout... the pedal goes almost to the floor making a grinding sound / vibration noise... and almost no braking force... not so bad when you're in the middle of the skidpad... but I was almost going to roll backwards into a wall once... really annoying.

That sounds like ABS... you always have the e-brake available, but I"m not sure lockup is what you really want. The pedal will sink with each pulse under ABS.

[Godzilla35]

Originally Posted by CSG Mike

That sounds like ABS... you always have the e-brake available, but I"m not sure lockup is what you really want. The pedal will sink with each pulse under ABS.

yeah, that's what I thought. Yeah, it's frustrating / scary because it's not like I'm left-foot braking or overcooking the brakes or even trying to stop from like 100 to 0. I'm literally spinning out at like 15-20? and most of the momentum is lost during the spin, I just need to stop. I see a lot of guys just drop the clutch and spin the tires forward, but I can't imagine that type of shock on the tranny when you're moving backwards is good.

Trying to find the best / safest solution to learn without worrying.

[brn12345]

So for people who have a tune on their car, what would happen if the pedal dance is performed? If I recall correctly on older ECU's knock correction is disabled in test mode and if the dance puts us in test mode, does that mean we also lose knock correction? On another note, when traction is disabled (3 sec hold down) does the car go into sport mode as well? The reason I ask this is because on my tune the normal mode throttle pedal settings are more aggressive than the sport mode.

[DougW]

Originally Posted by Element Tuning

Sorry guys what I'm talking about with pedal overlap is not "ice mode." It's simply the DBW throttle closing too slowly therefore delaying engine vacuum and subsequently brake booster assist. Pump the brake pedal while the engine is running, feels spongy with lots of travel, now engine off, pump the brake, and now it will be rock hard.

So if you transition from throttle to brake fast enough, you will be greated with that rock hard pedal and no vacuum assist momentarily. The brake booster is a mechanical device so you can't trick it.

"Ice Mode" has something to do with the ABS computer programming in response to the wheel speed data. I believe it's a response to excessive ABS intervention so to further reduce potential lock up its reducing line pressure via the ABS pump.

You can add an external reservoir or elect vac pump to assist, this is done all the time on big camed NA hot rods.
DougW

[Element Tuning]

Originally Posted by DougW

You can add an external reservoir or elect vac pump to assist, this is done all the time on big camed NA hot rods.
DougW

I run a Hydra EMS which has a much faster throttle so it's not an issue anymore.

I think for the poster that spins out and the pedal goes close to the floor I bet pad knock back is part of that along with the ABS pump dealing with that. Pad knock back is caused by flex in the hub/bearing and in turn the brake rotor pushes against the pads, pushing the caliper pistons in.

As a racer who has lost his brakesmore than once I always left foot tap the brake as I exit a series of turns to reset the brake pistons. This way as I brake at the end of the straight I'll have a hard pedal or I'll know I've had a brake failure. Sometimes when I'm going for a lap record I won't do this and the pedal almost always has way more travel. If 1 or 2 tenths of a second doesn't matter then check the brakes

Thanks,
Phil Grabow

[DougW]

Originally Posted by Element Tuning

I run a Hydra EMS which has a much faster throttle so it's not an issue anymore.

I think for the poster that spins out and the pedal goes close to the floor I bet pad knock back is part of that along with the ABS pump dealing with that. Pad knock back is caused by flex in the hub/bearing and in turn the brake rotor pushes against the pads, pushing the caliper pistons in.

As a racer who has lost his brakesmore than once I always left foot tap the brake as I exit a series of turns to reset the brake pistons. This way as I brake at the end of the straight I'll have a hard pedal or I'll know I've had a brake failure. Sometimes when I'm going for a lap record I won't do this and the pedal almost always has way more travel. If 1 or 2 tenths of a second doesn't matter then check the brakes

Thanks,
Phil Grabow

I hear ya I never had ABS or power brakes when I used to race IMSA but always left foot tapped just hopping something was there especially about mid way of a 24hr when nothing worked. Now everybody bitches if the ABS kicks in 2 feet short. Can the stock ecu's DBW not be reflashed to track 1/1 with the pedal?
DougW

[7thgear]

i can't seem to enage the pedal dance anymore :o

last time i did it was in the summer..

the only thing that changed is that i'm on winter tires right now and my TPS light is on, could this be interfering with the sequence?

also how warmed up does the car have to be, and will it simply not work if the car is cold?

[sw20kosh]

Originally Posted by 7thgear

i can't seem to enage the pedal dance anymore :o

last time i did it was in the summer..

the only thing that changed is that i'm on winter tires right now and my TPS light is on, could this be interfering with the sequence?

also how warmed up does the car have to be, and will it simply not work if the car is cold?

Car has to be warmed up. Once warm turn car off. Turn car on. Do the pedal dance.

Does this not work?

[CSG Mike]

Originally Posted by 7thgear

i can't seem to enage the pedal dance anymore :o

last time i did it was in the summer..

the only thing that changed is that i'm on winter tires right now and my TPS light is on, could this be interfering with the sequence?

also how warmed up does the car have to be, and will it simply not work if the car is cold?

Fully warmed up. Coolant will need to be at normal operating temp. Once the temp gauge is at the "normal position" from a fully cold start, it should be ready in another minute or so idling.

The engine warms up extremely slowly when idling... I usually sit there free revving up and down to about 2k rpm...

[kotoshi]

I'm going to try this at a Rallycross tomorrow. The symptoms definitely sound like what I've experienced with fast inputs and a bumpy surface.

[kotoshi]

So updates from today's testing. First I found it easiest to wait to start the sequence until the dash had finished it's start-up routine.
With the pedal dance done, I was able to take about two to four seconds on a ~65 second course. More important though was that the car never did anything unexpected, like would occasionally happen without it. This is very useful to know.
Also, I never got any ice mode or anything like that. I can say this made me faster at my local Rallycross course