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Engine Brake Mapping
Apr 15, 2008


 
Posted by Justin Rebelo Id_icon_gray at 06:22 AM on Apr 15, 2008 Post #1

Can someone explain engine brake mapping to me? I understand what engine brakes refers to, but I don't understand what this mapping number represents nor what increasing or decreasing it is supposed to do.

Is this something that could save you from a double-downshift blowing an engine by having it not affect the engine as much?

 
Posted by Andrew Carson Id_icon_gray at 07:56 AM on Apr 15, 2008 Post #2

As i understand it, Engine braking refers to the rear wheels only. As the car brakes very hard, the ECU determines the grip level (and locking) of the rear wheels, and to avoid locking, the ECU pours extra fuel into the engine to keep the rear wheels from locking up. This is why you see the current (2008) formula 1 cars lock up the rear wheels. They no longer have engine braking.

A lower number in Rfactor represents a higher level of engine braking. It has an effect on fuel consumption, but can give better stability under braking at the rear.

Thats about all I know.

 
Posted by Steve Smith Id_icon_gray at 10:08 AM on Apr 15, 2008 Post #3

Justin,

Think of it as a percentage of throttle being applied by the computer when you are on the brake pedal. A lower number represents a lower percentage of throttle being applied, a higher number represents a higher percentage of throttle. For example, let's say you set brake map to 5. That means that when you are off the throttle and applying brakes, the engine "computer" is automatically applying 10% throttle (10% of full throttle), so even though you are applying full brakes the engine "computer" is still giving the car some gas.

A higher percentage of throttle, which equals a higher brake map number in rFactor, will provide some rear stability under heavy braking, but will also tend to induce some corner entry understeer in slow corners. It also will have a small negative effect on fuel mileage.

A lower percentage of throttle, which equals a lower brake map number in rFactor, will help slow speed turn in, but can cause the rear wheels to lock up more suddenly if you are too aggressive on the brake pedal. It also will have a small positive effect on fuel mileage.

Brake map adjustments are most effective for helping the handling (corner entry) with very heavy braking from very high speeds into a very slow corner. It is a very fine tune adjustment.

 
Posted by Justin Rebelo Id_icon_gray at 01:17 PM on Apr 15, 2008 Post #4

Thanks a lot guys, that helps a lot.

To be clear, we're not talking about wheels 'locking up', per se, but rear wheels which are spinning either much faster or slower than the fronts, causing them to slip and not grip, correct?

 
Posted by Andrew Carson Id_icon_gray at 02:36 PM on Apr 15, 2008 Post #5

Justin, as far as I know engine braking keeps the rear wheels from locking up by spinning them in such a way. Steve explained it pretty clearly. By applying throttle automatically (like the engine braking does)under braking, you can't lock the rear wheels, but the spinning of the tires may be somewhat irregular if the engine braking is too high, which can affect turn in understeer and such.

Think about braking while applying the gas with your other foot. Thats the effect that you get in esscense.

I suppose Steve mentioned that lower numbers = lower engine braking effect. Opposite of what I thought. He's probably right, i'll take a look when I get home.

F1live had this to say about the subject:

"Under heavy braking in Formula One, the rear brakes can easily lock up as the weight is shifted towards the front two wheels and the EBS (engine braking system) has traditionally prevented the locking up at the rear from occurring."

 
Posted by Tristan Bayless Id_icon_gray at 04:50 PM on Apr 15, 2008 Post #6

The fastest way through a braking zone is with no automatic engine braking; this makes the braking distance shorter as the rear wheels are not being driven forward by the engine at all, which would make the front brakes work harder to slow down the vehicle in the same distance. But, as Andrew and Steve pointed out, this can be very tricky to do as you the driver must manually feed in a little bit of throttle as speed deteriorates, because the less speed you're traveling at, the less aero download is being applied to the rear wheels, and therefore the greater chance the rear wheels have of locking during a braking effort.

This means auto engine braking is really only an effective (or necessary) assister in mid-to-slow speed corners where the wings aren't working at their optimum.

 
Posted by Andrew Carson Id_icon_gray at 05:08 PM on Apr 15, 2008 Post #7

A thing i've noticed about my driving is that i automatically engine brake myself because of left foot braking. I never really come fully off the gas, which wouldn't be good in some cases, but is great in sim racing.

 
Posted by Jason Gudgen Id_icon_gray at 05:45 PM on Apr 15, 2008 Post #8

Sounds like a way around not being able to have ABS in F1 anymore. Audi tried to get around this same rule in touring cars (with their front drive cars, anyway) by joining the rear wheels together by axles with a viscous differential in between. If a wheel locked, the spinning wheel would cause torque to be transferred to the locked wheel unlocking it. You got to give them an "A" for effort.

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