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- Haifa
- Tomeru
- Tomeru
Thank you all for the information, it was truly an eye opener.👍👍👍
Making use of the correct gear applies engine braking and helps the car to be more stable rather than applying the brakes too much.
Obviously this is on entry but also sets you up for the exit as the revs are naturally correct for good acceleration.
So in conclusion, you do need to pick the correct gear for corners as the gear either side will provide poor/too much engine braking and slow exit acceleration.
What does torque have to do with it? The power curve and torque curve are equivalent. By using one, you are using the other.
It's just simpler to use power. The whole point of gearing is to maximize your horsepower, and thus your acceleration.
Just to avoid confusion, "torque" as used above is interchangeable with "power" or "horsepower".
Skipping gears doesn't help [in a real car]. It's best to shift down as soon as you're able to without blowing the engine (which can't happen in GT5, so ironically, it's best to jam down to a low gear and kill your engine so that you're not transmitting any power to the wheels that would fight your brakes).
If you want to slow down, you should be in the lowest gear possible, this maximizing engine braking (engine braking can be thought of as how fast your car slows down when you're not pressing the brakes or the gas).
When exiting the corner, you want maximum acceleration. But your tires can only transmit so much power. Basically, you need to use as close to 100% of your tires' traction as possible. Either do this by modulating the gas pedal, or by shifting up to a gear that does not spin your wheels severely, but is still in the power band.
peter_vod69 - fantastic post. Everyone should re-read.
How does engine braking help the car to be more stable? Do you mean trying to simulate the effects of trail braking?
Figure out what works in the game and forget about real-life racing principles, they don't always apply.
But to "forget real-life racing principles" sounds very limiting. I am more interested in the infinite.
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All I'm saying is, if you know what the hp curve is, you know what the torque is. The advantage of thinking in hp is that you don't need to figure out the multiplier for each gear.a quick overview:
http://www.vettenet.org/torquehp.html
In our case here we're talking about getting out of a turn. If you shift down into the lower gear but find yourself modulating the throttle in order to maintain accelleration traction, then you are likely better off staying in the higher gear- UNLESS your car is absent of mid-range torque and high on top-end horsepower (like a highly-tuned turbo 4cyl). If that is the case, shift down and make her scream, because hanging around in the higher gear will certainly be slower.
I didn't say skipping gears helps. I said it makes no difference, and you can choose to do so without penalty (if you are coordinated enough!). Also I do not advocate leaving the car in 5th gear as you try to slow down for a turn- of course you don't want the transmission fighting the brakes, which is what the clutch pedal is for.
In GT, engine braking helps and there are no downsides. Might as well use it.Race drivers do not use the engine to slow the car. They use the brakes.
If you find yourself shifting UP a gear when exiting a turn, then doesn't the question arise: "why did i shift down in the first place?"
In GT, engine braking helps and there are no downsides. Might as well use it.
Unless you are running without ABS, then there actually is a point to being careful with engine braking. Try it, you'll see once you are right on the threshold of braking grip, one gear down too many and you will have trouble controlling the rear of the car.
When exiting the corner, you want maximum acceleration. But your tires can only transmit so much power. Basically, you need to use as close to 100% of your tires' traction as possible. Either do this by modulating the gas pedal, or by shifting up to a gear that does not spin your wheels severely, but is still in the power band.
IRL I use engine breaking all the time, even for daily driving. I was taught to touch each gear downshifting. But I also use double clutching and synchronized shifting in daily driving so to each their own.
Why do you bother with all of this rubbish? Double clutching might be fine if you are driving something without synchromesh (IE a car built before about 1925, or an old truck, for example) but on modern cars it is redundant, and slow. Engine braking puts uneccessary stress on the engine and drivetrain, as well as unsettling the car, and shouldn't be done either. Why? Because brake discs/pads are wear items, gearboxes, differentials and engines are not.
In short, the scriptwriters of "The Fast and the Furious" were ignorant morons.
Which is quite different application to using it on the track.I've never found engine braking unsettles the car, in fact quite the opposite. It's also essential if you're coming down a steep hill, or just a long one.
I'm talking engine braking in the sense of a downshift, with a dab of throttle to rev match, rather than the horrible sensation of just changing down and letting the engine revs increase when the clutch is brought up.![]()
Compression Braking
Compression braking or as it is commonly know Engine braking is an often used and just as often misunderstood term. I hope in this post to clarify exactly what it is and how it functions as well as discuss its use, miss-use and disadvantages for track use.
In a future post I will also be looking at how Compression braking has been implemented in GT4.
How does Compression Braking work?
In the simplest terms Compression Braking is using the engine to slow the car. It occurs because unless the clutch is engaged and/or the brakes are applied the speed of the driven wheels is determined by the engine; remove your foot from the throttle and the engine will slow and with it the driven wheels. However if you remove your foot from the throttle and engage the clutch, the engine and driven wheels are not connected and the only thing slowing the car will be friction from the tyres and the resistance of the air, as a result the car will take much longer to stop.
This is all fairly simple stuff and it is possible to judge approximately what speed a car should be doing at any engine speed in a particular gear, using the MPH per 1,000 rpm figure, which is derived from the cars gear ratios, axle ratio and tyre diameter.
If for example we take the Ford GT, with the following MPH per 1,000 rpm figures as an example.
1 = 9.8
2 = 15
3 = 20.1
4 = 27.2
5 = 33.2
6 = 40.6
Now using these figures we can examine Compression braking both in gear and through the gears.
If the car is in 3rd gear at 5,000rpm the car speed would be approx 100.5 mph, if you lifted off the throttle completely and relied on the drop in engine speed to slow the car the speed would drop according to the engine speed (if you remain in 3rd gear) as follows.
5,000 rpm = 100.5 mph
4,000 rpm = 80.4 mph
3,000 rpm = 60.3 mph
etc
This clearly shows the relationship between allowing engine speed to drop and it slowing the car; the amount of time this would take depends on a number of factors, such as engine compression ratio (generally the high this is the quicker the drop in engine speed) and flywheel and driveshaft weight. Using this method to slow the car down will always be far, far slower that using the brakes.
Compression braking when changing down through the gears can have a far more dramatic effect as illustrated below (using the Ford GT figures).
The car is travelling at approx 100 mph in 3rd gear (approx 5,000 rpm) when the driver begins to brake slowing the car to 50mph, the speed required to take our imaginary corner.
At this point the gear is changed to 2nd with the revs at approx 2,000 rpm, when the clutch is disengaged the engine speed dictates a speed of 30mph (2 * 15mph per 1,000 rpm).
The car is travelling at 50mph, but the engine speed and gearing dictate that it should be travelling at 30mph. This 20mph difference in the speed the car is travelling at compared with the speed the engine wants to travel at is going to be transferred to the driven wheels and slow the car in a dramatic and un-controlled manner. In turn the wheels will also try to resist this rapid deceleration and speed up the engine.
If however the driver had blipped the throttle to approx 3,300 rpm before the clutch is disengaged then the engine speed would match the car speed and no additional braking would be experienced, keeping the car stable.
Compression braking on the road
Many driver use compression braking on the road when changing gear to help slow the car and with older cars it can help if the brakes are poor or fading. With modern cars it is generally considered unnecessary as the braking system is more that sufficient.
Many people would argue that using compression braking saves on wear and tear on the brakes, however just as many people would say that what you save in pads and discs you lose in wear and tear to the engine and drive-train. Its hard to say who is 100% right on this one as it would vary from car to car and driver to driver.
On a personal level I dont using compression braking when changing down as I consider the sudden braking force it generates too sharp and prefer the smoother experience you get with heel and toe downshift that match engine speed to road speed.
One useful aspect of in-gear compression braking is often used in off road driving when descending a steep slope, here the rev limiter and knowledge of mph per 1,000 rpm can be used to control your descent speed without touching any of the pedals.
Compression braking on the track
I would be surprised if many professional drivers use compression braking (even on endurance events) and I am yet to come across a race school that recommends its use. While it does help conserve the pads, it does no good to a race tuned engine; they are not designed to slow the car, but to power it.
With Compression braking it is very difficult to judge how much additional deceleration you will get, as a result if you are already at the threshold of braking (or near it) you could well overload the tyres grip level and lose control, flat spots on the tyres will result which will hammer your lap times.
Changing the pads on an endurance race spec car is relatively quick and easy, and a task regularly carried out in the pits during endurance racing. It is also far less time consuming to have to change the pads, than it is replace an engine component (or retire through engine failure) or lose time over a number of laps because you've just flat spotted a tyre.
I have watched numerous endurance races, and have session reviews of Le Mans dating back to the 1960's, also a documentary on the Morgan team at Le Mans and Bathurst. I can't remember ever hearing a driver talk of using compression braking out of choice. Now if the brakes have failed for some reason, you may not have a choice; but thats a different thing.
You should also remember that compression braking will only directly effect the driven wheels, shifting the brake bias in that direction. With the majority of race cars being rear wheel drive, this would mean a major brake bias to the rear wheels, if the car is anything other than straight you may now be in a situation of just trying to control the car rather than brake and setup the car for the corner entrance. Even if the car is in a straight line, if the car is running a high compression engine (which increases the effect of engine braking) it can be enough to lock the rear wheels and get the back of the car twitching. Neither of these scenarios is worth conserving a little bit of brake pad material. You would get more of a saving on the brakes through good brake control and technique than you ever will through engine braking.
A quick quote from Danny Sulivan (of the Skip Barber racing school) illustrates this point
"To put it into perspective, at Laguna Seca, which is hard on brakes, Rick Mears and I were team mates at Penske and Rick finished the race with only 70 thousandths of an inch of brake pad material left. I only used 70 thousandths of the pad in winning the race. People brake differently but can still run the same lap time, especially in a race"
The following is an extract from the Russ Bentley books "Speed Secrets - Profressional Race Driving Techniques"
"Again, the reason for downshifting is not to slow the car. I can't emphasise this enough. That's what brakes are for. Too many drivers try to use the engine compresion braking effect to slow the car. All they really achieve is upsetting the balance of the car and hindering braking effectiveness (if the brakes are right at the limit before locking up and you then engine braking to the rear wheels, you will probably lock up the rear brakes), and more wear and tear on the engine. Brake first, then downshift."
This is from Skip Barber's "Going Faster"
"What downshifting is really for.
We ask this basic question of every racing school class. The most frequent (and incorrect) answer is, "to help slow the car down." In a racecar with good, durable brakes (the majority of modern racecars), downshifting to help slow the car down is unnecessary. The brakes slow the car down. You downshift to get the car in the proper gear to exit the corner."
Now Russ Bentley has raced Indy cars, World Sports cars (including endurance) and is now a race instructor, Skip Barber should need no introduction, but the book I refer to has been written with the assistance of ten instructors from the Skip Barber Racing School.
Brakes slow the car, not the engine; unless your brakes are shot in which case you do not have a lot of choice, but unless you're Moss or Fangio you're not going to win like this.
Problems with Compression braking on the track
1. Its less effective than normal braking.
As Compression braking effects only the driven wheels it will have a major effect on the brake bias of the car; incorrect brake bias (or brake balance) can increase braking distances significantly. Even with 4WD cars the effect of engine braking is limited to the front/rear split of power distribution and will normally affect the brake bias negatively.
It is also not possible to accurately predict the level of Compression braking or modulate it once it has been applied, making accurate and controlled braking almost impossible.
2. It does not give more braking force if you are already at the limit
This one is a common myth of Compression braking, that it will allow you to get more braking force for free. While in the distant past braking systems were not powerful enough to exceed the grip limit of tyres (and this is a long way in the past), modern braking systems are more than capable of exceeding the grip levels (measured in straight line braking as the slip percentage) of the tyres.
If you are already at the braking threshold adding more braking force through compression braking is just going to exceed the slip percentage and lock the tyres.
Using the Ford GT example from above and assuming that the car was already braking at the tyres threshold (assume max 10% slip percentage for this example). If when the clutch is released (with the car at 50mph) the tyres are already using the full 10% slip in braking, the additional braking caused by compression braking (20mph vs. 50mph) will exceed the 10% max by a large margin, the rear wheels will lock, the tyres will flat spot, braking distance will actually increase and unless the car is totally straight the major rear bias will possibly cause a loss of control.
When to use Compression braking?
Obviously with road driving compression braking and its use is very much a case of personal preference; however on the track most instructors and drivers share the belief that the disadvantages more than outweigh the advantages (and some would argue that it has no advantages).
However should you find yourself in an older car (historic racing), suffering from brake fade or even brake failure then you have little choice but to use what ever method you can to slow the car.
As Skip Barbers book says:
In this case you certainly do use the downshift to slow the car down but its a last resort
Scaff has spoken and pretty much everything he said is irrelevant...no offense Scaff...unless it works in the game. I could care less what Danny Sullivan says or Rick Mears or Juan Fangio or Mario Andretti. None of those guys is sitting behind a DFGT racing a 600 hp street car on Spa, all of which exists only as bits and bytes. Unless PD programmed the effects of downshifting, braking, engine braking etc. to mimic real life perfectly which I seriously doubt, all that info is meaningless. And even if they did program it perfectly, we don't have to worry about blowing up an engine or wearing out the brakes, so our choices will be based on what makes us fastest, in the game, not what Danny Sullivan is doing when he has to worry about blowing up a $100,000 motor or losing his brakes on the last lap.
All that matters is what works in the game. If engine braking works and you're comfortable with it and run lap times you are happy with then do it. If it doesn't work for you and you want to brake entirely using the brakes then do that. There are no engine failures here, brake pads and rotors do not wear nor do you pay to maintain them. Do whatever you want that works for you. If PD had better testing facilites we could test these things out scientifically, but for now I'm going to do what feels right and generate the best, most consistent lap times for me, regardless of how Rick Mears feels about it...lol...![]()
Johnnypenso. None of those guys is sitting behind a DFGT racing a 600 hp street car on Spa, all of which exists only as bits and bytes.
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I've got to admit that my experiences with engine braking IRL is mainly with FWD cars. My current car is RWD but i've not really driven it in anger so to speak.