Can higher speeds be more economical?

Saving gasoline: tips from Rico Klein

On this page, Rico Klein gives interesting tips on how many liters of petrol can be saved with the appropriate driving style. In 2005 he proved that he knows a lot about driving and was named "Germany's best car driver 2005" by AutoBild magazine together with cooperation partners.

1. A braking process converts kinetic energy into heat. So DO NOT brake! *


The greater the weight of your car, the more important this point is. To brake you take the wind and the rolling resistance. If you have made a mistake and are too fast, which happens all the time in everyday life, you use the MOTOR to brake. Contrary to popular belief, rolling is a little more economical than braking the engine; In other words, with the engine brake I "destroy" more kinetic energy than I can "generate" with the saved gasoline. You can understand this effect very nicely if you have an on-board computer with average consumption. Even after a long and monotonous drive on the motorway, with a 12 carved in stone on the computer, a single roll-out (!) Into the exit is enough to reduce consumption to 11.7 for the entire route. All other driving maneuvers, from turning down third gear to applying the engine brake with brief zero consumption, no longer have any measurable influence on consumption

However, as indicated, the engine brake is of great importance in everyday life, so there are a few important points to consider here as well. As most of you know, the so-called overrun fuel cut-off means that I have no gasoline injection whatsoever when I completely take off the gas. However, comfort is always in the foreground in development today. Therefore, the idle injection does not start again at idle speed, as one might suspect, but already at significantly higher speeds. Usually it is between 1200 and 1500 rpm, sometimes even> 2000 rpm. If I continue to use the engine brake at this point, the injection takes place as if it were idling, but with a correspondingly higher frequency. High time to shift down a gear, or to hit the clutch and start rolling. Tries to feel or inquire about the operating speed of your overrun fuel cutoff.

But you can also save fuel with the brake. If I have to stop because the traffic is idle, I can often save several drops of fuel by braking sharply and rolling 10-20 m at walking pace. Usually it's green again before the car comes to a standstill and I save driving. This so-called degressive braking also serves road safety, as any good driving instructor will tell you. So there is no panacea for economical driving, you have to think about how best to use the fuel in every situation.

2. Reduce the pace


The physical relationship between travel speed and consumption is not always obvious. But you should always know that the lowest speed has far more effects on the cut than the highest. For example, if we drive 100km at 50km / h and 100km at 100km / h, this results in an average of only 66.67km / h. If, on the other hand, we drive the first 100km at 60km / h then you would only have to drive 75km / h on the second 100km to achieve the same travel time. Just watch the arrival time in your GPS. It is much easier to drive off 10 minutes earlier than to drive out 5 minutes. The bigger and more unfavorable your body is built, the more expensive it is for you to stand still.
The attached graphic is suitable to illustrate the relationship between vehicle, travel speed and consumption. It shows the theoretical total road resistance of 5 known vehicles. For a better overview, a weight of 1400kg was assumed for all. The Opel Calibra - which combines very little cross-sectional area with a good drag coefficient, the VW Tiguan - as an example of a modern SUV, as well as the Mercedes Vaneo, VW Glof V and Toyota Prius are represented. The Golf has the same drag coefficient as the Vaneo and (almost) the same cross-sectional area as the Prius.



To interpret the diagrams: The SUV has more air resistance than rolling resistance from around 55 km / h, the Calibra only at 78 km / h. So, assuming identical framework conditions, both would have the same consumption in l / h. But since we make a sensible calculation of the consumption in relation to the distance traveled, the SUV would already have 40% more consumption / 100km. If both drive 100 km / h, the SUV already consumes 60% more than the coupe. A mid-range car with an inexpensive shape, like the Prius, only comes with a 10% surcharge.
In real life, however, consumption does not drop as far as the driving resistances suggest. The reduced load reduces the efficiency (see point 4) and so there is an optimal speed for each car. In most cases this is between 50 and 70 km / h in the highest gear. So if you drive on Landstrasse 90, you will measure a difference, if you limit yourself to 40 in the city, on the other hand, you will see more consumption. However, it is particularly important to refrain from using the last reserves in small engines. Every revolution of the engine is additional effort and a small car with an extended three-cylinder can consume significantly more than a large engine in the medium speed range, even if it has to overcome slightly more driving resistance.

3. Shift up early


I generally drive in top gear in the city. As long as the speed does not drop significantly below 1500 rpm, this does not do any harm. When starting off, I'm already in 3rd or 4th gear before I cross the intersection. And don't think a passenger will notice any of it! Everything runs smoothly and smoothly and quietly.
There are no intersections in the consumption curves of the individual gears, i.e. it is always more economical to stay in high gear when the speed is sufficient. If you feel that the car no longer wants to pull, don't worry, that's the sign that it can't drink either! Anyone who has an on-board computer with instantaneous consumption can see this directly: You put the carrot on the gas and the consumption hardly increases as long as the speed remains low.

4. Accelerate at full throttle


So that I can get through the gears as quickly as possible, I always give 90% full throttle when accelerating. There, just below the full load enrichment and at low speed, every (conventional) gasoline engine has the highest efficiency. But don't step on the gas too wildly, so that you don't get greased unnecessarily. And of course always think of 1st, 2nd and 3rd!
Since different opinions clash here again and again, I have added a so-called shell diagram and colored it for a better overview.
You can see the red full throttle line at the top and the speed at the bottom. In between, the lines for different throttle positions are often drawn with percentages. But you can also imagine that these are roughly a flattened copy of the full load line at different heights.
This engine has its best consumption of 233 g / kWh at almost full throttle and around 3100 rpm in the dark green area. The green area with the 260 shows the area that you can keep in the city traffic when you have to accelerate. At half throttle you rarely come across the 280 line.
You can read something else out. If no power is required, i.e. only rolling around with little gas, then the specific consumption over all speeds is about the same. But since I generate the least power in top gear, I use absolutely less than in low gear with a higher speed, where more power is generated with the same specific consumption. Even if I were forced to give more gas to keep the pace, this would have a positive effect on the difference to the lower gear.



However, the desire for large throttle valve openings must not make you operationally blind. There is quite a margin between "the car is not going faster" and "the car is not going to slow down". Once I have reached my cruising speed, I should try to accelerate as little as possible.

In the case of a diesel engine, the consumption diagram usually looks very similar to that of a gasoline engine. The best efficiency is in the speed range of the maximum torque at around 90% load. In the case of torque-limited motors with a truncated torque curve, you can try to guess the course. Usually, however, the most favorable speed range should be 50 to 60% of the nominal speed. In practice, you should also bring a diesel with a lot of gas and high gears up to cruising speed quickly.
It is also interesting that a diesel is not significantly more economical than a gasoline engine in the optimal consumption window. Both engines need around 200g / kWh. The consumption advantage is mainly achieved in the area with low load, where the diesel is 400 g / kWh, but the gasoline engine is well over 600 g / kWh. This is also the reason why a shift in the operating point, for example through hybrid technology, achieves quite similar consumption values, with a significantly better environmental balance and greater comfort.

To be absolutely sure, get and read your own engine diagram. There are definitely differences there. Unfortunately, manufacturers find it very difficult to publish such data.

5. Use slipstream


If you follow the prescribed half speedometer, you have quite a good aid to lawn on the BAB. Observe from which side the wind is coming because it blows the slipstream away sideways. A bit offset to the Vorderman you can still nibble and see better ahead. Please do not drive up too close, on the one hand the risk of accidents increases enormously, on the other hand consumption also increases because point 1 can no longer be adhered to. Braking at high speeds is fatal to fuel consumption.

6. Steer gently and drive short distances


That is almost skimpy now, but whoever drives well inside can save several meters a year. Observe it on the autobahn, a lane further to the right or left definitely makes a difference. That doesn't count in terms of consumption / 100km, but it does count in the wallet. Of course, I don't cross all lanes on the BAB, but I definitely see whether I am using my lane or whether I am doing another overtaking maneuver.

7. Accelerate uphill and avoid braking downhill


Everyone has probably already experienced that a descent can heat the brake system to over the load limit. This amount of heat is of course not available for free. In addition to the usual kinetic energy, there is also potential energy on the mountain. On a steep, icy mountain, a descent speed of 1km / h can be too fast. I can't stop then. Conversely, it is of course initially effective if I approach an incline with a lot of gas in high gear. However, one is usually tempted to choose a shorter gear and extend it far in order to get up to speed as quickly as possible. As with the brakes above, this is deadly to the energy balance. It is best to try to accelerate or brake before or afterwards in order to conquer the mountain at the right pace. In practice, it has proven useful to sacrifice some speed uphill and go faster downhill.

8. Avoid idling


First something very mundane: buckle up first, then start. Often done differently. Most of the time, you can turn the engine off again before you have reached the final position. Of course, this is even more true if you last a long time. If you still haven't had enough, you can also turn off the engine when driving long slopes. This is of course forbidden because normally the power steering and brake booster fail, which can lead to the most serious accidents. It is better to buy a car that has this function built in and that automatically switches off the engine. Here the necessary components are electrically operated and continue to function as usual. Something very important at this point: Avoid unnecessary cold starts at all costs. In order to achieve a sufficiently ignitable mixture, the gasoline is filled in with a spoon, so to speak, during a cold start. A distance consumption of 60l / 100km is by no means uncommon for a tour to the bakery.

9. Optimize the car


First of all, the engine should be optimally maintained and adjusted. Even expensive tires with low rolling resistance are often the cheaper solution. On the whole, everything helps that makes it easier for the car to move, but many don't want to do without wings and wide slippers. Nevertheless, a list of tuning measures that can save at least a minimal amount of fuel:
  • Start / Stop automatic (available for retrofitting e.g. from Hella)
  • Mass tuning (also tidying up the trunk, etc.)
  • Alloy rims (but only with subtle tires)
  • Sport exhaust (also metal catalyst and manifold)
  • Air filter and intake optimization (polishing, isolating ...)
  • Low-viscosity oils and coatings
  • clean (especially at the front, but also antenna, etc.)
  • Sports mirror
  • Reduction of the radiator opening
  • smaller wiper blades
  • One-arm wiper
  • in very few cases spoilers (mostly the opposite is the case)
  • etc.

Conclusion


This text does not claim to be complete or correct. It is my own interpretation of known facts and their connection with my own experiences to achieve the most effective driving style possible. All tips have been confirmed several times, but if one or the other reader feels that there is a need for discussion, please collect information first and then send me an email (shortklww.de) to contact.
My goal is not to achieve a record fuel consumption, but rather a dynamic and safe driving style that is as practical as it is satisfying. With today's traffic density, I can spend a large part of my driving time using less gasoline than the person in front of me. Whether this fuel will benefit my wallet or my travel time will be decided later when the trip is free.
A pleasant side effect of saving fuel: If you already feel that using the brake is a small personal defeat, you still have this brake in reserve for emergencies. Anyone who brakes when something happens has significantly fewer options.

10/2011 Rico Klein klww.de>

*The notes are arranged according to their importance.