Perfect Shift Point

Manual transmission is the one to have if you love driving or riding. That's because, manual transmissions allow you to have full control over the engine power delivery, which cannot be asked of an automatic or a CVT.

Engine power delivery is nothing but how much of the engine power goes to the driven wheels. This can be controlled by altering the shifting point of each of the gears of the transmission system.

We'll first see the two extreme cases of shifting with an example: shifting to 5th gear at 20 kph in any vehicle forms one extreme of shifting point. When you do this, transmission snatch occurs. When the clutch is fully engaged and you give full gas, the engine might even stall. This is a scenario of the torque delivery being unable to match the torque requirement. Pressing on to 60 kph in 1st gear is the other extreme of shifting point. Here the engine revs too high and in most cases, even bounces off the rev-limiter.

The optimum shift point lies in between these two cases and that is a bit tricky to find. One must first decide the mode of driving--to conserve fuel or wring maximum performance from the engine. It is depending on this that the optimum shift point is determined. In cars, when a gear too high for the current speed is selected, the whole car will rattle. This can be had as an indication for a bad shifting point. Many drivers do this thinking that it will give good fuel economy. But the truth is, the mileage actually decreases. What actually happens is, the amount of fuel intake increases but with the volume of air sucked in remaining constant. This makes the mixture rich leading to incomplete combustion. This obviously wastes fuel and pollutes the environment.

At the same time, the engine should not be revved too high either. As a thumb rule, for fuel efficient driving, the optimum shift point can be the RPM which is just over half the redline RPM. For performance driving, the gear should be shifted at exactly the RPM where the manufacturer says the engine develops maximum power. This data can be had from the owner's manual.

Technorati Tags: Manual Transmission,Automatic Transmission,CVT

Technorati Tags: Four Stroke IC Engine,Engine Oil,F1 Engines,Dry Sump Lubrication

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^IF YOU'RE PASSIONATE ABOUT FORMULA 1, YOU MIGHT ALSO WANT TO HAVE A LOOK AT THIS.

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No Neutral Please!

I'll attempt to explain in brief why one should down-shift while braking. Assume that the car in question is a Swift Diesel. It has the following specs:

3rd gear ratio: 1.233

5th gear ratio: 0.725

Assume that you're driving the car at 100kph in 5th gear and that the engine is doing 2000 revs. Armed with the above data, we'll do a few really simple calculations to understand the theory behind:

If the gear ratio is 0.725:1, the driven wheels rotate once every 0.725 rotations of the engine. Which means, in our case, the wheels are rotating at about 2758 RPM (2000/0.725). The aim of braking is to reduce the speed of the wheels, which will automatically reduce the speed of the vehicle. This applies until the point where the wheels don't start locking up.

When 3rd gear is engaged at 100kph, the engine speed rises to 2466 RPM (2000*1.233) and the wheel speed drops to about 1662 RPM (2000/1.233). This is what we want, isn't it? We haven't braked at all but still using the transmission, we have just reduced the speed of the car. Here's the math behind:

At 100kph, in 5th gear, the engine is doing 2000 RPM. When 3rd gear is engaged, the gear ratio is changed from 0.725:1 (for 5th gear) to 1.233:1 (for 3rd gear). So, to get the engine speed, multiply 1.233 with 2000 (to get 2466 RPM) and to get the wheel speed, divide 2000 RPM by 1.233 (to get the reduced speed as 1662 RPM).

Result: Wheels which were rotating at 2758 RPM, are now, after down-shifting, rotating at 1662 RPM--a decrease of more than a thousand RPM. Exactly the result what we expect and need!

THE WORST CASE SCENARIO: Shifting to neutral!

Ok, so what happens when at 100 kph in 5th gear, we shift to neutral? The wheels are freed from the engine and so they start to rotate freely on their own. That is, the wheels continue to rotate at the same 2758 RPM, without slowing down. The momentum of the car will keep carrying it at the same speed. The air-resistance and the tyre friction will slow the car down but this amounts to a very minuscule resistance. The car will stop only after it has traversed a few kilometres of running! Hence the vehicle speed doesn't practically reduce at all! This'll require the driver to put extra pressure on the brakes, which reduces its life as well.

I hope this amply demonstrates that refraining from down-shifting and more seriously, shifting to neutral while braking is STRICTLY NOT A GOOD DRIVING TECHNIQUE. Most drivers, however, are doing this and I hope that they'll change to a better driving style in the future.

Technorati Tags: Gear Ratio,Swift,Braking

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| IF YOU'RE PASSIONATE ABOUT FORMULA 1, YOU MIGHT ALSO WANT TO HAVE A LOOK AT THIS.

| STAY IN TOUCH WITH WHEELS OF RAM. CLICK HERE. 

The Mid Corner Mystery

....you're bouncing off the rev-limiter in top gear doing about 200 mph. You spot a fast left-right chicane - that dips down - to be negotiated at 60 mph. You slam the brake pedal as hard as you can and in a space of 80 metres you've scrubbed the speed down from 200 to 60. Job done. Now, you breathe a relaxed air, yank the 'wheel to the left, allow the suspension to soak up any bumps mid-corner, yank it to the right again and off you go hunting the next apex. Simple. Or so you think.

In reality, once into the corner, you'll have the back end of the car swinging out (oversteering) if you are not on the throttle accelerating. But, if you accelerate too hard too soon, you'll have the front end pushing straight (understeering). The oversteer in this case is known "lift off oversteer". It's an oversteer not due to too much power getting transferred to the rear wheels (as is normally the case) but due to the rear axle getting lightened up. That's what happens when you suddenly lift off the throttle - weight transfer takes place loading the front end.

What's the solution then? Balance the car on the throttle. It means feeling the rear end and prodding the throttle just enough to just about transfer the weight to the rear that'll keep it glued to the track. It's a subtle art that racing drivers (need to) master.

Brake + Clutch or Brake and then Clutch

We do certain things without thinking about them as one of my friends says often. One such thing is driving cars. People who’re used to driving cars regularly, don’t have to think a second time about what they are doing. They use the gear lever and steering wheel as if they are extensions of their arm. They use the pedals as if they are just another part of their body.

When they brake for a round about, for example, they lift their right foot off the accelerator pedal and start depressing the brake pedal. They do this without even thinking what they are doing. It’s instinctive. All is well until now. What do they do next? They position their left foot directly over the clutch pedal even as they start braking. What they normally do as I have observed quite a number of times is, they bring the car to neutral! After bringing the car to neutral, they keep increasing the brake pressure on the brake pedal until they cross the round about. When they deem that it is safe to open up the throttle again, they position their left foot over the clutch pedal again, depress it and shift to a lower gear. Is it correct? Is bringing the car’s transmission to neutral while braking effective? The answer is a no with a capital N. Why not? I am not going to give you a straight answer.

Instead, do a simple activity that I have outlined below to get (feel) the answer for yourself.

Step 1: Put your car in first gear and accelerate to about 40 kph.

Step 2: When you have reached that speed, leave the accelerator pedal and immediately depress the clutch pedal.

Step 3: Just note how long it takes for the car to come to a stop. (Note down mentally, no need for stop watch and all!)

Step 4: Start all over again. Put the car in first gear, accelerate to 40 kph and leave the throttle. This time DON’T PRESS THE CLUTCH PEDAL. Again, note down mentally how long it takes for the car to come to a stop.

After this simple exercise, you’ll know for yourself if it’s correct to bring the transmission to neutral while braking. You’ll definitely feel the difference but, in case you can’t make out the reasoning behind my view, check out the answer here at Wheels of Ram a few days later.