Team-BHP - Cruise in 3rd gear, or keep shifting between 3rd & 4th?

Hi folks,

This question has stumped me for a long time now. And it is actually worsening with time because of near jam packed roads.

Here is the poser:

While driving on near choked roads there is this situation where you can keep driving at 3rd gear for comfort and yet reach 4th gear speeds. The other option is to change to 4th gear for perhaps just a minute or two and then because of traffic fall back to the 3rd. A really unhappy situation.

As a car driver who cares for his car, I do not like the protesting whine of my engine when I touch the 4th gear speed but remain in 3rd gear. If I listen to the engine then perhaps I will drive for less than a minute and it is back to 3rd gear.

Also I feel that repeated gear shifts will actually result in transmission losses and reduce mileage. Whereas driving constantly at 3rd gear during these conditions might not only be comfortable but also profitable.

I am not a new driver. In fact because I have been driving a car for well over 16 years now that this dilemma is getting stronger.

What is your opinion? And do you face this too?

The best way to drive I believe is to keep the engine in the optimum torque range. Anything low or high results in more wear and tear and low mileage - crankshaft load, knocking, uneven wear.

The use of the clutch is only to change gears and difficult initially and painful but with a little practice one can find a way to quickly change gears using clutch and drive only with throttle and engine braking; at times brake usage.

Quote:

Originally Posted by syravi (Post 2524179)

A question which has plagued me ever since I took to wheels. I usually up shift than drive in a lower gear at higher rpms.Of course, that also means frequent downshifting and clutch depressing. Eager to know others opinion on this.

ECM-controlled engines are programmed in a way that would actually save fuel if you carry on at a steady rpm (say 2000-2200) in 3rd gear, than shifting to 4th and lugging the engine at 12-1300rpm. This is because of the lower load on the engine in 3rd gear, and the engine running in its torque/power band, prompts the ECM to supply less fuel than if the engine was in 4th, out of its power band and being lugged.

Edit: This is reversed in case of mechanically controlled engines without ECM control (i.e. carburetted petrols or old diesels) where a lower rpm translated to better fuel economy.

Quote:

Originally Posted by syravi (Post 2524179)

While driving on near choked roads there is this situation where you can keep driving at 3rd gear for comfort and yet reach 4th gear speeds. The other option is to change to 4th gear for perhaps just a minute or two and then because of traffic fall back to the 3rd. A really unhappy situation.

I would recommend changing gears rather than running in a gear not intended for such speeds for FE and reducing wear. A whole minute of running on 4th gear does justify the upshift.

How you shift depends a lot on the car you drive and traffic conditions. On the Esteem Di with the aircon running, you have to upshift earlier for cruising but stay in lower gear if you are going uphill. If you are an enthusiastic driver, the Esteem will have you go through its gears like it were the keys on a piano. You get to use all 5 gears in the city unlike some other vehicles.

Quote:

Originally Posted by syravi (Post 2524179)

When I'm driving, if the traffic is such that I can just about upshift and stay that way only for a minute before downshifting again; I rather stay at the lower gear and maintain a steady speed.

Eg. I am at 20 km/hr on 2nd and can go at 30 km/hr on 3rd for a minute; I'd rather stick to 25 km/hr on the 2nd itself.

Constant changing of gears will no doubt hamper FE and possibly induce early wear and tear of mechanicals.

For the TDI engines, cruising at lower gears @ higher RPM is far better for the engine than trying to choke the engine at higher gears and lower RPM.

My jetta gives better FE when driven at the right gears.

Personal advice, stay in the power band of the torque curve all the time. For linear torque engines like the TDI staying at 3rd gear in this situation is very good and you have instant power anytime the traffic is easy.

Some Cars come with the Shift indicator that guides drivers to shift. Downshift indicators come up only when the RPM is well below 1000 or 1100 Diesel. But upshift comes after 2000 RPM.

It is better, from both engine wear and FE point of view, to be in the higher RPM band than in the lower RPM band, while driving steadily in dense traffic. If the 3rd gear in a petrol car does not cross 2.5K RPM, remain in it rather than going to 1.5K in 4th. Most of the modern petrol engines have a flattish torque band between 2K and 4k, hence you would not loose out on FE even if you are at 3+K RPM. In addition, you are saving both your clutch as well as your left leg from wear and tear!

This is what I do:

Now I'm doing about 30 km/h in 3rd gear and I know that I can't really do more than 40 in the given stretch and I will eventually have to slow down or brake. So as I accelerate upto 40 km/h, I swap to the 4th cog, and let it coast. The car's speed might come down, but I hold onto the gear for as long as I can without accelerating, and then switch to 2nd when the traffic starts to crawl or slow down considerably, or if there is a speed-breaker coming up and the speed of the car falls to 15-20 km/h.

NOTE: When in 4th gear (30-40 km/h - 1500 RPM), I do not accelerate at all. I let the car remain in that gear. If I need to accelerate a little, I would go back to 3rd, or if I'm doing 40 km/h, I will accelerate in 4th gear itself. Accelerating would lug the engine since there would be much more load on it in 4th gear, than in 3rd at the same speed. So I generally pick up speed and then switch to 4th when I know that I will be doing a consistent 50-60 km/h.

The FE in my 8-year old Santro seems to have gotten better once I began to practice this method.

I would advise to remain in the same gear as much as possible, as eventually you still have to stop.

Another approach could be to stay in the third gear and then let off the accelerator to cruise to your destination. This way you may even save up a little fuel. The higher revvs will allow the car to coast further without a throttle input.