Team-BHP - 6th gear for a car - Need, criteria, pros and cons

Quote:

Originally Posted by SPIKE ARRESTOR (Post 4402583)

These diagrams pretty much sum up the role of a transmission. Here you see 4-speed tractive force of an engine is used with a 4-speed transmission, and how tractive force is wasted without a transmission.

As I said, in theory the more gears the better as you will be able to follow the curve more closely. There are a few practical limitations on a traditional box of course. But I guess a CVT as invented by my clever fellow country man Huub van Doorn would do the trick. Always the most optimum transmission ratio.

Still, in practice, torque does/can substitute multiple gears as well (maybe not so much from a FE point of view though) as from a drivability point of view at least.

Jeroen

Quote:

Originally Posted by oil_burner (Post 4402510)

Sir, I too have an i20 elite in our family and I have driven it for a long time. There have been plenty of instances where I was cruising around 100 kmph and due to some reasons the speed went around 55-60 kmph. I had to downshift to 5th gear. However, in my Ford Aspire, the 5th gear itself handled it. This is the case on most of the roads especially on the 2 lane roads without dividers where we need very quick overtakes.

That's not a perfect comparison albeit the figures being pretty close. The gearbox is a very minute factor in the scenario you've provided. There are so many other factors like the torque for instance. The i20's torque of 220Nm is produced from 1500-2750 RPM while the Aspire's torque of 215Nm is produced between 1750-3000 RPM. Also, the peak power of i20's 90PS comes in at 4000 RPM while Aspire's 100PS comes in at 3750 RPM. You cannot compare a car by merely looking at the figures. There's more to it than that.

To begin with, try using this formula: Torque X RPM / 5050. This will give you a rough idea of the power generated and yet it's just a ballpark figure. The weight of the car, the BHP/ton, Nm/ton, the size of the tyres, the width are some of the factors that have a role in performance figures.

When I bought an Ertiga in 2012, I merely went by the power and torque figures. Prior to the Ertiga, I had a Swift and when the Ertiga came in, I saw the jump in power and torque figures and instantly decided that it's gonna be a treat to drive. Well, after purchase I found the Ertiga nowhere close to my earlier Swift. It wasn't the Ertiga's fault; it was mine as I was naïve enough to just go by the figures without factoring in the weight of the Ertiga compared to the Swift.

In all these influencing factors, a 5 or a 6 speed gearbox has very little influence and thus cannot conclude whether a 5 speeder is better or not than a 6 speeder with mere figures.

Quote:

Originally Posted by Sutripta (Post 4402620)

Hi Pratheesh,
You can fill us in on one of the most important aspects of a gearbox - cost. Esp interested in cost comparisons between CVTs and slushboxes. (Low power applications.)

Hi Sutripta Da,

I don't have info on costs. I've however something, which might be of interest to you.

http://www.gif-e.de/products/kegel-r...nsmission.html

Spike

Quote:

Originally Posted by SPIKE ARRESTOR (Post 4402583)

Attachment 1762274

Spike:)

In layman terms, what I understood from the picture that the highest gear of the transmission has the highest range of the speed. This is what I wanted to highlight. Imagine a similar graph for a 5 speed and a 6 speed gearbox. The best range will be offered in the highest gear. For a 6 speed unit, we need one extra gear shift. Also, do note that we rarely cross 120 kmph mark in our cars. In my case, I always drive between 90-100 kmph even if the road ahead is clear and is of excellent quality and I believe most of the people follow the same suite.

Further to my earlier post on this thread, as much as I love the 6th gear, it's only on larger-engine'd cars. Not the ones with small cars / diesels.

Example = I just returned from a road-trip with the Venue diesel and used 5th gear more than 6th on the Mumbai-Nashik highway (it's not an expressway). Reason is, these small diesels simply don't have the torque to pull from 80 kmph / 100 kmph in 6th if you drop your speed. A downshift is mandatory. On a typically Indian highway, you'll be downshifting too often (hence, my preference for 5th).

It's a different matter in say, the Jeep Compass or my C220 which pulled easily in 6th itself, if you dropped your speed or needed to increase it.

Ain't no one got time to look up ratios!? :uncontrol

The number of gears you've got mean zilch!, period :)

And more the number of gears is not always a good thing, like on some motorcycles they give you more number of gears while their counterparts have a cog or two less all the while having similar or even taller overdrives.

It mostly is to cover-up inadequate torque per gear by better spreading available torque, you could argue otherwise but to put simply the use of the transmission remains the same in all cases i.e make the best out of available torque.

Most of us get this confused because we've been taught by people who didn't know better to always drive in the tallest gear available.

Regards,
A.P.

Quote:

Originally Posted by GTO (Post 4613328)

I 100% agree to that sir. The 6th gear doesn't make sense with the smaller engines as they don't have enough grunt to pull effortlessly from low rpms. However, sometimes for relaxed highway cruising, the 6th gear does help in getting better fuel efficiency figures and the engine is at ease because the same speeds can be done at lower rpms because of the 6th gear. But this also comes with a downside. One will have to change gears more frequently on the highway as the situation may require the driver to downshift to the 5th if in case there is a need to slow down due to anything and the speeds drop below 80-90 kmph.

Quote:

Originally Posted by MrBeast (Post 4613606)

It all depends on the gearing ratios. In most cars the fourth gear is 1:1 and the fifth an overdrive. In case the 5th is 1:1 then only the 6th is over drive, but if both 5th and 6th are overdrive, then the 6th is added for relaxed drives at higher speeds, so is useful on open highways only to improve the FE.

Quote:

Originally Posted by Aroy (Post 4613735)

I absolutely agree to you sir. It all depends upon the gearing ratios and the engine power and torque figures. However, what I shared are a common observations which I made after driving 4-5 small engined cars with 6 speed gearbox. Every car behaves differently but in most cases, for engines upto 1.5L, 5 speed units are a better option when it comes to performance.

Quote:

Originally Posted by GTO (Post 4613328)

Reason is, these small diesels simply don't have the torque to pull from 80 kmph / 100 kmph in 6th if you drop your speed.

I agree with this, the last time I put the 6th gear on my i20 must have been 3 or 4 months back, because of 2 things, most of the roads in India are narrow and leave alone 6th, I can hardly slot into 5th, secondly, there is not much difference between the 5th and 6th gears of the i20, the 5th can hold speeds upto 130 to 140kmph, and hence there's no need for a 6th for speeds under the limits.

Quote:

Originally Posted by Aditya_Bhp (Post 4613837)

I agree to you on this. I too drove the i20 a couple of times and came out with similar observations. On a two lane road, with oncoming traffic, the 6th gear is almost useless. The speeds are too low for the 6th gear and even if we use the 6th gear, lower RPMs will not result in outright acceleration which is required for a quick overtaking maneuver and for that one will be required to downshift to a 5th or a 4th. The probability of this happening in a 5speed gearbox is less. Most of the cars have a 5th gear which gives us good acceleration above 65-70kmph, so downshifting may not be required always.

However, those who prefer to drive sedately or are ok if the speeds increase slowly may find the 6 speed gearbox on smaller cars not bad enough. I believe its a personal opinion and only those who want performance out of the car may notice such small things.