[itwasntme]

Originally Posted by landcruiser123

The Cruze had a cracker of a diesel (a large one!) and the engineers could get away with 5 well-space gears.

Originally Posted by wantarangerover

Larger displacement engines produce lots of torque so you don't need very short gears with lot of mechanical advantage down low, so you can get away with 'tall' gears which will take you to good speed with minimum gear changes.

My beloved pre-facelift Cruze was a large displacement 'cracker of an engine' but with hideous turbo lag below 1750 rpm . In moving slow city traffic, nearly all vehicles were faster in second gear before the turbo began spooling.

But on highways, it simply was superb. A 6th would have been nice but not a showstopper.

[Rocketscience]

Originally Posted by itwasntme

My beloved pre-facelift Cruze was a large displacement 'cracker of an engine' but with hideous turbo lag below 1750 rpm . In moving slow city traffic, nearly all vehicles were faster in second gear before the turbo began spooling.

But on highways, it simply was superb. A 6th would have been nice but not a showstopper.

Originally Posted by landcruiser123

The Cruze had a cracker of a diesel (a large one!) and the engineers could get away with 5 well-space gears. Not the case with the Creta. The spread of ratios in the 6 speed box is similar to the 5 speed box. The first 5 gears are slightly shorter with a slightly taller 6th (overdrive).

Landcruiser, this is somewhat what I was trying to explain is a misconception and itwasntme's explanation is a bit off track.

You see in Cruze's case it was the perfect example of need for 6th gear as itwasntme said that car had wholesale of turbo lag below 1800 rpm and it would have been benefited from having more and shorter initial gears to work around that lag better.
Also the gears were not that well spaced and especially the 2nd to 3rd had an unusual gap.

Coming to itwasntme's explanation actually that 6th gear which is needed is not even remotely in the top gear, the 5th gear in Cruze itself was plenty high for the task and it did 2000 RPM at 120 KM/h, I'am not sure a higher top gear is even mechanically possible for that engine.
If it had a 6 gear transmission the 6th gear could simply be identical in its ratio to the 5th we had, the gears 1-5 could be shorter then and could make a better spread of power and the lag could have felt a lot less, even in Creta, one of the major reasons the lag is not felt is the short gearing and better spread ratios, with a botched up 6th gear like I had explained.

Originally Posted by wantarangerover

In my Figo 1.5 tdci, I feel the need for an additional cruising gear, as it hits around 2k rpm at around 90 (maybe, not sure), and a 6th gear will probably give better cruising ability at a more relaxed rpm.

So when people say 'lack of 6th gear', it is since most of us have 5 gear manuals. In the olden days (15 years ago?) people would have said 'lack of 5th gear' !!. So I would not read too much into it, it just means lack of a good cruising gear.

Agreed with most of it, but what your Figo needs is a higher top gear and not necessarily a 6th gear, your 5th gear itself could have been made plenty high for optimal cruising which Ford for some reason did not do, you are right 90 at 2000 RPM for such a torquey engine in a sort of lightweight car is weird and your car could have benefited from a much higher top gear.
Sure a higher 6th ratio over and above your existing 5th is also a perfectly alright solution, but then if the company does not want to do that for cost saving or whatever reason, the least they can do is properly optimise the 5th gear.

[Kosfactor]

Originally Posted by Rocketscience

Sure a higher 6th ratio over and above your existing 5th is also a perfectly alright solution, but then if the company does not want to do that for cost saving or whatever reason, the least they can do is properly optimise the 5th gear.

One needs to understand that Power is a function of Torque & engine speed.
If a vehicle that weights 2000 Kgs need to maintain a road speed of 120 Kmph, it needs say 100 BHP (just a guesstimate).

If an Innova (old innova since you are familiar with it) needs put 100 BHP to the wheels for it to maintain 120 KMPH road speed, its engine needs to be spinning rather fast - close to 3000 RPM and that is what the gearing is expected to allow the engine to do.

A lot more powerful engine can handle this at lower engine speeds and therefore the gearing will be adjusted accordingly. In general American & European vehicles get their gearing & engine tuning wrong for our city traffic, its perhaps the emissions that gets them but it is what it is.

[itwasntme]

Originally Posted by Rocketscience

Landcruiser, this is somewhat what I was trying to explain is a misconception and itwasntme's explanation is a bit off track.

Very well analyzed, thank you. I meant to say the same thing but hey, it's a Omicron Friday.

But seriously, you are spot on: the problem with the Cruze was the big late-spooling turbo coupled with that unusual gap between 2nd and 3rd. I think they corrected it somewhat midway, when they brought in the newer engine with the facelift.

I did 111K km in 6.5 years. Great fun that car was

[IP_Man]

Nice thread

I will share my experience.

Safari Storme EX, first gear is too short. Most of the time I start in second from standstill. First gear never disappoint whenever you need torque. There is no need to slip clutch, just release clutch to get moving even on incline. But in Ladakh at high altitude and on some tricky steep incline (Zojila Pass), I had to raise RPM and release clutch to surge forward.

Second gear is tall. In back to back traffic I feel its tall ratio i.e. not adequate torque to build RPM past 1000.

Third is also tall in city traffic, need downshifting whenever traffic becomes dense.

Fifth is OK bellow 100. On plain road when RPM goes above 2000, subconsciously my hand try to shift to sixth which is not there

In short six speed gear would have spaced gears properly to enhance drivability on plain road and also on highway.

[PrasannaDhana]

Originally Posted by condor

However, what we are seeing is - in spite of the additional 80Nm, the 5 gear, 320Nm avatar is better.

Originally Posted by condor

Isnt it the other way round ? A 5 speed gear will mean the lesser changes at city speeds.

Feedback from friend who have tried both the 320 Nm 5 speed Storme and the 400Nm 6 speed is that the 5 gear version is more driveable.

Having owned both the versions, I disagree here.

The 6 speed 400 Nm is way better to drive vs 320 Nm 5 speed MT.

The difference gets even better on highways when the 6 speed gearbox can do highway speeds in a much more relaxed manner.

[condor]

Originally Posted by PrasannaDhana

Having owned both the versions, I disagree here.

This is what we had seen. Will convey your point to the person - unless he has not already seen this thread.

[PearlJam]

Originally Posted by Rocketscience

The Verna despite having 6 gears still had a somewhat sluggish response in lower RPMs (Turbo Lag)
....
So you see, 6th gear is not always needed and even it can't guarantee you an optimal highway cruising experience. It is much more nuanced than that as I tried to explain.

Yes, the Verna 1.6 CRDI has very tall gearing. And I think this is not a bad thing. A 100 kmph comes in around a lazy 1800 rpm on the 6th. But it does involve shifting to the 1st in some cases where other cars would have pulled off from the 2nd gear itself. But the 1st has more than enough power for all practical purposes. In short, I think they've struck the right balance.

Another characteristic I observed in the Verna was, there's a much lesser 'gap' between 4-5 and then 5-6. So many a time, I can simply shift from 4 to 6 directly, if I take the 4th to a bit higher RPM. So in this case, a tall 5th would have been more than sufficient, and could have potentially replaced the existing 6th as you mentioned.

However, the 6 gears are still very useful. When you want to maintain a constant speed, say 80kmph (the speed limit on some flyovers), the 4th is too aggressive, and 6th causes lugging. A 5th fits in perfectly here.

[Turbohead]

I believe there's a misunderstanding here - what the OP is trying to say is that the more number if gears in a car doesn't make it better by default. It all depends on how the ratios have been chosen for a given power output at various RPMs.

[audioholic]

Originally Posted by condor

Isnt it the other way round ? A 5 speed gear will mean the lesser changes at city speeds. And the gears are more useable this way, instead of more frequent changes.
Of course, the 6 speed gear box will contribute to better FE on the highways.

Feedback from friend who have tried both the 320 Nm 5 speed Storme and the 400Nm 6 speed is that the 5 gear version is more driveable.

Depends on how the ratios are spaced. Typical first gear ratios are 3.5-4:1 while the top gear(4,5 or 6) would be <0.8:1 and can go as low as 0.5:1 overdrives. Achieving a wide band of ratios with lesser gears would just mean that the driveability will take a hit and even though shifts required might look lesser due to number of gears, the spacing would mean that you should accelerate more in each gear, in order to take the speed to a comfortable RPM for the next gear to be able to continue the acceleration. Early shifting in this scenario will make the engine lug and if it cant deliver the required torque then its going to screw the driveability.

With higher number of gears, even though the initial and final ratio might be kept the same, the engine will always be in its comfort zone and each gear will have a wider driveable speed range which would actually reduce the shifts required when driving in city traffic or with frequent speed variations. But on the other hand, if a five speed gearbox with widely spaced ratio is added with a sixth cog with a much lower ratio, then thats not going to improve driveability in any way but just make the top gear benefit highway cruising.

Hence, its difficult to conclude in general about higher number of gears improving driveability or not. It depends on how well spaced the ratios are.

[venkyhere]

well written, @Rocketscience.

If I may, I want to add one small point :
Gearboxes for passenger cars (non-rally, non-drift applications) are made/chosen in tandem with the engine in such a way that the top speed is dictated by load-limitation rather than rpm-limitation or power-limitation

a) If the tallest gear (meant to provide the highest possible speed the car can achieve) is chosen such that the car 'hits a wall' speed very close to the redline rpm limit, that's a well chosen gear ratio. The car is load-limited.

b) If the tallest gear is made too short, the 'hit the wall' top speed is less than (a), because the engine cannot be allowed to run beyond the upper end of the redline. The car is rpm-limited. Bigger wheels+tyres can take it closer to the top speed in (a).

c) If the tallest gear is made too long, the 'hit the wall' top speed is less than (a), because the engine is not able to get to its peak-power rpm because the aero load-limit is reached at a lower engine rpm than the peak-bhp rpm of the engine. The car is power-limited. This is good for fuel efficiency. Smaller wheels+tyres can take it closer to the top speed in (a).

[neshga]

Nice read, I would also like to add my thoughts on the matter.

I was not aware of the Innova and Creta's borrowed gearbox and it's consequent highway cruising impacts.
The first thing would be on the selection of the final gear (not the final drive). The top speed of any car or bike depends on 2 major factors, it's maximum power and mechanical resistance. All ICEs have a operating rpm range and particular rpms where peak power and torque are produced (they are almost always at different rpms because of volumetric efficiency losses, the Koenigsegg freevalve technology addresses this very issue). The mechanical resistance comes majorly in the form of rolling resistance and aerodynamic drag. There are other losses along the system but let's not delve into that. The rolling resistance keeps increasing due to increasing inertia and the drag only adds to it. As the vehicle keeps going faster, the rpm range in which the power needed to accelerate is produced keeps reducing until the resistance is equal the the power produced. I think the manufacturer didn't opt to add another gear without redesigning the whole box because the new gear would have very poor usable range.


The other thing is you cannot simply add a gear in between the range while shifting the other gears up. As far as I know, gearbox ratios are determined using "preferred numbers", after deciding on the number of gears needed. This is done to make life easier for other designers and compatibility between parts.

For example, if I wanted to design a 6 speed gear box, I would need to first pick my ideal gear ratios according to the ICE power band, NVH requirements for that particular car, estimated speed the vehicle is predicted to run most of the time (could be more than 1 value), weight of the car, expected driving conditions, fuel efficiency, etc. With that determined, I would calculate my step ratio to produce the series(these series are basically geometric progression). It isn't even necessary to calculate all the gear ratios, we can also do it with the first and last gear and get the ratios in between from the series. Usually, the series is used to round off the intial ratios selected based on the design requirements. So, adding a gear ratio in between gears would result in 1 of the gears being too short and the other being too long for the engine. It's not to say that it's impossible, designers can choose to skip a number in a series and using that ratio would provide a smooth transition of speed for the car.

I've not touched up on these subjects in a while so please correct me if I'm wrong.

[akshye]

They make really good videos "for dummies" type:

https://www.youtube.com/watch?v=RpXmudGHTXk