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Old 14th October 2006, 15:21   #31
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Quote:
Originally Posted by mobike008
lots of people rest their hands on the gear knob and such long time habit can result in gear ratios getting messed up...so please dont use either the clutch or the GK for resting your body parts
This is a new one. I dont think resting your hand on the gear knob can mess up gear ratios. This is absolutely false. Dude it is not like we are pulling the gear lever or something. I pesonally have my left hand always on my gear lever and this is a very old practice. All the vehicle that I have owned have never caused any problems. Yes I agree with the resting your foot on the clutch part. That should not be done.

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Old 14th October 2006, 16:09   #32
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Quote:
Originally Posted by vikram_d
This is a new one. I dont think resting your hand on the gear knob can mess up gear ratios. This is absolutely false.
probably i exagerrated it a bit, if not messing up the gear ratios, definetly after a period of time the syncromesh feel of the gears will not be the same..experienced it in some friends car who have this habit. In anyways, it ain't a good practice
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Old 14th October 2006, 16:50   #33
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Could someone post the gear ratios of Esteem MPFI?

Last edited by dmitri : 14th October 2006 at 16:53.
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Old 14th October 2006, 17:33   #34
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Quote:
Originally Posted by mithun
In all the Maruti cars that I've driven, I the gear knocks if I shift to 5th at 40 KM/H. I'm wondering why Maruti is giving these kind of stupid infos just for the sake of FE ?
Not really true. In fact I drive my 800 exactly in the pattern Maruti recommends, when I am driving relaxed. When I am in a hurry, then of course, I have to up-shift at higher rpm's so as not to feel left behind.
Even in terms of FE, I have noticed that if I drive within the power band I get same or better FE rather than if I drive at high gears running low rpm's.
Simply, when the car responds to the throttle better rather than lagging, that means I am at the right rpm and right gear.
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Old 14th October 2006, 19:18   #35
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Quote:
Originally Posted by mobike008
probably i exagerrated it a bit, if not messing up the gear ratios, definetly after a period of time the syncromesh feel of the gears will not be the same..experienced it in some friends car who have this habit. In anyways, it ain't a good practice
syncromesh feel of the gears!!!..... I seem to have lost you there!
I do this at times.... and I think my gears are completely in sync!! after 60k kms..... and almost 6 years (if that is ok for "a period of time")

Maybe your friend's car did not have any gear oil.
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Old 17th October 2006, 09:37   #36
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I have previoucly owned 3 different cars all of which I drove for 1 lakh+ kilometres. And my left hand is always on the gear knob in city driving and I have never ever faced any problems with the gear box. All the vehicles had synchromesh gearboxes.
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Old 17th October 2006, 20:49   #37
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Come again.. have heard "synchromesh feel of gear" for the first time. Am I out of sync or gearboxes have started using NASA technology?

Quote:
Originally Posted by mobike008
probably i exagerrated it a bit, if not messing up the gear ratios, definetly after a period of time the syncromesh feel of the gears will not be the same..experienced it in some friends car who have this habit. In anyways, it ain't a good practice
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Old 18th April 2007, 15:45   #38
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Experts!

I want to clarify some of my doubts and forgive me if I sound stupid.

I am having Petra 1.6 and I was driving at a speed of arpund 80 kmph (in 5th GEAR) and I wanted to overtake a vehicle that is also doing almost same speed or slightly less. I floored the accelerator and felt underpowered to overtake (I was night and I could see incoming vehicles). Now having read the article mentioned above, I feel at that RPM (around 3000), probabily I cant get enough torque to accelerate quickly and overtake the car. Is this analysis correct? I downshifted the gear and overttok the car. Later on, whenever, I found the distaces during the overtaking is less, I preferred downgearing. I had previously driven Maruti 800 (Carburettor) and never felt these kind of things during overtaking.

Want to know whether this is normal and if yes, would I be down gearing during tight overtakins. Of course, one must avoid tight overtaking.
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Old 19th April 2007, 08:03   #39
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Quote:
Originally Posted by Subodh Kumar View Post
Of course, one must avoid tight overtaking.
Well you have answered your own question. Try to avoid tight overtaking situations but if you cant then down shifting is the right and sometimes the only option. No harm done.
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Old 19th April 2007, 11:00   #40
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Well .. on my Palio 1.2 NV in cruise mode, I shift into all gears somewhere around the 2000rpm mark give or take a hundred) .. Also, my gear shifts are more likely to be on the higher side of the 2K mark than on the lower.
When in race mode, I don't keep track of the RPMs anyway ..

When driving in cruise mode, my car averages around 14kmpl in the city (AC on for 30-40% time).
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Old 19th April 2007, 14:01   #41
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Quote:
Originally Posted by Subodh Kumar View Post
Want to know whether this is normal and if yes, would I be down gearing during tight overtakins. Of course, one must avoid tight overtaking.
There is one explanation why you never felt that on the 800.... the 800 has short gears and doesn't have an overdrive 5th gear.

5th gear is basically not meant for overtaking just cruising!.

Just as a rule... I would consider an overtaking safe if I can complete the maneuver in the 5th gear without flooring it.

Flooring at low RPMs takes the car a little out of control... as .. when you release the pedal.... there is a lag before the car actually starts braking!
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Old 19th April 2007, 14:19   #42
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Wheel RPM = Engine RPM x Gear Ratio x Final Drive
In majority of cars, the gear ratios are as follows
1st 0.25 ( = gearbox output shaft RPM / engine RPM)
2nd 0.5
3rd 0.75
4th 1.00
5th 1.10
Final Drive 0.25
Note: in some cases gear ratios are expressed in opposite manner (so 0.25 will be 1/0.25 = 4.00 etc.)
Since in 5th gear (sometimes also in 6th gear) gear ratio is more than 1.00, it is called overdrive.
As SLK said, overdrive is indeed for cruising not accelerating.
To accelerate on overdrive, one needs to raise the RPM to a very high level (which will put burden on engine) so better downshift to 4th and acceleration is available at lesser RPM.
It is always possible to calculate theoretically at which RPM you can shift for best result (it differs from car to car). You can see here for the formulas
http://www.team-bhp.com/forum/techni...tml#post152768 (Physics behind car's movement)
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Old 19th April 2007, 14:23   #43
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Dear Vikram
I went through many articles / discussion on relationship between Torque, RPM, power to enhance my own understanding of the subject. My submisson: at 80 KMPH (fully loaded Petra) steady state condition, Torque requied to be produced from the car is T1r and is equal to the torque generated T1g. Torque that can be produced at that rpm as per Torque speed curve at that gear: T1c; In order to accelerate, we require some Torque and that would come from (T1c-T1r). if this is small, it would take alot of time to accelerate. Is this right? secondly, when I went throgh the manual, in 5th gear I can reach a speed of approx 170kmph. Then it would take eternity to reach a speed of this value with such a small torque available in 5th gear.
honestly, I am confused.
Can anybody enlighten me.
Thanks a lot.
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Old 19th April 2007, 17:07   #44
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Quote:
Originally Posted by Subodh Kumar View Post
Dear Vikram
I went through many articles / discussion on relationship between Torque, RPM, power to enhance my own understanding of the subject. My submisson: at 80 KMPH (fully loaded Petra) steady state condition, Torque requied to be produced from the car is T1r and is equal to the torque generated T1g. Torque that can be produced at that rpm as per Torque speed curve at that gear: T1c; In order to accelerate, we require some Torque and that would come from (T1c-T1r). if this is small, it would take alot of time to accelerate. Is this right? secondly, when I went throgh the manual, in 5th gear I can reach a speed of approx 170kmph. Then it would take eternity to reach a speed of this value with such a small torque available in 5th gear.
honestly, I am confused.
Can anybody enlighten me.
Thanks a lot.
OK.. let me try and clarify the first part at least...
Torque is not a measurement of power....
Torque read along with RPM make up for power....

So comparing the car's acceleration only to torque is not right... its the power (which is a derived from torque and rpm).

Pr - is the requirement of power to move the mass of the car at that steady speed.
Pu - is nothing but the power being used in moving the mass of the car
So Pr=Pu

Now
Pc - is the actual power being generated by the engine as per the torque - RPM - power curve.

The difference in Power being used (Pu) and Power generated (Pc) is only due to gear ratio inefficiency. That said the gear is not the most efficient for that rpm.... to use up all the power.

And a gear can not be efficient through out its range.. it would only be efficient at a point where it can use up all the (Pu) = (Pc).

(Don't confuse with fuel efficiency here)

Till the Pu < Pc the car can accelerate.

So the most efficient gear ratio would be the one ... where you reach an RPM which generates the maximum power AND at the same time you have Pu = Pc (i.e. you actually use up all your 100bhp).

Acceleration would be again dependent on the difference between Pu and Pc... the more the faster.

*Did that make sense or help at all?*

Last edited by SLK : 19th April 2007 at 17:12.
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Old 19th April 2007, 18:19   #45
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SLK

I understand that Torque is not measurement of power; but at any point of time, it is available Torque that helps accelerate the car. I read it from this forum. Otherwise also at stable speed when, Pu = Pr; Tu = Tr but less than Pc / Tc. Now the need of acceleration comes, we floor the accelerator and at the same rpm torque generated increases from Tu to Tc. The Torque difference accelates the car, increases the speed and thus more torque and power for acceleration. That is my understanding.
Now, what surprised me was lack of Torque at 80kmph in Petra (1600CC) car.
Any way my doubt is clear now, the 5th gear is more for cruising or slow acceleration (overdrive condition) and not for fast acceleration / Torque / overtakingv. That explains the phenomena. Also, as I checked the manual today, max Torque in petra is at 4300 rpm, way above the existing rpm at 80kmph.

Thanks all for clarifying things.
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