Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 13th April 2006, 14:46   #1
BHPian
 
netarchie's Avatar
 
Join Date: Feb 2006
Location: Navi Mumbai
Posts: 397
Thanked: 8 Times
Default Overdrive ? - Information required please

what does this mean "Overdrive on 4th and 5th gear"

Note from moderator - Please look at Rule # 10.
Thread renamed.

Last edited by Rehaan : 14th April 2006 at 01:01.
netarchie is offline   Reply With Quote
Old 13th April 2006, 15:06   #2
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,953
Thanked: 15,648 Times
Default

Overdrive - Definition
A transmission in which the highest gear ratio is less than a one-to-one ratio. This means the drive shaft turns faster than the engine crankshaft. The overdrive feature saves fuel and, because the engine runs slower, engine wear and noise are reduced.

A ratio of 1:1 means that your driveshaft is turning at the same speed as the crankshaft.
Overdrive means that the driveshaft(which goes to the wheels) is turning at a speed higher than the crankshaft(driven by the engine).

Most cars have overdrive in 5th gear and many in 4th gear too.
tsk1979 is offline   Reply With Quote
Old 13th April 2006, 15:08   #3
BHPian
 
Revvhead's Avatar
 
Join Date: Apr 2005
Location: Bombay
Posts: 450
Thanked: 9 Times
Default

well i guess that means the both 4th & 5th are geared lower than 1:1, for these models.

Overdrive is basically any gear witha ratio lower than 1:1.

i.e at 1:1 ration for one rotation of the crank the wheels(driveshaft actually) should turn once,
in overdrive they turn 1.x times
Of course this is not taking into account differetial ratios etc.
before people come eatin my head.
Hope that sorts it out

Of Course
Revvhead is offline   Reply With Quote
Old 13th April 2006, 15:09   #4
Senior - BHPian
 
v1p3r's Avatar
 
Join Date: Feb 2005
Location: BLR - chasing cars...
Posts: 4,836
Thanked: 26 Times
Default

Erm, isn't overdrive when the output from the gearbox is spinning faster than the crankshaft? It can't be the final driveshaft, because those have a built in reduction ratio from the differential.

In most cars, 4th gear is normally 1:1 or very close.
v1p3r is offline   Reply With Quote
Old 13th April 2006, 15:14   #5
BHPian
 
Revvhead's Avatar
 
Join Date: Apr 2005
Location: Bombay
Posts: 450
Thanked: 9 Times
Default

Quote:
Originally Posted by Revvhead
Of course this is not taking into account differetial ratios etc.
before people come eatin my head.
Hope that sorts it out
there there, i did say driveshaft actually.
and i meant like the driveshaft leading to the diff as would be found in a RWD.
was just givin the simplistic explanation
Revvhead is offline   Reply With Quote
Old 13th April 2006, 21:04   #6
BHPian
 
netarchie's Avatar
 
Join Date: Feb 2006
Location: Navi Mumbai
Posts: 397
Thanked: 8 Times
Default thanks guys

So , it means in short the term had nothing to do with Speed of the car and rather it is for saving fuel.
netarchie is offline   Reply With Quote
Old 13th April 2006, 23:03   #7
BHPian
 
DaPilot's Avatar
 
Join Date: Mar 2006
Location: Newport (JC), NJ - USA
Posts: 187
Thanked: Once
Default

Overdrive should be used on the freeway/highway. Not in city driving. If you use OD in city driving, you will cause more wear to your transmission and also not gain any fuel efficiency.

Over drive essentially adds an extra gear to your drive ratio effectively lengthening your final drive ratio and causing your engine to maintain lower RPMs. In other words... an overdrive gear lets the engine run at a lower rpm to maintain the vehicle’s cruising speed. This is perfect for cruising on open roads but bad (over time) for stop and go or heavy traffic conditions (definately a NO NO for Bombay City traffic). So if your car has OD its best to switch it off while driving in the city
DaPilot is offline   Reply With Quote
Old 14th April 2006, 00:34   #8
Senior - BHPian
 
Deeps's Avatar
 
Join Date: May 2004
Location: Delhi/Noida
Posts: 1,090
Thanked: 67 Times
Default

Well, its hard to switch off overdrive on an M/T unlike the A/Ts that you are probably used to in the US.
Deeps is offline   Reply With Quote
Old 14th April 2006, 01:35   #9
BHPian
 
DaPilot's Avatar
 
Join Date: Mar 2006
Location: Newport (JC), NJ - USA
Posts: 187
Thanked: Once
Default

Quote:
Originally Posted by Deeps
Well, its hard to switch off overdrive on an M/T unlike the A/Ts that you are probably used to in the US.
You are right it is very easy in A/Ts but at the same time if you think about it.. it is quite simple for M/Ts also.... just dont use the gear that has OD when you are driving at a low speed (you will hear a knocking sound)

As pointed out earlier... any gear that has a ratio lower than 1:1 is called an overdrive gear. It's usually the fifth gear on standard transmissions, and fourth gear on automatics.
DaPilot is offline   Reply With Quote
Old 14th April 2006, 01:39   #10
SLK
Senior - BHPian
 
SLK's Avatar
 
Join Date: Feb 2004
Location: DL XX XX XXXX
Posts: 1,290
Thanked: 185 Times
Default

Quote:
Originally Posted by netarchie
So , it means in short the term had nothing to do with Speed of the car and rather it is for saving fuel.
Of course its everything to do with the speed of the car!
More speed less RPM thats why fuel saving.
SLK is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Swine Flu Information - Important Information in post#102 on Page 7 loving_alaap Shifting gears 206 25th August 2009 14:02
Information on Statesman rally required Revvmaster Shifting gears 3 3rd February 2009 22:38
Required---Information on Used Tata Sierra pkp SUVs, MUVs & 4x4s 5 27th April 2007 20:18
information required regarding Mahindra scorpio with 2.2l crde mash SUVs, MUVs & 4x4s 0 9th January 2007 14:34
Information about the Mahindra Classic required aggressive_anush SUVs, MUVs & 4x4s 3 1st October 2004 18:09


All times are GMT +5.5. The time now is 03:22.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks