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Old 21st September 2010, 15:32   #16
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Short reverse gear on an AWD/FWD might be helpful but i have trouble reversing our RWD Innova on an incline. The wheels tend to slip at the slightest hint of acceleration as most of the weight is on the front tyres.

The FWD vtec however, has no trouble tackling this slope in reverse.

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Old 21st September 2010, 15:55   #17
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Originally Posted by tsk1979 View Post
?? Reverse engaging when car is rolling?
Do not do so unless you want to wreck the gearbox. you cannot engage reverse when car is rolling. Only forward gears are syncromesh
I am not talking about engaging reverse when car is rolling.

Look at it this way- All pre-historic gear boxes have shorter reverse gear. Now we are fairly clear that modern gear boxes seem to have taller reverse compared to first.

Now, what has changed? Synchromesh came for all forward gears (And for reverse too-not here may be). Even engaging reverse is now more seamless. I am presuming that these changes forced the reverse to be taller. I do not know the inner stuff to explain how. I shall talk to experts and try to get some details

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Old 21st September 2010, 16:58   #18
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Quote:
Originally Posted by Shan2nu View Post
...The wheels tend to slip at the slightest hint of acceleration as most of the weight is on the front tyres.

The FWD vtec however, has no trouble tackling this slope in reverse.
That is all about traction.

Also, the Vtec going in reverse is being pushed up from the bottom, and from the side where the weight is. In the Innova, it's the wrong end on both counts - neither is the power being applied to where the weight is, nor is the power being applied at the better end (in this case).
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Old 21st September 2010, 19:51   #19
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Quote:
That is all about traction.

Also, the Vtec going in reverse is being pushed up from the bottom, and from the side where the weight is. In the Innova, it's the wrong end on both counts - neither is the power being applied to where the weight is, nor is the power being applied at the better end (in this case).
Yeah so having a taller reverse ratio than 1st, might make things easier, as it will not only reduce the amount of torque reaching the wheels, but also spread it over a wider speed range.

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Old 21st September 2010, 20:13   #20
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But a taller reverse means, you have to half clutch on reverse to control speed, and while reversing on steep slopes you need to half clutch otherwise the vehicle will stall.
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Old 21st September 2010, 20:54   #21
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Quote:
Originally Posted by Shan2nu View Post
Yeah so having a taller reverse ratio than 1st, might make things easier, as it will not only reduce the amount of torque reaching the wheels, but also spread it over a wider speed range.
But that will not compensate enough for the heavier load being towards the lower side the slope.

For effective movement, the push must be applied at a point & in a direction that will first negate the natural movement. In case of a car on a slope, I would say RWD for going up is best (push it uphill), and FWD for coming down (to get better braking). This is also the same concept for braking : front wheels have discs.

In case of the Innova, it is a RWD. And if you want to reverse up a slope, then the power is being applied on the wheels that are away from the where gravitational force is acting (to push the vehicle down the slope). On top of that, the weight is mostly at the far end of the point where power is being applied. So even a higher gear ration will not work in that situation.
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Old 21st September 2010, 21:38   #22
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But a taller reverse means, you have to half clutch on reverse to control speed, and while reversing on steep slopes you need to half clutch otherwise the vehicle will stall.
Yes, you need to do that on an incline. And this is only limited to RWD cars. An AWD vehicle can have very short reverse gear ratios and still not have a traction problem. I would have preferred a slightly taller reverse ratio on the Innova.

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But that will not compensate enough for the heavier load being towards the lower side the slope.
No, but it will help the driver feed in the torque more gradually and reduce the amount of torque reaching the wheels. The reason why the Innova spins its wheels is also bcoz the amount of turning force at the wheels is beyond the tyres traction capability. A short ratio means you end up with too much torque at very low rpm, so there's a very thin line between traction and slip.

Here's something on similar lines wrt traction and gearing.

On Thin Ice
If you've ever driven on ice, you may know of a trick that makes acceleration easier: If you start out in second gear, or even third gear, instead of first, because of the gearing in the transmission you will have less torque available to the wheels. This will make it easier to accelerate without spinning the wheels.


Source : http://auto.howstuffworks.com/differential3.htm

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Last edited by Shan2nu : 21st September 2010 at 21:49.
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Old 21st September 2010, 22:15   #23
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If you see the thread title I am specifically taking about MUV/SUV kind of vehicles.
My point of starting the thread was about the tall reverse gear which forces drivers to damage clutch on steep slopes, and also makes it impossible to reverse without half clutch
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Old 21st September 2010, 22:58   #24
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Originally Posted by bblost View Post
Is it because with the reverse gear engaged the vehicle is fwd instead of rwd.
Plus these wheels don't have the engine weight helping them gain traction.
Bingo!!! Spot on.
This is exactly what an old timer at one of the tata service centres told me.
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Old 21st September 2010, 23:48   #25
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Quote:
If you see the thread title I am specifically taking about MUV/SUV kind of vehicles.
My point of starting the thread was about the tall reverse gear which forces drivers to damage clutch on steep slopes, and also makes it impossible to reverse without half clutch
That's exactly why i brought up the Innova issue. Not all MUV/SUV's are AWD. So maybe the reverse gear is designed to be slightly taller, to make it easier for the driver to reverse the vehicle on an incline or in slippery conditions (Since front engined rear wheel drives have everything going against them when backing-up).

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Old 21st September 2010, 23:55   #26
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Quote:
Originally Posted by Shan2nu View Post
That's exactly why i brought up the Innova issue. Not all MUV/SUV's are AWD. So maybe the reverse gear is designed to be slightly taller, to make it easier for the driver to reverse the vehicle on an incline or in slippery conditions (Since front engined rear wheel drives have everything going against them when backing-up).

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Actually no MUV/SUV is AWD except for the expensive ones.
Taller reverse gear does not make it easier, it makes it more difficult as you have to burn clutch
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Old 22nd September 2010, 00:25   #27
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Quote:
Actually no MUV/SUV is AWD except for the expensive ones.
Taller reverse gear does not make it easier, it makes it more difficult as you have to burn clutch
Its not easier on the clutch, but its easier for the driver to feed in the right amount of torque to the wheels under low grip conditions. Moreover, we spend very little time in reverse gear as compared to forward gears.

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Last edited by Shan2nu : 22nd September 2010 at 00:38.
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Old 22nd September 2010, 10:03   #28
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Originally Posted by tsk1979 View Post
For example, if you engage reverse gear, release clutch completely, and let your vehicle putter in reverse at idle, the speed is pretty fast for control.
Ideally, the reverse gear should give you low speed. So when you reverse out of a garage or something, you do not need to keep pressing clutch to control speed.
This leads to another problem. When reversing up a slope, there is not enough torque in reverse gear, which leads to half clutching.

So why tall reverse gear, any logic?
Quote:
Originally Posted by Shan2nu View Post

On Thin Ice
If you've ever driven on ice, you may know of a trick that makes acceleration easier: If you start out in second gear, or even third gear, instead of first, because of the gearing in the transmission you will have less torque available to the wheels. This will make it easier to accelerate without spinning the wheels.


Source : HowStuffWorks "Differentials and Traction"

Shan2nu
This is based out of my observation on my TCIC Safari.

Reversing on plain land requires me to not release the clutch as otherwise the speed will be high.

Reversing on incline was never a problem. In front of my office, there is a steep slope. I need to park facing downward to the slope and it is one-way road. So to get out, I need to reverse. It is not a problem and I can drive in reverse releasing the clutch. Sometimes, however, to start, it requires me to slightly hold the clutch and start a little bit above 1100 rpm, and then I can totally release the clutch.

Observation on starting on thin ice is totally true. I had to do that even on my CR-V (4WD) Auto.

Last edited by sumannandy : 22nd September 2010 at 10:04.
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Old 22nd September 2010, 10:42   #29
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Quote:
Originally Posted by Shan2nu View Post
Its not easier on the clutch, but its easier for the driver to feed in the right amount of torque to the wheels under low grip conditions. Moreover, we spend very little time in reverse gear as compared to forward gears.

Shan2nu
A short distance can burn clutch. For example at a hill station the hotel parking had a very steep parking lot. An innova started reversing, and could climb on low rpm. I guess reverse is not so high in innova.
Next was a scorpio.
It kept stalling.
Then driver did half clutch to get her up, and after that we could smell the fried clutch. Probably shortened the life by 10,000kms in 1 minute.
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Old 22nd September 2010, 12:07   #30
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Just talked to my folks. I couldn't get any definit answer. Speculation is that it could be due to packaging issues of having an idler and reverse gear in a 5 speed gearbox. Old CJ series had a 3 speed box.

Btw, I know a person who could asnwer this. Have PMed him

Quote:
Originally Posted by tsk1979 View Post
Probably shortened the life by 10,000kms in 1 minute.
Adding to that you might need to wait till things cool off to normal and power to wheels is restored.
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