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Old 17th August 2009, 10:45   #1
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Unhappy FWD climbed a hill but RWD failed. Reason ?

Last week, I was on my way to a friend's house. The way to his house is through a rubber estate filled with loose gravels on red soil.

There were two vehicles : Omni & WagonR. Just before, climbing a steep incline on that mud road, all of the people stepped down since it was only walkable distance to his house. And, both the vehicles were left with only drivers.

Omni Story : I was driving Omni and tried to climb that incline. But the curious thing is that Omni was having high wheelspin. The wheel was simply rotating and the vehicle was not at all moving. So I parked the vehicle and walked that incline.

An onlooker told me that Omni failed because it's weight is less. He asked me to climb with people. But I dropped that idea since it was not confident inspiring to climb with an Omni.

WagonR Story : WagonR climbed the incline easily. Tried that with fully loaded, then also WagonR climbed without any hesitation.

What was the reason behind the wheel-spin that occurred in Omni ? Is that only because of the weight ?

P.S: Both the vehicles and their tyres were in top-notch condition.
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Old 17th August 2009, 10:48   #2
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Well weight is significant. FWD has the engine over the front which gives better traction and the Omni unloaded has very little weight over the back. Not sure if that's the only reason though
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Old 17th August 2009, 10:54   #3
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absolutely! FWD has better traction up slopes on account of the engine weight. This used to be very common in the hills when the first Maruti 800's came out in the '80's - we used to be chugging about rather stolidly in our old Ambys and Fiats and see these zippy little 800's whizzing past and charging about the hill roads in the Nilgiris!

I even remember a time when my Dad has actually reversed our old Amby up a very steep slope, because the car would simply not go up in 1st gear while facing forward as normal. But it does take a lot of skill to be able to reverse up a slope on a twisty road. I suppose in the old days necessity literally was the mother of invention and adaptability, having no real choice or alternative at the time.

Last edited by shankar.balan : 17th August 2009 at 10:55.
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Old 17th August 2009, 11:05   #4
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Exactly, weight is less over rear wheels of Omni and hence the wheelspin. I have read that Omni performs well even in Himalayan region and climbs inclines even with more than 6 passengers.
Rather than power or tyre problem it is the problem of less weight over rear wheels. Rather than with passengers, these things are best tried with luggage in Omni. Put in luggage in the rear and then try the same incline.

Also momentum is very important in these cases. Its even more dangerous to stop in between the incline. With proper momentum, this hurdle can be defeated.
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Old 17th August 2009, 11:13   #5
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Quote:
Originally Posted by shankar.balan View Post
I even remember a time when my Dad has actually reversed our old Amby up a very steep slope, because the car would simply not go up in 1st gear while facing forward as normal.
We used to see this quite often earlier with Amby's. Although the reason was the higher reverse gear ratio than the ratio of the first. However if the tyres are breaking traction, its a different ball game altogether.

In this case the condition of the tyre could also be pointer. Adding weight would have definitely helped.
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Old 17th August 2009, 11:16   #6
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I have my doubts whether it is as simple as that.

On an upslope the RWD had more weight than normal on the traction (rear) wheels, while the fwd has less weight than normal on the traction (front) wheels. In the Omni the engine is almost midship.

My own guess is that the tyre size is also different in the fwd vehicle which also helps in the grip. In addition the weight on the front wheel may still be higher in the fwd despite the weight transfer as outlined above.

The engine characteristics should be very similar since the WagonR/Estilo/Alto VX engine is just a 4/3 version of the old and trusty 800 engine.

In the
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Old 17th August 2009, 11:22   #7
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I think we are forgetting the most obvious reason tires. Omni by default come with cross ply tires and wagon R comes with radials. Its quite possible that the grip levels of wagon R were much more.
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Old 17th August 2009, 11:27   #8
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Quote:
Originally Posted by tsk1979 View Post
I think we are forgetting the most obvious reason tires. Omni by default come with cross ply tires and wagon R comes with radials. Its quite possible that the grip levels of wagon R were much more.
That Omni was fitted with radials.
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Old 17th August 2009, 11:29   #9
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Well in that case it can be due to weight of the engine on front tires, and also how fast clutch is released
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Old 17th August 2009, 11:38   #10
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Please correct me if I am wrong.

Quote:
Originally Posted by sgiitk View Post
On an upslope the RWD had more weight than normal on the traction (rear) wheels, while the fwd has less weight than normal on the traction (front) wheels. In the Omni the engine is almost midship.
I would like to compare this with moving an object up the stairs. Lets consider we are moving a table up the staris. The person higher up ( i.e. front wheels ) has some drawers on his side. The person who is lower in the stairs holding other end of table is not having load of drawers, but is holding just two end of support pillars.

In this case the weight that the person standing at the lower place of stairs has to push is more, but the weight above high hand ( tyres ) is not very high.

Now lets say that drawers is engine. This adds to weight that rear wheels have to push. In this case, again the overall weight transfer is there, but this is by no means will help the tyres to grip better significantly.

PS : This is just an example that I am trying to provide. Please do correct me if I am wrong.

Last edited by aaggoswami : 17th August 2009 at 11:39.
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Old 17th August 2009, 11:38   #11
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IMHO

In case of Ominis the weight is really not "amidship" but over the front axle. Put is some weight over the rear axle and see the difference. The same principle is also used some what to get vehicles stuck in slush moving with people climbing on to the rear fended and hopping in unison while the driver transfers power to wheels.

Another reason for the FWD drive vehicles being able to negotiate slopes / slush some what better is that the direction of force is aligned to the direction of travel (the front tires pointing the way you want to go). In the RWD drive vehicle you can feel the tail section sliding sideways when the steering is turned.

Last edited by sudev : 17th August 2009 at 11:40.
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Old 17th August 2009, 11:42   #12
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Usually RWD will climb slopes more easily than FWD since there is weight transfer to the rear which provides more traction to the driving wheels.

I think there could be 3 reasons why the tyres spinned -
1. Tyres / tyre pressure
2. Vehicle weight
3. Driver skill

I don't think this has to do anything with RWD vs. FWD. The tyres would probably not have slipped if there was more load.
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Old 17th August 2009, 16:16   #13
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Not only tricky slopes, I remember FWD having a distinct advantage over RWD when first starting the car (Boston). In fact, a couple of RWD car owners used to load their trunks with sandbags for better traction.

Of course, when it came to having fun in an empty car park, everyone wanted the keys to the RWD
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Old 17th August 2009, 17:01   #14
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I remember some forum members saying the exact opposite with regards to FWD vs RWD while climbing steep hills. I did a search and here is one link -

http://www.team-bhp.com/forum/travel...tml#post785866 (Another weekend trip to Darjeeling in an esteem)
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Old 17th August 2009, 18:59   #15
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Omni is what ? 38 bhp? Wagon R - 60 odd bhp? That itself is a huge difference. Add to the fact that Omni was unladen(less grip on rear wheels) and there could have been a difference in tyre grip as well.

Anyone wonder why rear wheel drives are not preferred in snow, especially if you have slopes? It is tougher to go up slopes in an RWD in slippery conditions, unless one uses tricks like sandbags etc.
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