[SmartCat]

Well, you learn something new all the time. I discovered recently - when a tractor was parked in front of my house, and I went around the beast to investigate - that tractors don't seem to have a rear suspension at all!



Then I figured out that even JCBs don't seem to have any axle mounted suspension system. But thankfully, the driver gets to sit on a seat that is mounted on springs - just like old black Atlas cycles.



Questions:

1) Am I the only one who didn't know that these machines never had axle mounted suspension systems?

2) Why don't they have axle mounted suspension, like most vehicles?

A few thoughts:

1) It can't be a "cost" issue - because tractors are quite expensive. Fitting a suspension system should not add too much to the final price.

2) It could be because Tractors and Backhoe loaders carry lot of heavy loads. But heavy loads don't seem to be an issue for 40 tonne trucks - they have a robust suspension system. Then why leave out backhoe loaders and tractors?

3) Could the size of the rear wheels be an issue for not having an axle mounted suspension?

[amit_purohit20]

Originally Posted by smartcat

Questions:

2) Why don't they have axle mounted suspension, like most vehicles?

Well there are tractors that have axle mounted suspension. For eg. John Deere has a 6000 series tractor which boasts of a fully suspended Front axle. The axle is suspended using Gas reservoirs.


Other than the axle suspension. The JD tractor also has a suspended cab and a air-suspended seat.

I have driven one of these tractors and jumped it over a very big sharp speed breaker. Trust me the feeling I got was that I am on a sofa or a waterbed. There was hardly any jerk transferred.

Fendt has a tractor which even has a rear axle suspension using springs.

In India one old tractor model had a single leaf spring attached to the front axle, although I dont remember the name.

Coming back to your question why do these vehicles dont have suspension?
Well tractors and Backhoe loaders are supposed to maintain a constant depth in ploughing/digging. For this it requires the movement of the body to be restricted so that we dont disturb the main tractor functions.

If we have a suspended tractor which bounces too much over undulations in a field then we cannot expect the implement to have a constant ploughing depth which is a requirement in agriculture.

The implements are attached to the tractor body which one would not want to move up and down much.

Suspension also affects the off-road vehicles stability.

As the speed of the tractor is less and the tyres big (which absorb more shocks) the need for suspension is felt less.

As tractors top speed mounts up as in European countries (as high as 50-60 kmph) the need for suspension is felt more during transport. Some of the tractors also come with four wheel braking, not so in Indian tractors.

Also nearly all tractor models have disc brakes as they have to cope up with lots of use/abuse and also need to stop not only the tractor but a tractor with two trolleys to rest.

If we still have a suspension in tractor then we need to take care of the above using other different methods. All this will incur cost and thats why Indian tractors donot have suspension.

Also the suspension should be such that it doesnot hamper the articulation of the front axle.(Remember the front axle of a tractor is mounted on a single pivot for better articulation.)

[SmartCat]

Originally Posted by amit_purohit20

Coming back to your question why do these vehicles dont have suspension?
Well tractors and Backhoe loaders are supposed to maintain a constant depth in ploughing/digging. For this it requires the movement of the body to be restricted so that we dont disturb the main tractor functions.

If we have a suspended tractor which bounces too much over undulations in a field then we cannot expect the implement to have a constant ploughing depth which is a requirement in agriculture.

The implements are attached to the tractor body which one would not want to move up and down much.

Amit, if near constant depth is required in ploughing a farm, not having an axle mounted suspension system would make things worse. If you have an axle mounted suspension, it would absorb some of the shocks and not transfer it to the body of the tractor. I would assume that the current setup results in farm attachments moving up and down a lot (along with the tractor driver)!

As the speed of the tractor is less and the tyres big (which absorb more shocks) the need for suspension is felt less.

Makes sense!

[audioholic]

Can someone please tell me where the brakes are located in the front wheels of a tractor used in the farm? Do they even have one? All I see is the linkage between the steering knuckle and the wheels.

[tharian]

What I could think of;

Tractors and backhoe loaders are traditionally off road application vehicles which hardly see on road action.
Along with that they have those huge wheels which will equally need big suspension for it to make any difference which is rather pointless when they vehicle is going to be on uneven land most of its life.

The other reason being, those wheels are not going to be loaded in anyway. Only the engine sit up front and the cab behind it. There is no other load these machines will carry, only pull.

The main point being, farming and construction vehicles that do not do much moving around and spends most of the time off the road, suspension is rather pointless and the driver seat springs are for comfort.

[thoma]

Seen many a JCB running on their maximum speed on road, bouncing away like a ball!

Apart, I feel that the force applied by the working equipment of the tractor or JCB, on the earth, will be absorbed by the suspension a bit. Remembering the extra effort I had to put pedaling a cycle with suspensions.

[wildsdi5530]

@amit_purohit20: Am I to understand that tractors do not have four wheel braking? JCB too?
I am never going to overtake both these vehicles in traffic anymore. We have a lot of them in Chennai and the way these drive (Cycle gap mein Lorry chalana), I thought with their good visibility and maneuverability, they were safe at speed. I just didn't know that they couldn't stop.

[amit_purohit20]

Originally Posted by smartcat

Amit, if near constant depth is required in ploughing a farm, not having an axle mounted suspension system would make things worse. If you have an axle mounted suspension, it would absorb some of the shocks and not transfer it to the body of the tractor. I would assume that the current setup results in farm attachments moving up and down a lot (along with the tractor driver)!

Makes sense!

Let us take an example of a Sports car to a family car, which one is softly sprung? Why do we require stiff suspensions for racing cars? I suppose one of the reason is to reduce bounciness induced by soft comfortable suspensions.

The moment you introduce a suspension there has to be a bounce to absorb the shock and return back to the initial position.

In a field suppose the rear right tyre of a tractor falls in a 1.5-2 feet pit (which is not uncommon), the suspension will compress making the tractor body to tilt more than it would have been without a suspension.

We want the tractor to hug the ground without any bounciness or vertical to and fro motion.

Originally Posted by audioholic

Can someone please tell me where the brakes are located in the front wheels of a tractor used in the farm? Do they even have one? All I see is the linkage between the steering knuckle and the wheels.

Front wheel brakes do not exist in indian tractors including Back-hoe loaders!
Reason cost and the notion that they are off-road vehicles and remain off-road.

Originally Posted by tharian

What I could think of;

Tractors and backhoe loaders are traditionally off road application vehicles which hardly see on road action.

The main point being, farming and construction vehicles that do not do much moving around and spends most of the time off the road, suspension is rather pointless and the driver seat springs are for comfort.

Not fully correct- 40% of tractors life usage is in transporting goods called haulage.
So its equally necessary to have good suspension on hard roads at high speeds.
Tractors top speed in India has increased from 25-26kmph to 32 kmph plus. And the demand for higher top speed is on the rise every year by year. Manufacturers are coming up with higher and higher speeds to satisfy the customer requirements but what about the brakes?

Along with that they have those huge wheels which will equally need big suspension for it to make any difference which is rather pointless when they vehicle is going to be on uneven land most of its life.

The fact that the vehicle will be on uneven land throughout its life itself puts a strong case for good suspension!

In India most tractor drivers suffer with stomach ulcers. Reason- The driver just after his lunch/ dinner has to sit on a tractor seat -one of the most horrible place to be on earth! Trust me on this or ask a Farmer to know more.
I am not a doctor but I think the food in your stomach rubbing hard (due to tractor bouncing) on the stomach lining must be to blame for ulcers. Just a physics guess, Correct me if I am wrong, Forum Doctors!

The other reason being, those wheels are not going to be loaded in anyway. Only the engine sit up front and the cab behind it. There is no other load these machines will carry, only pull.

A typical 65hp Indian tractor might weigh 1.8-2 tonnes. But when ballasted the weight goes to as high as 3.5-4.2 tonnes!

Tractors tyre are filled with water-70% for ballast and then add on ballast weights are mounted on wheels which one weight minimum weighs 36 kg.
Its not uncommon to see 3-4 weights on one rear tyre. Now do the math!

Also the loader bucket carries nearly a tonne of weight.

Originally Posted by thoma

Seen many a JCB running on their maximum speed on road, bouncing away like a ball!

Apart, I feel that the force applied by the working equipment of the tractor or JCB, on the earth, will be absorbed by the suspension a bit. Remembering the extra effort I had to put pedaling a cycle with suspensions.

Yep I agree, you explained it in a more simple way. Thanks

Originally Posted by wildsdi5530

@amit_purohit20: Am I to understand that tractors do not have four wheel braking? JCB too?
I am never going to overtake both these vehicles in traffic anymore. We have a lot of them in Chennai and the way these drive (Cycle gap mein Lorry chalana), I thought with their good visibility and maneuverability, they were safe at speed. I just didn't know that they couldn't stop.

Always stay away from these off-road contraptions. They do have good brakes made for sever use/abuse, but they are not so good on-road because of the high speed and the fact that they have brakes only on the rear wheels.

One more point here to be noted is that tractor disc brakes have friction disks (more surface area) and not disc pads like in cars.

Be very careful especially with Indian tractors carrying overloaded two trolleys. One overloaded trolley weighs around 12 tonnes!

Ideally the trolleys should have their own braking system, but again cost and our Indian laws do not help here. Very few trolleys in India have their own braking system in India, putting the burden on the tractors braking system which as per use is not designed for such usage. (Thank god that some designers design it for abuse, but still they are weak for on-road use)

Tractors do not have ABS neither do they have soft compound tyres to stick well on the road.

[tharian]

Originally Posted by amit_purohit20

Not fully correct- 40% of tractors life usage is in transporting goods called haulage.
So its equally necessary to have good suspension on hard roads at high speeds.
Tractors top speed in India has increased from 25-26kmph to 32 kmph plus.

Did the tractor come into existance for on road haulage?
They were made to do that just like bullock carts came into existance on road hauling stuff. This is my understanding.
On a lighter note, remember the animated movie 'Cars', there was a scene in which a herd of tractors were crossing the road and they were animated to look like cows.

Again , if they were meant for on road hauls, those meaty rear tyres would be smaller and with a usual pattern.
(I am referring to India)

Originally Posted by amit_purohit20

In India most tractor drivers suffer with stomach ulcers. Reason- The driver just after his lunch/ dinner has to sit on a tractor seat -one of the most horrible place to be on earth! Trust me on this or ask a Farmer to know more.

You did mention this in your previous post,
"I have driven one of these tractors and jumped it over a very big sharp speed breaker. Trust me the feeling I got was that I am on a sofa or a waterbed. There was hardly any jerk transferred."

Originally Posted by amit_purohit20

A typical 65hp Indian tractor might weigh 1.8-2 tonnes. But when ballasted the weight goes to as high as 3.5-4.2 tonnes!

Tractors tyre are filled with water-70% for ballast and then add on ballast weights are mounted on wheels which one weight minimum weighs 36 kg.
Its not uncommon to see 3-4 weights on one rear tyre. Now do the math!

Also the loader bucket carries nearly a tonne of weight.

I agree that they are loaded in the way you have mentioned. However, they are loaded with weights for a reason(counterbalance) and they are not going down a highway loaded like trucks in order to have leaf springs.

Like you had mentioned, those huge wheels and tires take care of the loads on off road duties.

[amit_purohit20]

Originally Posted by tharian

Did the tractor come into existance for on road haulage?
Again , if they were meant for on road hauls, those meaty rear tyres would be smaller and with a usual pattern.
(I am referring to India)

Tractors are used for haulage not only in India but europe too whether we like it or not.

You did mention this in your previous post,
"I have driven one of these tractors and jumped it over a very big sharp speed breaker. Trust me the feeling I got was that I am on a sofa or a waterbed. There was hardly any jerk transferred."

Please refer my post I was not talking about an Indian tractor. The tractor was a European tractor costing above 1.4 Crore INR!

I agree that they are loaded in the way you have mentioned. However, they are loaded with weights for a reason(counterbalance)

The weight used in tractors is not for counter balance. Its there to improve traction which is the primary purpose.
Some cases it acts like a counterbalance.

Like you had mentioned, those huge wheels and tires take care of the loads on off road duties.

I said this in Indian context, although it doesnot really take care much enough.
Otherwise we would find autoricshaw manufacturers trying to save cost with big tyres to save cost of suspension and the whole setup.