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Bob E G
02-12-2010, 12:57 PM
We have a sports turf application for a Bobcat A300. The AWS feature would make it a versatile machine for us.

My question is:
Equipped with Super Float Tires, what is the actual ground pressure (in psi).

I have heard different numbers all over the board, 38 psi being the highest. And other lower figures. Our turf tractor is around 9-11 psi. I was guessing that the A300 should be that or slightly higher, but not 38. Does anyone know the actual figure?

Thanks

bobcat_ron
02-12-2010, 02:39 PM
It can't be anymore than 14 psi.

Ground pressure can be calculated using the standard formula of pressure: P = F/A (object's weight divided by contact area)

Tigerotor77W
02-12-2010, 03:06 PM
Our turf tractor is around 9-11 psi. I was guessing that the A300 should be that or slightly higher, but not 38. Does anyone know the actual figure?



Ron's formula is right, but it's difficult to estimate the area a tire makes with the ground. If you're bored, you can figure it out by parking the machine, pouring water over the wheels and around the wheels, let the surrounding water evaporate, and then drive the machine off and calculate the area moist spot that the tire sat on.

But either way. How heavy is your tractor?

Dodge2
02-12-2010, 03:23 PM
Thats simple, all you have to do is measure the air pressure in your tires!!!!!
And with that information you could (if u wanted to) measure the contact patch.

Bob E G
02-12-2010, 08:04 PM
But either way. How heavy is your tractor?

I roughly figured my tractor's psi slightly different than your suggestion, although I like your method.

I just took a pencil and marked around the actual contact points of the tires. I figured square inches of contact per tire, added the square inches of the four tires, which gave me total square inches.

I can't remember that figure, now. But then I took the weight of the tractor=4000 lbs (approx) and divided by total square inches. As I recall it was 9 or 10 psi.

Operating weight of an A300 is 8673 lbs (according to Bobcat). The problem is, I don't own that machine. And I would need some help from you all to get either accurate measurements or specs with super float tires, in order to know the actual PSI

YellowDogSVC
02-12-2010, 11:23 PM
write to bobcat technical at bobcat.com . You would be surprised at the info they will get for you. The engineers have almost everything figured out somewhere you just have to ask and wait for a response. They have been very helpful on some of my crazy questions.

Tigerotor77W
02-13-2010, 01:13 AM
yellowdog's suggestion is a good one. Just don't let them feed you the "talk to your dealer" statement if you've already gone that path. :)

I've been thinking about this discussion, and the only thing I can come up with is that the tire's inflation pressure is roughly the same as the pressure the machine is exerting on the ground. If you do the calculation (and assuming it's accurate enough), suppose you have 2,000 pounds per wheel. For a tire filled to 40 psi, this means a contact area of 50 square inches. If you then take the weight and divide by the area, you get 40 psi. This isn't just magic with these numbers (I chose them to work out evenly), but the machine weight actually cancels out entirely, leaving just the tire inflation pressure.

If some of the assumptions hold up, this means that whatever pressure is in your tires is the pressure against the ground that tire exerts.

The reason I'm struggling with this is that I don't understand what happens if the machine is balanced, say, 90% of weight on two wheels and 10% on the other two. Or, put another way, if you pump up your car tires to 35 psi when the car is on the ground and then you lift the car in the air, what would your pressure gauge read?

Darryl G
02-13-2010, 01:16 AM
I was expecting see a picture of a Bobcat in a pond!

DiyDave
02-13-2010, 08:22 PM
Thats simple, all you have to do is measure the air pressure in your tires!!!!!
And with that information you could (if u wanted to) measure the contact patch.

Bingo, here's your answer!:waving:

Dodge2
02-13-2010, 09:38 PM
yellowdog's suggestion is a good one. Just don't let them feed you the "talk to your dealer" statement if you've already gone that path. :)

I've been thinking about this discussion, and the only thing I can come up with is that the tire's inflation pressure is roughly the same as the pressure the machine is exerting on the ground. If you do the calculation (and assuming it's accurate enough), suppose you have 2,000 pounds per wheel. For a tire filled to 40 psi, this means a contact area of 50 square inches. If you then take the weight and divide by the area, you get 40 psi. This isn't just magic with these numbers (I chose them to work out evenly), but the machine weight actually cancels out entirely, leaving just the tire inflation pressure.

If some of the assumptions hold up, this means that whatever pressure is in your tires is the pressure against the ground that tire exerts.

The reason I'm struggling with this is that I don't understand what happens if the machine is balanced, say, 90% of weight on two wheels and 10% on the other two. Or, put another way, if you pump up your car tires to 35 psi when the car is on the ground and then you lift the car in the air, what would your pressure gauge read?

the second paragraph is right.

say if you have a tire with 40 psi in the air and you then put the tire on the ground it will still have 40psi in it. Now if you put 500 pounds on it the pressure in the tire will still be 40 psi. The only change when you have a tire with no mass on it and mass on it will be the size of the contact patch of the tire on the ground.