5425 vs 4320 vs 3720 Surface Pressure

[morrisond]

I have a 5425 with R1's and a 1600 WAM. To simplify a bit, I'm thinking of getting rid of the 1600 and getting a 8-9' Finish Mower for the 5425 (But change the R1's to Turf Tires), or trade the 5425 to a 4320 or 3720. If it's going to destroy everything as it's just too heavy, and I would't mind a tractor with e-hydro so my wife can run the blower in the winter when I'm away.

They all have/Will Have cabs.

The only other thing I use the Tractor for is to pull a Lucknow S75PT Blower and JD MX6 Rotary Cutter.

Ideally I don't want to have to replace the blower or Cutter - I think the 4320 would be fine but 3720 maybe a little small.

So the question is the 5425 weighs over 7000lbs but it has larger tires. The smaller tractors are 3-4000 Lbs.

How big a difference in surface pressure with Turf Tires on all 3 is there?

Thanks and any suggestions are appreciated.

 

[jenkinsph]

I would think this would be determined by the tire pressure. If all of the tires were set at 12psi the surface pressure would be the same per square inch.

 

[boggen]

R1s = deep tread and skinny tire.
turf = shallow treads, and wide tires.
R4's = a mix between the 2 tires, partially deep treads, and a wide tire.

when tractor is in 4WD or MFWD = tearing up lawn.

if you need traction in winter, you can get a set of chains for any type of tire you go with.

8' to 9' finishing mower, you will be looking at a bat wing finishing mower with 3 decks. do you have 2 hydraulic ports on back. one to lift the outer decks, and another to lift the middle and entire frame up.

less sharply you turn, less chance you will tear up the lawn.

if you have 4WD or MFWD, if you change rear tires, you also will need to change front tires, to keep the gearing ratio correct, and keep from tearing up the front end / drive line / transfer case. when you do place tractor into 4WD / MFWD

check on what is required of "bat wing" finishing mowers. for HP at the PTO. and check against your tractor. HP at the PTO. finishing mowers are one of them things that can suck up HP.

the lighter a tractor / mower is, more likely you can get on the lawn sooner to cut it without making ruts. heavier the tractor is, more time you will need to weight to let things dry out before getting on the lawn to cut it.

================
Bah, can no long remember the name of the mower type. all i can remember is "gangs" blades are setup on a drum. and you just roll across the yard. they are old fashioned push mower (without an engine) the mower type reduces amount of HP needed by the tractor by a good amount compared to a rotating finishing mower. problem is they do not do so well in taller grass. *ggrr what is the name of them*

 

[pclausen]

If all of the tires were set at 12psi the surface pressure would be the same per square inch.

So if I have a 10,000 lbs tractor and set the tire pressure to 12psi, the pressure exerted to the surface is the same as a 4,000 lbs tractor set the same? Almost seems to good to be true!

 

[Zebrafive]

So if I have a 10,000 lbs tractor and set the tire pressure to 12psi, the pressure exerted to the surface is the same as a 4,000 lbs tractor set the same? Almost seems to good to be true!

If your tractor is too heavy it would be obvious if the pressure is too low. Tires would be too flat, might actually invert itself at the bottom. So you might not be able to run 12psi, but if you could, each tire would have to cover enough square inches (total of all four) to equal 10,000 / 12 = 833.34 square inches. You could also tell if the fronts did not have enough pressure if the tractor did not want to steer, but plows.

I agree with Steve, tire pressure will equal ground contact pressure.

 

[couchsachraga]

I'm a bit confused by this thread - perhaps I'm a bit dense, or don't realize how closely tires are matched to a tractor size-wise.

I completely agree that if the tire contact patch is bigger for a heavier tractor the ground PSI will be the same compared to a smaller one - as long as the ratio of weight / contact patch size is kept the same. Yes, you can increase the contact area by airing down a bit (off road trick, especially in soft ground), but that works with the lighter rig too. Actual tire PSI will only matter as it relates to the size of the tire contact patch you are working with.

So, my question that will clear things up for me (and perhaps others), On bigger tractors are the tires always sized to maintain the same contact area ration for a given weight? I know they get bigger, but given that some have cabs, some don't, etc... I'd assume (never good, hence the post) that it is a rough estimate and isn't really worrying about ground PSI. After all, heavier tractors pull better because they are heavier (assuming they have the hard ground and traction), and part of that traction is tires and weight on the contact patch (and tread, etc... etc...).

 

[jenkinsph]

So if I have a 10,000 lbs tractor and set the tire pressure to 12psi, the pressure exerted to the surface is the same as a 4,000 lbs tractor set the same? Almost seems to good to be true!

The pressure per square inch is the same the surface area of the four patches for the 10,000 lb tractor would be equal to 2.5 times the surface area of the 4000 lb tractor.

This assumes smooth tires such as R3 tires, the cleats on R1 tires can increase the surface pressure on the reduced bearing surface. If you compare R1 tires of the same tread design it still works the same.

 

[buickanddeere]

So if I have a 10,000 lbs tractor and set the tire pressure to 12psi, the pressure exerted to the surface is the same as a 4,000 lbs tractor set the same? Almost seems to good to be true!

Per square inch . A 2000 or 10,000 lb tractor with 10psi in the tires will push on the soil with 10lbs force on every square inch.

 

[LD1]

Tire pressure does NOT equal ground pressure. That is a common mis-conception. If the tires were rounded (no side wall) and a uniform density all the way across....then yea,that may be true. But tires have stiff side walls, and a tread section that isnt rounded.

Lets just explore a few comparisons here:

My front tires have 30 PSI in them. They rut things up pretty good with the FEL on, especially if I have a heavy load in the bucket. Now lets take the FEL OFF. The tires STILL have 30PSI in them, but MUCH less ground pressure as evident they dont rut as much.

Also, my rears are (R1's) set at 10psi. THe R-4 option for my tractor is MUCH wider and run at about 20psi. Does that mean that the R4's will rut twice as deep on soft ground??

What about the old mud-running truck I had that wore 16" wide boggers and I kept them @ 30PSI. Is that going to sink into the mud as much as a standard tire that is only ~9" wide and still 30PSI???? OR what about a kid on a bike with 1" wide tires @ 30PSI????

 

[pclausen]

So its all about effective contact surface area as opposed to psi alone to determine the surface pressure.

So unless I doubled my contact surface area when reducing my pressure in half, in real life, I probably only reduce the surface pressure by 5-15%, depending on lug type and sidewall stiffness.

That makes a lot more sense!