marrt
Platinum Member
This may have been discussed b/f but here goes.... I know PT does not recommend filled tires for the 400 series. But what about the 1400 and larger series?
Tires Filled Tires
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davesisk
Platinum Member
Marrt:
I don't know, but (just FYI)...both of my rear tires are filled, and interestingly enough, I just replaced one rear wheel motor and the other rear wheel motor has some minor seepage (can't detect where it's coming from, but the shell gets a little greasy after a few hours of use). Both front wheel motors are dry as a bone all the time, and those wheels are not filled. I don't know if this is coincidence or not, but I think PT does say that filling the tires puts addition wear on the wheel motors.
Just out of curiosity, does anyone know WHY filling the tires puts additional wear on the wheel motors? I can't see the polar moment of inertia of the wheel (resistance to a change in turning speed) being increased THAT much by adding a liquid to it???? Or maybe it is?
Dave
I don't know, but (just FYI)...both of my rear tires are filled, and interestingly enough, I just replaced one rear wheel motor and the other rear wheel motor has some minor seepage (can't detect where it's coming from, but the shell gets a little greasy after a few hours of use). Both front wheel motors are dry as a bone all the time, and those wheels are not filled. I don't know if this is coincidence or not, but I think PT does say that filling the tires puts addition wear on the wheel motors.
Just out of curiosity, does anyone know WHY filling the tires puts additional wear on the wheel motors? I can't see the polar moment of inertia of the wheel (resistance to a change in turning speed) being increased THAT much by adding a liquid to it???? Or maybe it is?
Dave
Charlie_Iliff
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Marrt & Dave:
The volume of PT tires is substantially smaller than conventional tractors, so the weight actually added isn't as significant. If weight is needed, however, that's one way to do it.
I think someone doing real calculations would have a hard time showing any significant increase in any loads on the axle and thus the wheel motor. Picking something up with a loader vastly increases the weight on the fronts, and then driving over anything rougher than a tabletop imposes shock loading spikes way above the weight being carried. Fluid in the tires doesn't increase static axle load at all, although it would increase the inertia of the wheel-tire combination. That will affect loading at high speeds over bumps, but because it will change (slow) any resonant component, it may be hard to say that it doesn't actually reduce the shock loading when you hit a bump. As Dave noted, the polar moment is increased, and gyroscopic effects are, as well, but I'd bet they are much smaller than the operating jolts we apply to the machines all the time. Without the benefit of testing, my gut feel is that fluid in the tires would be less hard on the axles than equivalent dead weight on the frame.
Marrt - are you going to be chief tester? /forums/images/graemlins/grin.gif
The volume of PT tires is substantially smaller than conventional tractors, so the weight actually added isn't as significant. If weight is needed, however, that's one way to do it.
I think someone doing real calculations would have a hard time showing any significant increase in any loads on the axle and thus the wheel motor. Picking something up with a loader vastly increases the weight on the fronts, and then driving over anything rougher than a tabletop imposes shock loading spikes way above the weight being carried. Fluid in the tires doesn't increase static axle load at all, although it would increase the inertia of the wheel-tire combination. That will affect loading at high speeds over bumps, but because it will change (slow) any resonant component, it may be hard to say that it doesn't actually reduce the shock loading when you hit a bump. As Dave noted, the polar moment is increased, and gyroscopic effects are, as well, but I'd bet they are much smaller than the operating jolts we apply to the machines all the time. Without the benefit of testing, my gut feel is that fluid in the tires would be less hard on the axles than equivalent dead weight on the frame.
Marrt - are you going to be chief tester? /forums/images/graemlins/grin.gif
Schultz
Gold Member
I think I may take the opposite stand. Providing the wheel motor bearings can handle the extra load, then I would say the weight on the frame would be preferred. As you mentioned Charlie when you load the bucket, you're adding a much higher load then the back tires normally see, so the bearings are likely capible of more loading.
My preference comes because the loading of the tires may add as much as 40lbs to each tire (5gal of fluid). I also agree with you this isn't much to worry about. However, this does create a heaver flywheel, so the wheel motor has to overcome this energy every time it changes speed, which might put more stress on the motor seals.
My preference comes because the loading of the tires may add as much as 40lbs to each tire (5gal of fluid). I also agree with you this isn't much to worry about. However, this does create a heaver flywheel, so the wheel motor has to overcome this energy every time it changes speed, which might put more stress on the motor seals.
Charlie_Iliff
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<font color="red"> this does create a heaver flywheel, so the wheel motor has to overcome this energy every time it changes speed, which might put more stress on the motor seals.
</font>
That's certainly true, but I wonder whether it is a significant load compared to the inertia of the whole machine, which the motors are handling all the time. If you add 160 lb. of dead weight to the frame, the wheel motors have to accelerate and slow that mass. If it's in the tires, they have to do the same, just rotational instead of linear. And there'd be some lag where the fluid and tire casing wouldn't move or accelerate at the same rates.
I guess my conclusion at this point is that I certainly don't know the answer. I just have a gut feel that the difference wouldn't be great.
</font>
That's certainly true, but I wonder whether it is a significant load compared to the inertia of the whole machine, which the motors are handling all the time. If you add 160 lb. of dead weight to the frame, the wheel motors have to accelerate and slow that mass. If it's in the tires, they have to do the same, just rotational instead of linear. And there'd be some lag where the fluid and tire casing wouldn't move or accelerate at the same rates.
I guess my conclusion at this point is that I certainly don't know the answer. I just have a gut feel that the difference wouldn't be great.
Schultz
Gold Member
After thinking about it more it probably doesn't matter all that much where the weight is. I agree the difference of workload on a wheel motor of a filled tire vs. a non-filled tire is very little compared to the load of the tractor itself. So, with that in mind any additional weight in a tire would have no additional effect on the wheel motor bearings. As far as stress goes it may be better to have it on the wheel. However, you can shift the CG more rearward with the same weight by hanging it off the tail of the tractor. Take your pick...
RonL
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I don't think that fluid in a tire would have a significant flywheel effect. Consider 40 pounds of fluid in a tire and 40 pounds of weight bolted to the tire. Stopping the spinning tire with the weight bolted on would involve having to stop the spinning weight also. Stopping the spinning tire with fluid would involve stopping the spinning tire but the fluid could continue to spin. Minus the friction against the interior carcass of the tire, of course. However, is stopping the forward momentum of both the same? If a tree falls in the forest..................
RonL
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marrt
Platinum Member
<font color="red">Marrt - are you going to be chief tester?</font>
I'm going to look at a 1430 and the owner said he filled the tires. I recall some discussion on this topic before and the conclusion, for the 425, was that Power-Trac didn't recommend it. The reason this would be helpful for the 425 is to take advantage of the hydraulic lift capacity to get more lift without risk of the PTP. One reason it may not be recommended is that it may stress the center articulated joint, as opposed to the wheel motors, when carrying a load. However, as you've noted, I really can't believe the difference is significant.
Maybe the guy filled the tires because he bought those whippy turf tires and was simply looking for more traction. /forums/images/graemlins/wink.gif /forums/images/graemlins/grin.gif I'll find out.
I'm going to look at a 1430 and the owner said he filled the tires. I recall some discussion on this topic before and the conclusion, for the 425, was that Power-Trac didn't recommend it. The reason this would be helpful for the 425 is to take advantage of the hydraulic lift capacity to get more lift without risk of the PTP. One reason it may not be recommended is that it may stress the center articulated joint, as opposed to the wheel motors, when carrying a load. However, as you've noted, I really can't believe the difference is significant.
Maybe the guy filled the tires because he bought those whippy turf tires and was simply looking for more traction. /forums/images/graemlins/wink.gif /forums/images/graemlins/grin.gif I'll find out.
Bob999
Platinum Member
Your point about additional weight adding loads to the center joint reminds me that when I visited PT I enquired about a then current TBN post about a broken heim joint on an 425. I was told that 1400 and 1800 series uses a different "design" (I think the reference was to materials) and that there had been no problems with broken joint components on these models. I also learned that the problem on the 425 was most likely a welding issue.
FOURTEEN
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"driving over anything rougher than a tabletop imposes shock loading spikes way above the weight being carried. Fluid in the tires doesn't increase static axle load at all"
You may have the answer here, but not realize it! The tires are not static!
It's not the weight of the filled tire that stresses the motors, it is more likely the shock loading. Tires are filled with air for a reason - to cushion and absorb shock. Filled tires are, by definition, mostly filled with incompressible liquid, so every shock is transmitted directly to the chassis. (Lay a wheel and tire on the garage floor. Hit the tire with a baseball bat as hard as you can. Not much happens. Now, hit the solid wheel the same way. You will be lucky if the bat doesn't break in your hands!!) Even railroad cars which ride on smooth steel have coil springs to cushion the ride. The air filled tires are the only suspension the poor PT has!!!
Why not just use the PT the way it was designed?? Is it worth damaging or breaking it just to lift a little extra!??!
You may have the answer here, but not realize it! The tires are not static!
It's not the weight of the filled tire that stresses the motors, it is more likely the shock loading. Tires are filled with air for a reason - to cushion and absorb shock. Filled tires are, by definition, mostly filled with incompressible liquid, so every shock is transmitted directly to the chassis. (Lay a wheel and tire on the garage floor. Hit the tire with a baseball bat as hard as you can. Not much happens. Now, hit the solid wheel the same way. You will be lucky if the bat doesn't break in your hands!!) Even railroad cars which ride on smooth steel have coil springs to cushion the ride. The air filled tires are the only suspension the poor PT has!!!
Why not just use the PT the way it was designed?? Is it worth damaging or breaking it just to lift a little extra!??!
