TN75 questions on R4 tire sizes

[ironpen]

My 2002 TN book calls for a -2% to -4% front rolling circumference lag for the supersteer and -1% to 4% lag for standard axles

Yes you are correct. That's where I got the numbers I just posted for him. I hope we can help this chap without costing him a year's salary!!

 

[overload]

i didn't realize they want lag on the supersteer vs the standard. so in theory i could measure my rolling circumference of my tires? they way i measured them was a method Firestone published by marking the side of the tires and counting the rotations. the current front tires are skid steer duplex tires and if i need to increase the size i will have to buy different front rims or do like you said and buy 24" for the back and just sell my rear rim's and tires.
My tractor is a 2005 TN75SA. another question i have-Mine has the auto 4x4 so on the dash it has a rocker switch that you can switch from auto to fulltime 4x4 or switch it off and of course there is a computer involved. Everytime you start up the tractor it is always in auto 4x4 so you have to use the rocker switch to flip it to 2wd since most everything i do only needs 2wd. is this normal? doe anybody else have this option?

 

[RickB]

i didn't realize they want lag on the supersteer vs the standard.

Negative lag is more well known as lead.

 

[overload]

so Rick are you telling me that they do want 2-4% lead on the supersteer. i know the difference between lead and lag this whole negative thing throws me off. maybe you could answer my last question on my last post on the auto 4x4

 

[ironpen]

Overload, my tractor has the same toggle switch you describe. I thought that you must have skid steer tires (see my previous post). I looked them up and did the math (inches x 24.5 (the number of millimeters/inch) x 3.1417 (pi) and came up with the 3112 millimeter circumference. Based on the chart in the tn75 operators manual is where I came up with the final numbers. I didn't find a tire that would fit your front rims that would be tall enough to work. Do you require 4wd a lot? If not maybe you should let sleeping dogs lie?? Your rear tires are so large that they went past the chart in my manual....but it is a linear relationship and I feel confident that by extending the graph, I gave you the right numbers. I asked the NH dealership if there was any change in tire specs b/w 2002 and 2005 and they said no. If you want me to scan and send you the pages out of my manual, I will be glad to do that. Just use the message function on the board to send me your email address. To me, it sounds like you either have to 1. get different rear rims and tires 2. somehow find a larger 19.5 inch tire 3. find another NH compatible front rim that will let you upsize the front tires 4. just live with a new set of front tires and minimize 4wd usage. There may be others who are more experienced with this to give you more sage advice. Let me know if you want me to scan and forward those pages.

 

[overload]

i've never done this rolling circumference thing before. i marked my tires and the ground and made one revolution then took the inches and converted them to mm came up with 4241.8-rear and 2965.45-front. i do have the book for the tractor but hadn't realized it had that chart that you talked about. i calculated as best i can what the tires would rolling circumference would be if new and came up with about 3150mm new tires. according to the chart new tires would be at the bottom of the scale so as they wear they quickly fall from lead to lag. i use 4x4 mostly for snow so i could live with that considering the other costs. you didn't answer the question if your's has auto 4x4 does it always go into auto 4x4 everytime you start it up? to me that's silly.

Thanks for your help

 

[RickB]

so Rick are you telling me that they do want 2-4% lead on the supersteer. i know the difference between lead and lag this whole negative thing throws me off. maybe you could answer my last question on my last post on the auto 4x4

The front axle on TN's with SuperSteer leads the rear. Fact.

 

[ironpen]

Yes my "auto 4wd" comes on with every startup. I looked up the 16.9x28's again and the diameter varies quite a bit....from 54 to 58 inches. I assumed when I gave you the numbers earlier that the one I saw when I looked up that size was pretty typical and they would all be the same. Your method of direct measurement is by far the best. I think you calculation for the front tire size is spot on. You are about 2.3 inches lacking in diameter. Maybe you can find something that will fit on the net? I assume you are looking for an r4 replacement type tire??

 

[ironpen]

I looked on the Titan/Goodyear tire catalog site. They have several different 15-19.5 r4 tires listed. They all say they are right at 40 inches in diameter......40 x 25.4 =1016 . 1016 x 3.1417 = 3191. Do you think some new tires might do it?? I would probably remeasure that rear tire rolling circumference one more time just to be sure it agrees with your first measurement.

 

[ksbrdmkr]

My TN55S default on start up is auto 4wd. The logic for the auto is when the back turns faster than the front the 4wd kicks in, starts to spin ( if the back get low on air pressure and the circumference decreases the 4wd kicks in quick). With smaller front tires your auto 4wd should not be very sensitive or at least that is the way I understand the logic.