38"s or 42"s ?

[SBMF 2015]

I have decided that I can justify a larger tractor. I have it narrowed down to either a JD 4650 or a JD 4850. Which ever one I get will be MFWD with duals. It's about a 50/50 split looking at used tractors they either have 18.4-38" or 20.4-42" . I think I would prefer the 42" tires, but at the end of the day is it worth the extra $ when it comes time to replace them?

 

[BFE]

We have a CIH 7130 with 18.4-42 and a JD 4640 with 20.4-38, both 2wd. Both will do about the same work as near as I can tell, but we're 99.9% notill. The taller tires seem to stay on top better in wetter conditions pulling the auger wagon.

That 4850 probably needs the extra rubber if you're pulling her hard.

 

[chevytaHOE5674]

BFE an 18.4-42 and a 20.8-38 are the same height.

I just spent a pile of money taking 80% tread 18.4-42s off, bought new rims and centers to put 20.8-38s on a tractor. Tractor pulls harder and rides nicer in rough ground. Since I don't have to squeeze between rows I want the widest tire possible.

 

[Dsth]

the 20.8-38 tires will give you more contact with the ground; therefor better traction in dirt and less soil compaction in wet soil. How many times do you plan on replacing tires? If both tractors currently have good tires at purchase time, it my only need one tire change in its lifetime. duals would probably only be on part time and not need replacing at all. so unless you plan on putting a lot of hours on annually, I would say the wider the better.

 

[SBMF 2015]

It will be doing most of the field work; chisel plowing, field cultivating, sub soiling. Take the duals off and haul grain to the elevator.
Some day it may run the chopper and planter if / when those get upgraded.
It's about 4 miles between farms and about 4miles to the elevator.

 

[BFE]

BFE an 18.4-42 and a 20.8-38 are the same height.

I just spent a pile of money taking 80% tread 18.4-42s off, bought new rims and centers to put 20.8-38s on a tractor. Tractor pulls harder and rides nicer in rough ground. Since I don't have to squeeze between rows I want the widest tire possible.

My 42's measured 4" taller than the 38's. Not a huge difference. Can't make the same comparison as you, given the different tractors, but they both handle the rough ground well.

 

[chevytaHOE5674]

Strange as an 18.4-42 and 20.8-38 usually spec within an inch of each other and are considered equal size when swapping on the rear of a MFWD tractor.

I took 18.4x42 firestones off and put 20.8x38 firestones on and the 20.8s are .5" taller and a spec over 3" wider. Doesn't seem like much but it really helps.