15.5 x 38 vs 18.4 x 34

chas036

Member
I have an oliver 1850 with 18.4x34 tires that needs replacing. I am thinking on replacing them with 15.5x38s because then I can use it more easily to pull my 4 bottom 14" trailer plow. Currently , I can't use it for that because with the 18.4 tires, it won't sit down in the furrow when trying to plow, but with the 15.5 tires, it would. I have a JD 730 that I have been using to plow with, but I would prefer to use the Oliver if I could.

My question is, will I loose pulling power on the Oliver by changing the tires to the 15.5s? I also want to continue to use my oliver to pull my 12ft culti-mulcher and 12ft disk which it currently does without a problem.
 
Maybe.... The 18.4 tires are wider by 3 inches, but the 38 dia. tires also have more tire on the ground because of the larger dia. 4 inches larger in dia. I would say about a toss up. Anyway, I doubt that the operator would notice any difference. I am curious about what others think. Ellis
 
If you are planning on 15.5 singles I think you would run into issues with traction. I have 15.5 singles on my John Deere 4010 gas and it's not enough tire even being loaded. Also 15.5's are short, I'm not sure how they compare to the 18.4x34. I think a 16.9x38 would be a better size but having limited experience plowing in furrow I'm not sure how well it would work.
 
15.5x38 tires are made as a low section-sidewall tire. No more rolling circumference than the 18.4x34s. The 15.5s would be a giant step backwards.
Hook the plow to the 1850 and see what happens. You will be surprised to see that the tire will actually fit in the furrow. We regularly put 20.8 tires into 16" furrows.
Loren
 
If the height and circumference of the two different tires are nearly identical, then there isn't a 4" difference in regard to the ground contact area. An 18.4 may have a higher sidewall than the 15.5. I am not sure of the heights of each tire, but the 15.5 is more likely to have a shorter sidewall.
SDE
 
Four and five bottom plows are pretty cheap. If your rims and wheel centers are good, it might cost less to switch to a 16 inch bottom plow than to replace the rims and wheels, especially if you would need to update your duals to match a smaller new main tire.
 
I have never seen 15.5 tires on a tractor that size. We have 18.4 tires on our 1650 and 1750. Pull a 16 inch Ford plow with plenty of room left in the furrow. I have to agree with Loren on this one. Hook it up and see what it does. Make sure your plow is set up right. Plow will not be set up right for the 1850 if it is set up for the 730 right now. If I was you I would keep the 730/plow setup you have and buy a mounted or semi mounted plow for the 1850. In our heavy ground an 1850 would be a 4 or 5 bottom 16" plow depending on how fast you wanted to go. Farm next door always plowed with a Massey 1100(same engine you have) and a 5 bottom 16" fully mounted plow. He did ok but sometimes had to really gear down. Too much plow for the tractor. I guess it really depends on your budget and what your looking to accomplish.
 
I've got to go along with buying a 4x16 plow. It'll be cheaper than different centers,rims and tires. I've got 16.9 38s on my White 2-105. That's 15 more horses than the 1850. It's a good fit for that tractor,but still a fair amount more tire than a 15.5.
 
I plowed with a 4020 with 18.4x34 tires and 5 14's for several years you never noticed it in the plowing job. it was nice and level. Now plow with 20.8's and 16 inch bottoms. Where are you getting your information that your setup won't work?
 
The 14? or 16? or 18? or whatever furrow spacing isn?t the important thing when fitting wide tires, its the share geometry and mold board throw. A small body with a short share won?t leave room for a tire while a long body with lots of throw will. I?ve got 650 metrics (about 24? wide) on the rear of the tractor and they can in a pinch squeeze into a 16? furrow from our KV, 18.4?s fit even better of course. Not a chance of getting either of them into one our old 16? plows furrow. Also can put furrow widening knife on if you want, trims the outside furrow wall so you don?t scuff your sidewalls. Won?t survive in rocks.
 
I would compromise and go with a 16.9x34 tire. You can use your same rims. Father in law did that decades ago on his 1850.
 
I am running 480:80:38 tires on a 3x14 plow in this picture fits in the furrows fine 480:80:38 tires are half an inch wider than 18.4.38 tire
cvphoto5282.png
 

According to the Firestone data book The 18.4 34 is 191 Sq.in. while the 15.5 38 is 200 sq. in.
 
There isn?t much height difference between an
18.4.34 and a 15.5.38 . When you compare an
18.4.38 to a 15.5.38 there is a huge difference
 
Stay with the 18.4x34's as you won't like 15.5x38's.....You won't have any problems running 18.4's in a 14" furrow.....I used to plow with a 856 IH that had 24.5x32's....I used it on in the furrow 5x16 IH,5x16 MM,or 6x16 AC plow's.....I also used a Oliver 1950 on the same plows and it had 23.1x34 tires..Both did a level job after a little adjusting.....I also pulled the 6x16 AC plow with a 7040 AC that had 20.8x38's...
 


Not one of you have mentioned the differences in tire Circumference (or Height) you will see between Brands of Tires..

My Firestone 15.5x38" are 2 1/2" shorter (in Height) than my GoodYear Titans...both like New..
 

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