18.4-34 vs. 18.4-38

swindave · Nov 29, 2020

i see several 100 or so hp tractors with either34 or 38 inch tires,
which is better ,or should i say, which puts more power to the ground?
38 is taller, but i heard the 34 is better for tillage, 38 for row crop work,
any thoughts or comments?
thanks

David G · Nov 29, 2020

Taller is always better.

fixerupper · Nov 29, 2020

A taller tire is better for both operations. A taller tire has less rolling resistance and has more tread surface on the ground.

fastfarmall · Nov 29, 2020

The 1206 Farmall tore the 18.4 -34 up , the bead slipped on the rim during testing in Texas, so that's when Firestone built the 18.4 -38 tire.

ss55 · Nov 29, 2020

Cost was important to many farmers back then, 34s were less expensive than 38s.

DeltaSteve · Nov 29, 2020

I read several years ago where a test was done on pulling 'power'. Two identical tractors(1206 IH). One was fitted with 18.4x34. The other,18.4 x38. Each had identical plows. Both tractors performed equal. Till they got to a really tough place. The tractor with 34" tires pulled away from the one with 38". Seems that the smaller diameter tire developed more torque/power due to the point of ground contact was less than the larger 38". More leverage.Interseting story.

Bob Bancroft · Nov 29, 2020

The only reason any tire would be better for row crop work is if it was narrower. I have 16.9x38 on my sprayer tractor. My planting tractor has 15.5x38 duals spaced on 30".

Bob Bancroft · Nov 29, 2020

Generally, for my purposes, in my soil, taller is better. But, not always! My sprayer could be bought with either 12x28, or 11x38. I went for the taller, as I assumed they had a bigger foot print. I found leveling the sprayer up to the tractor, and climbing up on the sprayer was quite high with the 38". AND, what really surprised me was, a tire chart showed the 12x28 had a bigger foot print than the 11x38! I was able to switch to the 28" tires.

Mike(NEOhio) · Nov 29, 2020

Nothing said about final drive ratios. Were they the same for both tractors? Smaller wheel will reduce the ground speed and and apply a bit more torque but the footprint will have some effect. Too many variables to draw a definite conclusion.

1206SWMO · Nov 29, 2020

No matter what I'm doing I'll take 38's all day long..

David G · Nov 29, 2020

Taller tires ride better too.

centash · Nov 29, 2020

But wouldn't the 34 inch tire result in a lower ground speed in the same gear, and thus more pulling power ?

Ben

2x4 · Nov 30, 2020

some disc mowers require 38's on 105 hp tractors. 34's are too low & the mower will be in the ground all too often.

shinnery · Nov 30, 2020

I think I would use whichever size fit the wheels on the tractor.

Traditional Farmer · Nov 30, 2020

I have both on tractors don't see a whole lot of difference,usually a tractor will run a size wider if running 34" tires than if they are running 38".

Ken Macfarlane · Nov 30, 2020

As noted below, right around 100 hp drawbar hp in working speed range you will slip the bead on 34" rim and need to move to 38" rims to get a longer bead surface. Or you can move to duals. SAE have a set of tables for max recommended drawbar hp on given size ag tires to prevent this.

Tx Jim · Nov 30, 2020

(quoted from post at 16:18:37 11/29/20) AND, what really surprised me was, a tire chart showed the 12x28 had a bigger foot print than the 11x38! I was able to switch to the 28" tires.

Bob
Do you have copy of that tire chart you refer to that states a 12x28 tire has larger footprint than a 11x38? I can't envision that being correct with the 10'' differences in rim diameters & difference in tire outside diameters.
Thanks, Jim

BarnyardEngineering · Nov 30, 2020

Tire technology has come a LONG way since 1965. Modern 18.4x34's can EASILY handle 100HP+ without slipping the bead.

Most of the reason you see "either-or" on 100HP tractors is because that's where the crossover is where the tractor has enough power to turn the bigger tire effectively.

With the 34's, you will have a slower ground speed and a little more "power" because of the smaller diameter of the tire.

At this stage of the game, what's "best" is what the tractor came with, because it is cost prohibitive to change. Tires are expensive. Rims are a expensive. Most of the time you also need different hubs too, so yet another expense.

Fordy20 · Nov 30, 2020

May not be a concern to your use, but I have a three point tool bar that use with my 4020 with 34" tires that would not clear 38" tires when fully raised.

Jeff M NY · Nov 30, 2020

I really wouldn't say cost prohibitive, but the expensive part I would agree with. Went from 18.4x34's to 18.4x38's on a Hydro 966 this spring. Step up rims and new tires. Works much
better on the Round Baler now. Raised the drawbar up quite a bit.

DR. EVIL · Nov 30, 2020

The "Step-Up rims" that fit on 34 inch cast centers and mount 38 inch tires are the best and most popular
and economical way to switch from 34 to 38 inch tires.
BTO I worked for had 18.4x34's on everything, both his old '64 4020-D's, and the new side console nfe
4020-D and 4320 with rops cab and heat & AC, and the 4020-G he bought well used, and a 4230-D with the
squirrel cage cab and turbo had qi.4x34's. I was pulling that 4320 in 4th gear chisel plowing one fall
for all she could give and no tire on rim slippage, were 23 degree Firestone All Traction Field & Roads.
I think tire BRAND makes a huge difference in tire on rim slippage.

Bob Bancroft · Nov 30, 2020

No. I don't remember if I found the information on line, or in an old Goodyear tire handbook I had. Can't seem to get that type of thing anymore. Everything is "electronic" media, which frustrates me. I have, in the past, had some success looking up tire data for Firestone and Titan tires. Recently I was trying to find that type of information, and had no luck. I just bought a tractor with 18.4R46 tires. My older tractor has 20.8R42. Found a chart right in the op manual. Static loaded radius on those tires is about identical! So I've got a smaller footprint/more pounds per square inch with the newer one. That spells more compaction to me.

But, yes, I agree that other information defies logic. Whatever I had was complete with rim size, rolling circumference, tread width, static loaded radius, footprint, etc.

BarnyardEngineering · Nov 30, 2020

So you'd just throw away a perfectly good set of 18.4x34 tires and rims, and replace them with 18.4x38's because they are "better?"

Dad has wanted to upgrade the 756 with 18.4x38's hundreds of times over the past 40 years. Every time he went and priced out alternatives, new rims, new tires, step rims, step lugs, 38" centers... It was always cost prohibitive, and that was BEFORE 2008 when oil prices went crazy, and tire prices shot through the roof, but never came back down.

18.4-34 vs. 18.4-38

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