1.5x38 Tires

I posted on the clasifieds, I am looking for a set of the above tires. I am going to try a set on the D17, and if they wont make it pull, then I am selling the tractors and going truck pulling.

Thanks Gerald, Yes 15.5x38.

Actually, if you want a REALLY GOOD primer on the effect of tire size on tractive effort, read the Wismer-Luth tractive effort prediction analysis.  The amount of drawbar tractive effort you obtain is dependant upon several factors... here's the most important:

Ratio of weight on driving vs. undriven wheels

Rolling resistance of both driven and undriven wheels

Diameter of driven and undriven wheels

Weight on driven wheels

SLIP

Applied HP.

The LEAST important factor, when you boil it all down, is APPLIED HP.  Why? Because once you've hit a certain level of slip, the amount of increase in applied HP makes only a small difference in drawbar effort.

The most important factors are wheel diameters and weight on the driven wheels.  Smaller diameter drive wheels present more traction surface to work against, and at the same time, reduce the amount of depression footprint into the soil, hence, lower rolling resistance.  Smaller diameter tires increase the depression footprint, and at incipient slip, wind up having to expound thrust to 'climb' rather than 'pull'.

As Gerald notes- the 'hurt' factor, is that going to a larger diameter drive wheel means you're losing mechanical advantage of drive ratio.  This is most frequently solved by turning a lower gear ratio (higher numerically) to compensate, but the side-effect is greater torque strain on the drive axleshafts, differentials, and bull-gear pinions.

There's also much, much to be said for operating technique-  picking the best-available 'line' down the track, running it not too fast, and not too slow, controlling direction, and being SMOOTH about it... bouncing the frontend, or zig-zagging down the track hurts pull performance, and oftentimes will damage stuff, so it's a game of balance.

You're doing it right, when you're pulled to the stop at the same time you run out of horsepower AND spin wheels to china.  When you make ONE improvement to one aspect of the formula, you'll need to make one improvement to another to take advantage of it... at that point, you'll be in the cubic-money race.


Edited by DaveKamp - 02 Sep 2011 at 3:31pm

Here is what the tractor looks like. I have enough power, never powered out, just spinout. The local Agco dealer has a set of 18.4x38 on some Belarus rims. I think I will try them and see if I can make it pull better. I am not sure why the H's amd M's can pull so good with the same tire I have. Is the secret having tires with 50% or less tread.

Most pullers prefer short treads it seems. I suppose it keeps the treads from folding over on the hard track. In loose dirt short treads makes for much better digging, spinning, and poor working the ground with the pulled implement at least that's how it works on my tractor.

Gerald J.

I've never pulled in full-size ag, but HAVE pulled with my Cub Cadet, and most of the guys that were REALLY hard-core, would go looking for USED ag-tread GT tires.  I believe the flatter profile was part of the reasoning, and the other very-well-might-be the fact that the tire compound was really hard.  This is a track-variable issue.

Some other things to consider (and this will only come from being THERE when it happens)... Watch those guys pull, and look closely at how their draft-system is rigged... hitching height is usually regulated, but WHERE the hitching point is located with respect to the center of the rear wheel DOES have an effect on pulling dynamics and weight transfer.  Also... when you're on the virge of spinout, are your front wheels on the ground, or in the air?  Are they stable in the air, or bouncing?

Are you spinning one or both wheels?  Are they?

And finally...  when you weigh-in, HOW is it done?  Is there a single platform scale, or a portable scale system?  How close to the weight limit ARE you?

The 12.4-42 I have on my big tractor are a beginning at the tall skinny swamp buggy tire. Mine were made by Goodyear, but the Goodyear Farm tire handbook I downloaded a few years ago doesn't admit they made them.



Much handier for spraying, not so much crop run over. The fronts are 11.00-16 four rib gave more crop clearance though the 12.4-42 are the same diameter as the original 18.4-34 which I need to put back on for snow work this winter.

Gerald J.

The tires you have now would probably do better if they were "top cut". Also if you pull alot and there are different types of ground your gonna need another set of wheels and tires so you can swap them out.