Tires 336d tire size and other questions

[joswanson]

I have a 1985 336D the tires on it are 13.6 - 26 rear Agriculture, and 8-16 front. These were on it when I bought it about 10 years ago and are in dire need of replacement.


Can anyone tell me if these are the correct size and also what is the rolling ratio for this machine?


Thanks

Joe

 

[normde2001]

Tractordata shows 28" wheel. If what you have works why not just replace them.

 

[HoyeTractor]

13.6-26 rear with 8-16 fronts was an optional turf tire size on that tractor.

 

[joswanson]

I am not having a lot of success finding Agriculture tires in this size and suggestions.

 

[joswanson]

Aaron

What size agri tires were specified??

 

[normde2001]

$36.99 - Deestone D321 13.6/--26 tires | Buy Deestone D321 tires at SimpleTire
You must buy wheels to use the specified 12.8- 28" tires.

 

[rScotty]

I have a 1985 336D the tires on it are 13.6 - 26 rear Agriculture, and 8-16 front. These were on it when I bought it about 10 years ago and are in dire need of replacement.
Can anyone tell me if these are the correct size and also what is the rolling ratio for this machine?

Thanks
Joe

First, congratulations! The YM336D was probably the finest tractor that Yanmar ever built. A real classic. Top notch in every department. I had one, let it get away...and still miss it.

I'll double check tomorrow; I still have an old tire.

But my notebook is usually accurate, and it agrees that those numbers you posted are the correct and original tires. One of the original sales brochures that I have show the rears as being 28" diameter, but I believe that to be either a misprint copy of the 2wd spec. Or maybe it was just out of date. More on that below.

On my 336D, when I measured the loaded rolling circumference of my slightly worn 13.6x26 & 8x16 Ag tires I got 90.25" linear inches of travel per revolution for the front tires and 146.0" for the rears. That is on a hard surface. Rolling circumference varies with the surface. On a soft surface it was 88.5 and 149. BTW, you have to measure rolling circumference in 2wd. Trying to do so in 4wd gives an error.

Using the hard surface numbers yields an Ag tire ratio of 146/90.25 = 1.618 rear over front.

Then measuring the internal gear ratio rear to front by jacking up one side and counting front to rear wheel rotation, I came up with an internal gear ratio of 61/36 = 1.694.
As an aside, along with the wrong tire size, my OEM Yanmar 336D shop manual specifies an internal mechanical ratio rear/front as being 1.743. I don't buy that number. Perhaps they changed the actual gearing and forgot to update the manual. Or just miscounted. I guess it is also possible that changes were made.

Anyway, using the numbers that I actually measured we come up with the front tires overdriving the rears by 4.7%. This is close to optimum to maintain steerage in 4wd. And it matched the way the tractor performed. So I believe my numbers are correct.

Don't order any tires until I double check the old tires I have outside. I'll post them then.

Enjoy, rScotty

 

[rScotty]

13.6-26 rear with 8-16 fronts was an optional turf tire size on that tractor.

Aaron, are you sure of that? That sounds like the Ag tire size not turfs. I know it is true that there were some rather stange narrow diamond tread balloon style turf tires shown as an option in the Yanmar literature at the time and it is possible that tire might have fit the 336D Ag rim. But I've never actually seen one of those tires, much less a set of them on a 336D. Maybe with your wider experience you have. And maybe they are even still available. If so, I'd be curious to know more about them.

The more commonly ordered optional turf tires for the 336D were the typical turf flotation type with a wide body which required different rims of smaller diameter and much wider than the Ag tire rims.
regards,
rScotty

 

[HoyeTractor]

According to my 336 parts book you could get 13.6-26 turfs, 13.6-28 turfs, and it also lists a 13.6-29 turf but I think that is a misprint. Then in the ag tire section it lists the 11-28 / 8-16 ag tire. I dont see any 13.6 ag tires in my book.

 

[rScotty]

According to my 336 parts book you could get 13.6-26 turfs, 13.6-28 turfs, and it also lists a 13.6-29 turf but I think that is a misprint. Then in the ag tire section it lists the 11-28 / 8-16 ag tire. I dont see any 13.6 ag tires in my book.

What I'm seeing in the parts book page you attached is a lot of tire and rim combinations. My guess is that Yanmar was trying to keep the front to rear 4wd ratio within certain bounds and did that by specifying different rims with different makes of tires.

All I know for sure is that mine worked well with the original Ag tire and rim combination that came on it. Having the front tires traveling at 4.7% more per revolution than the rears gives good steering and still is close enough to 1:1 to allow tire slippage to protect the driveshafts and transmission innards agains "wind-up" in 4wd.

I eventually changed over to Turf tires & rims ($$!!) on the YM336d and measured everything again. With the turfs, the overdriven ratio dropped from 4.7% to 0.2%. Darn near 1:1. That still worked well for maintaining steering control, but had an odd effect I hadn't expected. Since with almost a perfect 1:1 front to rear ratio there was now almost no "wind-up" happening in the drivetrain, the 4wd lever didn't want to stay where it was put. I eventually put a spring on the 4wd lever to keep it in position.
On the plus side, with essentially a 1:1 ratio I could shift into and out of 4wd on the fly even at road speed. Perfect syncronization.
rScotty