yanmar 336dtire help

[rScotty]

i got you , tall does not = rolling circumference, ….

What were your tires originally??

Yanmar originally had a rear tire 12.4/11 x 28 on the YM336d, but they changed the YM336d tire size
about half way through the model run to 13.6 x 26 Firestones. Of course this also meant that they had to change the internal gear ratios front to back...which they did.

I have the notes for our YM336d which was the later model.

The original OEM rears on our YM336 were Firestone (BridgeStone) All Traction Field & Road R1 6 ply.
13.6 x 26 6 ply tire mounted on a 12 x 26 rim*
Front to Back internal gearing was 1.694:1
The unloaded height of that tire is 49.5"

The rolling circumference (RC) Tire spec is 147" supporting 2760 lbs load @ 22 psi
Rolling circumference will vary with the load.
Measured RC on our tractor with a loader and back blade I got 147" to 148.5".
That was done with a series of averages on hard pack and pavement both 2wd & 4wd.

The problem was that Firestone doesn't make that old tire anymore. They make a tire that measures the same diameter and RC, but it is made to measure that on a modern 14.6 x 24 rim. So that would need a different wheel... ugh! Maybe someone else makes a tire to fit your rim that is the right height & RC.

The original OEM fronts on our YM336D were OHTSU 8 x 16 4ply R1 ag. mounted on a 16x6 UA rim*

*note that rim width for tractor tires was originally measured on the INSIDE faces of the rim where the tire contacts the rim.
you should check with each wheel or tire manufacturer to see how they measure width because automotive tires are measured differently for width.

rScotty

 

[hdwrench1]

my tires are the bridgestone 13.6 x26 . i measured the rc to be just shy of 48” . i have purchased a set of deestone replacements (8 ply ) , which measures about the same before mount and inflate . i also bought a set of deestone 8x16 fronts to match . hopefully it all works out when there mounted …. i will post results . i am looking for to completing this tire saga . kinda why i did all four ….should be a long time before this tractor needs tires again ….

 

[hdwrench1]

looking now for a set of front rims for the new tires if possible, i’d like to keep the fronts around (mounted) as there still in good shape

 

[bmaverick]

looking now for a set of front rims for the new tires if possible, i’d like to keep the fronts around (mounted) as there still in good shape

Make sure the front rims are identical size replacements. Your YM336D is 4WD and the tire ratio front and back need the perfect lead and lag range values to perform flawlessly.

Do you have the YM336 manuals? We got them at the YTOG for free.

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[hdwrench1]

i have the factory repair/ operation manual , i am looking for the parts manual…fo you know of a source for the front rims …? hoye is on back order . found them at asap/ old tractor but the bad reviews and lack of info concerns me ….

 

[hdwrench1]

What were your tires originally??

Yanmar originally had a rear tire 12.4/11 x 28 on the YM336d, but they changed the YM336d tire size
about half way through the model run to 13.6 x 26 Firestones. Of course this also meant that they had to change the internal gear ratios front to back...which they did.

I have the notes for our YM336d which was the later model.

The original OEM rears on our YM336 were Firestone (BridgeStone) All Traction Field & Road R1 6 ply.
13.6 x 26 6 ply tire mounted on a 12 x 26 rim*
Front to Back internal gearing was 1.694:1
The unloaded height of that tire is 49.5"

The rolling circumference (RC) Tire spec is 147" supporting 2760 lbs load @ 22 psi
Rolling circumference will vary with the load.
Measured RC on our tractor with a loader and back blade I got 147" to 148.5".
That was done with a series of averages on hard pack and pavement both 2wd & 4wd.

The problem was that Firestone doesn't make that old tire anymore. They make a tire that measures the same diameter and RC, but it is made to measure that on a modern 14.6 x 24 rim. So that would need a different wheel... ugh! Maybe someone else makes a tire to fit your rim that is the right height & RC.

The original OEM fronts on our YM336D were OHTSU 8 x 16 4ply R1 ag. mounted on a 16x6 UA rim*

*note that rim width for tractor tires was originally measured on the INSIDE faces of the rim where the tire contacts the rim.
you should check with each wheel or tire manufacturer to see how they measure width because automotive tires are measured differently for width.

rScotty

rScotty , do you have the r.c. of the front tire handy ? i’m running an 8”x16”. ?

 

[hdwrench1]

scotty , i found one of ur previous posts discussing the 336d tire issue, i found your r.c. front tire info along with the rim markings . thanks a million….

 

[rScotty]

rScotty , do you have the r.c. of the front tire handy ? i’m running an 8”x16”. ?

Ahh... a very good question ! Congratulations on thinking it through.
As you are finding, getting the right tires on a part time 4wd tractor can be a lot of skull work.

My stock fronts on the 336 were 8x16 OHTSU 8 x 16 4ply R1 Ag tire mounted on 16x6 rims!!
Rolling Circumference (RC) is listed as 90.4"
Overall loaded diameter is 31.1" and loaded radius is 14.4"

That sounds like the wrong tire on the wrong rim, wrong, but it turns out to be correct. The reason is tires tend to be measured on the outside width at their widest point, where rims are always measured between the inside faces of the rim where the tire contacts the rim. So a 16x8 tire on a 16x6 rim is just fine...even normal.

You may notice that in tire specs, the loaded diameter is NOT twice the loaded radius. The loaded tire is oval rather than round and the axle is nearer to the ground than to the top of the tire. That is why RC is not a simple calculation but needs to be measured.

I've got a stack of notes on tire swaps on the Yanmar 336 and for some reason I kept them.
Back about 1995 and just for fun, I measured the RC of our YM336D front tires and the number i got Was 90.25" in 2WD.
Measured 4wd* the RC is more variable and front tires measure too small & rears to large. I think that is because in 4wd the internal overdriven gear ratio causes the fronts to slip a little as they drag the rears.
So you end up measuring some mixture of F/R RC and traction of the measuring surface (asphalt)

I also measured the internal F/R ratio on our Yanmar 336d (late model) by jacking up one side in 4wd and turning the rear tire by hand. Welding rod ground to a point and clamped to the frame formed pointers.
It took 36 turns of the rear wheel to return both front and rear wheels to their original starting posiitions & turning the rear caused the front to turn 61 revolutions. Hence: 61/36 = a internal ratio of 1.694:1
The shop manual says that the ratio is 1.743:1, but either they are incorrect or else the older YM336d was different. Note that 62/36 would sure be an easier gear set to design with and also to machine - and at 1.722:1 it would almost match Yanmar's own spec. But I measured it several times on both sides and got what i got.

Using my measured numbers for gearing and RC, gives an OEm overdriving ratio of 4.7%. Frankly, I think that part time 4wd tractors should be designed closer to 2.5% overdriven. There is no downside in designeing the ratio even closer to zero as long as tire mfg differences & wear does not cause the overdriving percentage to be negative. If so, steering suffers.

YMMV, rScotty

* I now think that accurate RC measurements should be done in 2wd. Again, measure RC in 2wd.

 

[rScotty]

scotty , i found one of ur previous posts discussing the 336d tire issue, i found your r.c. front tire info along with the rim markings . thanks a million….

I don't recall that post - hope it was the same number as in the post directly above. That post above is correct.

 

[bmaverick]

i have the factory repair/ operation manual , i am looking for the parts manual…fo you know of a source for the front rims …? hoye is on back order . found them at asap/ old tractor but the bad reviews and lack of info concerns me ….

Go back to my 1st post here. We got the parts manual and its free in PDF download.

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