4WD Front to Rear Tire Ratios

[ovrszd]

This is nitpicky but might apply to the current discussion.

True 4wd tractors are center pivot tractors that are constantly in 4wd, no way to disengage, and none needed. They do not bind when turning or going straight. They are match geared. Only selectable mechanism is diff locks if equipped.

MFWD or FWA tractors on the other hand are selectable. They also bind in certain conditions. All of them do. Some guys will say their tractor does not bind when driving straight. Okay, but it will bind when turning. Some guys will say their tractor does not bind when turning. Okay, but it will bind when going straight. No way around it in Utility size and down tractors. Some high end, large AG tractors are electronically controlled and can disengage when turning to avoid binding.

So to apply this. Driving your tractor with FWA engaged all the time puts unnecessary stress on the driveline. That stress will show in tire wear for sure. That wear will mostly show in the front tires. They are making more revolutions than the larger rear tires and they have the added stress of guiding the machine. That stress can show in other ways but less likely.

To those that operate their tractor with FWA engaged all the time, I would ask, do you do the same with your 4wd truck??

 

[dragoneggs]

To those that operate their tractor with FWA engaged all the time, I would ask, do you do the same with your 4wd truck??

No, but I don't drive my 4wd truck on unpaved steep slopes! For the 1% of the time when I do go on pavement I sometimes shift out of 4wd just to work the system.

 

[samofsweden]

Hello Sam, Here's how to proceed with the numbers the dealer gave you:

You have that internal gear ratio for the 7040 which was given to you by your dealer: I believe it was 1.438 : 1.000. This is the basic F/R ratio that is set by the number of internal gear teeth. Unless you are to change to a different front or rear differential this will never vary.

From the Kubota web site on "build your own 7040" I looked up the tire options for the M7040 and came up with the chart here:

Agricultural Tires (R1)
FRONT - 9.5-24 R1 Titan Tru Grip Lug
REAR - 16.9-30 R1 DURA TORQ 17 mm holes
FRONT - 9.5-24 R1 Goodyear Dura Torque
REAR - 16.9-30 R1 Goodyear Dura Torque Cast
FRONT - 9.50-20 R1 Bridgestone Farm Service Lug M
REAR - 16.9-24 R1 Titan Hi Traction Lug TL 2.8"offset
Turf Tires (R3)
FRONT - 9.50-24 R3 Goodyear All Weather TL
REAR - 18.4-26 R3 Firestone All Non Skid (ANS) 17mm holes
FRONT - 29x12.50-15 R3 Titan Multi Trac 8stud
REAR - 21.5L-16.1 R3 Firestone Turf & Field
FRONT - LSW305-521R3 Titan Grizz LSW Soft Turf
REAR - LSW570-648 R3 Titan Grizz LSW Soft Turf
Industrial Tires (R4)
FRONT - 14-17.5 R4 Titan HD-2000
REAR - 16.9-24 R4 Titan Industrial Tractor Lug

So now we go get the the information needed to complete the calculations. As an example, I'll use the default tires (first option) and begin by going to the Titan Tire site and looking up the rolling circumferences for those tires .
(Titanｮ Tire catalog)

On the Titan site we see that they spec 124 inches as the rolling circumference for the 9.5 x 24 R1 fronts.
and we find that the 16.9 x 30 DURA TORQs on the rear have a rolling circumference of 175 inches - also from the Titan site.

Next we calculate how far the front tires roll for every single revolution of the rears and it is: 124 x 1.438 equals 178.315 inches.
The rear tire calculation is easy; for one single revolution the rears travel : 175 x 1.000 which equals 175 inches.

So already as we glance at the numbers we can see that the fronts are covering about three more inches of ground each time the rears rotate once. This is good! We are feeling confident that we have described the problem correctly.

Your actual ratio is : 178.315 divided by 175 or 1.0189:1 . If we just round it off for convenience we have 1.02:1 ..... or to say the same thing as a percentage we multiply that ratio by 100 and say the ratio is 102:100 or alternately we can just say the fronts are traveling about 2% faster than the rear tires.

In my design experience that is about exactly what you want. It would be interesting to go through the other tire options they offer and see how those options compare with their default choice. In the past I've found that tires with less traction can get by with a bit more difference in ratio; probably because they can slip easier and so take the stress off of the drive train.

My hat is off to Kubota for designing a good default F/R tire ratio. I didn't really expect anything less of them - but it is nice to see the numbers confirmed. If it were my tractor I would use that 2% overdrive as a target when replacing tires.
Enjoy!
rScotty

rScotty
Thanks alot for helping me out, very very kind of you:thumbsup:
Merry Christmas to you and all you other great girls and guys on this forum

/Sam

 

[Cr555]

"rScotty
My local kubota dealer got back with numbers, he said that the front travel is 1,438:1 compared to the rear wheels. Now I have to admit that im not 100% sure if my dealer got it right...these figures say 43% "overdrive" on the front wheels or have I got it totally wrong?"

I believe your dealer did get it right. Kubota refers to this number (1.438) as the final drive ratio. As explained to me by a Kubota representative, this simply means that for every complete rotation of the rear tire, the front tire rotates 1.438 times. This is precisely the information you need to calculate whether a proposed tire will work on your MFWD tractor. I was further advised (by Kubota) that the proper calculation you want to run is as follows:

(rolling circumference of the front tire / rolling circumference of the rear tire) x final drive ratio = lead/lag ratio

In the case of my B7300, the rolling circumference of the front tire is 61 inches. The rolling circumference of the rear tire is 86 inches. The final drive ratio (as furnished by Kubtoa) is 1.475. Therefore, the calculation works as follows:

(61 / 86) x 1.475 = 1.0462. Any number greater than 1 means you have the front wheel leading the rear. Any number less than 1 means the rear is pushing the front (bad). In my case, I have 4.62 percent front wheel lead. What is also interesting is that the Kubota technician I spoke with (from the Suwanne, GA factory) advised me that Kubota recommends 3 - 7 percent front wheel lead. This differs from the 1 - 5 percent front wheel lead you find typically recommended for 4WD vehicles. You might want to confirm this with your own dealer, but I was speaking with a technician who said he was responsible for handling tire issues such as this.

 

[sixdogs]

Assuming this is correct, and it appears to be, we should chisel it in stone somewhere so we don't have to remember the math.

For my 5520 Deere, the "ratio" number I got was something like .74 and then I mathed things out using the rolling circumferences from there. As a double check it wouldn't hurt to math out the rolling circumference on several of the known and already Kubota tire choices so you can check the math and confirm front to rear tire lead to see what those percentages are.

Glad this is finally resolved.

 

[LD1]

The math and formula are easy.

The hard part is uncovering the actual final drive ratio of the tractor. It is not a very well published spec.

For my L3400, the ratio is 1.56. Gives the 7x16 and 11.2x24 ags a 5% lead.

Using a range of 4% to 7%, the front tires have to be between 86 and 88.5" Rolling circumference.

I have actually been looking into all this crap lately. Wish I could find a different front tire. I like my ags on the back, but would sure like a stiffer and wider front tire. Less prone to thorns and flats. And wider for less rutting doing loader work. I havent found anything yet that I like unless I want to swap the backs to 12.4-24's

 

[ovrszd]

My Ford 3910 is .768 or 1.3 depending on how you look at it. I figured that out by setting the tractor on jackstands, taping the wheels and rotating the rears 10 revolutions while counting the front revolutions as well. Then using the Tyre Learn chart I posted a link to earlier it is easy to pick tire combinations that will work.

I'll get energetic and jack up the Kubota and check it out and post what I find. I expect the results to be very similar. Using the Tyre Learn chart the Kubota's tires set up a .7425 ratio. Curious to see if the revolution count comes close to that. It has very very little pull or bind when running in 4wd. If running on hard surface it's just enough to cause it to not want to unlock. A seesaw of the steering wheel while moving unlocks it though.

 

[rScotty]

Then using the Tyre Learn chart I posted a link to earlier it is easy to pick tire combinations that will work.

I didn't find that link. Maybe in some other thread? Be sure to use the tire's spec for rolling circumference. Calculating circumference from diameter doesn't work well; it comes close, but not close enough.
rScotty

 

[ovrszd]

I didn't find that link. Maybe in some other thread? Be sure to use the tire's spec for rolling circumference. Calculating circumference from diameter doesn't work well; it comes close, but not close enough.
rScotty

Scroll to the bottom of the link to find the charts.

 

[PILOON]

Couple of years ago I went thru all that front/rear math as my fronts were finished and a rim was rotted out due to previous owner having filled with calcium.
Front rims were just too pricy.

I lucked out as a tire surplus outlet had a perfect rim pattern to match.
I ended up with a pair of rider mower rears that matched my bolt pattern exactly and were 2X wider with the exact same diameter so that I kept the front/rear ratio that I needed. I did however need to beef up the centers as they were thinner. (cut out the old centers and weld added them to the new rims)
Probably have over 500 hours on this upgrade.
Paid $75.00 for 2 rims and 2tires.

 

[sixdogs]

...

It has very very little pull or bind when running in 4wd. If running on hard surface it's just enough to cause it to not want to unlock. A seesaw of the steering wheel while moving unlocks it though.

Sometimes my Deere is a little tough to get out of FWA but that's typical. Accelerate and back off or shifting is usually what it takes for me. I know that you know to stay out of FWA while on hard ground but others reading this may not know. Best to stay out of FWA while on a hard surface because it will chew up the font tires and can damage the front axle. The last part I think I read in the owner's manual.

For people very aggressively using FWA with heavy slippage where a lot of wear is involved I have seen them mount the front tires with the tire pattern going backwards. It looks dumb but seems to work.

 

[ovrszd]

Oh yeah, sixdogs, I'm one of the guys usually cautioning about overuse of 4wd. If doing a variety of FEL work I may engage/disengage 4wd several dozen times in a day. I was simply referring to doing a 4wd task, then driving away on hard surface before remembering to disengage. Rather than stop/reverse/start again, I just seesaw the steering wheel a couple times and it disengages.

There are several TBN members that claim to rarely disengage their 4wd. For them this discussion about front to rear ratio is critically important. For them their tractors suffer additional stresses as they chew off the tread of their front tires (changing the ratio) and then again when they add new front tires against worn rears.

Does that mean their tractors are doomed to fail?? No. It's simply small things that can be done to extend the life of the tractor's powertrain. No different than sixdog's discussion above.

 

[rScotty]

Oh yeah, sixdogs, I'm one of the guys usually cautioning about overuse of 4wd. If doing a variety of FEL work I may engage/disengage 4wd several dozen times in a day. .

Same here. Agree completely.
We engage 4wd if the job requires it and then disengage it when it doesn't. I like to think that most everyone with the kind of 4wd found on the tractors in this forum does the same. On the M59, JD310, or the compact Yanmars the engage/disengage cycle can be as often as a dozen times an hour if doing a lot of loader work, because I'll engage it simply to avoid spinning the rears when pushing the loader into a pile....and disengage while turning around to take the load somewhere. On the other hand, I'd have no hesitation about leaving it in 4wd all day on snow or ice or sloppy clay mud if needed for pushing or pulling work without load in the bucket.
It's all about traction. If I forget and leave it in 4wd when pulling onto a high traction surface - like on pavement - then that's just an "aw shucks & forehead-slapping" kind of mistake. Hopefully we will "feel" that mistake through the steering wheel and of course then we slow down or stop to disengage the front axle. Although as you say, we do forget it some times and certainly we expect the tractor to be able to take a reasonable amount of that abuse without complaining. It would be a sad, surprising, and disappointing thing if it didn't. All of which doesn't stop it from being abuse, though. The same rules apply to the similar type of 4WD found on our Ford F250 PU, JD310, and the old '72 K10 Chevy PU.

Now the "going to town car"....which is a '97" Toyota Land Cruiser FJ80....is a different kind of animal altogether. It has a more modern and complicated All Wheel Drive (AWD) instead of the old 4WD we've been discussing. It's not just a difference in terminology, because its AWD has a center differential plus limited slip in the driveshaft between the fronts and rear axles. That enables it to stay in AWD mode all the time regardless of traction. There's not even a way to change out of AWD; no reason for it. That's modernization for you; the older 1985 FJ60 LandCruiser which preceeded it didn't have AWD. It worked like the more primitive tractors....or the modern Ford F250 PU.
luck, rScotty

 

[dragoneggs]

Oh yeah, sixdogs, I'm one of the guys usually cautioning about overuse of 4wd. If doing a variety of FEL work I may engage/disengage 4wd several dozen times in a day. I was simply referring to doing a 4wd task, then driving away on hard surface before remembering to disengage. Rather than stop/reverse/start again, I just seesaw the steering wheel a couple times and it disengages. There are several TBN members that claim to rarely disengage their 4wd. For them this discussion about front to rear ratio is critically important. For them their tractors suffer additional stresses as they chew off the tread of their front tires (changing the ratio) and then again when they add new front tires against worn rears. Does that mean their tractors are doomed to fail?? No. It's simply small things that can be done to extend the life of the tractor's powertrain. No different than sixdog's discussion above.

I am 'one of those' guys. I use my BX on a very sloped property (except for my big paved parking area in front of my house. I learned my lesson a couple of times forgetting to engage 4WD when starting out and heading down to get to work on terracing or burn piling, whatever and have scared the carp out of me. When I occasionally drive onto the pavement I always feel the bind and usually switch out if I am going to do much turning at all. It's easier for me to feel it than to remember before it's too late.

 

[ovrszd]

Now the "going to town car"....which is a '97" Toyota Land Cruiser FJ80....is a different kind of animal altogether. It has a more modern and complicated All Wheel Drive (AWD) instead of the old 4WD we've been discussing. It's not just a difference in terminology, because its AWD has a center differential plus limited slip in the driveshaft between the fronts and rear axles. That enables it to stay in AWD mode all the time regardless of traction. There's not even a way to change out of AWD; no reason for it. That's modernization for you; the older 1985 FJ60 LandCruiser which preceeded it didn't have AWD. It worked like the more primitive tractors....or the modern Ford F250 PU.
luck, rScotty

Scotty,

The wife's '11 Jeep Grand Cherokee is the same way. I'm a 4wd nut and don't own anything 2wd. I sat in that vehicle when she first got it with owners manual in my lap and went thru all the options and processes. Knowing fully well that my wife would struggle with the choices. When I was done I still did not think I fully understood the selections and what they did. Bout the time I was talking loudly to myself Terry opened the passenger door and got in, saying what'd ya figure out?? I closed the manual and said, see this knob with snow, auto, sand, blah, blah blah settings?? Always, always leave it in auto. That will take you anywhere you will be driving this vehicle. :confused3:

 

[ovrszd]

I am 'one of those' guys. I use my BX on a very sloped property (except for my big paved parking area in front of my house. I learned my lesson a couple of times forgetting to engage 4WD when starting out and heading down to get to work on terracing or burn piling, whatever and have scared the carp out of me. When I occasionally drive onto the pavement I always feel the bind and usually switch out if I am going to do much turning at all. It's easier for me to feel it than to remember before it's too late.

Yep, I understand that. When I'm in the timber, which is steep, I'm almost always in 4wd. But I'm also ballasted pretty heavy in the rear and if traction is good can back up some pretty steep terrain in 2wd.

 

[rScotty]

I am 'one of those' guys. I use my BX on a very sloped property (except for my big paved parking area in front of my house. I learned my lesson a couple of times forgetting to engage 4WD when starting out and heading down to get to work on terracing or burn piling, whatever and have scared the carp out of me. When I occasionally drive onto the pavement I always feel the bind and usually switch out if I am going to do much turning at all. It's easier for me to feel it than to remember before it's too late.

Are you talking about using the brakes when going downhill? That's sort of the same thing - but for a different reason. Many compact tractors have brake drums on the transmission countershaft instead of on the axle shafts. And unlike cars, compact tractors don't tend to have dedicated front wheel brakes at all.
The result being that in 2wd mode all tractors made like that will only brake the rear tires - which can sure create some excitement going downhill! Especially with a load in the bucket....
But because the brakes are on the countershaft, they are able to distribute the braking effort to all of the various axles and shafts which are directly connected to the transmission. When you engage 4wd that includes the fronts....at least a little bit.
What was a problem has now become a virtue...
rScotty

 

[dragoneggs]

Are you talking about using the brakes when going downhill? That's sort of the same thing - but for a different reason. Many compact tractors have brake drums on the transmission countershaft instead of on the axle shafts. And unlike cars, compact tractors don't tend to have dedicated front wheel brakes at all. The result being that in 2wd mode all tractors made like that will only brake the rear tires - which can sure create some excitement going downhill! Especially with a load in the bucket.... But because the brakes are on the countershaft, they are able to distribute the braking effort to all of the various axles and shafts which are directly connected to the transmission. When you engage 4wd that includes the fronts....at least a little bit. What was a problem has now become a virtue... rScotty

I honestly haven't looked at the brake design on mine. If I don't engage the 4WD going downhill in one section, I start hopping and there is nothing I can do to stop, brakes make it worse. Having the front wheel in gear provides the braking I need I guess.

 

[ovrszd]

I honestly haven't looked at the brake design on mine. If I don't engage the 4WD going downhill in one section, I start hopping and there is nothing I can do to stop, brakes make it worse. Having the front wheel in gear provides the braking I need I guess.

Yeah, that hopping down the hill is not a good feeling. Really doesn't matter where in the driveline the brake application happens as long as it only affects the rear axle. When in 2wd applying the brakes going down a hill will only slide the rear tires. When in 4wd the rear axle and front axle rotate at the same approximate speed. So brakes applied to the rear axle will also slow or stop the front axle. So braking is dramatically improved.

Funny side note. When sliding down a hill in 2wd all that's required to reduce or stop movement is to drop the FEL bucket. But in the panic of it all, a guy never thinks to do that.

 

[rgmosley]

Richard, Here is a picture of my rear axle on my 3910. The axle diameter is 5.5" and the wheel fits the flange very tight.



Thanks, Bob