Does the B8200 4WD have a lagging Front/Rear setup or negative slippage?

[perry]

I am a new owner of a used B8200. I have been reading online about tires and front to rear gear ratios. I read in the goodyear handbook http://www.goodyear.ca/tires/farm/handbook.html that there should be a positive slippage of up to 5%, that the front tires should lead the rear tires. Mainly that the front tires should slightly pull relative to the rear tires.
Using the tire specs in the manual and calculating the front/rear gear ratio, I determine that the B8200 has a negative slippage. The rear tires are pushing instead of the front tires pulling. Is this correct and proper? My info is below.

I jacked up the right side and rotated the rear tire 20 turns.
The front tire rotated 31.75 turns
Front/Gear ratio = 31.75/20 = 1.588

I happen to have turf tires that match what is specified in the B8200 manual.
Front tire Turf = 24x8.5-12
Rear tire Turf =13.6-16

According to firestoneag the rolling circumference for the 24x8.5-12 is 70 in and the 13.6-16 is 115 in.
http://www.firestoneag.com/compact/tiredetails_pf.asp?ref=1881&artid=359-750&conv=1&subref=168&subid=168

http://www.firestoneag.com/compact/tiredetails_pf.asp?ref=1813&artid=345-210&conv=1&subref=147&subid=147

From what I've read the calculation is:
1.588 x (70/115) = 0.9667
(0.9667-1) x 100 = -3.3%
and supposedly negative bad (the rear tires are pushing).

My question is;
What is going on here? What am I missing in my understanding of this stuff?

Thanks for any input.

 

[dusty-t]

Hi Perry, I don't Know the math but I have a b8200 Hsd with the same size tires as yours only in r4s. I don,t get much pull either way. dusty

 

[perry]

I do not know the math either. I am just following the goodyear handbook

http://www.goodyear.ca/tires/farm/pdf/GoodyearFarmHandbook_1.pdf

on page 14.

My guess is that this math cannot be used for the B8200 but if not then is there another method for properly sizing tires for this tractor?

 

[SockPuppet]

I went through this same stuff with my B8200. I had R4s installed as part of the deal when I bought it. The tires are 12.4-16 in the rear and 23X8.50X12 in the front. I measured the actual dia. and multiplied by pi to get the circumference.

My actual diameters are 22.5 and 36.5. which worked out to 70.65 and 114.61 inches. I ended up with a 1.622 ratio with my method.

I got stumped then because I didn't know the gear ratio of the tractor...

Since the tractor's strewn around the garage right now I figured I'd revisit the question in a month or so.

 

[perry]

I have the OE front tire size listed for the B8200 as 23x850x12 (not 24x850x12) with a 23.3" mounted diameter

The following are 3 thoughts (me thinking out loud) however feel free to comment.

1) I got my operator's manual from my local dealer. It does say 24x8.5-12. Could there be a change in tire specs somewhere along the years? The back of my manual says "reprinted october 2003" After researching online for tires and after going to my local tire shop (my Kubota dealer is not as close) I found out that the 23x8.5-12 were very common and the 24x8.5-12 very uncommon.

2) Okay forget that calculation I did earlier. Straight forward geometry using the diameters of the same firestone tire specs says:

Front tire diameter is 23.5". Its circumference (pi*d) is 73.83".
It rotated 31.75 times so it would have covered a total of
(31.75 rotations) x (73.83 inches per rotation) = 2344 inches.

Rear tire diameter is 38.5". Its circumference is then 120.95".
It rotated 20 times so it covered a total of 20 x 120.95 = 2419 inches

Since I did the tire rotations with the tires off the ground the rear tires "want" to cover 2419 inches of ground while the front only "want" to cover 2344 inches of ground.

The front really are lagging behind the rear.

Will doing this experiment driving along a straight line counting rotations change things significantly?

3) As to the leading or lagging, I read online that some think it is very important to have the front tires lead the rear. If this is true then I am wondering should I be concerned about my used B8200? Is this an issue the tractor manufactures struggled with and eventually solved over the years which means I should be cautious about tire sizes and putting chains on both front and rear tires. The local kubota dealer refused to sell me chains for front and rear because of this maintaining of correct positive slippage issue. Have many of the B8200's succumbed to this issue (not haveing positive slippage) over the years except those like mine possibly because mine was strictly used on snow for snowblowing and nothing else. Or is this a non-issue for this tractor with thousands of them still going strong today?

And then wouldn't chains on rear only or front only be worse than chains on both front and rear?

Confused? I am.

 

[SockPuppet]

I noticed on another forum you posted this question that someone recommended testing your wheel travel on pavement both in and out of 4WD. I would not do it that way. Unless your running at exactly the same distance with both front and rear, running on pavement in 4WD is a bad idea. With either positive or negative ratio, the wheels need to slip.

For the same reason I would think that chains on the front would cause stress on the drivetrain if you also have chains on the rear.

Edit: Chains on the front aren't a bad idea, my feeling is that too many people use 4WD more than it should be. In the context of having such poor traction that they are required, they're a great idea. Taken with the subject of this thread, putting them on to maintain the correct ratio of F/R, the ratio shouldn't be a real problem under a no traction condition.

 

[perry]

My snowblower is front mounted and with turf tires a lot of times the tractor goes straight when I'm trying to turn.

 

[garyf]

Perry... sounds like your diff lock is engaged(rear wheels) try reversing for a bit then going forward then turn to check that it has disengaged. You can also try the brake on each side to be sure it is disengaged.

 

[SockPuppet]

My snowblower is front mounted and with turf tires a lot of times the tractor goes straight when I'm trying to turn.

This is a nice front wheel solution:
http://www.mytractorforum.com/showthread.php?t=102827

 

[perry]

Well I contacted kubota and turns out Vic's method is pretty close at least for my tractor.

The front to rear gear ratio is 1.691. I attached the file they sent me.
Using the tire circumferences shown in the file, 69.7" and 116" gives (using the goodyear formula) a positive slippage of 1.61%. So my method of determining the gear ratio was either wrong or I needed to do more than 20 rotations.

Thanks everyone.