Maintaining 4wd 'balance' after tyre change

[TomOnTractorByNet]

The JD 855 is listed on Tractordata as having 33x12.50-15 rear turf and 23 x 8.5-12 front turf tyres.

I have read that, if you change your tyres to a different size, it will affect the 4wd balance. What is the dimension that needs to be maintained in order not to adversely impact 4wd operation?

Thanks in advance.

 

[MikePA]

What are you trying to accomplish that requires changing tire size?

 

[mrmikey]

I would assume that it would be the ratio of the circumference of the front to rear tires that have to remain the same. I.E. if the front tires circumference was 30" and the rear was 120" the ratio would be 4:1,. It's a factor of the transfer case, front and rear differential ratios and tire diameter, since it's only the tires you're changing and no internals it's all you have to be concerned about.....Mike

 

[TomOnTractorByNet]

I would assume that it would be the ratio of the circumference of the front to rear tires that have to remain the same. I.E. if the front tires circumference was 30" and the rear was 120" the ratio would be 4:1,. It's a factor of the transfer case, front and rear differential ratios and tire diameter, since it's only the tires you're changing and no internals it's all you have to be concerned about.....Mike

Thanks Mike. That makes sense to me. I assume there is some tolerance built in, as the ratios would be slightly disturbed by replacing a set of bald rears with a set that have full treads. Yes/no?

 

[mrmikey]

Just a guess but I don't know how there could be any tolerance built in, all solid gear connection front to rear, no place to slip other than connection from ground to tire tread. That's why they tell you not to use fwd on pavement, same reason not to use you diff lock on pavement/hard ground, no slip.....Mike

 

[TomOnTractorByNet]

Just a guess but I don't know how there could be any tolerance built in, all solid gear connection front to rear, no place to slip other than connection from ground to tire tread. That's why they tell you not to use fwd on pavement, same reason not to use you diff lock on pavement/hard ground, no slip.....Mike

So I really need to know what that ratio is on the 855 as well as the circumference of tyres sets I may be looking at.

 

[/pine]

Although there are many older threads addressing this issue...here is a link to a recent thread...you may have to wade through some moot debates but there is some viable information in the thread...

http://www.tractorbynet.com/forums/owning-operating/302785-question-any-problem-adding-larger.html

 

[RG1]

Just a guess but I don't know how there could be any tolerance built in, all solid gear connection front to rear, no place to slip other than connection from ground to tire tread. That's why they tell you not to use fwd on pavement, same reason not to use you diff lock on pavement/hard ground, no slip.....Mike

There has to be a tolerance built in to allow for tire wear, changes in inflation pressures etc. The main thing that will change is the amount of lead in the front tires, and there's a small variance that is allowable. When I bought my JD 4500, I had a choice of either 13.6X28 R1 or 14.9X24 R1 for the rear, and either with the same 8X16 fronts R1"s. there's plenty of reading here on this subject in one thread alone recently.


OP-

This is lifted from Tractordata.com for the 855 tires choices when it was new-



John Deere 855 Tires:

Standard tires (ag/R1): Front: 4.00x15. Rear: 9.5x16 (2WD)
Front: 6x12. Rear: 9.5x16 (4WD)
Lawn/turf front: 23x8.50-12
Lawn/turf rear: 33x12.50-15

If you want to switch to R1's, but use your 15" rims, you will need to find a tire that matched the rolling circumference of the original 9.5X16's. Same for the front, though I doubt you'll find R1's that will fit the wider rim of the turf tires on it now.

 

[TomOnTractorByNet]

I know where I can get my hands on a pair of Kumho 33x12.5x15 Mud Terrain tyres in good condition for reasonable cost compared to rear turf tyres, and wonder if they would upset the 4wd geometry. Based on all the valuable comments on here, it would seem not. Unless I'm missing something else???

 

[94BULLITT]

I know where I can get my hands on a pair of Kumho 33x12.5x15 Mud Terrain tyres in good condition for reasonable cost compared to rear turf tyres, and wonder if they would upset the 4wd geometry. Based on all the valuable comments on here, it would seem not. Unless I'm missing something else???

Since your original tires were 33'' tall and the new ones are everything will work fine.