New tires for my B7100

[B7100_Norway]

Hi. I contacted my local tire supplier here in Norway. And sent him the spec sheet from the manual. But he could not find correct ratio for BTK tires based on manual.

So the problem is ...what is the correct ratio:

According to the original tires on my tractor - Bridgestone Farm service lug W
front: 6-12 Rolling Circum: 1691 mm and OD 572 mm (my calculator gives the rolling circ 1797 mm)
Rear : 8-16 Rolling Circum: 2306 mm and OD 783 mm (my calculator gives the rolling circ 2460 mm)

Is ratio front/ rear ( 0,733 ) or rear/front (1,36) - ( with calculator rolling circ: F/R = 0,73 or R/F = 1,37 )

But in the spec from the manual :

Front : 650 mm and 700 mm ? - rolling circum: 2042 mm (650) and 2120 mm
Rear : 825 mm rolling circum: 2592 mm

F/R with 650 mm : 0,79 F/R with 700 M : 0,82 - R/F with 650 mm : 1,27 R/F with 700 mm : 1,22

Does this mean, as long as tire ratio is between F/R 0,79-0,82 or R/F 1,22-1,27 then the tires are ok ?

But my original tires are not within this ratio..... ???

 

[85Hokie]

The one problem with all these calculations is that a tires stated SIZE are not really the diameter - while in a perfect world it should be, it is not the case.

I went through this in great detail as you are doing - what I found out was, I'll use an example of a 29" tire - which would be close to your 737mm (these are turfs I am using in my example on a B7100) is supposed to be 29" in diameter, giving a circumference of 91" - but if you take a string and "do the math" you'll find that could be 90 ish or 92 ish DEPENDING on the manufacture of the tire - and I have seen slight differences in the same exact tires being a little bit off.

Inflation has a big part in this too - place a large PSI ( Pascal for you) and the diameter will be larger - lessen the PSI and it will have a flat spot where it touches the ground.

I try to allows use 4wd on a surface that will allow something to slip - I cut grass in 4wd all the time and when I have to be on the street for a bit I try to drive straight and/or keep one side of the tractor on the grass.

There was an old saying - the 2% rule, keep within the 2% of the original ratio of factory tires.

Here is something most never pay attention to - the fronts wear a hellva lot faster than the rears, why? Well they turn 2+ times faster and on most tractors with 4wd the fronts actually spin a ratio a bit faster than the rears, thus PULLING the tractor rather than pushing.

I think if you are close - and keep off hard surfaces, you should be fine in 4wd. HTH

 

[B7100_Norway]

Thanks 85hokie.
My tractor is not HST, but normal geared tractor.
I read another post, which stated the ratio is 1,464 :1.

Do you know the official ratio ?