Tire issues M7040

samofsweden · May 3, 2012

Hi.
I aiming to buy new tires to my M7040HD /year 2009.
Its running on R4s today.
Im looking for the gear ratio to calculate right tire dimensions/(turn ratios)
Anyone know if its the same gearbox(gear ratio) if you buy a tractor with R4s or AG tires?

Some manufactors do change the gear ratio so you get the right
drive between front and rear tire. front tire should turn 2-3 % more than rear tires.

Thanks
/Sam

big bubba · May 3, 2012

sam: i would be very careful deviating from the factory specs on ft./rear tire size. there may be a way of calculating something different, but i understand it does not take much to damage the 4wd system with sizes other than for what it's designed.
surprised that they are worn already on a '09. good luck

sixdogs · May 3, 2012

Seems common sense that the ratios are the same for both sets of tires.
I have switched lots of tires over the years and you need to get it right. If you search Firestone tires they have a great booklet on calculating ratios of front and rear rolling circumference. Do it once and you're a pro forever.
Kubota probably already lists tire choice options on their website.

Oh, I forgot--most ag tire dealers carry the ratios needed in some sort of master tire book.

gwdixon · May 3, 2012

From the Kubota website:

Agricultural Tires (R1)
FRONT - 9.5 x 24 STEEL BIAS AA /REAR - 16.9 x 30 STEEL BIAS
FRONT- 9.5 x 24 STEEL BIAS AA / REAR - 16.9 x 30 CAST BIAS DA
FRONT - 9.5 x 20 /REAR - 16.9 x 24 STEEL BIAS CA

Turf Tires (R3)
FRONT - 9.5 x 24 STEEL BIAS CA /REAR - 18.4 x 26 STEEL BIAS DA
FRONT - 29 x 12.5-15 STEEL BIAS AA /REAR - 21.5 x 16.1 STEEL BIAS DA
FRONT - LSW305-521 NHS STEEL BIAS AA /REAR - LSW570-648 NHS STEEL BIAS AA

Industrial Tires (R4)
FRONT - 14 x 17.5 STEEL BIAS AA /REAR - 16.9 x 24 STEEL BIAS AA

These are the options for a M7040. Different gearing for the tires is not indicated.

samofsweden · May 3, 2012

Guys, thanks for your respons and good input!
Well here in Sweden the new M7040s are sold with
12.4-20 in front and 16.9-30 Which is written 320/85-20 front and 420/85-30 at the rear.
The front tires looks abit wider than the 9.5-24 which I find useful.
So question is does the 12.4-20 and 9.5-24 has the same turning size?

Big Bubba, well no the R4s arent worn already, the tractor sits to low for forest work, thats why I might change tires.

samofsweden · May 3, 2012

gwdixon said:
From the Kubota website:

Agricultural Tires (R1)
FRONT - 9.5 x 24 STEEL BIAS AA /REAR - 16.9 x 30 STEEL BIAS
FRONT- 9.5 x 24 STEEL BIAS AA / REAR - 16.9 x 30 CAST BIAS DA
FRONT - 9.5 x 20 /REAR - 16.9 x 24 STEEL BIAS CA

Turf Tires (R3)
FRONT - 9.5 x 24 STEEL BIAS CA /REAR - 18.4 x 26 STEEL BIAS DA
FRONT - 29 x 12.5-15 STEEL BIAS AA /REAR - 21.5 x 16.1 STEEL BIAS DA
FRONT - LSW305-521 NHS STEEL BIAS AA /REAR - LSW570-648 NHS STEEL BIAS AA

Industrial Tires (R4)
FRONT - 14 x 17.5 STEEL BIAS AA /REAR - 16.9 x 24 STEEL BIAS AA

These are the options for a M7040. Different gearing for the tires is not indicated.

Thanks for the information GWdixon!

samofsweden · May 3, 2012

sixdogs said:
Seems common sense that the ratios are the same for both sets of tires.
I have switched lots of tires over the years and you need to get it right. If you search Firestone tires they have a great booklet on calculating ratios of front and rear rolling circumference. Do it once and you're a pro forever.
Kubota probably already lists tire choice options on their website.

Oh, I forgot--most ag tire dealers carry the ratios needed in some sort of master tire book.

Ok I will check out Firestones webb!

CHDinCT · May 3, 2012

Can't you check your current rolling circumference by marking your pavement and tires at the 6:00 location and then rolling the tractor forward until the mark comes back around to 6:00, then measure the distance between the two pavement marks. With that information for both the front and rear tires, shop for Ags with very close rolling circumferences. This assumes your local dealers can tell you the RC of Ag tires they sell.

Edit: Actually, you can calculate the ratio of front to rear rolling circumference and then just look for a set of Ags that have the same or very close ratio; don't have to be the same sizes as your R4s.