Tyre size problem

[dunk]

Hi all, can anyone tell me the correct inter actual ratio for my ZB6001 with serial number 25805. The problem is tyre size. I know from previous help on this site that my ZB is almost a B6100D but it has different size tyres on it than are quoted in the owners manual. Manual quotes 6-12 front 7-16 back I have 5-12 front and 7-14 back. They are bridgestone and are old, side walls far gone.
Kubota has told me the ratio for B6100D (had to tell them what they wanted to hear) 1.464 but I just can't make the math work. Tractor seems OK with tyres that are on it, but need to replace them. Any sugestions for replacements. Duncan.

 

[eserv]

To see how close your ratios are you can do a simple test. Find a level place where you cam drive the tractor at least 50 ft in a straight line. put a mark on the ground by both a front wheel and a rear wheel and a corresponding mark on the tire drive the tractor forward in four wheel drive for the 50 or so feet then put it in two wheel drive and back up till the rear wheel mark lines up again with the mark on the ground. the front tire should be close to it's mark to if the ratios are right. I like to see them within 1/8 turn on the front wheel in 10 turns of the rear. I know it's kinda crude but gives you a good base. If you divide the circumference of the rear tire by the circumference of the front tire you'll get the tire ratio. It's not the GEAR ratio but if the ration is OK with tires you have and you maintain the same ratio with the new tires you will be OK. It is better to have the front wheels slightly faster than the rears than to have them slower but I try real hard to get them real close to the same speed!
Ed

 

[TopGear]

Hi Dunk

My B6000 also has 5x12 fronts and 7x14 rears but the manual says it should have 6x12 and 8x16. Remember these refer to the rim size not the tyre +rim. I think what you will find is the fronts are the same diameter but just an inch wider - hence you can probably put 6x12 tyres on those rims you have at the front - but check this out with a tyre guy. Your back 7x14 tires will have large rice lugs on them and when you compare them to a 8x16 rim and tyre with non gray market rice tyres the actual outside diameters will be pretty close. I have brought a set of second hand rims in 8x16 and will be putting these on my beast next tyre change as the 8x16 tyre size is easier to find over here.
Indeed if you are running them on dirt or a non hard surface I think ed's little test will be fine.
So I wouldn't worry too much about the tyre sizes. 5x12 and 7x14 are grey market and 6x12 and 8x16 are non-grey market. However they all have the same gearing in both versions. So basically whatever you can get your hands on cheap. Just remember 8x16 won't fit on your 7x14 rims.

Cheers John

 

[dunk]

Many thanks for the tips. I will try them out and let you know how it goes. It is amaizing that tec info is so hard to find for ZB's. It is the fear of getting it wrong with the tyres, when having the ratio confirmed would make it a simple task. Modern tyres come in all sizes but the one you need! If anyone else has ideas I would like to hear them. Thanks again, Duncan.