I have a ford 1120 4x4 with 29x12.5-15 turf tyres on the rear that are quite worn. I have an opportunity to purchase a pair of lug tyres and rims 16x6 ie overall diameter of 28 inches as apposed to the current 29 inches.
Do you think these tyres would be suitable for this tractor? I have a feeling that they are going to be very similar in diameter because the 29 incher's are really worn but the 28 inchers are new.
Thanks
Matt
You want to match what is called the "rolling circumference". Most tractor tire manufacturers provide that spec, although some divide it by 3.14 and call it "rolling diameter". Regardless of what they call it, "rolling measurements" are measured by driving the tractor rather than by wrapping a tape around the tire. That's because for tractor tires with their lugs and low pressure it is hard to come close enough by wrapping a tape around a tire. Sometimes you have no choice but to go with wrapping a tape, but a rolling measurement tells a bunch more. It also enables you to match tires by looking it up in a tire manufacturer's data book, since that is the spec they list.
I've done rolling circumference measurements two ways. One is to put some sort of marker on the tire tread - maybe tape a wrench to a tire lug - and then drive in a straight line on soft ground for a few tire revolutions and measure between the marks on the ground.
The other way is to put a splotch of paint on the tire tread and then drive down a paved road. Then measure between the paint splotches on the road.
You'll be surprised at how much difference it makes to be on a bit of slope or not driving perfectly straight.
If you do that with what you have for tires now you'll always have a usable number. That is if what you have is working OK in 4WD.....isn't too hard to shift out of 4wd, it doesn't skid while turning, and nothing has broken recently in the drive train. Then you'll at least know what ratio you are trying to match when you start swapping for different tires.
I learned all this when changing over to turfs on my own tractor. Those turfs cost serious dollars as well as requiring a wider wheel. But then I ran across such a good deal on a set or rear used tires+wheels that it was worthwhile to buy brand new tires for the front to keep the right ratio.
good luck, rScotty
