Need tire help

[Chris]

Hi: I have been away from this board for almost a year, but still recognize some of the names. Before posting, I did some searching, but was not able to get enough info out of past posts, so here goes.

I have a 1980 B7100 4WD. I've had it for about 2 years. A year or more ago, I contemplated getting new tires, and since I only use the thing for general yard maintenance and landscaping, I was interested in turf (R-3) or industrial (R-4) tires. I believe the ag tires on the machine are the originals, and they are practically slicks by now. The sizes on the tires (and in the manual) are (Front) 6-12-2PR, and (Rear) 8-16-4PR.

I went to a Kubota dealer in a nearby town and asked for a quote on some tires. He said he didn't even fool with them, he just referred me to a large distributor in town that also happens to be the distributor that handles all the tires for the fleet of cars, truck, forklifts, etc., where I work.

I did nothing for a year, but, this spring, I decided to treat myself to a new set. I think I was told a year or so ago by the good folks at Carver that I would not likely be able to get turfs or industrials that would work on my rims, so I sent an e-mail request for a price quote on a set of ags from this distributor. They were very prompt and responded with what seemed like an excellent price (about $250 + tax + mounting) for all 4. I assumed that since I had asked for a quote on ag tires with the above dimensions, and since they were a large, industrial distributor of some repute, that they would know what they were talking about.

Long story short (too late for that), the price they gave me was for something other than the ag tires I needed. When they picked up my old tires/wheels at my work (what service!) they realized that the tires they had were not the same thing that I had on the tractor. They then ordered the right thing, mounted them, and returned them to me at work along with a bill for $798.38.

As you might expect, I was taken aback. They are being very good about trying to "work with me". I have told them I am not paying for the tires. They have asked me what I want, and are going to try to make me happy. They "think" they have a set of turfs that will fit, and they are going to bring them by to show me.

Now for my questions: What exactly do the numbers mean in my tire sizes? How do I know what else will fit on my rims? What is the deal with the front to back ratio? I gather from past posts that it is critical, but how is it measured? Is it based on diameter or circumfrence? If it is circumfrence, wouldn't it change as the tread wore down? If it is based on diameter, is my ratio 3:4 based on the tire sizes listed above?

Thank you for your vast amounts of wisdom and knowledge.

Chris in SW Va.

 

[Kelvin]

Chris,

All I can say is good luck.

I also have a B7100 (1979?) 4wd. I wanted a set of turf tires in addition to my Ag tires. As with most Kubota tractors (and probably all makes of tractors) the 4wd turf tire rims are a different size from the 4wd Ag tire rims. Note that for Ag tires the 6-12 size is used on a lot of different Kubota tractors (it is also used on my B2150) so I would think that they would be reasonably priced.

One key bit of information that you need to know is that the newer B7100s use a 6 lug front wheel where the older models like yours use a 4-lug front wheel. Thus you need to be careful if you find a good deal on B7100 wheels.

I found a used set of turf tires & rims (with 4-lug front wheels) to fit my B7100 for around $250. They came with 20.0x8.00-10 tires on the front where the B7100 manual calls for 20.5x8.00-10 on the front (and 29x12.00-15 on the rear). Only problem is that nobody makes the 20.5x8.00-10 tire anymore and I was getting some binding while using 4wd with the smaller tire. So I tried a set of 21.0x8.00-10 tires (which is the tire size used on the B7100's replacement, the B7300) and am pleased with this setup.

Somewhere awhile back I posted a lot of information on this subject as I was searching for the tires.

I was told that you could special order a set of turf tires and rims from Japan for around $1000 or so. If that information is accurate then I would stay with the older tires or go all the way to the new turf tires/rims if I were in your shoes.

Hope this helps,
Kelvin

 

[WVBill]

Chris:

I was in a very similar situation last year. My Father in law gave me his 1978 B6100 with Ag front and rear. Part of the deal was he made me promise to replace the ag's with wider tires to improve the stability of the tractor. He was very concerned because he had tipped it over one time years ago.

So, like you, I began a quest of research to find a set of R-3's or R-4's that would fit. Yeah, right!

What with front-to-back rations, rim sizes, etc. it was getting to be an impossible task - or one that would cost big bucks - as you found out.

Here's what I ended up doing. I had figured out what the ratio on my tractor is, and by researching the tire manufacturers on the web, determined the rolling circumference of my 6-12 front and 7-16 rear Ags. That allowed me to search for R-3/4 tire sizes that had the same rolling circumference.

That done, I sat down with my Kubota dealer and he found that he had a pair of nearly new rear R-3's of the right size on rims that matched my tractor. Could not find fronts to match.

Sooo... for about $300 I now have a "schitzo" tractor: Ags on the front and big ole' wide turfs on the back. I find it a pretty good combination actually. I normally run around in 2WD and the fronts don't cause any damage to my grass. When I need traction that the turfs can't handle, I pick up a load of dirt in the FEL, drop it into 4wd and those front Ags dig in and provide just the added pull needed.

To answer your specific questions go to http://www.firestoneag.com/products for some good detailed info.
Your Kubota dealer should be able to tell you what the ratio is for your tractor. Or you can measure it by putting a mark on your front and rear tires and counting the number of revolutions the front one makes for each rear one (do this many times and take the average). It is based on tire circumference. It will change as the tread wears but it will still be within the limits.