Tire and wheel options for the 7100, doing my homework

[lsmurphy]

FWIW-

I increased RC on both front and rear and mine is noticeably more smooth than before. No binding what so ever.

 

[Sterno]

The old tires didn't bind but the fronts did seem to pull a bit hard.
Originals were Bridgestone 6-12 front and 7-16 rear.

I think I may have found the problem, there are some differences in the tooth counts of the gears on the 2nd and reverse shafts inside the transmission. As it looks like the front driveshaft runs off the front of the reverse shaft, a change in ratios inside the trans will cause a change in front/rear ratio.
It's late and I'm going to try to figure out the ratio for the B6100 tomorrow.

So beware y'all. The B6100 and B7100 transmissions are NOT identical and the 1.464 ratio apparently only applies to the B7100!

 

[Sterno]

Just couldn't let it be....

The 4wd gear pair on a 7100 is a 16/24 set whereas a 6100 uses a 15/25 set

So
15 divided by 25 = 0.6 and
16 divided by 24 = 0.6667

0.6667 divided by 0.6 = 1.111

Now if we take the 1.464 ratio from a 7100 and divide by 1.111 we get a ratio of 1.317.
This makes sense when I look at the original tires which were 90RC rear and 69.5 RC front (90/69.5=1.295)

..... anyone in the market for a pair of 8-16 tires, less than 50 yards travelled on 'em?

 

[lsmurphy]

You increased the rear by 10" RC and not the front.

 

[Steve NC]

I see that this an older thread but it looks like a good place to start. I have 1982 B7100D (gear drive). My rear turf tires are getting in foul shape and will soon replacing. A friend of mine that worked for a local dealership picked up a set of turfs off of a newer B series tractor(tires only) They are titans 31x13.50 r15. My tractor currently has 29x12.50 r15 on it now. I am still running the original front turf tires. Has anyone tried using this size on a B7100? If so, did they cause any clearance problems or problems with the 4wd?

 

[Bulldog]

I don't know about clearance issues but with any 4wd if you increase the rear tire size you have to do the front as well. So yes, it would create a 4wd problem.

 

[ShaunRH]

If you want to go with something akin to your turfs, with a little more traction, you might go this route:

http://www.summitracing.com/parts/sum-85-5883 or http://www.summitracing.com/parts/crr-3425764p/overview/

http://www.ebay.com/itm/Kenda-Kleve...s_Car_Truck_Tires&hash=item259694bf88&vxp=mtr

I have no idea if the bolt pattern is correct, you'd have to measure that, but the other 7100 shown has a six lug pattern, so I just picked that one.

Mathmatically, the RC of a 235/75r15 should closely match your current 29" diameter tire.

235 x 0.75 = 176.25
176.25 = 6.938"
6.938 x 2 + 15 = 28.876"

Now that's all the math fit to print but it doesn't mean that it will be perfect. And those are mud tires, not AG tires so traction won't be the same but they should roll on grass nicely.

So $350 might get you a set of new rear tires.

Then again, I have no idea if you are trying to stay with turf or switch to AG.

 

[Steve NC]

Thanks for the replies guys, I thought about it afterward and realized I left out some details. I am trying to stay with turfs on these rims, I have a set of ag tires and rims for this tractor as well. One of the benefits of growing up next door to my uncle's dealership when this tractor was bought new. My family sold Kubotas during the late 70s to the mid 80s. The tread is about worn off the tires and I'm just looking for replacements. The tires I described in my earlier post are at the local dealership where my friend works. They are used and I can get them for $20 a piece. I have only seen pictures of them and haven't been over there to see them in person yet. For the price, I figured they are worth a look and would be great if they worked. I was hoping since both numbers are larger on the tire (height and width) that they would cancel out each other and I would get about the same RC to keep the 4wd from causing problems. I rarely use 4wd when these tires are on the tractor. It spends the majority of its time cutting grass with a woods rm59.

 

[OldeEnglish]

I put some new turfs on my b7100 last month, got them off of eBay. The rears are a Carlisle multi track 10 ply $490 shipped. The fronts are a Kenda load star 10 ply $120 shipped. It wasn't much extra money for the 10 ply, hopefully they won't get punctured this summer with all of the bush hogging I need to do!

 

[Cr555]

Very interesting discussion. What I have learned so far:

1) With a MFWD tractor, it is important to match the front and rear tires to maintain the proper lead/lag ratio between the front and rear tires, i.e., the front tires should lead the rear tires by 1 - 5 percent. Any lag is BAD. 1-2 percent lead is ideal.

2) Some advocate decreasing tire pressure to compensate for slightly oversize tires. From what I have been able to glean from elsewhere, changing tire pressure doesn't have much effect on the rolling circumference of a tire. See the link below:

https://www.youtube.com/watch?v=_2l5bOhHNxU

3) The lead/lag relationship become more critical when operating on pavement (basically, always shift into 2WD when on pavement), and when using your FEL (added weight on front end magnifies the stress on the drivetrain if lead/lag is not correct).

4) Decreasing the rear tire size (w/o changing the front), or increasing the front tire size (w/o changiing the rear) increases front wheel lead. Increasing the rear tire size, or decreasing the front tire size decreases front wheel lead (and may create a "lag" condition).

5) Kubota never makes it easy to determine your tractor's inter axle ratio.

6) I'm going to use 2WD except when I really, really, really need 4WD.

 

[Cr555]

I had some difficulty confirming the technical specs for the Firestone Turf and Field tires that came with my Kubota (B7300 & B1750). Attached are the Firestone spec sheets for anyone interested. I am also trying to confrm the inter axle ratios for both the B7300 and B1750 (hopefully Kubota USA will respond -- no luck at my dealer).