4WD B7100 mismatched tires

[Eise]

I only got my B7100 recently, and it came with turf tires. Now one of the front tires is flat, the rubber is badly cracked too.. so I need new front tires. Now I've been looking into which tires I need, and I figured out that the current tires are mismatched.

The turf tires the manual says you need to use are 20.5X8.00-10 on the front and 29X12.00-15 on the back. This would mean I need to get new rims and tires on the front and back, this isn't really an option budget wise. The tires on the back are 9.00-16 Continental turf tires and are still in good condition, now I want to figure out if there are tires for the 12" front rims that would give the right ratio.

The rolling circumference for the back (29X12.00-15) is 2180mm (~86") and 1536mm (~60") on the front (20.5X8.00-10). That's a ratio of 1.42, as long as I stick to that same ratio it should be fine, right?

 

[Eise]

Another thing I'm running into is that I can't find specs for the 9.00-16 rear tires, is there a way to get a good calculation for the rolling circumference?

 

[100 td]

This could be like a "which oil thread"!
Park on concrete, measure from ground to top of rim, measure rim diameter, take half of rim diameter from first height. Multiply x 2 then result by 3.14159

 

[Eise]

Hi, thanks. I just did the measurement and calculation and got 2607mm (~102.6", sorry.. I'm a metric guy) Divided bij 1.42 that makes 1835mm (~72.2") to look for in the front tires.

I did some looking around and that's not gonna be easy to find..

Closest I could find are some 6.00-12 tires, but the manufacturer doesn't specify the rolling circumference. (I've attached the datasheet) If I try to approximate the RC I get 1767mm (~69.6") which is 3.7% off.

 

[Eise]

Looking into this some more, I think that combination would give a 0.23% lag. Now I know this is not ideal, but I don't think it will be a disaster either. It should be an improvement over what was on it anyway, which I calculated must have been a 7.7% lag.

6.50-12 tires would be ideal, but those don't seem to exist.

Would a 0.23% lag cause damage to the gearing? I know it will affect the handling some, but I can live with that I think.

 

[85Hokie]

Looking into this some more, I think that combination would give a 0.23% lag. Now I know this is not ideal, but I don't think it will be a disaster either. It should be an improvement over what was on it anyway, which I calculated must have been a 7.7% lag.

6.50-12 tires would be ideal, but those don't seem to exist.

Would a 0.23% lag cause damage to the gearing? I know it will affect the handling some, but I can live with that I think.

I truly do not believe that ANY 4wd engagement is 0.0% lag or push!!!!

If a machine was in 4wd on concrete all its life, the TIRES would wear to a pattern that would place it close to 0% ....but that will not be a good thing!

The real solve for this is : get tires that are very close.....but more importantly.......DONT use 4wd if the surface will NOT allow for some slip!!!

I cut grass on the side of hills ....in 4wd all the time.....if I get on the street to move a good bit, I take it back to 2wd.

SO if you have places that will allow a little push/pull with the new tires, you will be fine.

 

[Eise]

I truly do not believe that ANY 4wd engagement is 0.0% lag or push!!!!

If a machine was in 4wd on concrete all its life, the TIRES would wear to a pattern that would place it close to 0% ....but that will not be a good thing!

The real solve for this is : get tires that are very close.....but more importantly.......DONT use 4wd if the surface will NOT allow for some slip!!!

I cut grass on the side of hills ....in 4wd all the time.....if I get on the street to move a good bit, I take it back to 2wd.

SO if you have places that will allow a little push/pull with the new tires, you will be fine.

Thanks! I wouldn't dream of engaging the 4WD on a paved surface, it will be used in the pasture mostly, which is very level (as is almost everywhere here in The Netherlands ) so even then it will probably be in 2WD a lot of the time.

I think this combination of 9.00-16 in the back and 6.00-12 in the front will have to do untill I have the budget to get some new (wider) rims with proper tires.

 

[North Idaho Wolfman]

What was the size of the front tire that were on it that your replacing?

 

[Eise]

It had 155/75 R12 'Vredestein' car tires in the front.

 

[North Idaho Wolfman]

You could still stay with a "car" tire if you like.
They look like they are about the right size to get the job done.

I use truck tires on the rear of my B7100 and they work incredibly well!

 

[Eise]

Truck tires aren't a bad idea! The 6.00-12 tires I'm getting are 'car' tires, I don't know why the sizing format is different though (maybe they are meant for classic cars).. but they are closer to the right RC than the next regular 'car' tire size at 155/80 R12.

 

[Firefighterontheside]

I don’t know much about it, but I’ve read numerous times that it is good for the front tires to overdrive the rears by a little. Is the bit you’re off over or under on the front compared to the back with the tires you’ve found?

 

[Eise]

I don’t know much about it, but I’ve read numerous times that it is good for the front tires to overdrive the rears by a little. Is the bit you’re off over or under on the front compared to the back with the tires you’ve found?

It's a minute amount under, which I know is not ideal. But it's the best I can do without changing all the tires. (As I said it used to be a substantial amount under)