Adding taller tires to JD 850

[Arkaybee]

My JD 850 needs a bit more ground clearance in order to straddle some raised beds while cultivating.
My thoughts are to change out the wheels/tires to larger diameter ones.

I am sure the relative sizes of the front and rear wheels/tires have to be maintained as they are now.

The thing that concerns me is the increased ground speed that would result from adding the larger
diameter wheels/tires.

I don't know, yet, what size the new wheels should be to give acceptable clearance.
Anyone have any suggestions?

Would it be necessary to change any of the transmission gearing to prevent too much speed?

How does one calculate the ground speed of a larger set of wheels?

The JD850 has 11.2-24 rear tires and has 8 forward speeds (four in Hi (3.8, 5.4, 8.0, 11.7 mph and
Low= 0.8, 1.1, 1.7, 2.5 mph). It might not be a problem since the first gear is rather slow but one does not want too much speed when carefully hipping rows of flowers and ornamentals (which is what I will be doing.

The tractor manual states a 17.0 % slower speed for the rear tire size of 13.6-16.

I assume that this tire is 50% smaller diameter (16" vs 24").

Is it a fair assumption to assume a similar increase in ground speed if the diameter was increased another 50% (e.g. to 30" or 36")?

Presently I hip each row from one side at a time because the flowers on top of the raised beds get abused by the bottom of the tractor when I straddle each row. However, I think I could do a better job with fewer passes and less soil compaction if I could straddle the row and hip both sides at once.

Thanks for your insight and for sharing your experience.

 

[Zebrafive]

The 16" and 24" is the wheel size. Not tire size. So not 50% smaller. I'll bet if you compared the actual radius of the two there would be a 17% difference, since that's what the manual quote for a speed difference.
If you change to 20% taller, in theory it should be 20% faster........if it can pull the taller tire.
Do you have 4 wheel drive? That would determine the ratio front to rear you have to maintain. You can't add the same increase in diameter to both front and rear (unless you are talking percent change)

 

[sixdogs]

Look up "rolling circumference" in the tire sales catalogs. Do the math on the tires you have and then an algebraic formula since you know the speed and circumference of the first tire and the circumference of the second tire. Piece of cake once you do it the first time and you have their given examples for comparison.

Now, if you have 4WD is sort of game over because you will need to have a ratio between the front and rear so the front pulls the rear by a few percent. You will have to find the right circumference front to match. If you are 2WD forget about this.

Bigger tires would indeed change your ground speed but probably not enough to matter. Those little JD's with a 4 x 2 trans are pretty slow In 1st gear.

You can find nearly any size tire or wheel. I once had 9.5's x 42 on the rear of a cultivator tractor. It was so tall I got a little scared in certain situations.

 

[Arkaybee]

Zebrafive;[/B]3499562]The 16" and 24" is the wheel size. Not tire size. So not 50% smaller. I'll bet if you compared the actual radius of the two there would be a 17% difference, since that's what the manual quote for a speed difference.
If you change to 20% taller, in theory it should be 20% faster........if it can pull the taller tire.
Do you have 4 wheel drive? That would determine the ratio front to rear you have to maintain. You can't add the same increase in diameter to both front and rear (unless you are talking percent change)

Thanks for the feedback; I will look into what you suggest and report back later.

The tractor is 2-wheel drive.

Arkaybee

 

[Arkaybee]

Look up "rolling circumference" in the tire sales catalogs. Do the math on the tires you have and then an algebraic formula since you know the speed and circumference of the first tire and the circumference of the second tire. Piece of cake once you do it the first time and you have their given examples for comparison.

Now, if you have 4WD is sort of game over because you will need to have a ratio between the front and rear so the front pulls the rear by a few percent. You will have to find the right circumference front to match. If you are 2WD forget about this.

Bigger tires would indeed change your ground speed but probably not enough to matter. Those little JD's with a 4 x 2 trans are pretty slow In 1st gear.

You can find nearly any size tire or wheel. I once had 9.5's x 42 on the rear of a cultivator tractor. It was so tall I got a little scared in certain situations.

sixdogs:

Thanks for your input. I will do some of the math you suggest and see what it looks like.

The little JD 850 is 2-wheel drive only and as you said 1st gears in low range is 0.8 mph= pretty slow, so the ground speed might be within needed range to work with much taller wheels/tires.

Your help is appreciated.

Arkaybee

 

[BATTY54]

Have you seen the John Deere cultivator model 900HC? Not sure what wheels and tires it uses or if the axels are made different.

 

[sixdogs]

Have you seen the John Deere cultivator model 900HC? Not sure what wheels and tires it uses or if the axels are made different.

Rears are 28" but the Deere 950 tractor is built higher. Here's a Case-IH 265 I used to own.

http://www.tractorhouse.com/listingsdetail/detail.aspx?OHID=7561123

Tractor built higher but has 42" rear wheels. Was scary high.

 

[Arkaybee]

Rears are 28" but the Deere 950 tractor is built higher. Here's a Case-IH 265 I used to own.

http://www.tractorhouse.com/listingsdetail/detail.aspx?OHID=7561123

Tractor built higher but has 42" rear wheels. Was scary high.

SIXDOGS

Wish I could try one of those Case-IH 265 machines. It might be a great cultivator machine.

Arkaybee

 

[Arkaybee]

Have you seen the John Deere cultivator model 900HC? Not sure what wheels and tires it uses or if the axels are made different.

BATTY54

Many times I have wished I had bought one of those JD 900HC tractors. I got such a good deal on the 850 that I chose it. Plus, there weren't any of the JD 900HC's around although a local dealer did have a used one for sale a few years afterward.

Arkaybee

 

[sixdogs]

SIXDOGS

Wish I could try one of those Case-IH 265 machines. It might be a great cultivator machine.

Arkaybee

It was intended for ginsing and I bought it out of Wisconsin. It would make a great cultivating machine but a better parade vehicle.
It was just too high for my intended purpose so I sold in and am surprised to see it again.