Tires Any disadvantage to using smaller diameter tires

   / Any disadvantage to using smaller diameter tires #1  

froggy

Veteran Member
Joined
Jul 14, 2001
Messages
1,076
Location
Cooke County, Texas
Tractor
JD4320 with TNT, electric diverter, cruise control and air suspension seat.
I will be purchasing a new tractor next year, either a TC55 or TN60/70 or possibly a JD 5320 or 5420. Was wondering what the disadvantages would be to purchasing a new tractor with smaller diameter R1 tires? For instance, instead of getting rear tires of say 16.9-28 or 16.9-30, what about ordering rears of 16.9-24? This would also call for a less wide tire in the front: 8.3-24 vs 9.5-24 or 11.2-24 in front.

The advantage I see would be a lower center of gravity for the tractor, which I believe would be a plus. Other than a lower overall weight, would there be any other disadvantages?

Thanks,

froggy
 
   / Any disadvantage to using smaller diameter tires #2  
Taller tires seem to pull better, one disadvantage of the 24's is that you lose a few inches of clearance. Tires are a customers preference, I get the biggest and widest I can because I need the clearance and flotation. I guess that is the biggest drawback, you might get stuck or hung up a lot easier then I will with the same machine.
 
   / Any disadvantage to using smaller diameter tires #3  
Froggy, because you reduce the circumference of the tire you will also lower the ground speed for any given gear and increase the torque. This might have some disadvantages for ground engaging implements. You may tend to spin your wheels easier.
 
   / Any disadvantage to using smaller diameter tires
  • Thread Starter
#4  
Robert,

Saw the R1 24s were an option and are similar in size to the R4s. I know I don't want R4s becuase of the type of land I'm loking at in Cooke County (either black clay or sandy).

The tractor I have now (an old IHC 2wd) has very tall narrow R1 tires, but I don't drive it in wet conditons. This will change when I purchased my new property and later get a 4wd one.

Thanks for your input.

Doyle
 
   / Any disadvantage to using smaller diameter tires
  • Thread Starter
#5  
Jim,

I hadn't thought of that. Another reason to go with larger tires.

Thanks,

Doyle
 
   / Any disadvantage to using smaller diameter tires #6  
You will feel the rough ground more with smaller diam tires than with larger diam.

Its the reason I didn't go with the smaller tires and a Deere 855, rather than waiting for the Deere 4300. Demo'd an 855 and was not happy with travelling across a pasture.

But your lower center of gravity may outweigh that as a disadvantage. /forums/images/graemlins/wink.gif
 
   / Any disadvantage to using smaller diameter tires #7  
froggy, while I don't think this will affect you, my NH 1920 with turf tires (which are 7 inches smaller in diameter) causes the backhoe to drag when loading/unloading on the trailer. Bill C
 
   / Any disadvantage to using smaller diameter tires #8  
froggy,
you will get the best traction from the tallest and widest tyre you can get. The amount of tire sitting on the ground on a large tyre compared to the small is very significant in regards traction. A large tyre will wear slower, and if you need weight at any time you can put more in the large tire hence more weight, with this last point i will also point out loading tyres lowers your centerer of gravity very significantly.
GO THE BIGGEST MOTHERS THEY WILL GIVE YOU. /forums/images/graemlins/wink.gif
 
   / Any disadvantage to using smaller diameter tires #9  
One thought - Just so you are working with actual differences - you should try to find the true static loaded radius and rolling circumference of the exact tires in question (from the tire mfg. web site). Sometimes there's less (or more) difference than you might guess just going by the nominal tire size. I'm not sure what specific oem tires JD or NH are using on those models - but here are the numbers for the common Titan bias R1's:

Static loaded radius / rolling circumference

16.9/24 - 24/157
14.9/28 - 24.8/163
16.9/28 - 26/170
16.9/30 - 27/176

Actually for those exact tire models it looks like the differences work out pretty close to what you'd expect in radius (which will set the ground clearance) - but that can change depending on specific tire series.
 
   / Any disadvantage to using smaller diameter tires #10  
The only advantage is the lower center of gravity and, if it is an advantage to you for some reasons, the 2" lower height.

The major disadvantage is less traction and flotation. The 26" tire will have a smaller footprint due to the different radius of curvature. You will lose 2" of ground clearance and any mounted implement will lose 2" of ground clearance. The drawbar and pto shaft will be 2" lower and the angle of an attached pto shaft on a trailed implement may change.

I wouldn't worry about the reduced ground speed, you should have enough gear choices to move up a gear if necessary, especially with a powershift. Your top road speed will be reduced by about 8% but on the other hand if you have an application where you need to go very slow you will be 8% slower.
 
 
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