Adding tractor tire fluids to tires can negatively impact your tractor’s ride quality, especially when loading the rear tires, according to John Deere. If your tires are bigger than stock you probably, like myself, have spend a lot of time trying to WAG (wild ass guess) your actual MPH when going down the road. Converting tire sizes to reduce compaction can help by reducing ground pressure from your equipment. Tire manufacturers should provide their tires’ rolling circumference (RC) or the RC Index (RCI) values in their published product data to allow growers to calculate the right size tire fitment from front to rear for their equipment to ensure the right amount of positive slippage or pulling power for the given gear ratio. Summary: When wheel/tire conversions are needed or wanted, you need to consider the best options that will help accomplish your goals. You get it de-mounted. The next higher RCI is always ~5.4% higher (+/- .2 % Tolerance), which means a factor of ~1.054. MFWD tractors are 4-wheel drive vehicles with different sizes of tires on the front and the rear. Although many radial sizes match the bias sizes in a conversion, there are instances where they don’t. The index is a grouping of tires that are all within about 4 inches of each other in outer diameter (OD). The tire circumference difference can theoretically be calculated by the RCIs or the RCI difference: For example, if the transmission ratio is 1.27 and the tire circumference ratio is 1.30, this would mean 2.36% lead for all tire combinations with 5 RCIs difference (1.30/1.27 = 1.0236) on this machine. Compaction: If a farmer determines that compaction is limiting his ability to produce the highest yields and quality, an assessment needs to occur to identify the cause of the compaction. Search × Search × Main Menu; Company . In order to provide solutions that are flexible to an evolving global market, the equipment manufacturers or OEMs offer their machinery with tires of different diameters or widths for the same machine to adapt their equipment to the specific needs of that grower or crop. If you look in the Michelin data book, however, not all tires have a published RCI. If the tractor is mainly used for field work, lead percentage may be chosen on the upper tolerance of the permitted tolerance band, as little higher lead values allow sharper field end turning with engaged MFWD compared to lower lead values. The thing that the end user needs to consider is the gear ratio of the tractor and the lead/lag ratio. In this situation, a person may have to change wheels and tires when converting to radial tires. If so, be sure the investment will pay out over the normal operations and normal conditions that you will be farming in. From the manual, obtain the rolling circumference of the tire desired for the rear wheel. For four-wheel drive tractors, dual tires increased the pull/weight ratio at a given slip level when compared to singles. Traction: If you have trouble pulling implements in high torque applications, grain carts or any other application with a reasonable amount of slip you may need to increase your traction. This balance is the tractor gear ratio also known as, “the lead or lag ratio”. Front: 9.5-20 (6PR), Rear 13.6-28 (6PR) U60. For the front tires to pull successfully and produce the right amount of pulling power with the right “slip” to stay within the tractor gear ratio, the proper tire slip needs to be between 1% to 5% = “positive slip”. Ag practices around the world differ based on crops grown, soil conditions, moisture content and environmental conditions. This tractor was manufactured by the Kubota from 1998 to 2000. Typically, a farmer wants to produce the highest yield with the best quality at the least cost of production. Michelin Ag More torque can be sent to the wheels in first gear than in fifth gear because first gear has a larger gear-ratio by which to multiply the torque. If you put a plug through the outside it seals the outside, but doesn’t necessarily seal the inside. They look cool and have the potential of being very functional, but they may also be robbing you of power/gas mileage. 3) RCI spread – Not all tire sizes can be assigned to specific RCI group (remember the -0.2 to +0.2 spread of RCI) and some will fall outside this spread. The tractor was taken off road and placed in 4WD. The smaller front tires must travel faster to stay in the same ratio or time that the larger rear tires travel as they roll. Scott Sloan: Ag Product Manager / Global LSW. order to select the tires that will adequately match the tractor’s front-to-rear gear ratio. For a tire size to be considered within a specific RCI, the calculated RCI of the tire must be between -0.2 to +0.2 of the RCI for that group. All information is provided in this blog solely to provoke thought. 4WD front tires must be properly matched to the rear tires (0 percent to 5 percent overrun) to prevent excessive front-tire wear, unnecessary powertrain loads, and overall poor tractor performance. Using the chart, first cross reference your current gear ratio and tire diameter to find your approximate RPM at 65 MPH. On some surfaces you may find that the front tires are dragging the rears, and on other surfaces that the rears are push-sliding the fronts. By Joel L Nicoll in forum New Holland Owning/Operating, Family and Friends (Announcements & Notices), Changing tire size on a four wheel drive tractor, Trying to understand tire size and ratios, Tire pressure and front wheel drive lever for YM1601D. For instance, are you operating at the optimal inflation pressure? The rear tire is considered a group 48 RCI and the front is considered a group 43 RCI. This is the method I used. Even the data from the same tire manufacturer may vary for the same tire size, if multiple tire lines exist or if there are tires with different load indexes within the same tire line. What do a lot of people do? Using the above equation and the RCI data, as well as the OEM tractor gear ratio, any grower can quickly determine if their equipment will allow switching or evolving to larger tires without compromising their required gear ratio slip rate percentage. Also be sure you understand the air pressure requirements at different operating loads and speeds and determine if you are going to be able or willing to make changes on air in the field. We recommend the check to confirm the lead and acceptable technical data for each tire change individually. Michelin does not publish RCI for all tires because some tires may fall within a grey area, meaning depending on the load and inflation pressure, these tires will fall within one of two RCI numbers. Switching from bias tires to radial tires would be a smart move in the right circumstances. Front: 11.5-20 (6PR), Rear 14.9-28 … See the following calculation: It is very important you keep this in mind when are converting one size of tire to another, or in some cases, even between tire manufacturers. Tire/wheel conversions for traction reasons is not very common since these conversions would likely be to a narrower tire that will increase traction but also increases ground pressure along with compaction potential. 120 pounds is a common weight used per engine horsepower. The Kubota L2500 compact utility tractor used the Kubota D1403 diesel engine. If the front tires OD are increased without and change to the rear the tractor will have a higher over travel, which means the tires will be spinning too fast causing faster wear and potential issues with the tractor not disengaging from the front wheel assist without some work. So, the tire always has to be de-mounted from the rim for a proper repair. So how do we find the new set of tires and keep the proper front/rear tire gear ratio required by the tractor manufacturer? On the other hand, in the case of utility and compact tractors moving away from an Ag bar design to and industrial lug design, both of these are fairly common. Your email address will not be published. One of my favorite up-fitment examples for a very popular tractor setup is switching out 480/80R50 and 380/80R38 sets to VF480/95R50 and VF380/95R38 sets. Wheels will have to be changed because of the sizes and widths of the tires used. This is the method I used. Well, the patch doesn’t work either, not by itself. However, with front wheel drive tractors (MFWD) the relationship between the front and the rear axle, called interaxle ratio, must be maintained in order to have the best traction performance and to avoid transmission issues. A general recommendation is a 60-40% split, with 60% of the weight in the front. One of the key tools that is used to adapt or convert tires from crop to crop or grower to grower is the RCI or rolling circumference index. The transmission must be geared so that both fronts and rears turn at basically the same speed, since the fronts will turn more revolutions. In other words, the front tires will turn more times as the tractors moves forward for every rear tire full revolution. Because of the increased air pressures and load carrying capacities of IF/VF tires, it would be wise to check the standard wheels being used. An example is the 480/80R50 rear and 380/80R38 combination on MFWD. Greg W. Gilland: Business Development & Ag Segment Manager. Does anyone know of any restrictions on size, i.e., circumference? For some select large Deere tractors, you can look at the frame for indicator: In the case of a 4-Step Tractor, you simply select a RCI 48 Rear and matching RCI 44 Front. If you are looking for narrower options, simply move to the left of the RCI 48 480/80R50 for rear tire options, then move to the left of RCI 43 420/85R34 for front tire options. If you need assistance with this, all Michelin Ag reps are equipped with the tools and knowledge to walk you through this. The rolling circumference is the distance in inches that a tire travels in one revolution. If you are working with the Rolling Circumference Index group system, most MFWD tractors need to have fronts and rears that are 5 steps apart in the RCI, like a 50 Group in the rear and a 45 Group for the fronts. What is important when selecting different tire sizes is that the difference between the rear tire RCI and the front tire RCI is the same as the tires being replaced. Use our lead/lag calculator to make sure you have the right tires for the job at the right ratio. Tire Rack has offered a tire shaving service that has been primarily used for preparing competition tires for racetrack use. A yellow crayon mark was placed on the top of the tires for easy revolution counting while driving. https://www.titan-intl.com/en/resources/Lead-Lag-Calculator. Smaller tires on a steering axle would allow for sharper steering angles. The next higher RCI is always ~5.4% higher (+/- .2 % Tolerance), which means a factor of ~1.054.”, ALLIANCE, “If you are working with the Rolling Circumference Index group system, most MFWD tractors need to have fronts and rears that are 5 steps apart in the RCI, like a 50 Group in the rear and a 45 Group for the fronts.”, MAXAM, “If you have too much positive slip ratio (above 5%) you will have “excessive” work by the front tires pulling the rear tires equates to a loss of efficiency and higher fuel consumption. Keep in mind that when changing tire sizes on front wheel assist tractors you need to maintain your lead/lag ratios to enable the tractor to operate mechanically within the design parameters. This is the value referred to by some OEMs when they mention that the ratio between the front and rear axles is 5 steps. Select tires with suitable load-bearing capability. If converting to these higher technology type of tires does not satisfy ground pressure reduction goals then you may opt for a wheel/tire conversion to tires with a larger air chamber. What the RCI difference is between the front and rear axle, as this should be kept constant. When selecting tires for your MFWD tractors, you want to make sure to maintain the proper ratio of rolling circumference for your tractor. Well, a 480/80R50 Michelin Agribib 2 has an RCI of 43, therefore it will match several front sizes that have an RCI of 43 (13.6R38, 420/85R34, 380/80R38, etc.) The difference in those two groups is 5. Overall tractor weight . If you measure the circumference of the front tire and then the difference you should be able to calculate the % lead of the front axle. Tire Combination Guidelines, Up To 40 km/h (25 mph) The size ratio of front wheels to rear wheels must produce a 1 % to 6 % on tractors with PowrQuad and PowrQuad PLUS transmissions. OEM engineers physically test each tire combination using the correct inflation pressure for the load before they release these tire combinations and offer them for sale. Lift the tractor off of the ground and mark both the front and the rear tires. Tyre size. If you have a “negative” slip result, the front tires will experience a braking effect that creates a loss of pulling power, more fuel consumption and reduced steering capability. Performance of a 4WD tractor can be optimized by controlling the power distribu- tion between the front and rear axles. As a rule, the “ideal” tractor gear ratio between the front axle and the rear axle (IAR or Inter-Axle Ration) ranges from 1.2 to 1.5. There is not a tire combination that is a “one size fits all” situation and often different operations would require different sets of tires for the same equipment. Inch-Wide rows identify sizes in a conversion, there are no issues closer your... 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