If the lead is very low, a tractor tends to go straight even with turned steering wheels, like it does when diff lock is engaged. What do a lot of people do? The MAXAM Ag tire catalog provides our tires’ RC, RCI and diameter specifications, to assist growers in determining any technical information necessary to support their equipment needs or potential tire size evolution. The Kubota L2500 is a 2WD (L2500F) or 4WD (L2500DT) compact utility tractor from the L series. Be careful: “close” may not be close enough, and it will be an expensive lesson. This Index is created using the tire’s Rolling Circumference (RC). We recommend the check to confirm the lead and acceptable technical data for each tire change individually. The Rolling Circumference Index (RCI) is a grouping of tires based on the rolling circumferences. You don’t need a rim change, there are normally no clearance issues, and you can lower ground pressure by up to 52%. Determine if you already have the correct size, load index and type of tread on the unit before you move to make major changes. These differences could allow, depending on the tire brand and their tolerances, the same tire size from one brand to be included in one RCI group and another brand tire to be included in a different RCI group. This is defined as a “5 Step Tractor.” The tires need to have a 5 Step difference on the RCI Chart (RCI stands for Rolling Circumference Index.) The rear tire is considered a group 48 RCI and the front is considered a group 43 RCI. 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. Most tire/wheel conversions are done to gain footprint or increase tire volume (actually, they’re both the same thing), lowering air pressure and thereby reducing compaction. To optimally exploit the four wheel drive of a tractor, the value of the front wheel lead should be between +1% and +5% (ground speed front tyres > ground speed rear tyres). The idea is as long as the rear and front RCI’s are 5 steps apart they will work on the tractor. 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. Local tire dealers are also a great resource in navigating through the appropriate options for the best fitment. For example, a front RCI 38 and rear RCI 43 (43-38=5) should have the same ratio as a front RCI 43 and rear RCI 48 (48-43=5). The torque from the engine is what moves your car. Each MFWD tractor must maintain a balance between “positive slippage” or front tires pulling, and “negative slippage” when the front tires are slower or lagging therefore resisting the push from the rear tires. There are options available to decrease your ground pressures and the best option for your operation should be investigated. Again, before you invest in new tires and rims, be sure you are already at the correct and lowest air pressure and see if moving to VF tires or perhaps just a slightly wider or taller tire on the same rim can meet your needs. By entering the published rolling circumference of the front, rear or both and the gear ratio of the tractor it will tell you the target rolling circumferences of the tires that are needed to make the combination work. The ratio between the number of revolutions in the front and rear axle is very important in a mechanical four-wheel drive (this is determined by gears in the gearbox). The tractor was taken off road and placed in 4WD. This balance is the tractor gear ratio also known as, “the lead or lag ratio”. This could change some due to the type of implements used. Maxam Tire International Example: OE allows 1.0 – 3.5% lead. 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. Replacing front tires on 4WD 1920 I need to replace the front farm tread tires on my 1995 Ford 1920 that I purchased new. The thing that the end user needs to consider is the gear ratio of the tractor and the lead/lag ratio. Equipment like sprayers (same size tires all around the equipment) or equipment with hydrostatic drive (like combines) are not affected by mandatory equivalent rolling circumference when changing tire sizes. These tractors have the same sizes of tires all the way around like a 4-wheel drive truck. MAXAM publishes in our Ag catalog both the tires rolling circumference and the tire RCI value to assist growers in ensuring the tires chosen for their equipment can operate within their MFWD gear ratio limits or needs. There are several instances where it might make sense to change or convert tire sizes and wheels on tractors. Important: whenever you change sizes on MFWD units, you must maintain the correct lead/lag by keeping in mind the RCI—the Rolling Circumference Index, which factors in the length on the ground of one full rotation and the height of the tire (don’t worry, it’s on a chart from your tire manufacturer). NOTE: In order to choose proper tire combination, MFWD clutch ratio for your tractor … U70. Each OEM publishes their recommended Gear Ratio for each model MFWD or MFWA tractor they manufacture. If you know your gear ratio and tire size you can get a fairly close idea here. One method uses the “standard” format and the other is the “metric” format. Required fields are marked *, Designed by Elegant Themes | Powered by WordPress. Titan offers an online lead/lag calculator to assist in the selection of tires. The tire RC will change (not too much) depending the inflation pressure used for the load on that specific equipment. So how do we find the new set of tires and keep the proper front/rear tire gear ratio required by the tractor manufacturer? In the instance where RCI is not available, you may need to calculate the mechanical lead. 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. If you need assistance with this, all Michelin Ag reps are equipped with the tools and knowledge to walk you through this. If you’re looking for more footprint and thinking about a larger tire, you need to be sure you won’t have too much tire— if your tires are too big, you won’t be able to gain what you want as insufficient weight will not provide full footprint at low inflation pressures. Most North American MFWD tractors have a gear ratio of approximately 1.332. Posted by James Tuschner | Mar 2, 2020 | Size Options, Uncategorized | 0 |, TRELLEBORG, “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.”, TITAN, “The tire industry has developed the RCI (Rolling Circumference Index) system based on the OD (Overall Diameter) of tires to assist manufacturers in the proper of selection of tire size combinations that will work.”, CONTINENTAL, “The Rolling Circumference Index (RCI) is a grouping of tires based on the rolling circumferences. Overall tractor weight . 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. There are many occasions when an end user is looking to change the tire set up on their tractors, such as going from narrower row crop section widths to more of a floatation configuration. 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. To continue our example of the 500 hp 4WD tractor at 60,000 pounds, this tractor should weigh around 33,000 pounds on the front axle and 27,000 pounds on the rear axle. What´s behind the RCI values? Combine conversions to a flotation setup is usually a drastic change to maximum flotation. Tyre size. 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. Each RCI group has a logical, even progression of RC where each RC is 5.4% larger than previous one. Front: 9.5-20 (6PR), Rear 13.6-28 (6PR) U60. Remember, tires are considered part of the tractor transmission. Make sure they are built to handle the higher pressures and loads these tires will carry.”, Trelleborg Wheel Systems That's the right concept....and the method that you are describing works for a 4wd car or truck or for anything where the front and rear tires are identical, inflated the same, and assuming that the loading of the front axle is the same as the rear. For a field work tractor, I would use the 3.4% option, for a tractor used often in road transport, I would choose the 1.1% lead option. Now that also leads us to another problem. 1) Tire size – Each standardized tire size has theoretical calculated dimensions called nominal values. I'm not 100% sure that your statement is correct. 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. RCI difference = 5 = 1.054 x 1.054 x1.054 x 1.054 x1.054 = 1.054 ^5 = 1.30, Old tires RCI 41 & RCI 46: (4275mm & 5550mm) = 5550 / 4275 = 1.30, New tires RCI 42 & RCI 47: (4505mm & 5850mm) = 5850 / 4505 = 1.30, Allow the Chosen Equipment to fulfill its purpose. 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. It is necessary to be very careful when changing sizes on these tractors. Most tractor manufacturers impose a mechanical lead of between 0% and 6%. If so, be sure the investment will pay out over the normal operations and normal conditions that you will be farming in. 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. Solve for your Crawl Ratio. for front tire over-speed up to 5% (consult with the tractor manufacturer for the preferred lead percentage). For example, operating in low buildings or if a lower center of gravity is required (for use on steep inclines). Select tires appropriate to the tractor's top speed. In order to be able to consider all tires (including the ones out of the RCI spread) and to assure we have correct front axle lead; we need to use the actual Rolling Circumference (RC) of both tires and the interaxle ratio for that specific tractor model for our calculations. They should both be turning at close to the same speed. You may have a situation where you have the right tires, but need a central tire inflation system (CTIS) to take advantage of them. In a Deere service recommendation sheet for tire loading, they suggest a preferred 40% volume fill for liquid ballast, but the long-standing tradition of tire loading is 75% fill , which is the maximum John Deere suggests. The purpose of this would be to increase flotation, reduce soil compaction, better comfort and! Crayon mark was placed on the top of the tractor off of the weight in the data. Business of making money ratio to maintain the correct tire air pressure Overinflation Crushes traction performance 43 RCI Overinflation traction. Online lead/lag calculator to assist in the business of making money grown, soil conditions moisture... *, Designed by Elegant Themes | Powered by WordPress OE allows 1.0 – 3.5 % and. The higher pressures and the rear and 380/80R38 sets to VF480/95R50 and VF380/95R38 sets a John... 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