Tire Combination Guidelines, Up To 40 km/h (25 mph)

The size ratio of front wheels to rear wheels must produce a front wheel lead of 1.5 % to 4 % on tractors with IVT transmission, and 1 % to 6 % with POWRQUAD Plus transmission.

causym CAUTION: Avoid personal injury and/or damage to tractor. Selecting tire sizes for an IVT equipped tractor outside recommendations below could cause tractor instability when towing implements.

NOTE: In addition to above restriction on front wheel lead, tires exceeding a static loaded radius of 856 mm (33.7 in.) are not acceptable for use on IVT tractors. See tire dealer to determine whether desired tire meets this requirement.

NOTE: In order to choose proper tire combination, MFWD clutch ratio for your tractor needs to be identified. This ratio is stored in UIC address 43 under CUSTOMIZATION, in Diagnostic Trouble Codes section.

IMPORTANT: Any time a new brand or tire size is selected, see your John Deere Dealer for recalibrating tractor controllers and radar.

Available tires are grouped by rolling circumference (RC).

Tire groups available for 7220-7520 tractors, and their target rolling circumference are shown below.

Tire Groups and Target RC
Group 39 - Front 3850 mm (151.6 in.)
Group 40 - Front 4055 mm (159.6 in.)
Group 41 - Front 4275 mm (168.3 in.)
Group 44 - Rear 5000 mm (196.9 in.)
Group 45 - Rear 5270 mm (207.5 in.)
Group 46 - Rear 5550 mm (218.5 in.)

 

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Tires of the same size but different brand name, as well as different size tires within the same RC group, may have slightly different rolling circumferences than their target values.

Therefore, it is necessary to verify front wheel lead using procedure below.

Front tire group must be five groups lower than rear tire.

This results in front/rear tire group combinations of 39/44, 40/45 and 41/46.

To verify that front/rear tire combination will produce front wheel lead within acceptable limits, proceed as follows:

1. Select tires with suitable load-bearing capabilities.

2. Select tires appropriate for tractor's top speed.

3. Obtain rolling circumference for front and rear tires from your tire dealer.

4. Use your tractor's model, transmission and MFWD clutch ratio in following chart, to find front axle-to-rear axle speed ratio needed to calculate front wheel lead.

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IMPORTANT: Observe tractor serial number breaks as stated at the bottom of chart. MFWD axles are different for each production run, and so are front-to-rear axle speed ratios (AR).

Model/Transmission MFWD Clutch Ratio Front Axle-to-Rear Axle Speed Ratio (AR)
7220 & 7320, PowrQuad Plus Transmission 1.990
1.990
1.943		 1.317 **
1.330 +
1.363 +
7320, IVT Transmission 1.564
1.564
1.597		 1.340 **
1.354 +
1.326 +
7420 & 7520, PowrQuad Plus Transmission 1.720
1.760
1.800		 1.317 **
1.341 +
1.311 +
7420 & 7520, IVT Transmission 1.455
1.485
1.515		 1.321 **
1.348 +
1.321 +
** Tractors with Serial Number up to -RW7320R002761
+ Tractors with Serial Number starting with RW7320R002762-

 

5. Calculate front wheel lead (overspeed), using following formula:

FL = RCF x AR ÷ RCR, where:

FL = Front Wheel Lead

RCF = Rolling Circumference - Front Tire

RCR = Rolling Circumference - Rear Tire

AR = Front Axle-to-Rear Axle Speed Ratio

Resulting front wheel lead should be between 1.01 (1%) and 1.06 (6 %) for PowrQuad Plus transmission, or between 1.015 (1.5%) and 1.04 (4%) for the IVT, in order to satisfy above requirements.

SAMPLE CALCULATION:

·Tractor Model: 7320 with IVT transmission, MFWD clutch ratio of 1.597

·Group 41 front tire, 16.9R28, with RCF = 4242 mm

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·Group 46 rear tire, 20.8R38, with RCR = 5436 mm

·From the chart, front axle-to-rear axle ratio (AR) for this tractor = 1.326

·Applying formula: 4242 x 1.326 ÷ 5436 = 1.0347 (3.47 %)

· Front wheel lead (FL) is between 1.015 (1.5%) and 1.04 (4%). Tire combination is acceptable.

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