Are Radial Tractor Tires Cost Effective?
James C. Frisby
Department of Agricultural Engineering, University of MissouriColumbia
When Pirelli Co. developed the first radial tractor tire in 1957, the company claimed it would develop 20 percent greater traction with less slippage at equal load than an equivalent biasply tire. (Forrest, et al. 1962) Subsequent research has confirmed that radial tires have the advantage in tractive efficiency. H. Erdal Ozkan, state extension specialist at Ohio State University, has reviewed all available research results related to field performance of tractors equipped with radial and bias ply tires.
Author  Increase in tractive efficiency for radials 
Seleznev and Kovalez (1968)  13 percent
 Bohnert and Kenady (1975)  7 percent
 Hoffman (1983)  8 to 9.5 percent
 Hausz and Akins (1980)  7 to 13 percent 
In most cases, the research was done with the same wheel slip for radial and bias tires. This may have kept the radial tires from reaching the predicted 20 percent advantage.
Drawbar pull tests were reported as follows:
Author  Wheel slip  Soil  Advantage of radial 
Forrest (1962)  less than 15 percent  Sand Loam Clay  8 percent 23 percent 21 percent 
Thaden (1962)  16 percent  —  29 percent 
Mumgaard and Rudakov (1975)  15 percent  Firm  15.5 percent 
Bohnert and Kenady (1975)  —  Tilled Sod  14.6 percent 18.8 percent 
GeeClough (1977)  20 percent  —  58 percent 
Field capacity and fuel consumption were studied:
Author  Increase in field capacity for radials  Reduction in fuel consumption for radials 
Seleznev and Kovalez (1986)  10.7 percent  13 percent
 B.F. Goodrich Co. (1981)  12.3 percent  12.8 percent
 Bohnert and Kenady (1975)  —  16.4 percent
 Hauck and Kucera (1983)  2.1 percent  6.5 to 8.1 percent
 Hausz and Akins (1980)  5 to 7 percent  6 to 10 percent 
Conditions used by investigators were not constant, and results cannot be directly compared. Radial tires, however, do seem to have the advantage in every category except purchase price. Resistance to abrasive wear seems about the same for radial and bias tires, but radial tires have much longer tread life than bias tires. Radial tires will have service life 25 to 40 percent longer than equivalent bias tires (Ozkan, 1986).
Ownership cost usually includes depreciation, interest on investment, tax, shelter and insurance. For a comparison of tires, the difference in tax, shelter and insurance cost was thought to be negligible and was omitted. The capital recovery factor was used to estimate ownership cost because it accounts for both depreciation and return on investment.
To compute annual tire ownership cost; unit tire cost; fuel cost for radial and bias tires; labor cost for radial and bias tires; and total savings per hour and hours use required to break even, use the following equations:
Equation 1.
TOC =  TP(IR (1 + IR)^{}n) (1 + IR)^{n}  1 
TOC = Tire ownership cost ($)
TP = Tire purchase price ($)
IR = Annual interest rate (decimal)
^{n} = Average service life (years)
Equation 2.
UTC = Unit cost ($/hour)
AU = Annual tire use (hours/year)
Fuel cost for radial and bias tires may be computed using Equations 3 and 4.
Equation 3.
F_{B} = Fuel cost for bias tires ($/hour)
GPH = Fuel consumption for bias tires (gallons/hour)
UFC = Unit fuel cost ($/hour)
Equation 4.
FR = Fuel cost for radial tires ($/hour)
RF = Reduction in fuel consumption for radial tires (decimal)
Labor cost for radial and bias tires may be estimated as follows:
Equation 5.
LR = Labor cost for radial tires ($/hour)
LB = Labor cost for bias tires (the assumed hourly wage rate)
IFC = Increase in field capacity for radial tires (decimal)
Total savings per hour and hours required to break even are computed as follows:
Equation 6.
NSH = (F_{B} x F_{R}) + (L_{B}  L_{R})  (UTC_{R}  UTC_{B}) 
NSH = Net savings per hour ($/hour) for radials
UTC_{R} = Unit ownership cost for radial tires ($/hour)
UTC_{B} = Unit ownership cost for bias tires ($/hour)
Equation 7.
BE = Tire use required for radial cost to break even with bias cost (hours)
TP_{R} = Tire purchase price for radial tires ($)
TP_{B} = Tire purchase price for bias tires ($)
Example calculations:
Assumed input data:
Tractor maximum PTO power = 150 hp
Tractor annual use = 625 hours
125 hours stationary (tires not used)
500 hours mobile (tires used)
Diesel fuel cost = $1/gallon
Cost for 2 radial tires = $1,500
Cost for 2 bias tires = $1,000
Expected bias tire life = 2,500 hours (5 years)
Labor cost = $5.20/hour
Increase in field capacity for radial tires = 10 percent
Expected increase in life for radial tires = 30 percent
Expected fuel saving for radial tires = 6 percent
Average interest rate = 9 percent
Fuel efficiency for tractors with bias tires = 14 hphours/gallon
Annual tire ownership cost (using Equation 1):
TOC_{B} =  1000 (0.09(1 + 0.09)^{5} ) (1 + .09)^{5}  1  = $257.09/year 
TOC_{R} =  1500 (0.09(1 + 0.09)^{5})
(1 + 0.09)^{5}  1)  = $385.64/year 
Unit tire cost (using Equation 2):
UTC_{B} =  $257.09/year
500 hours/year  = $0.51/hour 
UTC_{R} =  $385.64/year
500 hours/year  = $0.77/hour 
Fuel cost (using Equations 3 and 4):
Fuel efficiency with bias tires (given) = 14 hphours/gallon
Fuel consumption =  ____150 hp____
14 hphours/gallon  = 10.71 gallons/hour 
F_{B} = 10.71 gallons/hour x $1/gallon = $10.71/hour 
F_{R} = 10.71 (1  0.06) = $10.07/hour 
Labor cost (using Equation 5):
L_{B} = $5.20/hour
L_{R}  =  __L_{B}__ 1 + IFC  =  __5.20__ 1 + 0.10  = $4.72/hour 
Total savings per hour (using Equation 6):
NSH = (10.71  10.07) + (5.20  4.72) + (0.77 + 0.51) = $0.86/hour 
Use required to break even (using Equation 7):
BE =  1500  1000 0.86  = 581.39 hours 
_____581.39 hours_____
500 hours mobile use/year  = 1.16 years 
References
B.F. Goodrich. 1981. Power saver radials — save eight ways and then some! B.F. Goodrich Tire Division, 500 S. Main St., Akron, Ohio.
Bohnert, L.F. and T.D. Kenady. 1975. A comparative analysis of radial and bias R1 drive tractor tires. SAE Paper No. 751185.
Forrest, P.J., I.F. Reed and G.V. Constantakis. 1962. Tractive characteristics of radialply tires. Transactions of the ASAE 5(2):108115.
GeeClough, D.M. McAllister and D.W. Evernden. 1977. "Tractive performance of tractor drive tires: A comparison of radial and crossply carcass construction." Journal of Agricultural Engineering Research 22:385395.
Hauck, D.D. and H.L. Kucera. 1983. Radial tractor tires. Cooperative Extension Service, North Dakota State University, Fargo, North Dakota.
Hausz, F.C. and H. Akins. 1980. Optimizing tire/vehicle relationships for best field performance. SAE Paper No. 801021.
Hoffman, R. 1983. "Return of the traction tests." Farm Journal 107(11):1821.
Mumgaard, M. and N. Rudakov. 1975. Radial versus biasply tractor tire performance. University of Nebraska Tractor Testing, Lincoln, Nebraska.
Ozkan, H.E. and A. Yahya. 1986. Radial tires — are they economical? Paper No. 861025. American Society of Agricultural Engineers. St. Joseph, Michigan.
Seleznev, I.I. and N.M. Kovalez. 1968. "Assessment of the operating characteristics of radialply tractor tires." Soviet Rubber Technology 28(3):19691970.
Thaden, T.J. 1962. "Operating characteristics of radialply tractor tires." Transactions of the ASAE 5(2):109110.
Copyright 1999 University of Missouri
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