Spicer Tire Matching Guidelines and Calculations - Manual (Page 2)

TIRE MISMATCH CALCULATION
Dmax – Dmin Dmax = Larger Average Tire Circumference
Dmin X 100% = Tire Mismatch Dmin = Smaller Average Tire Circumference
SAMPLE TIRE MISMATCH CALCULATION
TIRE
LOCATION
YOUR TIRE
CIRCUMFERENCE
(IN INCHES) NOTE 1
FORMULA
REFERENCE
LETTERS
LEFT – OUTER
LEFT – INNER
40.86
40.90 LO
LI
FORWARD
AXLE
RIGHT – OUTER
RIGHT - INNER
40.62
40.56 RO
RI
LEFT – OUTER
LEFT – INNER
40.25
40.12 LO
LI
REAR
AXLE
RIGHT - OUTER
RIGHT – INNER
40.38
40.19 RO
RI
(FORWARD AXLE – Side to Side) Mismatch Calculation %
(LO + LI) divided by 2 (40.86 + 40.90 = 81.76 divided by 2 = 40.88) which = Dmax dimension
(RO+ RI) divided by 2
(40.62 + 40.56 = 81.18 divided by 2 = 40.59) which = Dmin dimension
% Mismatch =
40.88 – 40.59
40.59 X 100 = .71 %
(REAR AXLE – Side to Side) Mismatch Calculation %
(LO + LI) divided by 2 (40.25 + 40.12 = 80.37 divided by 2 = 40.18) which = Dmin dimension
(RO+ RI) divided by 2
(40.38 + 40.19 = 80.56 divided by 2 = 40.28) which = Dmax dimension
% Mismatch =
40.28 – 40.18
40.18 X 100 = .25 %
(FORWARD AXLE to REAR AXLE) Mismatch Calculation %
FORWARD AXLE = 40.86 + 40.90 + 40.62 + 40.56
4 = 40.73 Avg
REAR AXLE = 40.25 + 40.12 + 40.38 + 40.19
4 = 40.23 Avg
The % of Tandem Mismatch = 40.73 – 40.23
40.23 X 100 = 1.24 %
1.24 % is below the recommended 1.25 % mismatch, and therefore acceptable.
NOTE 1: These measurements are examples only. Reference the front page of this
bulletin for methods on how to obtain your tire measurements.