Rolling resistance measurements on the 1.7m roadwheel and Clayton twin roll simulator, and outdoor fuel consumption and coastdown tests were compared for tires specially formulated to illustrate differences. Twin roll results correlated poorly with the other tests, especially for grouped radial and bias tires. Thermal analysis showed that the twin roll test accentuates the tread region more than the 1.7m test. Equations including tire type, tread hysteresis and sidewall hysteresis correlate twin roll results well with the other tests. Twin roll rolling resistance specifications may not result in minimum fuel consumption if these factors are not considered.