Measurements of dynamic friction forces at the gear tooth contact were undertaken using strain gages at the root fillets of two successive teeth . Results are presented from two gear sets over a range of speeds and loads . The results demonstrate that the friction coefficient does not appear to be significantly influenced by the sliding reversal at the pitch point , and that the friction coefficient values found are in accord with those in general use . The friction coefficient was found to increase at low sliding speeds . This agrees with the results of disc machine testing .