Bobtail testing data published in the literature are limited and the difference in deceleration of a bobtail configuration compared to a tractor-trailer has not been fully evaluated in the past. The authors seek to increment and update previous research on the topic.
This paper presents detailed braking characteristic information obtained from full scale instrumented testing of a bobtail vehicle at various speeds. Brake timing is analyzed for the tested condition to determine the overall braking characteristics. The findings of this study are compared to 1) other testing performed with the same tractor configured with a trailer at different loading conditions and 2) to results published in literature for both bobtail vehicles and other loading conditions for both 6×4 and 4×2 tractor axle configurations.
The brake timing data were collected during several days of full scale instrumented testing of a tractor and semitrailer performed at the Transportation Research Center in East Liberty, Ohio. Instrumented braking tests were performed at two speeds of 13.4 m/s (30 mph) and 27 m/s (60 mph) for the three configurations discussed in this paper including a bobtail condition, an unloaded semitrailer configuration and a full gross weight semitrailer condition. These straight-line braking tests were performed on dry concrete surfaces.