Diesel Locomotive Wheel Arrangements

Diesel locomotive wheels are typically described by the number of powered and unpowered axles per truck. For example, a GP9 has 2 trucks, each having 2 axles and 2 traction motors. Thus, a GP9 is designated Bo-Bo, where the 'o' means no unpowered axles. Usually the o's are left off, leaving the more common designation B-B.

Powered Axles	Unpowered Axles
A=1, B=2, C=3, D=4	o = 0, 1 = 1

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An EMD E-unit or ALCO PA has 3 axles per truck, the center axle without a motor. These are designated A1A-A1A.
The most common of B-B's, the Blomberg, basically unchanged since 1939!

EMD's DDA40X trucks each had 4 axles and 4 tractions motors. It is designated D-D.
EMD's Flexicoil truck with three powered axles is a C-C.

EMD's low-friction radial truck.
GE's high-traction HTTC truck.

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This page last updated 7/4/2001

An EMD E-unit or ALCO PA has 3 axles per truck, the center axle without a motor. These are designated A1A-A1A.	The most common of B-B's, the Blomberg, basically unchanged since 1939!
EMD's DDA40X trucks each had 4 axles and 4 tractions motors. It is designated D-D.	EMD's Flexicoil truck with three powered axles is a C-C.
EMD's low-friction radial truck.	GE's high-traction HTTC truck.