Speed Matching: Make Two Locos Run Together

Two locomotives only consist smoothly if they run at the same speed — otherwise one drags the other across the whole throttle range. Time each loco over a marked distance at three throttle settings, and this tool shows how far apart they run and the decoder CV changes that bring them into step.

Measured track distance

Mark two points on straight track and time each loco crossing them. Run each loco at the same throttle notch for its low, mid, and high pass — longer time = slower.

Pass times (seconds to cross)

Low (crawl) Mid (cruise) High (top) Master Slave

Slave’s current speed CVs

CV2 (Vstart)

CV6 (Vmid)

CV5 (Vhigh)

Read these from the slave first so the suggestions scale from its real values.

Average mismatch (low / mid / high)

—

Point	Master	Slave	Slave vs Master
Low	—	—	—
Mid	—	—	—
High	—	—	—

Set these slave CVs

CV	Current	Set to

Scale speed = measured model distance × scale ratio, over the pass time (HO = 1:87.1). Matching scales each governing CV by target speed / measured speed from the slave’s current CV, clamped 0–255 and kept monotonic (Vstart ≤ Vmid ≤ Vhigh). Motor response isn’t perfectly linear with voltage, so treat these as a strong first pass — re-measure and nudge for a tight match (back-EMF decoders match more repeatably). Program the values with the DCC CV Builder, or see Scale Speed for the scale-speed math.