How to speed match DCC locomotives

Step by step

1. 01

   Step 1: Pick a reference loco

   Choose a smooth runner as the standard and set its curve first. Matching everything to one loco is easier than chasing a number.

   Next: step 2
2. 02

   Step 2: Set the starting speed (CV2)

   Set the throttle to speed step 1. Raise CV2 (Vstart) until the loco just moves smoothly, without lurching. CV2 sets the motor drive at step 1 (NMRA S-9.2.2).

   Next: step 3
3. 03

   Step 3: Set the top speed (CV5)

   At full throttle, time the loco over your measured distance and lower CV5 (Vhigh) until it reaches a sensible scale top speed. ESU's decoders use CV5 to limit maximum speed.

   Next: step 4
4. 04

   Step 4: Set the mid point (CV6)

   At half throttle, adjust CV6 (Vmid) for a sensible middle speed. Keep the order start < mid < top, as ESU advises. Some decoders only use CV6 with a three-point curve enabled.

   Next: step 5
5. 05

   Step 5: Time each loco at three throttle settings

   Pick, say, step 10, 50% and 100%. Time the reference loco, then adjust each other loco's CV2, CV6 and CV5 until its times match within a second or so.

   Next: step 6
6. 06

   Step 6: Fine-tune with trims or a speed table

   Many decoders support forward and reverse trims (CV66, CV95 – scale factor n/128) and a 28-point speed table in CV67–94, turned on by CV29 bit 4 (NMRA S-9.2.2). Use trims if a loco is faster one way than the other.

   Next: step 7
7. 07

   Step 7: Match momentum

   If locos will run together, give them similar acceleration and deceleration (CV3, CV4). The NMRA formula is CV × 0.896 s ÷ speed steps per step, but some makers use their own units – ESU's LokPilot uses value × 0.25 s from stop to full.