diff --git a/arch/victor9k/encoder.cc b/arch/victor9k/encoder.cc
index 17c6fe68..46d177fa 100644
--- a/arch/victor9k/encoder.cc
+++ b/arch/victor9k/encoder.cc
@@ -47,8 +47,9 @@ public:
 		Victor9kEncoderProto::TrackdataProto trackdata;
 		getTrackFormat(trackdata, physicalTrack, physicalSide);
 
-		for (int sectorId : trackdata.sectors().sector())
+        for (int i = 0; i < trackdata.sector_range().sector_count(); i++)
         {
+            int sectorId = trackdata.sector_range().start_sector() + i;
 			const auto& sector = image.get(physicalTrack, physicalSide, sectorId);
 			if (sector)
 				sectors.push_back(sector);
@@ -63,8 +64,9 @@ public:
 		Victor9kEncoderProto::TrackdataProto trackdata;
 		getTrackFormat(trackdata, physicalTrack, physicalSide);
 
-        std::vector<bool> bits(trackdata.bits_per_revolution());
-        unsigned clockRateUs = 166666.0 / trackdata.bits_per_revolution();
+        unsigned bitsPerRevolution = trackdata.original_data_rate_khz() * trackdata.original_period_ms();
+        std::vector<bool> bits(bitsPerRevolution);
+        double clockRateUs = 166666.0 / bitsPerRevolution;
         unsigned cursor = 0;
 
         fillBitmapTo(bits, cursor, trackdata.post_index_gap_us() / clockRateUs, { true, false });
diff --git a/arch/victor9k/victor9k.proto b/arch/victor9k/victor9k.proto
index b44c1934..fb21faf3 100644
--- a/arch/victor9k/victor9k.proto
+++ b/arch/victor9k/victor9k.proto
@@ -6,18 +6,20 @@ message Victor9kDecoderProto {}
 
 message Victor9kEncoderProto {
 	message TrackdataProto {
-		message SectorsProto {
-			repeated int32 sector = 1 [(help) = "write these sectors (in order) on each track"];
+		message SectorRangeProto {
+			optional int32 start_sector = 1 [(help) = "first sector ID on track"];
+			optional int32 sector_count = 2 [(help) = "number of sectors on track"];
 		}
 
-		optional int32 min_cylinder = 1        [(help) = "minimum cylinder this format applies to"];
-		optional int32 max_cylinder = 2        [(help) = "maximum cylinder this format applies to"];
-		optional int32 head = 3                [(help) = "which head this format applies to"];
+		optional int32 min_cylinder = 1            [(help) = "minimum cylinder this format applies to"];
+		optional int32 max_cylinder = 2            [(help) = "maximum cylinder this format applies to"];
+		optional int32 head = 3                    [(help) = "which head this format applies to"];
 
-		optional int32 bits_per_revolution = 4 [(help) = "number of bits on this cylinder"];
-		optional double post_index_gap_us = 5  [(help) = "size of post-index gap"];
+		optional double original_period_ms = 4     [(help) = "original rotational period of this cylinder"];
+		optional double original_data_rate_khz = 5 [(help) = "original data rate of this cylinder"];
+		optional double post_index_gap_us = 6      [(help) = "size of post-index gap"];
 
-		optional SectorsProto sectors = 6 [(help) = "write these sectors (in order) on each track"];
+		optional SectorRangeProto sector_range = 7 [(help) = "write these sectors on each track"];
 	}
 
 	repeated TrackdataProto trackdata = 1;
diff --git a/doc/disk-victor9k.md b/doc/disk-victor9k.md
index 21f019e1..f8721a09 100644
--- a/doc/disk-victor9k.md
+++ b/doc/disk-victor9k.md
@@ -6,7 +6,25 @@ which used a disk format very reminiscent of the Commodore format; not a
 coincidence, as Chuck Peddle designed them both. They're 80-track, 512-byte
 sector GCR disks, with a variable-speed drive and a varying number of sectors
 per track --- from 19 to 12. Disks can be double-sided, meaning that they can
-store 1224kB per disk, which was almost unheard of back then.
+store 1224kB per disk, which was almost unheard of back then. Because the way
+that the tracks on head 1 are offset from head 0 (this happens with all disks),
+the speed zone allocation on head 1 differ from head 0...
+
+| Zone | Head 0 tracks | Head 1 tracks | Sectors | Original period (ms) |
+|:----:|:-------------:|:-------------:|:-------:|:--------------------:|
+| 0    | 0-3           |               | 19      | 237.9                |
+| 1    | 4-15          | 0-7           | 18      | 224.5                |
+| 2    | 16-26         | 8-18          | 17      | 212.2                |
+| 3    | 27-37         | 19-29         | 16      | 199.9                |
+| 4    | 38-48         | 30-40         | 15      | 187.6                |
+| 5    | 49-59         | 41-51         | 14      | 175.3                |
+| 6    | 60-70         | 52-62         | 13      | 163.0                |
+| 7    | 71-79         | 63-74         | 12      | 149.6                |
+| 8    |               | 75-79         | 11      | 144.0                |
+
+(The Original Period column is the original rotation rate. When used in
+FluxEngine, the disk always spins at 360 rpm, which corresponds to a rotational
+period of 166 ms.)
 
 FluxEngine reads these.
 
diff --git a/src/formats/victor9k.textpb b/src/formats/victor9k.textpb
index b77f4bfc..42841486 100644
--- a/src/formats/victor9k.textpb
+++ b/src/formats/victor9k.textpb
@@ -1,5 +1,80 @@
 comment: 'Victor 9000 / Sirius One 1224kB SSHD GCR variable sector (ro)'
 
+image_reader {
+	filename: "victor9k.img"
+	img {
+		tracks: 80
+		sides: 1
+		trackdata {
+			sector_size: 512
+		}
+		trackdata {
+			track: 0
+			up_to_track: 3
+			sector_range {
+				start_sector: 1
+				sector_count: 19
+			}
+		}
+		trackdata {
+			track: 4
+			up_to_track: 15
+			sector_range {
+				start_sector: 1
+				sector_count: 18
+			}
+		}
+		trackdata {
+			track: 16
+			up_to_track: 26
+			sector_range {
+				start_sector: 1
+				sector_count: 17
+			}
+		}
+		trackdata {
+			track: 27
+			up_to_track: 37
+			sector_range {
+				start_sector: 1
+				sector_count: 16
+			}
+		}
+		trackdata {
+			track: 38
+			up_to_track: 47
+			sector_range {
+				start_sector: 1
+				sector_count: 15
+			}
+		}
+		trackdata {
+			track: 48
+			up_to_track: 59
+			sector_range {
+				start_sector: 1
+				sector_count: 14
+			}
+		}
+		trackdata {
+			track: 60
+			up_to_track: 70
+			sector_range {
+				start_sector: 1
+				sector_count: 13
+			}
+		}
+		trackdata {
+			track: 71
+			up_to_track: 79
+			sector_range {
+				start_sector: 1
+				sector_count: 12
+			}
+		}
+	}
+}
+
 image_writer {
 	filename: "victor9k.img"
 	img {
@@ -75,11 +150,98 @@ image_writer {
 	}
 }
 
-decoder {
+encoder {
 	victor9k {
+		trackdata {
+			original_data_rate_khz: 500
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 0
+			max_cylinder: 3
+			original_period_ms: 237.9
+			sector_range {
+				start_sector: 1
+				sector_count: 19
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 4
+			max_cylinder: 15
+			original_period_ms: 224.5
+			sector_range {
+				start_sector: 1
+				sector_count: 18
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 16
+			max_cylinder: 26
+			original_period_ms: 212.2
+			sector_range {
+				start_sector: 1
+				sector_count: 17
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 27
+			max_cylinder: 37
+			original_period_ms: 199.9
+			sector_range {
+				start_sector: 1
+				sector_count: 16
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 38
+			max_cylinder: 48
+			original_period_ms: 187.6
+			sector_range {
+				start_sector: 1
+				sector_count: 15
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 49
+			max_cylinder: 59
+			original_period_ms: 175.3
+			sector_range {
+				start_sector: 1
+				sector_count: 14
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 60
+			max_cylinder: 70
+			original_period_ms: 163.0
+			sector_range {
+				start_sector: 1
+				sector_count: 13
+			}
+		}
+		trackdata {
+			head: 0
+			min_cylinder: 71
+			max_cylinder: 79
+			original_period_ms: 149.6
+			sector_range {
+				start_sector: 1
+				sector_count: 12
+			}
+		}
 	}
 }
 
+decoder {
+	victor9k {}
+}
+
 cylinders {
 	start: 0
 	end: 79