01 What makes it unique
The Momentum 399M is a fifth-wheel toy hauler 44 ft 10 in long with a 12 ft 6 in garage, on three axles with three slide-outs and a 60-gallon fuel station. It is on Grand Design’s Momentum roster for 2027.
Grand Design’s page lists an unloaded vehicle weight of 19,170 lb, a GVWR of 23,500 lb and a pin weight of 3,406 lb. It publishes no cargo carrying capacity, so none is printed or computed here. Tanks are 140 gal fresh, 104 gal grey and 52 gal black, and it sleeps 5.
Grand Design’s page names the 395MT and 396DB as comparison floorplans.
How the 399M differs from the other eleven Momentum fifth wheels. Most distinctive first. Each rank counts only the siblings that publish that field, and a figure most of them share is left out.
- Dry weight, 19,170 lb: heaviest of twelve; next are the 395MT and 396DB (19,100 lb).
- Pin weight as a share of dry weight, 17.8%: second-smallest of twelve, between the 320G (17.6%) and the 351MS (19%).
- Length, 44 ft 10 in: fifth-longest of twelve, between the 381MS (43 ft 11 in) and the 394G (44 ft 11 in).
- Sleeping capacity, 5: smallest of twelve, level with the 350G; next are the 320G, 325G and three others (6).
- Pin weight, 3,406 lb: sixth-lightest of twelve, between the 363G (3,100 lb) and the 344M and 394G (3,500 lb).
- GVWR, 23,500 lb: highest of twelve, level with the 381MS, 392M and two others; next is the 394G (22,500 lb).
- Grey tank, 104 gal: largest of twelve, level with the 325G, 344M and three others; next is the 363G (102 gal).
Next to the 395MT, the nearest lighter floorplan by dry weight, the 399M is 70 lb heavier by dry weight, has a pin weight 354 lb lighter, is 1 ft 6 in shorter, has a grey tank 26 gal larger, has a black tank 26 gal smaller and sleeps two fewer; the two publish the same GVWR, exterior height, fresh tank and slide-out count.
02 Full specifications
Dimensions
- Exterior length
- 44 ft 10 in
- Exterior width
- 8 ft 5 in
- Exterior height
- 13 ft 6 in
- Chassis
- 101″ wide body · 5-side aluminum cage
- Garage / flex length
- 12 ft 6 in
Weights
- Dry / unit base weight (UVW)
- 19,170 lbs
- GVWR (max loaded)
- 23,500 lbs
- Net cargo / payload
- Not published by Grand Design
- Hitch / pin weight
- 3,406 lbs
Capacities
- Fresh water
- 140 gal
- Grey water
- 104 gal
- Black water
- 52 gal
- LP gas
- 60 lbs · 2 tanks
- Refrigerator
- 20 cu. ft.
Construction
- Chassis
- 101″ Wide Body Super Chassis w/ drop-frame storage
- Body
- 5-side aluminum cage · 101″ wide body
- Sidewalls
- High-gloss gel coat · frameless tinted windows
- Roof
- Worry-Free composite w/ lifetime warranty · walk-on
- Underbelly
- Fully enclosed and heated underbelly and storage area
Running gear
- Hitch
- Fifth-wheel (in-bed) · MORryde® pin box
- Suspension
- MORryde® Independent Suspension 2.0 w/ disc brakes
- Leveling
- 6-point hydraulic
- Tires
- Heavy-duty H-rated · 17.5″ H-rated aluminum wheels
- Spare
- 17.5″ undermount
- Tire size
- ST215/75R17.5R LRH
- GAWR, as Grand Design lists it
- 21,000 lbs
Garage
- Garage / flex length
- 12 ft 6 in
- Ramp
- Ramp door w/ Keyed Alike™ latches
- Tie-downs
- 2,500 lb rated flush-mount tie-downs
- Fuel station
- 60 gal · dual tank
Galley & systems
- Refrigerator
- 20 cu. ft. 12-volt
- Air conditioning
- 30,000 BTU
- Furnace
- 35,000 BTU
- Water heater
- Tankless
- Solar
- 330W roof-mounted panel · 50 AMP controller w/ Bluetooth · inverter prep · 2 USB dock ports
- Shower
- 40″ x 30″
Sleeping & layout
- Sleeps
- 5
- Slides
- 3
- Awnings
- 3
- Hitch type
- Fifth-wheel (in-bed)
- Primary bed
- 60 X 80 Queen Bed (King Opt.)
How these published figures sit against the rest of the catalogue: fifth wheel pin weight and payload; fresh, grey and black tank sizes; camper trailer size chart.
Drawn to scale
Size, with end view
Holding tanks
Axles, wheels and nose shape are schematic; not a floorplan. Data: dataset.
Towing it
Check your vehicle. Enter the ratings from your owner’s manual and the door-pillar placard.
Compares your figures with this page’s published GVWR (23,500 lb) and the upper loaded pin estimate (5,875 lb, a rule of thumb). Your vehicle’s placard and the trailer’s own weight label govern.
Loaded range: 15–25% of GVWR on the pin, a rule of thumb, not a measurement of this unit. No truck ratings or hitch classes (why; NHTSA, DOT HS 809 433).
03 The Momentum floorplan family
Momentum is Grand Design's toy-hauler family, and it spans four rosters across both tow types. The full-size Momentum fifth wheel is the flagship — a 101-inch wide-body coach on MORryde independent suspension with disc brakes, carrying a 60-gallon dual fuel station. The Momentum G-Class fifth wheel sits below it on MORryde CRE3000 suspension and a Rotoflex pin box with a 30-gallon fuel station, and the G-Class travel trailer puts that same garage behind a bumper pull. The Momentum MAV is the compact end — the lightest and cheapest way into a Momentum garage, and the one roster with no fuel station at all. The 399M on this page is highlighted; each other profiled plan links to its own page. The full MY2027 catalogue runs to 28 floorplans across the four rosters; eight are profiled in depth here and the rest are catalogued on the line hub with their weights.
| Floorplan | Roster | Type | Length | Garage | Sleeps | Notable |
|---|---|---|---|---|---|---|
| 351MS | Momentum | 5W | 39′ 11″ | 11 ft | 6 | 11 ft garage, sleeps 6, 3 slides |
| 344M | Momentum | 5W | 39′ 11″ | 11 ft | 6 | Entry Momentum — lowest GVWR of the ten, tightest payload |
| 381MS | Momentum | 5W | 43′ 11″ | 15 ft | 6 | 15 ft garage, sleeps 6, 3 slides |
| 392M | Momentum | 5W | 45′ 11″ | 17 ft | 9 | Sleeps nine, longest fifth-wheel garage in the family |
| 395MT | Momentum | 5W | 46′ 4″ | 14 ft* | 7 | 14 ft* garage, sleeps 7, 3 slides |
| 396DB | Momentum | 5W | 46′ 4″ | 10 ft 10 in | 7 | 10 ft 10 in garage, sleeps 7, 3 slides |
| 399M | Momentum | 5W | 44′ 10″ | 12 ft 6 in | 5 | 12 ft 6 in garage, sleeps 5, 3 slides |
The full-size Momentum is Grand Design's luxury fifth-wheel toy hauler and the top of the family — a 101-inch wide-body coach on MORryde independent suspension with disc brakes, a 60-gallon dual fuel station and a 20-cubic-foot refrigerator. Pin weights here are factory dry figures and a toy hauler's real loaded pin climbs hard once the garage is full — weigh the loaded coach against your truck's payload and rear-axle rating. The other Momentum fifth-wheel floorplans are catalogued on the line hub.
04 Notes on this floorplan
12 ft 6 in garage, 60-gallon fuel station
Garage / flex length and fuel station as printed on the 399M page.
Pin 3,406 lb on 19,170 lb UVW
Grand Design’s pin weight is 17.8% of its unloaded weight; the loaded figure is higher.
30,000 BTU A/C, 35,000 BTU furnace
Climate equipment as Grand Design lists it for the 399M.
140 fresh / 104 grey / 52 black
Tank capacities in gallons, from the 399M page.
05 How it compares
Named by Grand Design’s 399M page as a comparison floorplan: UVW 19,100 lb, GVWR 23,500 lb, 46 ft 4 in.
Named by Grand Design’s 399M page as a comparison floorplan: UVW 19,100 lb, GVWR 23,500 lb, 46 ft 4 in.
Every current Momentum floorplan, all four rosters, side by side.
07 Where this floorplan sits
Closest sibling: the Momentum 396DB, nearest on the published figures. It differs on 4 of the 8 fields both publish (this plan first): length 44 ft 10 in vs 46 ft 4 in; sleeps 5 vs 7; dry weight 19,170 lb vs 19,100 lb; hitch weight 3,406 lb vs 3,760 lb. They match on GVWR, fresh tank, grey tank and black tank.
| Momentum fifth-wheel plans | This plan | Position, low to high | Range |
|---|---|---|---|
| GVWR (lb) | 23,500 | 8–12 of 12 | 16,400–23,500 |
| Dry weight (lb) | 19,170 | 12 of 12 | 12,603–19,170 |
| Hitch weight (lb) | 3,406 | 6 of 12 | 2,300–3,760 |
| Length | 44 ft 10 in | 8 of 12 | 35 ft 6 in–46 ft 4 in |
| Fresh tank (gal) | 140 | 5–12 of 12 | 98–140 |
| Grey tank (gal) | 104 | 7–12 of 12 | 52–104 |
| Black tank (gal) | 52 | 1–7 of 12 | 52–104 |
| Sleeps | 5 | 1–2 of 12 | 5–9 |
Either side of it by GVWR: Momentum 396DB matches it at 23,500 lb GVWR.
| Nearest Momentum fifth-wheel siblings | Length | Sleeps | Dry (lb) | GVWR (lb) | CCC (lb) | Hitch (lb) | Fresh (gal) |
|---|---|---|---|---|---|---|---|
| Momentum 399M | 44 ft 10 in | 5 | 19,170 | 23,500 | — | 3,406 | 140 |
| Momentum 396DB | 46 ft 4 in | 7 | 19,100 | 23,500 | — | 3,760 | 140 |
| Momentum 392M | 45 ft 11 in | 9 | 18,114 | 23,500 | 5,386 | 3,650 | 140 |
| Momentum 344M | 39 ft 11 in | 6 | 15,910 | 19,000 | 3,090 | 3,500 | 140 |
| Momentum 394G | 44 ft 11 in | 7 | 16,400 | 22,500 | 6,100 | 3,500 | 98 |
| Momentum 395MT | 46 ft 4 in | 7 | 19,100 | 23,500 | — | 3,760 | 140 |
All 24 Momentum floorplans: Momentum line hub.
| Other lines, nearest by GVWR | GVWR (lb) | Dry (lb) | Sleeps | Length |
|---|---|---|---|---|
| 399M | 23,500 | 19,170 | 5 | 44 ft 10 in |
| Solitude 414LJMJ | 23,500 | 19,000 | 6 | 42 ft 10 in |
| Riverstone 442MC | 23,845 | 18,591 | 6 | 43 ft 9 in |
| Model G 3950 | 23,000 | 18,700 | 8 | 45 ft 5 in |
| Cyclone 3913 | 21,000 | 15,435 | 8 | 46 ft 5 in |
| Nightfall 397NHD | 21,000 | 15,674 | — | 45 ft 0 in |
| Sandstorm 4017GX | 21,000 | 15,674 | — | 45 ft 0 in |
Against the 399M: the Solitude 414LJMJ is 2 ft shorter and sleeps 1 more; the Riverstone 442MC is 345 lb heavier and 1 ft shorter and sleeps 1 more; the Model G 3950 is 500 lb lighter and sleeps 3 more.
08 Common questions about the 399M
How much does the 399M weigh?
19,170 lb dry; 23,500 lb GVWR, the most it may weigh loaded.
What is the pin weight of the 399M?
3,406 lb as published, 18% of the dry weight (median across 411 fifth wheels here: 19%).
What size tow vehicle does the 399M need?
A tow rating of at least 23,500 lb, plus payload for the loaded pin weight, passengers and cargo.
How many people does the 399M sleep?
It is rated to sleep 5. 10 of the 12 Momentum fifth-wheel floorplans that publish a count sleep more.
What are the tank capacities on the 399M?
Fresh 140, grey 104, black 52 gallons. Off hookups, fresh water runs out first.
How long is the 399M?
44 ft 10 in overall, tongue or pin box included.
From the figures above.
09 What this page publishes, and what it does not
14 of the 18 fields this catalogue tracks are published for the 399M. Not published: cargo capacity (CCC), interior height, axle count, tire size (a description is published, a size is not).
Sourcing rules: methodology.
10 Manuals & documents
Sources: granddesignrv.com (linked below); the full source note is at the foot of the page.
11 NHTSA safety record
NHTSA holds 19 recall campaigns and 201 owner complaints (model years 2005 on) against the Momentum line. They are counted separately: a recall is a confirmed defect with a remedy, a complaint one owner’s unverified account.
What to look at on a used one. Across the 201 complaints filed on this line the most-reported components are structure (41%), unknown or other (19%) and suspension (10%).
Recall coverage here is not complete, and complaints are owners’ unverified reports (how this record is built). Check a specific VIN at NHTSA before you buy. Full tables are on the Momentum line page.