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2026 Harley-Davidson Fat Boy: specs, gearing and calculators
Wide 160 mm front and 240 mm rear tyres on 18-inch wheels, the shortest trail in the range, and the Milwaukee-Eight 117 Custom. Every figure below links to its source, and every calculator opens with the Fat Boy’s own numbers.
Know your version. Fat Boys have used the Evolution, Twin Cam and Milwaukee-Eight engines since 1990. These figures are for the 2026 bike with the 117 Custom; check your model year before using them for parts or settings.
MotoWild Lab
Calculators with the Fat Boy’s numbers filled in
Each one opens with the published figures for the 2026 Fat Boy: the Milwaukee-Eight 117’s bore and stroke, the gear ratios, belt pulleys, tyre sizes, rake and weight. Change any number to match your bike, see the formula worked through, and switch between imperial and metric.
2026 Fat Boy specifications
Figures as published, with the sources underneath. Power and torque are Harley-Davidson’s US ratings; seat height is laden (with a rider aboard) unless stated.
| Spec | 2026 Harley-Davidson Fat Boy |
|---|---|
| Engine | Milwaukee-Eight 117 Custom, 1,923 cc (117 cu in) 45° V-twin |
| Power (claimed) | 103 hp (77 kW) at 4,800 rpm |
| Torque (claimed) | 126 lb-ft (171 N·m) at 3,000 rpm |
| Bore × stroke | 103.5 × 114.3 mm (4.075 × 4.5 in) |
| Compression ratio | 10.3:1 |
| Weight | 694 lb (315 kg) in running order |
| Seat height | 25.9 in (658 mm) laden; 675 mm unladen |
| Fuel tank | 5 US gal (18.9 L), including about 1 gal (3.8 L) reserve |
| Rake / trail | 30° / 4.1 in (104 mm) |
| Wheelbase | 65.0 in (1651 mm) |
| Wheels | Cast 18 / 18 in |
| Transmission | 6-speed; primary chain 34/46, final belt 32/66 |
| Gear ratios (overall) | 9.311 / 6.454 / 4.793 / 3.882 / 3.307 / 2.79 |
| US price | $22,599 (starting MSRP) |
Sources: motorcycle.com · totalmotorcycle.com · torquepedia.com · harleydavidsonofsaltlakecity.com · harley-davidson.com. Where sources disagree we show the range.
Gearing
Fat Boy gear ratios and road speed in every gear
Six speeds, a 34/46 primary chain and a 32/66 final belt. The table works the published overall ratios back to the gearbox ratios and gives road speed at three engine speeds.
| Gear | Gearbox ratio | Overall ratio | At 2,000 rpm | At 3,000 rpm | At 4,000 rpm |
|---|---|---|---|---|---|
| 1 | 3.337 | 9.311 | 16 mph 26 km/h | 25 mph 39 km/h | 33 mph 53 km/h |
| 2 | 2.313 | 6.454 | 24 mph 38 km/h | 35 mph 57 km/h | 47 mph 76 km/h |
| 3 | 1.718 | 4.793 | 32 mph 51 km/h | 48 mph 77 km/h | 63 mph 102 km/h |
| 4 | 1.391 | 3.882 | 39 mph 63 km/h | 59 mph 95 km/h | 78 mph 126 km/h |
| 5 | 1.185 | 3.307 | 46 mph 74 km/h | 69 mph 111 km/h | 92 mph 148 km/h |
| 6 | 1.000 | 2.790 | 55 mph 88 km/h | 82 mph 132 km/h | 109 mph 175 km/h |
In 6th: 60 mph: 2,200 rpm · 70 mph: 2,570 rpm · 80 mph: 2,940 rpm
Gearbox ratios are the published overall ratios divided by the primary (46/34) and belt (66/32) ratios. Speeds use the rear tyre's unloaded circumference (2,040 mm); under load it rolls a few percent shorter, so real rpm is slightly higher. Published overall ratios: totalmotorcycle.com.
Tyres and wheels
Stock tyre sizes
Confirm against the sidewalls on your bike and the owner’s manual, including the load index, speed rating and whether the tyre is bias (B) or radial (R).
| Version and years | Front | Rear | Rims | Source |
|---|---|---|---|---|
| Harley-Davidson Fat Boy 2026 | 160/60R18 | 240/40R18 | Cast 18 / 18 in | motorcycle.com |
Side by side
Fat Boy vs Breakout
The same figures for both, on the same basis.
Head-to-head · MotoWild data
- Ready to ride, the 2026 Harley-Davidson Breakout is the lightest here, roughly 6 kg (13 lb) less than the 2026 Harley-Davidson Fat Boy. Makers weigh differently, so treat small gaps as a draw.
Seat height (laden, as published)
A range means sources disagree. Lower is easier at a stop, but weight and seat width matter too.
Weight, ready to ride
Figures as published, with their basis. Wet, kerb and full-tank weights are close but not identical, so a few kilos either way is a draw.
Fuel tank
| Spec | 2026 Harley-Davidson Fat Boy | 2026 Harley-Davidson Breakout |
|---|---|---|
| Engine | Milwaukee-Eight 117 Custom, 1,923 cc (117 cu in) 45° V-twin | Milwaukee-Eight 117 Custom, 1,923 cc (117 cu in) 45° V-twin |
| Power (claimed) | 103 hp (77 kW) at 4,800 rpm | 103 hp (77 kW) at 4,800 rpm |
| Torque (claimed) | 126 lb-ft (171 N·m) at 3,000 rpm | 126 lb-ft (171 N·m) at 3,000 rpm |
| Weight | 694 lb (315 kg) in running order | 681 lb (309 kg) in running order |
| Seat height | 25.9 in (658 mm) laden; 675 mm unladen | 25.6 in (650 mm) laden; 26.2 in (665 mm) unladen |
| Fuel tank | 5 US gal (18.9 L), including about 1 gal (3.8 L) reserve | 5 US gal (18.9 L), including about 1 gal (3.8 L) reserve |
| Rake / trail | 30° / 4.1 in (104 mm) | 34° / 5.7 in (145 mm) |
| Wheelbase | 65.0 in (1651 mm) | 66.7 in (1694 mm) |
| US price | $22,599 (starting MSRP) | $22,999 (starting MSRP) |
| Tyres | 160/60R18 / 240/40R18 Cast 18 / 18 in | 130/60B21 / 240/40R18 Cast 21 / 18 in |
Versions and model years
- Harley-Davidson Fat Boy: Fat Boys have used the Evolution, Twin Cam and Milwaukee-Eight engines since 1990. These figures are for the 2026 bike with the 117 Custom; check your model year before using them for parts or settings.
- Harley-Davidson Breakout: The Breakout returned for 2023 with the Milwaukee-Eight 117. Earlier Breakouts (Twin Cam engines from 2013, then the Milwaukee-Eight 107 or 114 from 2018) have different engines and figures. EU spec sheets list 168 Nm of torque; the US figure of 126 lb-ft (171 Nm) uses a different test method.
Figures: motorcycle.com · totalmotorcycle.com · torquepedia.com · harleydavidsonofsaltlakecity.com · harley-davidson.com · motorcycle.com · totalmotorcycle.com · aeharley.com · bartelsharley.com · harley-davidson.com · riders-share.com.
Model history
Which Fat Boy do you have?
Engines and frames have changed over the years, so older bikes have different figures.
2026 Fat Boy in pictures
Harley-Davidson guides and comparisons
Harley-Davidson · GuidesMilwaukee-Eight 117 Big Bore and Stroker Math: Displacement and CompressionWhat a bigger bore or longer stroke does to a 117: cubic inches, compression with the same clearance volume, and why kits…Updated Oct 27, 2026
Harley-Davidson · GuidesHarley-Davidson Belt Drive: Pulley Changes, Belt Length and Axle PositionHow a toothed final drive belt is sized, how far the axle moves when you change a pulley, and what to check…Updated Oct 27, 2026
Harley-Davidson · GuidesHarley-Davidson Softail Gear Ratios and Highway rpm (2026), Worked OutOverall ratios to gearbox ratios, road speed in every gear, rpm at 60, 70 and 80 mph for each rear tyre, and…Updated Oct 27, 2026
Harley-Davidson · CompareHarley-Davidson Fat Boy vs Breakout (2026): Same Engine, Different Front EndsBoth have the 117 Custom and a 240 rear. Rake, trail, front wheel size and wheelbase are where they differ, and the…Updated Oct 26, 2026
Harley-Davidson · Compare2026 Harley-Davidson Cruisers Compared: All Eight Softails by the NumbersWeight, power, seat, tank, geometry, rpm at 70 mph and price for every 2026 Softail cruiser, with power-to-weight and chassis families.Updated Oct 26, 2026
Harley-Davidson · GuidesMilwaukee-Eight 117 Classic vs Custom vs High Output: What ChangesSame bore, stroke and compression, three claimed outputs. What differs, which 2026 models get which, and what BMEP and piston speed say.Updated Oct 26, 2026Fat Boy FAQ
Why does the Fat Boy have so little trail?
Its published trail is 4.1 in (104 mm), well below the 5.5–6.2 in of most of the range. The wide 160 mm front tyre changes how the bike turns in, and the geometry is set to suit it. Use the rake and trail calculator to see how trail depends on rake, fork offset and wheel size.
What tyres does the 2026 Fat Boy use?
160/60R18 front and 240/40R18 rear, Michelin Scorcher 11 radials.
How heavy is the Fat Boy?
694 lb (315 kg) in running order, as Harley-Davidson quotes it.