2017 Specialized Demo I Alloy vs 2015 Trek Session DH 27.5
The XL is the Trek Session DH 27.5 size closest to your EXTRA LONG Specialized Demo I Alloy. We match frame stack and reach. This is a geometry comparison, not a fit recommendation; stem, spacers, handlebars and saddle setup also affect your riding position.
What changes on the Trek Session DH 27.5
Compared with the Specialized Demo I Alloy in EXTRA LONG, the Trek Session DH 27.5 in XL places the top of the head tube 11 mm lower and 4 mm further back, relative to the bottom bracket. Its wheelbase is 5 mm longer, which can contribute to stability at speed.
- Frame stack
- −11 mm
- Lower front end
- Frame reach
- −4 mm
- Shorter frame reach
- Wheelbase
- +5 mm
- Longer: steadier at speed
- Head angle
- +0.7°
- Steeper: sharper steering
- Chainstays
- +13 mm
- Longer: more planted
The two frames
Only the Specialized Demo I Alloy is drawn. The Trek Session DH 27.5 numbers we have for size XL are missing the seat angle.
Geometry side by side
| Measurement | Specialized Demo I Alloy EXTRA LONG | Trek Session DH 27.5 XL | Difference |
|---|---|---|---|
| Reach | 460mm | 456 | −4 mm |
| Stack | 614mm | 603 | −11 mm |
| Head tube angle | 63.5° | 64.2° | +0.7° |
| Seat tube angle | 74° | not listed | |
| Effective top tube | 636mm | 638 | +2 mm |
| Chainstay length | 430mm | 443 | +13 mm |
| Wheelbase | 1248mm | 1253 | +5 mm |
| BB drop | 12mm | 14 | +2 mm |
| BB height | 342mm | 364 | +22 mm |
| Standover | 698mm | 775 | +77 mm |
| Seat tube length | 367mm | 390 | +23 mm |
| Head tube length | 105mm | 115 | +10 mm |
Differences are the Trek Session DH 27.5 minus the Specialized Demo I Alloy. Full charts: 2017 Specialized Demo I Alloy, 2015 Trek Session DH 27.5.
Where each sits in its class
Specialized Demo I AlloyTrek Session DH 27.5
Each bike is ranked against the other downhill bikes on Quiver, on frame geometry alone. Not your hand position or ride feel.
What each ships with
The stock build of each bike's first listed trim. Parts that match are dimmed.
| Part | Specialized Demo I Alloy8 I Alloy | Trek Session DH 27.588 DH 27.5 |
|---|---|---|
| Fork | RockShox BoXXer RC | RockShox BoXXer |
| Rear shock | Fox Van RC | not listed |
| Shifter | SRAM X7 | SRAM X9 |
| Derailleur | SRAM GX | SRAM X-0 |
| Cassette | SRAM PG-1030 | SRAM PG-1050 |
| Chain | SRAM PC-1031 | KMC X10 |
| Crankset | SRAM Descendant | TruVativ Descendant DH |
| Pedals | Specialized Bennies | Wellgo MG-1 |
| Tire | Specialized Butcher, Specialized Slaughter | Bontrager G4 Team Issue |
| Hub | Specialized spacing | not listed |
| Brake | SRAM Guide R | Avid Code |
| Stem | Specialized P.Series | Bontrager Rhythm |
| Grips | Specialized Sip Grip | not listed |
| Saddle | Specialized Phenom Comp | Bontrager Evoke 2 |
| Frame | not listed | Trek Alpha Platinum |
| Wheelset | not listed | DT Swiss FR2150 |
| Handlebar | not listed | Bontrager Rhythm Elite |
| Headset | not listed | FSA NO.57E |
| Seatpost | not listed | Bontrager Rhythm Elite |
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