Velopedia Bicycle Archive
Surly Lowside - Blue Monday
Mountain bicycle from the Velopedia specification archive.
Selling this bike? Create a Bike History Report
- Model year
- Not published by manufacturer
- Original MSRP
- $1,799.00
- Sizes
- XS, S, M, L, XL
- Weight
- 28 lb 1 oz for Medium
- Geometry
- 5 manufacturer sizes · Ride analysis
- Archive ID
- 900000933
- Catalog verified
- August 19, 2026
Current market
Snapshot not yet availableProtected live updateReady after page interactionAutomated crawlers do not trigger marketplace requests.
Move, scroll, tap or type to start the protected update.
Velopedia analysis
What the specifications mean
The rims and tires are tubeless-ready, but that label does not confirm the bike is currently set up without tubes; tape, valves, sealant and tire condition still matter. On the steel frame, paint damage and moisture entry deserve attention because corrosion can begin at scratches, vent holes or internal surfaces. The 27.5-inch/650B label corresponds to a 584 mm bead-seat diameter, which is the dependable reference for tire and rim compatibility.
Tire setup
Tubeless-ready
The rims and tires may support tubeless use, but the bike may still be running tubes.
Frame material
Steel
Paint damage and moisture entry matter because corrosion can start externally or inside the frame.
Wheel standard
650B · 584 mm
The ISO bead-seat diameter is the dependable tire and rim compatibility reference.
Bottom bracket
Threaded interface
Shell width, thread standard and crank-spindle interface still require confirmation.
Used-bike inspection
If you’re buying this bike used
Before any test ride: both brakes should stop the bike firmly and release cleanly; both wheels should run true and be securely attached; tires should have no casing damage; and the headset, handlebar, stem, cranks and pedals should have no looseness or play.
Follow the full used-bike inspection order →- FrameCheck paint chips, vent holes and the inside of the seat tube for corrosion. Also look for dents, bent tubes and cracking around welded or brazed joints.Inspect the frame and fork →
- BrakesTest each brake separately and confirm it stops firmly and releases cleanly. Inspect the pads and braking surfaces for wear or contamination, and check the cables or hoses for damage.Inspect the brakes →
- DrivetrainShift through the full range under light load, measure chain wear and inspect the cassette or freewheel teeth. Skipping or hesitation can indicate wear, poor adjustment or mismatched parts.Check drivetrain wear →
- Wheels & tiresSpin both wheels and watch the rims for side-to-side or vertical movement. Check for dents, cracks, loose or uneven spokes and hub play, then inspect both tire casings for cuts, cracking or exposed threads. If it is set up tubeless, confirm both tires hold pressure and ask when the sealant was last refreshed.Check wheels and tires →
- Bottom bracketTurn the cranks slowly, feel for rough bearings and check for side-to-side play. Creaking under load deserves investigation but does not identify the source by itself.Inspect the bottom bracket and shell →
Bike-specific inspection checklist 20 checks based on 5 archived component groups Open checklistClose checklist
This checklist uses the archived equipment for this bike. It cannot confirm the condition, service history or later component changes of the example in front of you.
Identity and fit
Follow the full used-bike inspection order →Archived: Surly Lowside - Blue Monday · Mountain · Published sizes: XS, S, M, L, XL
Frame and fork
Inspect the frame and fork →Archived: Frame: Surly Lowside - 4130 Chromoly, Natch tubing, double-butted main triangle, TIG welded, E.D. coated · Fork: Surly Lowside - 4130 Chromoly, Natch tubing, double-butted tapered fork blades, TIG welded, E.D. coated · Steel
Drivetrain
Check drivetrain wear →Archived: Crankset: SRAM NX Eagle, 32t · Bottom bracket: SRAM PowerSpline, BSA, 73mm · Cassette: Surly 17T Cog w/ Spacer Kit, silver · Chain: KMC X9
Brakes
Inspect the brakes →Archived: Brakes: Brake Calipers: Tektro HD-M275/276, 2-piston; Brake Levers: Tektro HD-M275/276; Rotors: Tektro 160/160mm, 6-Bolt
Wheels and tires
Check wheels and tires →Archived: Wheel size: 27.5"; 26" · Rims: WTB ST i35 TCS 2.0 27.5", 32h · Hubs: (F) Novatec 15 x 110mm, silver / (R) Novatec 12 x 148mm, silver · Front tire: Maxxis Rekon+ 27.5" x 2.8", 60 TPI, tan sidewalls, tubeless-ready, WTB TCS Sealant included · Rear tire: Maxxis Rekon+ 27.5" x 2.8", 60 TPI, tan sidewalls, tubeless-ready, WTB TCS Sealant included
Controls and contact points
Archived: Headset: FSA Orbit ITA, Silver · Handlebar: Surly Sunset (Painted to match frame) · Stem: Sunday Freeze Stem Top-Load, Silver · Seatpost: Promax SP-2019, Silver · Saddle: WTB Volt Medium, silver rails
Before and during the test ride
Follow the full used-bike inspection order →Interpretation based on the archived manufacturer specifications. Confirm exact fit and standards before ordering parts or performing service.
Have you owned this bike?Help preserve its real-world history by sharing your owner experience.
Share the details that would help another rider understand how this model fits, rides and holds up over time. Velopedia reviews every contribution before publication.
Already contributed? Send me a fresh private edit link
For privacy, Velopedia shows the same confirmation whether or not an experience exists.
Frameset
| Frame Construction | Surly Lowside - 4130 Chromoly, Natch tubing, double-butted main triangle, TIG welded, E.D. coated |
|---|---|
| Frame Material | Steel |
| Fork | Surly Lowside - 4130 Chromoly, Natch tubing, double-butted tapered fork blades, TIG welded, E.D. coated |
| Fork Material | Steel |
Drivetrain
| Shifters | N/A |
|---|---|
| Front Derailleur | N/A |
| Rear Derailleur | N/A |
| Crankset | SRAM NX Eagle, 32t |
| Bottom Bracket | SRAM PowerSpline, BSA, 73mm |
| Cassette | Surly 17T Cog w/ Spacer Kit, silver |
| Chain | KMC X9 |
Brakes
| Brakes | Brake Calipers: Tektro HD-M275/276, 2-piston; Brake Levers: Tektro HD-M275/276; Rotors: Tektro 160/160mm, 6-Bolt |
|---|
Cockpit & Contact Points
| Headset | FSA Orbit ITA, Silver |
|---|---|
| Handlebar | Surly Sunset (Painted to match frame) |
| Stem | Sunday Freeze Stem Top-Load, Silver |
| Saddle | WTB Volt Medium, silver rails |
| Seatpost | Promax SP-2019, Silver |
Wheels & Tires
| Hubs | (F) Novatec 15 x 110mm, silver / (R) Novatec 12 x 148mm, silver |
|---|---|
| Rims | WTB ST i35 TCS 2.0 27.5", 32h |
| Spokes | 14g stainless, silver |
| Front Tire | Maxxis Rekon+ 27.5" x 2.8", 60 TPI, tan sidewalls, tubeless-ready, WTB TCS Sealant included |
| Rear Tire | Maxxis Rekon+ 27.5" x 2.8", 60 TPI, tan sidewalls, tubeless-ready, WTB TCS Sealant included |
| Wheel Size | 27.5"; 26" |
Size-specific frame data
Geometry
Manufacturer-published geometry normalized for consistent archival comparison. Effective top tube and reach remain separate measurements because they describe different aspects of fit.
| Measurement | X-Small | Small | Medium | Large | X-Large |
|---|---|---|---|---|---|
| Seat tube | 316 mm | 366 mm | 416 mm | 466 mm | 516 mm |
| Effective top tube | 570 mm | 590 mm | 610 mm | 630 mm | 650 mm |
| Head tube | 110 mm | 125 mm | 140 mm | 155 mm | 170 mm |
| Head-tube angle | 70° | 70° | 70° | 70° | 70° |
| Seat-tube angle | 74° | 74° | 74° | 74° | 74° |
| Chainstay / rear center | 425 mm | 425 mm | 425 mm | 425 mm | 425 mm |
| Wheelbase | 1068 mm | 1089 mm | 1110 mm | 1131 mm | 1152 mm |
| Bottom-bracket drop | 55 mm | 55 mm | 55 mm | 55 mm | 55 mm |
| Reach | 414.5 mm | 429.3 mm | 445.3 mm | 461 mm | 477 mm |
| Stack | 542.2 mm | 560.3 mm | 574.4 mm | 588.5 mm | 602.5 mm |
| Standover height | 700 mm | 729 mm | 762 mm | 792 mm | 823 mm |
| Fork offset / rake | 47 mm | 47 mm | 47 mm | 47 mm | 47 mm |
| Fork length / axle-to-crown | 420 mm | 420 mm | 420 mm | 420 mm | 420 mm |
| Crank length | 165 mm | 165 mm | 165 mm | 170 mm | 170 mm |
| Stem length | 48 mm | 48 mm | 48 mm | 48 mm | 48 mm |
| Handlebar width | 820 mm | 820 mm | 820 mm | 820 mm | 820 mm |
Geometry source: Manufacturer HTML geometry table ↗ Measurements can vary by configuration, wheel size, or flip-chip position where noted by the manufacturer.
Geometry interpretation
What this geometry means
X-Small geometry
Riding position
A 414.5 mm reach paired with 542.2 mm of stack gives this size a moderate frame proportion: roomy enough when standing without pushing strongly toward either a very low or very upright front end.
Handling tendencies
A 70° head angle combined with a 1068 mm wheelbase points to quicker-steering and more responsive steering and chassis behavior. The longer the chassis and slacker the front end, the more the bike tends to favor composure over very quick direction changes. A 425 mm rear center is compact, which tends to make rear-wheel weight shifts and tight direction changes easier than a long-rear-center layout.
Small geometry
Riding position
A 429.3 mm reach paired with 560.3 mm of stack gives this size a moderate frame proportion: roomy enough when standing without pushing strongly toward either a very low or very upright front end.
Handling tendencies
A 70° head angle combined with a 1089 mm wheelbase points to quicker-steering and more responsive steering and chassis behavior. The longer the chassis and slacker the front end, the more the bike tends to favor composure over very quick direction changes. A 425 mm rear center is compact, which tends to make rear-wheel weight shifts and tight direction changes easier than a long-rear-center layout.
Medium geometry
Riding position
With 445.3 mm of reach and 574.4 mm of stack, the frame has a relatively long, low proportion that should leave plenty of room when standing and put the front end toward the lower side of modern mountain-bike fit.
Handling tendencies
A 70° head angle combined with a 1110 mm wheelbase points to quicker-steering and more responsive steering and chassis behavior. The longer the chassis and slacker the front end, the more the bike tends to favor composure over very quick direction changes. A 425 mm rear center is compact, which tends to make rear-wheel weight shifts and tight direction changes easier than a long-rear-center layout.
Large geometry
Riding position
With 461 mm of reach and 588.5 mm of stack, the frame has a relatively long, low proportion that should leave plenty of room when standing and put the front end toward the lower side of modern mountain-bike fit.
Handling tendencies
A 70° head angle combined with a 1131 mm wheelbase points to quicker-steering and more responsive steering and chassis behavior. The longer the chassis and slacker the front end, the more the bike tends to favor composure over very quick direction changes. A 425 mm rear center is compact, which tends to make rear-wheel weight shifts and tight direction changes easier than a long-rear-center layout.
X-Large geometry
Riding position
With 477 mm of reach and 602.5 mm of stack, the frame has a relatively long, low proportion that should leave plenty of room when standing and put the front end toward the lower side of modern mountain-bike fit.
Handling tendencies
A 70° head angle combined with a 1152 mm wheelbase points to quicker-steering and more responsive steering and chassis behavior. The longer the chassis and slacker the front end, the more the bike tends to favor composure over very quick direction changes. A 425 mm rear center is compact, which tends to make rear-wheel weight shifts and tight direction changes easier than a long-rear-center layout.
Across the size range
From X-Small to X-Large, reach grows by 62.5 mm and stack by 60.3 mm, showing how the frame becomes both longer and taller through the published size range. The rear center stays essentially constant at about 425 mm across sizes, so most of the wheelbase growth happens in the front half of the bike rather than by lengthening the rear triangle.
Geometry describes frame proportions and likely tendencies, not a ride test. Rider proportions, cockpit setup, tires, suspension settings, wheel configuration, and component choices can materially change how a bicycle fits and feels.
Gallery
Specifications are presented as a reference. Components may vary by market, size, production run, or later manufacturer revisions.