The 4130 Road, stripped to the two parts that decide how a bike rides.

Double-butted 4130 chromoly frame and matching chromoly fork. Everything else is up to you.

The 4130 Steel Line earned its namesake from the double-butted 4130-grade chromoly used on the frame and fork — strength without compromising weight. This is the road version: classic lines, modern clearance, and an interface list with nothing proprietary on it anywhere.

Why start with a frameset

Because you already know what you want, and you'd rather not pay for parts you're going to replace.

Maybe you have a groupset sitting in a box. Maybe you've been collecting rim-brake components while everyone else moved to discs and you finally want a modern frame to hang them on. Maybe you just want to build something that's yours rather than buying something that's everyone's.

This frame is designed for that. Every interface on it is an established standard with decades of parts behind it — new, used, cheap, expensive, whatever you're working with.

Build it 1x or 2x

The complete bike ships 1x8 with a 42T ring, which is the right call for most riders. The frame is not limited to it.

The frame supports a full 2x drivetrain, with a maximum chainring size of 50/34T. If you want a traditional compact road setup with a front derailleur and the tight gear steps that come with it, the frame accommodates it.

That makes this an unusually flexible platform. Build it simple and singlespeed-adjacent with a 1x, or build it as a proper geared road bike with a compact double and a wide-range cassette. Same frame either way.

700 x 40c clearance

The frame clears up to 700 x 40c, which is a long way past what road frames of this shape used to allow.

That's the difference between a bike restricted to smooth pavement and one that handles the roads people actually ride — cracked asphalt, construction plating, rough bike lanes, the gravel connector between two paved sections. Run 28s if you want a fast summer setup, run 38s or 40s if you want comfort and puncture resistance, and change your mind whenever you like.

That figure is for the frame and the fork, and it holds whether you build 1x or 2x — the clearance doesn't change based on how you set up the drivetrain.

Actual fitment varies with rim width and tire brand — a 40c on a wide rim measures wider than a 40c on a narrow one.

The geometry

Road geometry, tuned by size rather than scaled from one drawing.

• 425mm rear center across every size — chainstay length stays constant, so the balance between front and rear doesn't shift as the frame gets bigger
• 45mm fork offset across every size — consistent trail and steering feel from a 49 to a 62
• 65mm BB drop — low enough for stability and cornering confidence, high enough for pedal clearance
• 72° head angle on 49 and 52, 73.5° on 55, 59, and 62 — the smaller frames get a slacker front end to keep toe overlap manageable and handling calm
• Seat angles from 74.5° down to 73° as the frame grows, putting every rider in a comparable position over the bottom bracket

It's a classic road position — not a racing crouch, not an upright hybrid. The kind of fit you can hold for four hours.

Built on standards you can actually build on

No press-fit bottom bracket to creak. No proprietary seatpost. No integrated cockpit that locks you into one stem length. Nothing on this frame will be hard to find a part for in ten years.

Sizing

Five sizes. Height ranges below, with inseam as a cross-check — inseam is the more reliable guide when you're picking your own cockpit.

• 49 cm — inseam 26.5" – 28.5"  ·  riders 5'5" – 5'8"
• 52 cm — inseam 28.5" – 31"  ·  riders 5'7" – 5'10"
• 55 cm — inseam 31" – 32.5"  ·  riders 5'9" – 6'0"
• 59 cm — inseam 32.5" – 34"  ·  riders 5'11" – 6'3"
• 62 cm — inseam 34" – 36"  ·  riders 6'2" – 6'7"

Sizes overlap on purpose. If you fall between two, the smaller size gives a more nimble, upright fit and the larger one stretches you out. Full numbers — reach, stack, standover, wheelbase, and tube lengths for every size — are on our geometry chart.

What's included

• Frame
• Fork
• Headset
• Seatpost clamp

Everything else is yours to choose. The headset and seatpost clamp being included matters more than it sounds — they're the two small parts that are easy to forget when you're ordering a build, and the two that stop the project dead when they don't show up.

Frame weights

Frame, fork, headset, and seatpost clamp:

• 49 cm — 7 lb 5 oz
• 52 cm — 7 lb 8 oz
• 55 cm — 7 lb 10 oz
• 59 cm — 8 lb 0 oz
• 62 cm — 8 lb 4 oz

That's steel, and steel weighs what it weighs. What you get for it is a frame that takes a hit and keeps its alignment, absorbs road buzz instead of transmitting it, and can be repaired by any competent framebuilder rather than written off.

Specifications

• Frame: Double-butted 4130 chromoly steel, TIG welded
• Fork: 4130 chromoly steel, 1-1/8" threadless steerer
• Headset standard: 1-1/8" threadless
• Bottom bracket shell: 68mm English threaded
• Seatpost: 27.2mm
• Brake type: Rim brake, caliper
• Hub spacing: 100mm front / 130mm rear, quick release
• Drivetrain: 1x or 2x, max chainring 50/34T
• Max tire clearance: 700 x 40c (frame and fork)
• Bottle mounts: Two
• Sizes: 49, 52, 55, 59, 62 cm
• Included: Frame, fork, headset, seatpost clamp

Want to get technical? Full Geo / Specs here.