A 650b/29er rigid steel frame designed around a real fit constraint — heel clearance on the drive-side chainstay — that production frames can't solve. Open geometry, full spec, build it yourself.
The 1992 Trek 990 geometry, documented and adapted for a modern build. Late-80s ATB proportions that still make sense. Riser bars. Flat pedals. Hand this to a builder.
Rigid steel 26" town bike with dirt-tourer DNA. Dual wheelsize. Four sizes. Designed to be handed to any small independent builder and said: build me this.
Built around a constraint most production frames can't address: pronounced toe-out gait, wide feet, heel that tracks directly into the drive-side chainstay at cadence. The geometry follows from that human body — not from a catalog or a trend.
Dual wheelsize with geometry that barely notices the swap. 650b for gravel and road, 29er for trail days. Offset 55mm, trail ~68mm — a mildly low-trail character that pairs well with a loaded front end.
This is a personal build, documented openly. Take the geometry. Adapt it to your body. Find a builder who can work with it.
| Dimension | Value | Notes |
|---|---|---|
| Head Tube Angle | 71° | |
| Seat Tube Angle (eff.) | 73° | |
| Seat Tube (c-t) | 530mm | Designed for ~188cm / 6'2" rider |
| Top Tube (effective) | 614mm | |
| Head Tube Length | 195mm | Structural stack — no spacer tower needed |
| Chainstay Length | 450mm | Ovalized drive-side for heel clearance |
| BB Drop | 59mm | |
| Fork ATC | 445mm | Custom segmented CrMo, 12×100mm thru-axle |
| Fork Offset | 55mm | |
| Trail | ~68mm | Mildly low-trail — works well loaded |
| Wheelbase | ~1119mm | |
| Stack | ~660mm | Approx. — verify with builder |
| Rear Spacing | 135×10mm | Sliding dropouts (include insert) |
| Front Axle | 12×100mm TA | |
| BB Shell | 68mm BSA | English threaded |
| Seatpost | 27.2mm | |
| Head Tube | 1-1/8" (EC34) | |
| Brake Mount | Flat mount disc | |
| Bottle Mounts | 5 | Down tube, seat tube, under down tube |
| Setup | Tire | Est. OD | Notes |
|---|---|---|---|
| Primary gravel | 700c × 40mm Panaracer GravelKing | ~678mm | Primary road / gravel wheelset |
| Trail | 29 × 2.2" Rene Herse Fleecer Ridge | ~735mm | Trail wheelset — swaps with same disc alignment |
The 1992 Trek 990 got a lot right. This is a documentation of that geometry — not a clone, not a copy-and-sell — rebuilt with modern components in mind and shared openly. Attribution is clear: this is adapted from Trek's original 1992 spec.
Late-80s ATB proportions: unhurried head angle, honest BB drop, chainstays long enough to be stable without being sluggish. The kind of bike that used to be normal and is now hard to find.
Take the geometry, bring it to a small builder, and make something that lasts.
| Dimension | Trek 990 (20") | Notes |
|---|---|---|
| Head Tube Angle | 71° | From original Trek spec |
| Seat Tube Angle | 74° | From original Trek spec |
| Seat Tube (c-c) | 508mm / 20" | |
| Top Tube (effective) | ~575mm | Derived from original dimensions |
| Chainstay | 430mm | From original Trek spec (43.0cm) |
| BB Drop | ~65mm | Estimated from original F / G dimensions |
| Fork ATC | ~400mm | Standard 26" CrMo fork range |
| Trail | ~70mm | Estimated at original fork spec |
| Wheelbase | ~1060mm | Estimated |
| Wheel | 26" | |
| Rear Spacing | 135mm QR | Adapt to 142×12 for a new build |
A rigid steel 26" town bike with dirt-tourer DNA. Coffee runs, taco pickups, gravel paths, and looking like it just got back from somewhere interesting.
Dual wheelsize capable: 26" knobbies and 650b × 47mm on the same frame — geometry barely notices. Four sizes, S through XL. All dimensions chosen on purpose.
This spec is free. Take it to any small independent builder and say: build me this. That's the whole point.
| Dimension | Value | Notes |
|---|---|---|
| Head Tube Angle | 71° | Unhurried. Holds a line. Lets the front rack do its job. |
| Seat Tube Angle (eff.) | 73° | Knees over pedals. Not aggressive, not lazy. |
| Chainstay Length | 445mm | Consistent across all four sizes. |
| BB Drop | 68mm | Puts you in the bike, not perched on it. |
| Fork ATC | 400mm | Custom CrMo, matched to frame. |
| Fork Offset | 43mm | |
| Trail | ~72mm | Neutral-to-stable. Handles a front load without twitching. |
| Rear Spacing | 142×12mm | Thru-axle, fixed vertical dropouts. |
| BB Shell | 68mm BSA | English threaded. |
| Seatpost | 27.2mm | Classic diameter. Easy to source everywhere. |
| Headset | EC34 / 28.6 | 1-1/8" external cup. Or EC34/30. |
| Dimension | S | M | L | XL |
|---|---|---|---|---|
| Rider Height | 5'4"–5'7" | 5'7"–5'10" | 5'10"–6'1" | 6'1"–6'4" |
| Seat Tube (c-t) | 440mm | 470mm | 500mm | 530mm |
| Head Tube Length | 100mm | 120mm | 140mm | 160mm |
| Top Tube (eff.) | 535mm | 555mm | 575mm | 595mm |
| Stack | ~566mm | ~585mm | ~604mm | ~623mm |
| Reach | ~361mm | ~374mm | ~387mm | ~400mm |
| Front-Center | ~582mm | ~600mm | ~618mm | ~636mm |
| Wheelbase | ~1023mm | ~1041mm | ~1059mm | ~1077mm |
| Standover (est.) | ~720mm | ~745mm | ~770mm | ~795mm |
| Setup | Tire | Est. OD | Est. Width |
|---|---|---|---|
| Gravel | 650b × 47mm GravelKing SK | ~678mm | ~49–50mm |
| Trail | 26 × 2.2" Rene Herse Rat Trap Pass | ~671mm | ~55–57mm |
| Town | 650b × 42mm slick | ~668mm | ~44mm |
| Max 26" | 26 × 2.3" RH Rat Trap Pass | ~676mm | ~57–59mm |
OD varies ~10mm across all combinations · BB height shifts ~5mm · HTA shifts <0.3° · The bike doesn't notice.