About Slackjack
We've spent over 50 years building off-road bikes by hand, so it felt right to put some of that off-road DNA into a gravel bike.
Meet the Slackjack: a gravel bike designed around a 40mm suspension fork and a dropper post. It takes tyres up to 50mm, with plenty of mud clearance, and its geometry is nimble and quick on the flat but handles like an XC bike on the trail.
Add rack mounts and a few extra bottle bosses, and the Slackjack becomes a proper go-anywhere adventure bike.
Factory Pilots Riding The Slackjack
Technical Specifications
| Specification | Detail |
|---|---|
| Tyre clearance | Fits 50mm tyres with ample mud clearance |
| Seat tube | 31.6mm as standard (27.2mm optional), dropper ready with cable exit hole |
| Head tube | Top ZS44/28.6 | Bottom EC44/40 |
| Bottom bracket | 68mm BSA threaded |
| Complete bike weight | Available on request |
| Customisation | Two sets of bottle bosses standard (extra sets £30/pair); Rack mounts: £60 extra |
| Recommended stem | 60-70mm |
Tubing Used
| Tubing | Material / Details |
|---|---|
| Downtube | Reynolds 853 (2 options on diameter, depending on riding intensity and weight) |
| Top tube | Reynolds 853 (2 options on diameter, depending on riding intensity and weight) |
| Seat tube | Reynolds 631 |
| Chainstays | Columbus |
| Seatstays | Columbus |
Geometry Chart
| Slackjack | XS | S | M | L | XL | XXL |
|---|---|---|---|---|---|---|
| ST | 450 | 470 | 490 | 510 | 530 | 560 |
| HT | 110 | 120 | 130 | 140 | 150 | 160 |
| ST Angle | 74 | 74 | 74 | 74 | 74 | 74 |
| HT Angle | 68 | 68 | 68 | 68 | 68 | 68 |
| Reach | 380 | 390 | 395 | 405 | 410 | 420 |
| Stack | 553 | 562 | 571 | 580 | 589 | 599 |
| BB Drop | –70 | –70 | –70 | –70 | –70 | –70 |
| BB Height | 275 | 275 | 275 | 275 | 275 | 275 |
| Chainstays | 435 | 435 | 435 | 435 | 435 | 435 |
The reasons a Curtis feels different.
Since 1972, we've built steel frames recognised among the finest in England.
Fillet Brazing
Brian Curtis' signature brazing technique creates beautiful rippled joints and airtight tubes, protecting Curtis frames from internal rust.
Discover fillet brazing
Made To Order
Every frame is made to order in Somerset, this is what makes a Curtis special. In the configurator, change every part of your new frame.
See how we build each frame
Premium Steel
Reynolds, Columbus, Dedacciai, and T45 are cherry picked frame by frame for an unmatched strength-to-weight ratio, and ride feel.
Explore our premium steel
Worldwide & domestic shipping
Order your Curtis directly online, with domestic and worldwide delivery available for every frame. Alternatively, collect your frame from our workshop.
Start your order






