Frame Information
With over 50 years specialising in handmade off-road dirt bikes we felt it would be appropriate to put some of that off road DNA into a gravel bike one that has been designed for a 40mm fork and dropper post and can accommodate a 50mm tyre with plenty of mud clearance combined with geometry that is nimble and quick on the flat stuff and handles like an XC bike on the trail.
Meet the Slackjack suspension fork and dropper post specific gravel machine.
Simply by adding rack mounts and some extra bottle bosses the Slackjack can be turned into one amazing go-anywhere adventure bike.
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 steelFactory 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 |






