BMC mountain bike sizing: Fourstroke, Twostroke and Fourstroke AMP LT
BMC's current mountain range is focused on cross country. The Fourstroke is the full suspension XC bike, the Twostroke is the XC hardtail, freshly relaunched, and the Fourstroke AMP LT is a light down country e MTB. All three share BMC's long reach, short stem race philosophy, so the cockpits feel roomy and the numbers run generous. Pick by reach and height, remembering that sizing down feels more playful while sizing up feels more stable. See what is in stock on our BMC collection.
Please note. These recommendations are indicative and a starting point, not a guarantee of fit. Proportions, flexibility and terrain all matter, so read the reach and stack numbers with the height bands and confirm against the exact bike before you buy.
Quick size finder
| Rider height | Leg length (inseam) | Fourstroke (XC) | Twostroke (hardtail) | Fourstroke AMP LT (e-MTB) |
|---|---|---|---|---|
| 160 to 172 cm | 70 to 78 cm | S | S | S |
| 172 to 180 cm | 78 to 83 cm | M | M | M |
| 180 to 188 cm | 83 to 88 cm | L | L | L |
| 188 to 198 cm | 88 to 93 cm | XL | XL | XL |
How to measure yourself
Height. Stand barefoot against a wall, heels together and back straight. Mark the top of your head and measure straight down to the floor.
Leg length (inseam). Barefoot, feet about 15 cm apart, press a hardback book spine up into your crotch as a saddle would sit. Measure from the top of the book to the floor. On a mountain bike your inseam helps with standover clearance and footing at a stop.
BMC Fourstroke
The Fourstroke is a full suspension cross country bike with long reach, a short stem and a slacker than typical front, so it rides more like a trail bike than an old school racer.
| Size | Reach (mm) | Stack (mm) | Rider height |
|---|---|---|---|
| S | 437 | 584 | up to 172 cm |
| M | 457 | 592 | 172 to 182 cm |
| L | 477 | 600 | 180 to 188 cm |
| XL | 500 | 615 | 188 cm and up |
Fit character: long and stable, an XC bike with trail confidence.
BMC Twostroke
The Twostroke is a modern race hardtail with a long reach and a notably slack head angle, racy but confident as speed builds. The latest generation is dropper post compatible.
| Size | Reach (mm) | Stack (mm) | Rider height |
|---|---|---|---|
| S | 432 | 600 | up to 172 cm |
| M | 455 | 605 | 170 to 180 cm |
| L | 475 | 610 | 178 to 188 cm |
| XL | 497 | 617 | 188 cm and up |
Fit character: racy and confident, a modern long reach hardtail.
BMC Fourstroke AMP LT
The Fourstroke AMP LT is a light down country e MTB that rides much like the regular Fourstroke, with a slightly taller stack and steeper seat and a very short stem for balanced weight over both wheels.
| Size | Reach (mm) | Stack (mm) | Rider height |
|---|---|---|---|
| S | 437 | 594 | up to 172 cm |
| M | 457 | 605 | 172 to 182 cm |
| L | 476 | 615 | 180 to 188 cm |
| XL | 496 | 627 | 188 cm and up |
Fit character: light and balanced, an e MTB that rides like a normal bike.
What BMC riders find
Reviewers love the roomy, efficient position of the Fourstroke and do not miss a longer stem, and because reach is generous, riders between sizes sometimes find one size feels compact and choose to size up. The relaunched Twostroke is praised as fast and stable with unusual comfort for a hardtail and strong climbing from its steep seat angle. The Fourstroke AMP LT wins credit for natural, balanced handling and a high fun factor on descents while staying light for an e MTB.
Between two sizes?
At a size boundary let your riding decide. Size down for a shorter, more playful and flickable feel on tight trails. Size up for a longer, more stable cockpit that stays calm at speed, which also suits the generous BMC reach if you like a roomy fit. Comparing reach and stack with a bike you already ride is the surest guide.
Shop BMC mountain bikes
Check current models, builds and availability on our BMC collection.
Not sure which BMC suits your riding, or stuck between two sizes? We are happy to help. Talk to our concierge.
Stack and reach figures are drawn from official BMC data where possible, and the rider height bands are BMC's own published guidance, which overlaps between sizes by design. This guide covers BMC's current mountain range; the older Trailfox and Speedfox trail bikes are discontinued and are not included. Always confirm geometry against the exact bike and model year before buying.
