Sizing a Factor gravel bike
Factor keeps its gravel range tight and fast: the aero Ostro Gravel and the featherweight LS. The single most important thing to know is that Factor runs one unified fit across its road and gravel bikes, so a given size carries a long reach and a low stack. Expect a racy, road inspired position rather than a tall, upright one, and do not be surprised if your Factor size is a touch smaller than an endurance bike you have ridden before.
Browse the range: all Factor bikes at Bikeroom.
Please note. These sizes are indicative, a starting point and not a guarantee. Factor itself prefers a personalised fit form over fixed height charts, so treat the ranges below as a guide and confirm against your own measurements and riding style.
Quick size finder
Find your height, check the matching leg length, then read across to each model. Because both bikes share Factor's race geometry, sizing up gives a slightly more relaxed reach while sizing down sharpens the handling and lowers the front end.
| Rider height | Leg length (inseam) | Ostro Gravel (aero) | LS (lightweight) |
|---|---|---|---|
| 158 to 168 cm | 73 to 78 cm | 49 | 49 |
| 167 to 173 cm | 77 to 81 cm | 52 | 52 |
| 172 to 178 cm | 80 to 84 cm | 54 | 54 |
| 177 to 183 cm | 83 to 87 cm | 56 | 56 |
| 182 to 188 cm | 86 to 90 cm | 58 | 58 |
| 187 to 195 cm | 89 to 94 cm | 61 | – |
The LS tops out at a size 58, so taller riders are pointed to the Ostro Gravel and its size 61.
How to measure yourself
Height. Stand barefoot with your back to a wall, heels together, and look straight ahead. Rest a flat object on your head, level against the wall, mark the point and measure from the floor.
Leg length (inseam). Barefoot, feet about 15 cm apart, press a book up into your crotch as if it were a saddle. Keep it level against the wall, mark the top edge and measure from the floor to the mark. This matters more than height for setting saddle height and standover.
Ostro Gravel (aero gravel racer)
The Ostro Gravel borrows its win everywhere attitude from the Ostro VAM road bike: aero tube shapes, a sub 900 gram frame and clearance for 45 mm tyres. Available in 6 sizes from 49 to 61, it carries the longest reach of the two and is built for going fast on mixed surfaces.
| Size | Reach (mm) | Stack (mm) | Rider height |
|---|---|---|---|
| 49 | 377 | 515 | 158 to 168 cm |
| 52 | 385 | 535 | 167 to 173 cm |
| 54 | 394 | 555 | 172 to 178 cm |
| 56 | 402 | 580 | 177 to 183 cm |
| 58 | 412 | 605 | 182 to 188 cm |
| 61 | 422 | 625 | 187 to 195 cm |
Fit character: aggressive and aero, a road racer's position carried onto gravel for riders who chase speed.
LS (lightweight gravel racer)
The LS was Factor's first gravel bike and remains a pure lightweight racer, with a frame under 1 kg and clearance for tyres up to 43 mm. Offered in 5 sizes from 49 to 58, it pairs a fractionally taller stack with a slightly shorter reach than the Ostro Gravel, giving a road like all rounder feel that many riders love for long days.
| Size | Reach (mm) | Stack (mm) | Rider height |
|---|---|---|---|
| 49 | 372 | 530 | 158 to 168 cm |
| 52 | 378 | 547 | 167 to 173 cm |
| 54 | 383 | 566 | 172 to 178 cm |
| 56 | 392 | 585 | 177 to 183 cm |
| 58 | 401 | 605 | 182 to 188 cm |
Fit character: light and lively, a road leaning all rounder that stays comfortable when the miles stack up.
What Factor riders find
Reviewers and owners consistently describe both bikes as fast, precise and unmistakably road bred. The Ostro Gravel draws praise for its stiffness and composed handling at speed, feeling like a race bike that happens to eat gravel. The LS earns its reputation as a light, crisp climber that puts the road into groad, rewarding riders who value low weight and a nimble front end. The common thread is a purposeful, forward position, so flexibility and core strength help you get the best from either frame. Riders coming off relaxed endurance bikes often need a ride or two to settle into the lower, longer stance.
Between two sizes?
If you land between two sizes, let your riding style decide. Choose the smaller size for a lower, sharper, more aggressive front end and quicker feeling handling, which suits racing and riders with a shorter torso. Choose the larger size for a longer, more stable reach that eases the strain on long rides and suits riders with more length in the torso and arms. Remember Factor's integrated Black Inc bar and stem has a fixed width and length, so a professional fit before you order is the surest way to confirm both frame size and cockpit.
Shop Factor gravel
- All Factor bikes including the Ostro Gravel and LS
Still unsure which Factor gravel bike or size is right for you? Talk to our concierge.
These sizes are guidance, not a fitting guarantee. Stack and reach figures are official Factor data confirmed via geometrygeeks. Rider height and leg length bands are indicative only, since Factor publishes a personalised fit form rather than fixed per size height charts, and the inseam ranges are estimated. The LS is Factor's earlier gravel model, now largely succeeded by the Ostro Gravel, and remains available at Bikeroom on a used basis. Always confirm against the exact bike and model year before buying.
