Twenty-two sizes. Not twenty-two frame SKUs across a range of bikes, but twenty-two geometry configurations of one model, the Atherton A.150M, spanning 415mm to 535mm of reach in 10mm steps. Most manufacturers give you four or five. Atherton gives you a number that would be commercially insane for anyone using moulded carbon, and the geometry chart that results is the most interesting single document in mountain biking this year, because it lets you watch, in 10mm increments, exactly what happens to a bike’s proportions when the front end grows and the back end mostly does not.
The A.150M is the mixed-wheel version of the A.150: 150mm rear travel on Dave Weagle’s DW6 six-bar linkage, a 205x60mm trunnion shock, a 160mm fork (170mm compatible), 29in front and 27.5in rear, and a chassis of 3D-printed titanium lugs bonded to carbon tubes. Head angle is 64.5° across every size. Bottom bracket height is 339mm across every size, 4mm lower than the 29in A.150. Frame only is £4,999, with complete builds from £7,299 up to £9,199, per Bikerumor’s launch coverage.
The full chart
Every row below is taken from Atherton’s own A.150M geometry chart. Head angle (64.5°), BB height (339mm) and BB offset (16mm) are identical on all 22 sizes and are omitted to keep the table readable. Front centre and the front-centre to rear-centre ratio are the only calculated columns, derived by subtracting chainstay from wheelbase.
| # | Size | Reach | Stack | Stack:Reach | Seat tube | Head tube | Eff. STA | Chainstay | Front centre | Wheelbase | FC:RC |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 415 Low | 415 | 618 | 1.49 | 395 | 90 | 77.5° | 430 | 746 | 1176 | 1.74 |
| 2 | 425 Low | 425 | 618 | 1.45 | 395 | 90 | 77.5° | 430 | 756 | 1186 | 1.76 |
| 3 | 435 Low | 435 | 618 | 1.42 | 395 | 90 | 77.5° | 430 | 766 | 1196 | 1.78 |
| 4 | 445 Low | 445 | 627 | 1.41 | 395 | 100 | 77.5° | 430 | 780 | 1210 | 1.81 |
| 5 | 455 Low | 455 | 627 | 1.38 | 395 | 100 | 78.25° | 435 | 790 | 1225 | 1.82 |
| 6 | 455 Reg | 455 | 636 | 1.40 | 420 | 110 | 78.25° | 435 | 795 | 1230 | 1.83 |
| 7 | 465 Low | 465 | 627 | 1.35 | 395 | 100 | 78.25° | 435 | 800 | 1235 | 1.84 |
| 8 | 465 Reg | 465 | 636 | 1.37 | 420 | 110 | 78.25° | 435 | 805 | 1240 | 1.85 |
| 9 | 475 Low | 475 | 627 | 1.32 | 395 | 100 | 78.25° | 435 | 810 | 1245 | 1.86 |
| 10 | 475 Reg | 475 | 636 | 1.34 | 440 | 110 | 78.25° | 435 | 815 | 1250 | 1.87 |
| 11 | 485 Reg | 485 | 627 | 1.29 | 420 | 100 | 78.25° | 435 | 820 | 1255 | 1.89 |
| 12 | 485 Tall | 485 | 636 | 1.31 | 440 | 110 | 78.25° | 435 | 825 | 1260 | 1.90 |
| 13 | 495 Reg | 495 | 636 | 1.29 | 420 | 110 | 79° | 440 | 835 | 1275 | 1.90 |
| 14 | 495 Tall | 495 | 645 | 1.30 | 440 | 120 | 79° | 440 | 840 | 1280 | 1.91 |
| 15 | 505 Reg | 505 | 636 | 1.26 | 420 | 110 | 79° | 440 | 845 | 1285 | 1.92 |
| 16 | 505 X-Tall | 505 | 645 | 1.28 | 460 | 120 | 79° | 440 | 850 | 1290 | 1.93 |
| 17 | 515 Tall | 515 | 645 | 1.25 | 440 | 120 | 79° | 440 | 860 | 1300 | 1.95 |
| 18 | 515 X-Tall | 515 | 658 | 1.28 | 460 | 135 | 79° | 440 | 866 | 1306 | 1.97 |
| 19 | 525 Tall | 525 | 645 | 1.23 | 440 | 120 | 79° | 440 | 869 | 1309 | 1.98 |
| 20 | 525 XX-Tall | 525 | 658 | 1.25 | 480 | 135 | 79° | 440 | 876 | 1316 | 1.99 |
| 21 | 535 Tall | 535 | 645 | 1.21 | 440 | 120 | 79° | 440 | 879 | 1319 | 2.00 |
| 22 | 535 XX-Tall | 535 | 658 | 1.23 | 480 | 135 | 79° | 440 | 886 | 1326 | 2.01 |
All dimensions in millimetres. Actual seat tube angle runs 73.8° to 76.1°. The calculated ratio column runs 1.735 to 2.014, which matches the 1.73 to 2.01 figure quoted in Pinkbike’s first ride, published 31 August 2026. That agreement between Atherton’s published table and an independent report is the reason I am confident the chart above is correct.
The ratio: 1.74 to 2.01 inside one model
Front centre is the horizontal distance from bottom bracket to front axle. Rear centre is the chainstay length. The ratio between them tells you, roughly, where the rider’s mass sits between the two contact patches, because the rider’s mass is approximately stacked over the bottom bracket.
On size 1, the bottom bracket sits 63.4% of the wheelbase back from the front axle. On size 22, it sits 66.8% back. That sounds small. It is not. Across 22 sizes of one bike, the front centre grows 140mm, from 746 to 886, an increase of 18.8%. The rear centre grows 10mm, from 430 to 440, an increase of 2.3%. The front of the bike gets eight times more growth than the back.
The consequences are the classic complaints of short and tall riders, and the chart explains both. Low ratios put the rider proportionally further forward. That is good for front tyre bite in flat, off-camber corners and bad for margin on steep terrain, because there is less bike ahead of you to stop the rotation. Small riders going over the bars is not a skill deficit; it is a geometry outcome. High ratios do the opposite. Sizes 19 through 22 are proportionally rearward-biased bikes: extremely secure when the trail points down, and requiring a deliberate, committed weight shift to make the front tyre grip when it flattens out. Tall riders who describe a bike as “washing out in flat turns” are describing a ratio near 2.0.
Where is the balance best? Sizes 8 through 14, covering 465mm to 495mm of reach, sit between 1.85 and 1.91. That band is where a 150mm trail bike’s proportions generally land when a designer is not fighting a moulded rear triangle, and it is the part of this range that needs no apology. Sizes 1 through 3, at 1.74 to 1.78, are the most forward-biased, which is a defensible choice for a 415mm reach bike aimed at a light rider who needs front grip more than they need a long front centre. The compromised end is the top: sizes 19 through 22 are all at or above 1.975.
The arithmetic of fixing that is instructive. Front centre is set by the front triangle and fork, so it cannot be traded against chainstay length. To bring size 22 back to the 1.885 ratio of size 11, the chainstay would need to be 470mm. To bring it back to size 1’s 1.735, it would need 511mm. Neither number exists on a production trail bike, and 470mm would demand a different linkage, a different yoke and, in all likelihood, a different chainring clearance solution. The point is not that Atherton got it wrong. The point is that nobody has solved it, and the A.150M chart is the clearest published evidence of how far from solved it is.
Three chainstays across twenty-two sizes
The steps fall at 430mm for sizes 1 to 4 (reach 415 to 445), 435mm for sizes 5 to 12 (reach 455 to 485), and 440mm for sizes 13 to 22 (reach 495 to 535). Each is 3mm shorter than the equivalent 29in A.150, which uses 433/438/443mm, a direct consequence of the smaller rear wheel.
Why only three? Because the rear centre is the expensive part to vary. Reach is changed by printing a different head tube lug and cutting a down tube and top tube to different lengths, which costs Atherton essentially nothing per unit. Chainstay length is bound up with the DW6 linkage: change it and the leverage curve, anti-squat and anti-rise all move, and each variant needs its own validation. Three rear ends is already generous; most brands ship one.
The drift within each band is the thing to watch. The 430mm band spans a ratio range of 0.079, the 435mm band 0.081, and the 440mm band 0.116. The widest drift is in the band that covers the most sizes and the tallest riders, which is exactly backwards from where you would want it. A fourth step, say 445mm from size 17 upward, would have pulled sizes 17 to 22 back under 2.0 and cost roughly 0.03 of ratio. Whether that was a kinematic constraint or a validation cost, Atherton has not said.
What “Tall” actually means
The suffixes (Low, Reg, Tall, X-Tall, XX-Tall) do not change reach. They change stack and seat tube length at a fixed reach. Compare sizes 21 and 22, both at 535mm reach: 535 Tall has a 440mm seat tube, a 120mm head tube and 645mm of stack. 535 XX-Tall has a 480mm seat tube, a 135mm head tube and 658mm of stack. Same reach, 13mm more stack, 40mm more seat tube.
The wheelbase difference (1319 vs 1326mm) is not an independent design decision. Extending the head tube by 15mm along a 64.5° axis pushes the front axle forward by about 6.5mm, which is the 7mm you see in the table. That also nudges the ratio from 1.998 to 2.014, so a Tall size is always marginally more rearward-biased than its standard twin.
The correct way to read these is as bar-height and dropper-length variants. A “Low” size with a 395mm seat tube takes a 200mm+ dropper on a rider who would normally be limited by insertion depth. An “X-Tall” or “XX-Tall” gives a rider with long legs and a long torso the stack they need without forcing them onto a longer reach they do not want, and without a 40mm stack of headset spacers changing the effective steering feel. That is the genuinely useful part of this system, and it is worth more to most riders than the 10mm reach steps.
Why the DW6 and the lugs make 22 sizes possible
Atherton’s frames are built from carbon tubes bonded into titanium lugs produced by additive manufacturing, EFBE Category 5 certified, a construction method Pinkbike described at the model’s first look as made viable by the fact that the company’s inventory is powdered titanium rather than finished frames. A moulded carbon front triangle requires a tool costing tens of thousands of pounds per size. Twenty-two of them is not a business. A printed lug requires a file. Changing reach by 10mm means printing a head tube lug at a different angle and cutting two tubes to a different length. The marginal cost of a size is close to the marginal cost of a frame.
The DW6 six-bar linkage is what makes that work structurally, because the suspension hardware is concentrated in a rear module that can be held constant while the front triangle varies. The honest caveat is that Atherton publishes no kinematic data. Both Blister’s full review and Pinkbike note that leverage ratio and anti-squat curves are not disclosed, so any statement about them is inference from ride feel. Blister’s testers inferred high anti-squat from how high the bike rides under power. That is a reasonable read, but it is a read, not a number, and this site will not treat it as one.
Choosing a size, including if you are tall
Two useful anchors exist. Blister’s testers, both 6ft, rode size 11 (485 Reg). Pinkbike’s reviewer, around 191cm, rode size 11 as well but stated he would buy size 14 (495 Tall) instead. Both data points suggest the range runs long relative to its numbers, and that the Tall variants earn their place well before you get to the extremes.
At 6ft, size 11 or 12 (485mm reach) is the sensible default, with 12 preferred for the extra 9mm of stack and the 440mm seat tube. At 6ft 2in, sizes 14 or 16 (495 Tall or 505 X-Tall). At 6ft 4in, which is where I sit, the honest recommendation is size 17 or 18 (515mm reach), and 18 specifically if you have ever run more than 20mm of spacers on a trail bike. Its 658mm stack is the tallest front end here, and its 1.28 stack-to-reach ratio is the best available above 505mm of reach.
I would not automatically take 21 or 22 at 6ft 4in, and the chart is why. Size 21 gives you 20mm more reach than size 17 and exactly the same 645mm stack, which drops the stack-to-reach ratio to 1.21, the lowest number on the bike. You would be buying a longer, flatter, more rearward-biased bike with a ratio of 2.00. Riders over about 6ft 5in, or those who genuinely prefer a stretched, stable position on steep terrain, should take 22 over 21 without hesitating: the XX-Tall’s extra 13mm of stack and 40mm of seat tube are the difference between a bike that fits and a bike you are reaching down to.
The wider lesson is that 10mm steps let you separate two decisions that are normally welded together. Almost everyone shopping for a trail bike is really choosing stack and being handed reach as a side effect, or the reverse. Here you can pick a reach, then pick a front end height, and the only price is that you have to actually read the table.