Specialized Aethos geometryRoad · 2026 · 6 sizes, from 49 to 61

The Specialized Aethos is a road bike available in 6 sizes, from 49 to 61. Stack ranges from 522 to 627 mm and reach from 373 to 404 mm. Its position sits between racing and endurance. All sizes share 410 mm chainstays.

Stack522–627mm

Reach373–404mm

Head angle71.4–73.5°

Chainstay length410mm

Low BB

What size Aethos do I need?

Enter the stack and reach of a bike that fits you well and we will tell you which size is closest and how to set it up.

Stack in mm Reach in mm Compare on Fitbikefy →

49S 522 · R 373

52S 538 · R 377

54S 559 · R 384

56S 580 · R 391

58S 606 · R 398

61S 627 · R 404

Enter your stack and reach to see which size fits you best.

Geometry chart by size

Measurements in mm and degrees, as published by Specialized. The ones that matter most for choosing a size are in bold.

Size	49	52	54	56	58	61
Stack	522	538	559	580	606	627
Reach	373	377	384	391	398	404
Effective top tube	508	526	544	557	572	584
Head tube length	114	128	150	169	198	218
Head angle	71.4°	72.1°	72.5°	73.0°	73.0°	73.5°
Chainstay length	410	410	410	410	410	410
Wheelbase	978	981	992	998	1,013	1,020
Front centre	581	584	594	599	614	621
BB drop	77	77	75	75	74	74
BB height	266	266	267	267	269	269
Fork length	372	372	372	372	372	372
Fork offset	50	50	50	47	47	47
Trail	62	58	55	55	55	52
Standover	719	737	759	779	805	834
Seat tube (method not stated)	450	470	490	510	535	570
Seat angle (method not stated)	75.5°	74.5°	74.0°	74.0°	74.0°	74.0°

Source: Specialized official website · data from 11 Nov 2026.

Stack and reach of every size

Higher means a taller front end; further right means a longer reach. The blue dot is your search.

Character of each size

Compared with other road bikes. Further right means more of that quality.

Positionracing → relaxed

Steeringcalm → quick

Pedallingrearward → forward

Bottom brackethigh → low

Wheelbaselively → planted

Rear endstable → agile

Bikes with similar geometry (size 54)

The closest size of other road models, by stack and reach.

ModelΔ stackΔ reach

Specialized S-Works Aethos · 542026±0 mm±0 mmCompare →

Cube Attain SLX · 53 cm2026+2 mm±0 mmCompare →

Cube Attain · 53 cm2026+2 mm±0 mmCompare →

Wilier Triestina Rapida · M2027−3 mm+1 mmCompare →

Cannondale SuperSix EVO · 542026−4 mm±0 mmCompare →

Ridley Grifn RS Road · S2027+4 mm−1 mmCompare →

Aethos or S-Works Aethos? In size 54 they have exactly the same stack and reach (559 / 384 mm): the difference is in the frame and build, not the position.

Frequently asked questions

What size Aethos do I need?

It depends on your position, not just your height. The most reliable way is to compare the stack and reach of a bike that fits you with those of each size (from 522/373 mm in size 49 to 627/404 mm in size 61). The size finder on this page shows the closest size and the stem and spacers you would need.

What are the stack and reach of the Aethos in size 54?

Stack of 559 mm and reach of 384 mm, with an effective top tube of 544 mm and a head angle of 72.5°.

Is the Aethos a racing or an endurance bike?

In between. In size 54 its stack-to-reach ratio is at percentile 57 of road bikes: neither very low nor very tall.

Does it have the same geometry as the S-Works Aethos?

In size 54, yes: same stack and reach. If one already fits you, the same size of the other will put you in the same position.