Shimano Ultegra FC-R8100 Crankset - 172.5mm | 50/34t

Shimano Ultegra FC-R8100 Crankset - 170mm | 52/36t Shimano

Shimano Ultegra FC-R8100 Crankset - 172.5mm | 50/34t

Shimano Ultegra FC-R8100 Crankset - 172.5mm | 50/34t

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Is the Shimano Ultegra FC-R8100 172.5mm the Right Crankset Length?

The Shimano Ultegra FC-R8100 in 172.5mm is the in-between arm length that many riders have used for decades as a compromise between the stiffness advantages of longer cranks and the comfort of shorter ones, built on Hollowtech II with hollow forged crank arms and a Hollowglide outer chainring for quick, precise 12-speed front shifting. The 172.5mm length remains a well-established choice for riders with a slightly longer inseam or those who transitioned from 175mm and found 172.5 a comfortable reduction. The 50/34t compact chainring makes this an especially versatile package for mixed terrain, climbing-heavy routes, or any rider who prefers the wider gear range of a compact over a 52/36t mid-compact.

2x12-speed, Hollowtech II 24mm axle. Compatible with Shimano 12-speed road derailleurs (Ultegra R8100, Dura-Ace R9200) and requires a compatible 12-speed Shimano road bottom bracket (SM-BBR60 for threaded, SM-BB72-41B for press-fit). Chainrings are replaceable. For the rider who knows 172.5mm is their number and wants the compact 50/34t gearing in the Ultegra 12-speed package, this is the exact spec to order.

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Specifications

  • Model: FC-R8100
  • Series: Shimano Ultegra
  • Speed: 2x12-speed
  • Arm Length: 172.5mm
  • Chainrings: 50/34t (compact)
  • Interface: Hollowtech II (24mm axle)
  • Compatible BB: SM-BBR60 (threaded), SM-BB72-41B (press-fit)
  • Compatible Derailleurs: Shimano 12-speed road (Ultegra R8100, Dura-Ace R9200)

FAQ

What is the advantage of a compact 50/34t over a mid-compact 52/36t?

Compact gearing provides a lower minimum gear for easier climbing, especially useful on steep grades, for riders who prioritize endurance over outright speed, or when paired with a wide-range cassette. Mid-compact 52/36t provides higher top-end gearing for faster speeds but a somewhat tighter range.

Is 172.5mm a common arm length to stock?

172.5mm has historically been very popular, used by many riders as the halfway point between 170 and 175. With the recent trend toward shorter cranks, 170mm has become more common, but 172.5 remains widely used by riders in the 175-180cm height range.

Can I upgrade the chainrings to a 52/36t configuration later?

Yes. The chainrings on the FC-R8100 are user-replaceable. Shimano sells the R8100 52/36t and other configurations as separate chainring sets.

Best For

Road cyclists running Shimano 12-speed who need a 172.5mm arm length with compact 50/34t gearing for climbing-heavy routes, endurance riding, or mixed terrain.

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