Boost Spacing

Summary

Boost Spacing is a hub and drivetrain standard introduced to widen axle widths, increase spoke bracing angles, and improve frame stiffness and tire clearance. First launched in mountain bikes, Boost has since influenced trail, enduro, gravel, and even e-MTB frame and wheel design.

Key Facts

  • Introduced: 2015
  • Category: Concept
  • Also known as: Boost 148, Boost 110, wider hub standard
  • Used by / Found on: MTB, gravel, trail, enduro, e-MTB, some XC bikes
  • Rear Hub Spacing: 148 mm (vs. 142 mm standard)
  • Front Hub Spacing: 110 mm (vs. 100 mm standard)
  • Chainline Shift: 3 mm outward for wider clearance
  • Impact: Requires compatible frame, hub, and crankset spacing
  • Official site: https://www.sram.com (originated with SRAM/RockShox)

Overview

Boost Spacing is a wheel and drivetrain standard designed to improve bike handling, frame stiffness, and component compatibility in modern off-road bikes. Announced in 2015 by SRAM and Trek, Boost redefined front and rear hub widths, moving away from legacy standards that had persisted since the quick-release era.

Traditional MTB hub spacing — 100 mm front and 135/142 mm rear — left limited room for wide tires, progressive geometry, and stronger wheel builds. The Boost system addressed these limitations by expanding both front and rear axle widths:

  • Front hubs widened from 100 mm to 110 mm
  • Rear hubs widened from 142 mm to 148 mm

This 6 mm increase at the rear (and 10 mm up front) might sound minor, but it allowed for crucial design changes. Wider hub flanges enable stronger, more evenly tensioned wheels. It also let frame designers shorten chainstays, increase tire clearance, and support wider tires without compromising drivetrain alignment.

Boost spacing quickly became the de facto standard on trail, enduro, and all-mountain bikes — and has since migrated into gravel and e-bike applications as riders demand stronger wheels and greater clearance.

How It Works

Boost Spacing affects several parts of a bike simultaneously: hub width, axle length, chainline, frame spacing, and crank design.

Rear Hub: 148 mm

Boost rear hubs are 6 mm wider than the older 142 mm thru-axle standard, with 3 mm added to each side. This spreads the hub flanges outward, which increases the bracing angle — the angle between each spoke and the hub flange.

  • Benefits:
    • Stronger, stiffer rear wheels
    • Allows shorter chainstays
    • Improves tire and mud clearance
    • Supports 1× drivetrains with better chainline

Front Hub: 110 mm

Boost front hubs are 10 mm wider than the old 100 mm standard. RockShox led this change with Torque Cap-compatible fork dropouts for even more stiffness.

  • Benefits:
    • Stronger front wheels with wider spoke angles
    • Better tracking under steering load
    • Increased compatibility with larger front tires and fenders

Chainline Shift

Boost spacing shifts the chainline outward by 3 mm. To accommodate this, crankset manufacturers released Boost-specific crankarms or direct mount chainrings with additional offset. This helps prevent drivetrain rub and ensures smooth chain movement across wider cassettes.

Frame Compatibility

Boost spacing is not backwards compatible with non-Boost frames. Rear triangle spacing must match the 148 mm hub, and fork lowers must accept the wider 110 mm front axle. However, many frame builders embraced Boost spacing because it enabled:

  • Tighter rear ends (shorter chainstays)
  • Bigger tire clearance (up to 2.8″ in many cases)
  • Modern geometry with long front-centers and slack head angles

Adoption & Controversy

Boost Spacing was not universally welcomed at launch. Some critics viewed it as an unnecessary new standard, calling it “change for the sake of selling more parts.” Others argued it was a practical evolution, not unlike the move from 26″ to 27.5″ and 29″ wheels.

Despite the criticism, Boost has become the default in nearly all mountain bikes beyond the XC race category. It’s also been widely adopted in:

  • Gravel bikes: For extra clearance, especially in adventure/touring builds
  • eMTBs: Where higher torque demands stronger rear wheels and dropout interfaces
  • Plus bikes: For fat 2.8–3.0″ tires that don’t fit in legacy 142 mm frames
  • Trail and enduro bikes: Where stiffness and geometry flexibility are priorities

Boost even paved the way for Super Boost Plus (157 mm rear spacing), another evolution meant to bring DH strength to aggressive trail bikes — though that standard remains niche.

Manufacturers that embraced Boost early — like Trek, Santa Cruz, Pivot, and Specialized — redesigned entire frame lines to take advantage of its benefits. Over time, aftermarket support followed, with Boost hubs, cranks, and forks becoming standard on most OEM builds.

Notable Implementations

  • Trek Fuel EX and Remedy: First major platforms built around Boost
  • Santa Cruz Hightower / Bronson: Full suspension frames leveraging Boost for stiffness
  • Specialized Stumpjumper: Adopted Boost in redesigns post-2017
  • RockShox Boost forks: With Torque Cap compatibility for enhanced stiffness
  • WTB, DT Swiss, Industry Nine Boost hubs: Widely used in performance wheelsets
  • SRAM Eagle drivetrains: Designed with Boost spacing as a baseline

Related Terms

References

  • SRAM Boost Standard Technical Overview
  • Trek Technical Docs: Boost 148 White Paper
  • RockShox Fork Compatibility Guides
  • Pinkbike: “Boost — What Is It and Why Should You Care?”
  • BikeRadar: “Boost Hub Spacing Explained”
  • Santa Cruz Product Geometry Notes
  • WTB and DT Swiss Hub Product Manuals
Scroll to Top