Boost vs Non-Boost Hubs: Spacing and Compatibility

Boost hubs are 110 mm wide at the front and 148 mm wide at the rear, while non-Boost hubs use 100 mm and 142 mm over-locknut dimensions. These 10 mm (front) and 6 mm (rear) increases shift the flanges outward and change the chainline, making wheels stiffer but incompatible without adapters or new frames.

What Are Boost and Non-Boost Hub Sizes?

Hub spacing is measured as the over-locknut dimension (OLD) — the distance across the hub from the outside face of one locknut to the other. This must match the frame or fork's dropout spacing.

• Non-Boost (standard): 100 mm OLD front, 142 mm OLD rear.
• Boost: 110 mm OLD front, 148 mm OLD rear.

Both standards normally use thru-axles: 15 mm diameter front and 12 mm rear. Boost hubs require longer axles to accommodate the wider hub shell.

Boost vs Non-Boost Hub Spacing

The exact dimensions are:

The 10 mm front and 6 mm rear widen the hub flanges, improving spoke bracing angle and stiffness. The rear also shifts the cassette outboard by 3 mm for better tire clearance and a Boost chainline of 52 mm (vs 49 mm non-Boost).

What Is Boost Hub Spacing?

Boost is a modern standard introduced by SRAM in 2015. It increases hub width to allow wider flange spacing without making the frame's Q-factor (pedal stance width) wider. The result: a stiffer wheel with similar weight.

Boost front = 110 mm OLD
Boost rear = 148 mm OLD

What Is Boost Spacing?

“Boost spacing” refers to the frame/fork droput width matching Boost hubs. A Boost fork has 110 mm dropouts; a Boost frame has 148 mm rear dropouts. You cannot fit a Boost wheel into a non-Boost frame (or vice versa) without an adapter.

Compatibility Between Boost and Non-Boost

Can you use a Boost wheel in a non-Boost frame?

No, not directly. The hub is too wide for the dropouts. Some hubs have interchangeable end caps, but the actual OLD remains fixed; only special reducing adapters (e.g., 148→142) exist for rear hubs with a 6-bolt rotor, but they are rare and not recommended.

Can you use a non-Boost wheel in a Boost frame?

No. The wheel would rattle side to side and the disc rotor would not align with the caliper. Adapters (spacers) can widen a 142 mm hub to 148 mm, but they move the rotor and cassette, often causing chainline and brake issues.

Fork compatibility

Front wheel swaps are more forgiving because the front wheel doesn't affect drivetrain. A 100 mm hub can be spaced to 110 mm with two 5 mm spacers, but the rotor must be re-shimmed. Better: use a hub with swappable end caps that convert the OLD.

What About Tire Sidewall Numbers?

Tire sizing (e.g., 29×2.4) is independent of hub standard, but Boost frames often clear wider tires because the chainstays can bow outward more. Always check the frame's max tire clearance, not just the hub spacing.

Summary

For new bikes, Boost is standard on mountain bikes and some gravel bikes. Non-Boost remains common on road and older bikes. When replacing a wheel, match the hub OLD to your frame and fork, and double-check brake rotor size and axle type.