Rear Triangle Spreader

A flat tire on a modern road bike is a five-minute job. A flat tire on a commuter with internally-geared hubs, fenders, a chain guard, and a kickstand is what your day becomes when one rolls through the door. The wheel won't come out of the frame without removing half the bike, the shop charges a flat-rate tube replacement, and the labor turns the job into a money-loser before the tire is even pulled. The Rear Triangle Spreader 1678/2BI-US keeps the five-minute job a five-minute job.

What the tool does

Disconnect the non-drive axle nut on the hub. Slip the spreader between the hub flange and the inside of the rear chainstay or seatstay. Turn the spreader's handle to extend the body, which spreads the frame laterally away from the axle on the non-drive side. Within a few rotations of the handle, the rear triangle has enough gap to slip the tire and tube off the rim without removing the wheel from the frame at all.

The tool works on most internal-hub builds, fender-and-rack-equipped commuters, and any frame configuration that traditionally requires dismantling accessories to remove the wheel. The hub stays in the frame, the chain stays on the cog, the fenders and accessories stay attached. The wheel rotates in place while you work the tire off and back on.

When to reach for it

The 1678/2BI-US is a shop-productivity tool more than a riding-mechanic tool. It pays off on internally-geared hubs (Shimano Alfine, Rohloff, Nexus) where chainline reset is non-trivial, commuters with fenders or racks bolted to the dropouts, step-through frames where the chainstay yoke crowds the wheel exit, chain-guard bikes (Dutch-style city, e-cargo), and any time the labor-cost of removing the wheel exceeds the cost of spreading the frame.

Compatibility

The spreader fits standard road and MTB rear ends with QR or thru-axle hubs. The tool is designed for steel and aluminum rear triangles, which respond predictably to controlled lateral spread within their elastic range. For carbon frames, consult the frame manufacturer before applying any lateral force; most carbon manufacturers explicitly disclaim aftermarket spreading, and we don't recommend using the 1678/2BI-US on a carbon rear end without that conversation first.

Specs

• Operation: handle-driven mechanical spread on the non-drive side
• Compatibility: most steel and aluminum QR or thru-axle rear ends; carbon requires frame-maker consultation first
• Pair with our glass-fiber-reinforced tire levers 1657 for the tire-off step that follows
• Made in Slovenia by Unior

Includes: Spreader body, drive handle.

Made in Slovenia, since 1919

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The 1678/2BI-US is a shop tool through and through; most home mechanics never need it, and most pro shops pay for the tool on the first hard commuter flat that comes through the door. The value is measured in hours of shop throughput, not features per ounce.

Pro tip from our mechanics

Spread the frame just enough to clear the tire. More spread is not better; the spreader works because lateral force on a steel or aluminum rear end is well within the frame's elastic range, but the elastic range has limits. Open the gap to fit the tire bead through and stop there. Once the tire is off, drop the spread back, do the patch or tube swap, and re-spread for the reinstall.

The Rear Triangle Spreader pairs naturally with our Dropout Alignment Gauges 1692/4 and the Hanger Genie family. The three are the rear-end-service trio for shops working on bikes more complex than racing road bikes. The trio's place in the rear-end workflow is in our Tech Tips: How to save a bent mech hanger →