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Suspension forks typically have a bridge which connects the two lower legs. In the past, this also provided a hanger for the rim brakes. I always thought though that the main purpose was to ensure that the two legs remained parallel in compression, so that there was no torsion on the front axle.

I've noticed some MTB suspension forks that are bridgeless. In these systems what prevents the legs from compressing at different rates and twisting the axle? Can we broadly say a bridgeless suspension is weaker than a bridged one?

rock shox

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    You don't even need 2 legs - Canondale Lefty forks for example, work fine. – Batman Jan 23 '17 at 19:27
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    The photo you included looks similar to the fork in bicycles.stackexchange.com/questions/42076/… so the distinction might be inverted vs traditional. – Jamie A Jan 23 '17 at 19:38
  • They will compress at different rates as one has the spring and the other the damper (usually) – Chris H Jan 23 '17 at 19:44
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    As far as I know the purpose of these bridges was only to increase stiffness for the brakes, and came as an integration of brake boosters into fork design. Horseshoe shaped brake boosters were quite popular in the nineties. Through axles probably make the forks stiffer towards torsion. Example picture of one on a replica re-build of some famous downhill racer's bike. – gschenk Jan 23 '17 at 22:26
  • @gschenk the brake boosters were primarily to limit flex of the canti brake bosses. They were always optional. – Criggie Jan 24 '17 at 3:14
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No, you can't broadly say "Bridged suspensions are stronger". It's depends on many things, including the design of the system, materials used, build quality, etc.

As Batman mentioned, Cannondale's Lefty suspension is stronger than most traditional systems and isn't bridged, or even bridgeable.

Inverted, or "upside-down" systems, like the one in your photo, have other considerations as well, outlined in this question. To your question, the thru axel keeps the stanchions bound together, preventing different rates of compression.

I think we will see fewer front forks with suspension bridges in the future and more inverted systems, as the technology trickles out to less expensive builds and the cost of manufacture drops.

  • I would think regularly oriented forks will likely stick around as the inverted design is inherently more exposed to scratches on the stanchions. Also weird cable routing. – Paul Jan 24 '17 at 4:56

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