Mar 05 2009
Floating Bottom Bracket Suspension
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This particular idea was pioneered by GT as a basis for their I-Drive suspension system. This system places the bottom bracket along with the crank assembly component on a pivot point that is separate from both the front and rear triangle of the bike resulting in the bottom bracket and crank assembly effectively floating. This is the unique feature that distinguishes the floating pivot design from other active full suspension systems which have the bottom bracket mounted on either the front or rear triangle of the bike.
The floating bottom bracket design maintains most of the quality characteristics associated with VPP and horst link/four bar suspension systems. The floating bottom bracket design has the technology within the design to minimise pedal bob (if correctly calibrated) and also remains resistant to braking compression. This means that even under braking the suspension remains active making for a smoother riding experience for the user and improves the traction of the bike by keeping the back wheel in contact with the ground for longer.
It is general opinion that the floating bottom bracket design has potential to be a brilliant all round solution, however although models have improved, there is still a lot of improvement to be done. One problem with this type of suspension is the added weight which comes purely due to the complexity of the design, although the current I-Drive is now much lighter than the original, it is still a little on the heavy side, making climbs tricky.
It is not just the I-drive that utilise this floating bottom bracket design, there are a couple of other manufacturers that make use of the idea, however they each have their draw backs. One flaw comes from having the crank assembly mounted on a floating pivot, because of this a special front derailleur has to be fitted to counteract the motion created at the pivot point, despite this there are instances and cases of shifting trouble on the front gears. It is also noted that this type of suspension causes the seat post to be at a slightly unfavourable angle with some riders making a correct pedalling position difficult to achieve.
All in all, this system has some good points, eliminating pedal bob and compression under braking, however it still lacks some of the simplistic refinement found in other suspension solutions.
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