SRAM G8 und G9 Nabenschaltungen: Unterschied zwischen den Versionen

Sheldon Brown's Internal-Gear Calculator

The G8 8-speed internal-gear hub was introduced in 2013, and the G9 in 2014. Production was discontinued in 2015. The G8 was offered in three versions:

The G9 was offered only in a disc brake version (which may also be used without the disc). Drive ratios (in italic for the G9 only) are:

The shell of G8 and G9 is somewhat larger than that of the discontinued i-Motion 9, but the internal mechanism is much simpler, and the G8 and G9 weigh less.

The following specifications have been released, or measured:

The G8 and G9 are grease-lubricated. These hubs require periodic cleaning and relubrication. Cleaning and relubricating these hubs when new is a good idea, even though it voids the warranty, because factory lubrication often doesn't stand up to bad weather conditions. The coaster-brake version of the G8 requires high-temperature grease for the brake mechanism, like earlier SRAM coaster-brake hubs; otherwise lubricate with Phil Wood oil for the gears and boat-trailer grease in the bearings for the least drag consistent with good resistance to contamination. Unlike with the i-Motion 9, the disc-brake mounting holes do not extend all the way through to the inside of the hub, but you could drill one hole through (with the hub disassembled so you can clean out metal chips) to use it as a lubrication port. Mark which one you drilled. See the information on lubrication in the main article about internal-gear hubs on this site.

The G8 uses a proprietary indexed twist shifter which fits only a flat handlebar but an owner reports that this shifter does not work properly. Very unusually, the G8 is compatible with an indexed derailer shifter, SRAM 3.0 series -- see article decribing how to use one. An aftermarket shifter for drop bars may be available. The G9 uses a two-lever trigger shifter.

A German blogger who has tried a G8 reports that it runs quietly and shifts smoothly. Reader Brian Sorenson reports:

Other than that, it does what it says on the box. Adjustment is dead simple and it has a nice quiet sound to it. Efficiency seems on par with similar hubs, and shifting even under load is smooth.

The G8 and G9 have a first stage with three decrease ratios, followed by a second stage with direct drive and two increase ratios.

G8 internals

G8 sun gear pawls

The G8 has no direct drive (1:1) ratio, and all but the two lowest gears (three lowest for the G9) use both stages, so efficiency can be expected to be lower than with some other internally-geared hubs. Three additional drive ratios would be possible if the first stage had direct drive-- but with the gear tooth counts of this hub, all but the highest ratio would fall close to others, and the jump to the highest would be large. The lack of direct drive may be to avoid an awkward shift, as with the Shimano 7-speed.

I thank Brook Fowler for passing along technical specifications, Taras Bereznyak for analysis and calculation of gear ratios, Torben Finn Laursen for photos of the G8's internals and the schematic diagram, Zack B for pointing the way to additional information about the G9, Brian Sorenson for his feedback and Aaron Goss for publishing rebuilding information.

== Siehe auch ==

Installation instructions for the G8 and G9 hubs