SRAM i-Motion 9 Nabe

Dieser Artikel behandelt die inzwischen eingestellte i-Motion 9 Nabenschaltungsnabe von SRAM. Wenn man etwas allgemeinere Informationen zu Nabenschaltungen sucht, kann man im Artikel Alles über Nabenschaltungen mehr erfahren. Etwas mehr Informationen zu speziellen Themen rund um Sachs und SRAM Nabenschaltungen findet man im entsprechenden Artikel. Sheldon Brown hat die Nabe auch in seinem Online gear calculator for internal-gear hubs (englisch) gelistet.

Wiederaufbau der Nabe?

The SRAM i-Motion 9-speed hub, introduced around 2006, offered a wider range and more even steps than the competing Shimano Nexus 8-speed. The i-Motion 9 was offered in four versions:

disc brake with a standard 6-bolt rotor fitting;
brakeless -- which also could be used with a disc brake, as it is identical to the disc-brake version except for a dustcap;
coaster brake;
and, i-Brake (large external drum brake -- this version may also be used without the brake).

Drive ratios are:

Ratio 0.542 0.621 0.727 0.853 1.000 1.172 1.375 1.611 1.844 Step 14.6% 17.1% 17.3% 17.2% 17.2% 17.3% 17.1% 14.6%

The i-Motion 9 was rather large and heavy -- 2.4 kg (5.3 pounds) for the coaster-brake version, 1.9 kg (4.2 pounds) for the others, not counting external brake parts. A mechanic at Harris Cyclery once described this hub as a "cannonball." It has been discontinued as of this writing, but in the spirit of completeness, we cover it, especially as SRAM has provided meager information about it.

Some people really like this hub, and if that is you, give it extra care, and don't overstress it.

Also note: a reviewer on a German Web page says:

"Diese Nabe ist nur im Vorwärts-Betrieb nutzbar. Rückwärts schieben oder wackeln an der Ampel bringt das Getriebe in merkwürdige Zustände."

Translating:

"This hub is usable only in forward mode. Pushing the bicycle backwards or track-standing while waiting at a traffic light puts the mechanism into unusual states."

I think this means that rearward rotation of the wheel turns the sprocket backward and actuates the coaster brake, but I'm not sure. A plain coaster brake can freewheel backwards without turning the cranks.

Technische Dokumentation

I have documented disassembly of the disc-brake/brakeless version of this hub (PDF file). The hub is rather complicated, but an accomplished mechanic should be able to read the instructions in reverse and reassemble the hub from individual internal parts -- unlike the earlier 12-speed Elan hub, whose axle assembly was only rebuildable with factory tooling.

There are a couple of hitches, though: SRAM doesn't supply individual replacement parts. The gear unit was only ever sold as a single part, and SRAM does not stock replacement parts for its internal-gear hubs in the USA. Also, an internal nut is destroyed in disassembly and is not available for replacement. Aaron's Bicycle Repair in Seattle, Washington, USA has had replacement nuts fabricated and sells them. Aaron is assembling a stock of spare parts and can rebuild these hubs.

The SRAM 2010 technical manual (also available in German) covers removal and replacement from the shell of all versions of the hub, and servicing the coaster brake. The instructions in the manual should be followed in connection with my PDF disassembly instructions. Note RAM's warning about damaging the right-side outer dust seal during disassembly. I'm not sure whether there is a workaround.

Parts lists for all versions of the hub are in the SRAM 2010 spare parts catalog in English and German, but again, SRAM doesn't stock spare parts in the USA.

Montage und Wartung

The SRAM online user's manual provides good information on installation, in English, and versions are available in several other European languages, linked here.

The hub should be removed from the shell, cleaned and re lubricated, even when new, because factory lubrication is inadequate. See the information on lubrication in the main article about internal-gear hubs on this site. The disc-brake and brakeless versions (possibly also the i-Brake version) can be re-oiled through one of the brake mounting holes. These should be closed off with machine screws when not in use: the plastic cover supplied with the brakeless version does not seal well.

Anti-rotation washers are different from those of other SRAM internal-gear hubs except the newer G8 hub. As this is a rotary-shifting hub, different anti-rotation washers are needed depending on the angle of dropout slots, as shown in SRAM's manuals. Shimano Nexus antirotation washers can be made to fit with some filing.

The axle flats are aligned vertically to face the cable attachment forward. Except with vertical dropouts, the washers do not hold the axle flats parallel with the dropout slots, and so an older bicycle with narrow slots will need to have the slots widened. File the underside of each slot only, so as not to misalign the axle. Also, the overlocknut spacing of this hub is 135 mm, and many bicycles need to have the frame respaced -- possible, though, only with steel frames.

The axle should be secured and chain slack adjusted before securing the reaction arm of the coaster brake or i-Brake to the left chainstay -- as with any hub brake that has a reaction arm.

The chainline is 49 mm. The hub uses a non-standard sprocket, supplied only in sizes of 18 through 22 teeth. As it is a flat sprocket, it can be flipped over to double its wear life; also, its life can be greatly prolonged by replacing the chain frequently, or grinding away the hooks which a worn chain wears into sprocket teeth. The hub was available only for 32 and 36-hole spoking.

The brake lever in the i-Motion 9 IBS SL integrated brake/shifter is direct-pull brake compatible and will not work correctly with other brakes, except some disc brakes. The same is true of the matching BL 60 brake lever.

Wie die Nabe funktioniert

The i-Motion 9 has an unusual planetary gear system with four concentric parts instead of the usual three. From the outside to the inside, there are:

a ring gear;
a cage made of two parts locked together with lugs around the outside, the larger (right) end of which has stepped planet pinions that engage the ring gear in the previous step, and the smaller (left) end of which includes another ring gear.
a cage which carries planet gears that engage the ring gear in the previous step and also carries two sun gears, one, the other, or neither of which may engage the planet gears in the previous step;
a single sun gear, locked to the axle, which engages the planet gears in the previous step.

These parts are shown in steps 25 through 29 of my disassembly sequence.

Power is applied at the right side of the hub, as usual, and taken off at the left side. Thanks to the two ring gears, power may go from right to left inside the hub, then to the right, and then back again to the left. The two cages and the ring gear may be engaged or disengaged at either side of the hub. In this way, the same gear train can achieve both increase and decrease ratios, including ratios using both planetary systems.

Shifting is by means of a cam which pushes shifter elements to the left along the axle. I haven't taken the time to scope out the shifting sequence, though I have managed to calculate the drive ratios based on gear tooth counts. My example hub doesn't have a coaster brake, so I'm not sure just how that is engaged either.

Sheldons i-9

Sheldon installed a SRAM 9-speed on one of his bicycles and wrote about it here.

You may look up the gear ratios in his Online Internal Gear Calculator.

Siehe auch

Quelle

Dieser Artikel basiert auf dem Artikel SRAM i-Motion 9 Hub von der Website Sheldon Browns. Originalautor des Artikels ist John Allen.

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