How does a hammerschmidt crank work

One is greater than two. There are two gears: and Overdrive. In , everything is locked and spinning together. Turn the pedal once and the chainring goes around once. In Overdrive, the ratio is approximately Turn the pedal once and the chainring goes around about 1. The Truvativ HammerSchmidt transmission is a planetary gear design that when engaged and locked down gives you a chainring to pedal revolutions.

When cable is released and the overdrive is engaged, you get 1. At first, the Truvativ HammerSchmidt takes some getting used to…partly because our brains are so front derailleur trained that a new front transmission seems foreign.

When you combine that with the swapped front shifter setup large front paddle goes easier while smaller front paddle goes harder , it takes a ride or two to get used to the new system and lack of shifting issues on the front end.

Just riding along, the HammerSchmidt performs exactly as described. You get crisp, fast shifts between the two ratios whether you are moving or not. Under climbing load, the shifts are consistent and allow you to change ratios quickly even when hammering out of the saddle. The ISCG mounts consist of three special frame holes around the bottom bracket shell that allow the installation of various chain retention systems.

Adaptor plates bolted between the shell and bottom bracket are not acceptable. The system will load the mounting tabs torsionally, and it is important the tabs be integrated as part of the frame. This assembly collar plate secures simultaneously against both the bottom bracket shell face and the ISCG tabs.

The tab surfaces should be machined to insure they are parallel to the surface of the bottom bracket shell. Additionally, and more importantly, the distance from the shell face to the tabs must be cut to be equal to the predetermined supplied spacers thickness. The kit comes with spacers in sets of three in thickness of 0. In some cases, no spacer is used at all. By using these spacers the transmission system planetary and sun gear will be correctly aligned. Begin frame preparation by measuring the width of the bottom bracket shell figure 4.

Truvativ specifies certain tolerances for the three common shell widths:. Nominal 68mm shells: If the shell is wider than the tolerances it can be machined narrower as needed. If a shell is narrower then the tolerances, it may be necessary to machine and then add a spacer according.

If the shell face is very close to or equal to the lower end of the tolerance, consider not machining this shell face. Begin by facing the bottom bracket shell face as you would normally prepare a frame. This ensures the bearing surfaces of the bottom bracket spindle are parallel and square to the axis of the thread.

If using the BTS-1 leave the threaded inserts in place. These will guide the mounting tab cutter. The cutter fits the handle of the BFS-1 bottom bracket facing set. The holder also fits the handle of the BTS-1 tapping and facing set. A series of shims allow the cutter to reach and cut mounting tabs that are inboard of the bottom bracket shell face.

Before facing, inspect the mounting tabs relative to the shell face. The tabs may be flush with the shell face figure 8. The tabs may also be lower inboard of the shell face figure 7. Figure 7. ISCG tabs are further inward, or "lower", then the shell face. The Truvativ cutting tool bolts to the Travativ mounting plate. The inner perimeter of the mounting plate will push against the shell face, with no facing occurring. With no spacers between cutter and holding plate, the cutter will be in the same plane as the shell face.

By installing spacers behind the cutter, the cutter will be positioned further and further inward relative to the shell face. Hefty, gravity-oriented sleds were an accepted norm, alongside a contingent expectation that they could be pedaled up the hills they were so adept at smashing down, regardless of how ungainly that upward progress was.

Multiple chainrings and front derailleurs were sorely taxed by long-travel suspension working over rough ground, chain guides were generally only good for single rings, and single-ring systems at that time were limited in range.

This was the zeitgeist into which the HammerSchmidt was born. It offered lightning-fast and precise shifting between two ratios: and a It could even be shifted while coasting or backpedaling. It cleaned up a difficult area of suspension design, allowing builders to compose their suspension kinematics around a single chainring. If it was so great, why did HammerSchmidt disappear?

The packaging of the planetary gears has some unique side benefits to complement the instant shifting. First off, having just a single small-diameter chainring gives gobs of ground clearance.

Add in the tough built-in bashguard and you can attack large boulders or logs with more speed and aggression than usual, all without having to worry about bending a ring or breaking a tooth.

Mirroring the outer guard is another inboard plate, both of which work with the small box guide up top for unbeatable chain security. When properly set up, the chain cannot derail regardless of the terrain, and no two-ring guide on the market can top the HammerSchmidt in that respect. The chainline is also optimised so that every cassette cog is fully accessible with no risk of derailleur cage or chainring rub.

So while there are only two front ratios, the total number of usable gears is quite generous compared to conventional two-ring setups where some combinations are only marginally functional. Finally, the system is quite well sealed, especially if you use full-length cable housing.

In addition to the close-fitting parts, proper rubber contact seals are placed at key points to prevent mud or water intrusion. If and when the system does get contaminated, the guts are reasonably easy to access for servicing, too.