Rataspakan tyyppi

Noissa kuvissa ainakin toinen pakka (HG) on 8-rattainen, toinen (IG) on seiska. HG:n ja IG:n välinen ero on ketjujen leveydessä, joita itse asiassa on kolmea eri tyyppiä: vanha HG 7,4 mm, nykyinen HG 6,6 mm ja IG 7,1 mm. Sinänsä pakat sopivat samaan akseliin, mutta tuo vanha/uusi HG aiheuttaa vähän ongelmia.

Google on muuten aika hyödyllinen työkalu tiedon hakemiseen, sillä löytyy mm. tälläinen selitys http://utahmountainbiking.com/UMBphpBB2/viewtopic.php?t=6&view=next&:
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HG stands for Hyper Glide, IG for InterGlide. Shimano first came out with HG chains in '91. In '94, Shimano went from 7 speed to 8 speed and in '95 they introduced the IG drivetrain. The new IG replaced the old HG on the upper end Shimano lines. IG chains were designed to run specifically with IG chainrings and cassettes. In '99, Shimano introduced the 9 speed drivetrain (or Mega 9). This included a new narrower chain, chainrings and cassette and they brought back the HG chain prefix. Got all that?

The main difference between IG and HG is the chain width. IG chain is 7.1 mm wide, HG 6.6 mm wide. (The old HG is 7.4 mm wide.)

Today, HG means 9 speed drivetrain. IG is pretty much for 8 speed drivetrains. As for the numbers that follow, the bigger the number, the better the chain (supposedly). For example, the HG-53 is Deore, HG-73 is LX and HG-93 is XT. The XTR chains are completely different. They start with CN-7700.

According to Shimano, you can run any IG chain with any HG cassette. But, as for the chainrings, " The 9-speed chainring teeth are reprofiled for narrower chains, therefore you can not use an 8-speed chain [on Mega 9 chainrings]".
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http://www.shimano-nordic.fi/publish/content/cycle/snc/sw/fi.html;jsessionid=4239c5a7-e40a-ad41-81f7-03eedb33fc51