HG70 vs HG90 cassettes

[Woz]

Is it not also true that the ramping etc is different if the jump is 1, 2 or 3 etc cogs difference......i was told that by a rep years ago, but ive never paid close attention as i rarely swap out cogs in a cassette.?

It's true - but that comes under the banner of tooth profile and position for me.

Basically, a low end cassette will have fewer "gates and ramps" to allow the chain to displace smoothly when the gear change happens over one revolution of the cassette. Hence a more "clunky" change. Without looking in my cassette box, I think HG40 or lower is only 3 gates when you get in the largest sprockets.

The higher end cassettes will have more "gates and ramps" giving the impression the gear change is quick, smooth and precise because the are more opportunities for the chain to derail over one revolution. There are four gates with HG50 road if I recall correctly. The other thing which Shimano have done on higher end cassettes is improve the ability to make say a three sprocket downshift in one go (provided of course the shifter can do it, XT level if memory serves me right).

The above is one of the main reasons why you can't mix sprockets (successfully) between model types.

I routinely split cassettes; saves weight dumping the rivet, makes cleaning easier and checking teeth wear against a new sprocket. I won't even bother looking for 7 speed cassettes, just get an 8 speed and leave of either the largest or smallest sprocket and change the spacers.

In several cases I have made my own cassette combinations, but to be honest it's getting a bit pointless since discovering SRAM offers better thought out combinations.

 

[Once A Hero]

I've got 4Nr. 7speed 'HG' cassettes in amongst my spares, perhaps I'll dig them out and see if I can play spot the difference.

 

[FluffyChicken]

The letters you talk about for the grouping are because of the ramps.
Match the letter to the next cog and it'll ramp properly. Which is why some have two, so you can move to a different group of cogs.

(if there are ramp/profiling on the back side, then you are into modern mid 90s, IG onwards era).

 

[Tootyred]

I thought that might be some way of identifying the ramping. Very interesting.

Do you know of a chart or anything fluffy? I would be interested in an anorak kinda way.....not that i would ever use it!.

 

[JimBob22]

Agree ,in a very anorak way it would be good to c some info on the ramping..
Still going thro the German info site,then going on Mastermind, Specialist subject: Shimano cassettes !!

 

[Tootyred]

I've started so i will finish......

 

[Woz]

AFAIK, the letters are arbitrarily assigned, just to make a unique identifier. I would hazard a guess Shimano
relates them to the stamp press design / version with there own look up table never published. I have found no logic
whatsoever in the meaning of the letters themselves.

No such dummies guide table exists, instead it's a matter of going through the techdocs and
having the cassette in front of you. The low level spare part product number of individual sprockets and cluster of
sprockets (groups riveted together or mounted on an AL spider) can also help.

As FC says, a sprocket with two cog group stamps (often on a 15T or 16T, and perhaps another one around the 19T, 20T, 21T) will allow you to split and combine cassettes (keeping with the same model number and speed). It's why you can take a lower portion of a road cassette (giving you tight close ratios) and mate it with a upper portion of a MTB cassette (giving wider jumps). For years I was doing this since I could never get along with Shimano's stupid 11T to 13T to 15T jump on most MTB cassettes.

I think a lot of this low level fiddling stems more from the road side where cadence is important TBH. BITD you would go in the LBS
and pull sprockets off a hugh Mallard table to build your own custom cassette / freewheel. Shimano got a lot of flack that
they never made a true corn-cob for time trialist so hacking cassettes up was the way to go. In fairness, Shimano at least gave
an identification system to do so, but commercially they never really wanted you to hack cassettes up and buy individual sprockets.

Still, if you want to optimise your gearing for your terrain it's worth poking in to, but it's getting a redundant fiddle as the offerings and number of speeds as increased. It's probably quite rare that you can't find the "right gear" with todays kit.

 

[Woz]

Happy Days. Long gone in quest of indexing and smooth shifting.

 

[FluffyChicken]

May just happen to have this I scanned some time ago, oddly one is still in the tiff file format so the forum didn't like it (hence the naff screenshot).

Must put these catalogues up at some point.
Ages since I scanned them in..

 

[Once A Hero]

I've got 4Nr. 7speed 'HG' cassettes in amongst my spares, perhaps I'll dig them out and see if I can play spot the difference.

Here’s my selection, the 3 from the left all seem to be the same finish, whilst the one on the far right is much shinier.
By the OPs reckoning, that’s 3 x HG70s and 1 x HG90. Maybe