MrCjolsen

The PG-970 is on my bike with about 3000 miles on it. I have a PG-950 for when it wears out. The cogs look identical. The only difference is that the 970 has pretty orange spacers and weights a little less. Does it work any better than the 950?

One more thing. I'm pretty adept at taking apart Sram cassettes and putting them back together. Could I just take the worn cogs off the 970 and replace them with the 950 ones if I still want the pretty orange spacers?

jemoryl

Based on my experiences with Campy cassettes, I'm guessing that you would be correct in assuming that weight is the only significant difference. I suppose you could settle the spacer issue with a careful side-by-side comparison.

asmallsol

(Being a material's engineering student, and I'm going to just go by assumptions here)

Being different weights, their metrological composition is different. This means that there is going to be a difference in strength and toughness in the two cassettes. On the higher end Shimano cassettes, they actually use a Titanium alloy on half the gears where you need a lightweight metal and Chromalloy where weight isn't as big as an issue and you would rather have a tougher metal

MrCjolsen

So the cheap cassette will have the tougher chromoly on all of their gears? Is this one of those heavier=stronger sort of things?

asmallsol

Steel is an extremely tough metal but the cost is weight. You can build a bike to be bullet proof, capable of a million miles for next to nothing but it will be extremely heavy.

In engineering, strength in your number one concern with trying to use as little weight as possible. Where extra strength is needed, weight can be sacrificed. However, with clever engineering principles, weight can be added without effecting the performance much.

Take my wheels that I am running right now, the Dura Ace WH7700. Nimples need to be used on wheels and are large masses in the spoke equation. However, Shimano decided to mount them on the hub instead of rim. This reduces the rotational momentum by bringing mass closer to the center. With the cassette, I am sure they have similar reasons. Larger gears have a larger axis resulting in a higher momentum, so the mass of the gear is reduced by applying titanium, however, the smaller gears have smaller axis so the rotational momentum is less effected by a little mass addition.

The material the part is made of only tells a third of the story. You can give me a peice of wire, and within 10 minutes, I can change the materials properties without adding any extra elements and make something that is strong and ductile, or make it weak, stiff, and brittle.

However, the density of a metal is not always the best figure of overall weight that the part will finally weigh. Take the age old question steel vs aluminum. Aluminum is approximately 3 times lighter then steel, however, steel is 3 times stronger. This means that your going to have to either have thicker tube walls on the aluminum, or just overall bigger tubes to have a frame with the same strength of a steel one. Over all you end up with the same weight (although this doesn't really apply to the cassette)

jemoryl

This is not true with Campy. In the current lineup all the steel cogs will wear and shift the same. Record cassettes use titanium alloy for the larger cogs to save weight (and that is just a few grams). Nobody who pays for their own equipment would be wise to use a cassette with alloy cogs, IMO. Some of the weight differences for the all steel clusters comes from the way they are constructed (carriers vs. no carriers, size of holes, etc.); the steel itself is the same and has the same surface treatment.

What I am trying to say is that if SRAM is anything like Campy you are probably not getting much for your extra $$$ when you upgrade your cassette. The lower SRAM road group (Rival?) is still aimed at a pretty fussy market, so I doubt the associated cassette would be crap.

G60

you mean 'metallurgical'?

metrology is the science of measurements, metallurgy studies the makeup of all types of metals.

metallurgy seems more appropriate in this case.

G60

why not? steel is an alloy.

i'm not a metallurgist , but i am a stickler for the facts.

asmallsol

lol, guess I didn't read my spell check very well.

jemoryl

I think pedant is the word you are looking for.

npoak

SRAM 970 cassettes are far better shifting and make less noise when shifting....especially noticable with a full SRAM drivetrain. Other than that shift feelthey are slightly lighter....both wear about the same, in my experience.

jemoryl

I'll take your word, but I am surprised that there is an actual difference in the shifting/noise for two such similar products from a major manufacturer.

Oh, I just tried to find these cassettes at the SRAM website: unless I didn't try hard enough, they are not too keen showing what their product specs are. A pretty crappy website, IMO. Looking at some vendors it appears the 950/970 are 9-speed mountain cassettes. I thought the OP was asking about road cassettes, given the forum topic.

Patriot

The cogs between the 970 & 950 are exactly the same. The weight differance is in the spacers, and possibly more steel reemed out in the 970's cogs to lighten it up a bit.

That said, my 10s Veloce cassette is excatly the same as my Chorus cassette, only the chorus is drilled out more, and has lighter spacers.

Record and Dura-Ace cassettes use low gear Titanium cogs to drop the weight only. Ti is a softer metal, so those cassettes are known to not last as long as the all steel versions. Unless you are racing, it really is best to go with a cassette with all steel cogs for longevity purposes. When some bikes are used for alot of low gear climbing, those Titanium cogs may only last 1500 miles in many cases.

All this said, OP...

if you are dying to save weight, get the 970. But if you don't care about an extra 20g or so, the 950 is fine. There is no differance in their performance. The cogs are exactly the same, with the same machining and chrome finish. Even the SRAM people told me this when I asked a while back when considering there cassettes for my bike. If anything, the 950 will be better for toughness and longevity, because I think it uses alloy spacers vs composite for the 970.