DA cassette question
 

Hello , I recently bought a nicely built 98 Lemond Zurich. I'm a older rider living in a very hilly area
and am used to riding a triple , so I need some lower gearing. Can I go 27 or larger with a 7700
DA 9 speed(frt and rear) ? Before I start thinking of a compact I thought I change the cassette out the first. Also since I'll look for a used cassette will Ultegra and 105 work ?.
Thank you , Bruce

First, the easy answers. Yes...both Ultegra and 105 cassettes will work on your wheel and you'll be fine with a 27 tooth cassette with your setup.

You could probably go with a 28 tooth cog on the back (I think SRAM makes a 12-28) but anything bigger would likely require going to a long cage derailleur (I'm assuming the current der is a short cage) and probably a new chain.

I've regularly swapped 11-23 and 12-27 cassettes on my DA bike. No problem at all. And, I prefer Ultegra or 105 cassettes. You save a few grams but DA is twice as much money.

What cassette do you have installed now? You may need extra chain length if you're going from say a 23 biggest cog to a 27 or 28.

Good point. Especially if it was sized according to the Big-Big method.

Thanks for the quick responses. I have an 11-23 on it now with standard 53 -39 upfront . Bruce.

Don't confuse a road "long" cage derailler with a MTB derailler that can handle bigger cogs. Road deraillers are generally spec'd up to a 28 tooth rear cog regardless of cage length while MTB deraillers can handle up to 34 (sometimes 36) again regardless of cage length. Cage length only determines how much chain slack the derailler can handle (tooth differential between smallest and biggest front chainring plus same for rear cassette cogs).

If you go to a road long cage der. you can use a 30t cog on a 12-27 cassette. To make the change you will need a 13t first position 8pd cog. You remoive the 12 and 13 and use the spacer on the 30. Because the 13 and the 30 are at the ends of the travel the 8sp cogs will work fine.
Replace the 39 with a 38t ring for a little lower. That will give you a 34" low gear.

No. Cage length has nothing to do with capacity - the largest cog a derailleur can handle. Cage length only affects how much chain slack there can be in the drive train.

frisky, Shimano RDs are all rated at 27T capacity, but typically handle 30T without problems. Larger than that and you need a MTB derailleur. You may or may not need to lengthen your chain. When you put a bigger cassette on, measure it. I often swap a 23T and 27T, and need to make no chain adjustments.


Oops, I see joejack got here first.

Why use an 8-speed cog? I use 9-speed first position 13's on my 9-speed cassettes. In one case I used an 8-speed 13 and ground down the spacer to the 9-speed thickness for better shifting.

My favorite 9-speed cassette is a 13-26 that I put together from various parts including the middle cogs from an XTR. Very light with close ratios.

Not all road rear deraillers and drop out configs will allow you to use a 30 tooth cog. 27 is the spec from Shimano and with anything bigger you are beginning to push your luck. While it works for some, it definitely does not work for every bike/derailler.

100% false.

Cage length determines the capacity of a derailleur to take up chain slack

http://en.wikipedia.org/wiki/Derailleur_gears

Changing to a wide cluster > 27 *usually* exceeds most short cage RD's capacity.

Only about 0.1% of the people who regularly state that shimano derailleurs handle more than 27t understand how it came about and why it can actually be *lower* than 27 given the right bike.

Care to explain? I'd like to hear your thoughts on this as I honestly haven't taken the time to understand it.

I did about the same thing to build a 13x27 9-speed cassette. I started with a 12x27, discarded the 12 and 13T cogs and added a 13T first position cog salvaged from a 13x25 cassette and added a single 16T cog and spacer.

The problem with doing that now is getting a 16T cog of any "speed". They just aren't available any more and took some real scrounging back when I did this about three years ago.

Bullcookies. I used the wrong term ("capacity' - what is the correct term, anyway?). But I was correct on both points. Max cog size is determined by the parallelogram geometry. Cage length does not determine max cog size, only the ability to take up slack.

It is possible that a setup with a large rear cog will have too much slack for a short cage, but it is also possible that it won't. To the contrary, a very large cog will always exceed the ability of the RD to shift to it.

Main reason was actually marketing. 27 being the biggest Shimano made when the spec was published. If you went out and bought a 28 SRAM it gave them an exit from standing behind it..

Irrelevant. We're discussing why that figure is not a 'hard' limit and why it may vary from bike to bike. Even with the exact same cogset + rear derailleur installed.

http://www.bbinstitute.com/dl/dx_demo_chapter_32.pdf

Refer to page 32-19

No you're not.

It's clear you don't understand the difference between max cog size, how it's determined and what it changes. It has nothing to do with "parallelogram geometry". Your misuse of the term capacity is a further indication. Read page 32-21 & 32-22 of the pdf I linked above, in addition to 32-19.

I suppose one should respect Barnett's, but I don't buy it. If cage length is the determining factor, then why isn't the long cage version of the same derailleur rated for a larger cog size? Likewise, why is a MTB RD with the same cage length rated for a different max. cog size?

I believe that you are mis-reading a rather poorly written section. True enough. But wrap itself is not the sole determining factor. Nor is it the major factor. They are saying only that wrap is a factor.

Btw, this may be another terminology issue. Barnett's doesn't define "cage length". (A rather curious oversight.)

I understand it to mean the distance between the two pulley axises (sp?). If it's understood as pivot to guide pulley - or something similar - then they're saying essentially the same thing as I am.