Duane Behrens

A friend asked me to post my reaction to replacing my original 12-25 cassette with a new 12-30 cassette. The bike: a Specialized Tarmac, standard Shimano 105/ 53-39 crank, Ultegra 12-25 cassette, Ultegra short-cage rear derailleur.

Mechanical: Surprisingly, the new cassette didn't require replacement of the chain. Even better, the original short-cage derailleur seems to work fine, with the B-screw set to near-full stop.

Riding descents: I know it's my imagination - both cassettes have 12 teeth on their smallest cog - but the new cassette made me FEEL as if I was pedaling faster in the largest frong/smallest rear cog combination. In any case, I'm spending a lot more time on the larger front chain ring on the flats, while staying away from the largest cogs in back. That has been nice.

Ascents: Well. I'm glad I didn't take the incremental step of switching to a 12-27; I'm not sure I would have noticed any difference. There is a noticeable - not huge - difference with the 12-30. I'm able to sit now through the steepest section of my normal climb much more easily. I used to stand the entire way with the chain in the smallest front ring and the 5th largest cog in back. Now I'm able to just put it in the largest cog out back and spin up the hill.

Smoothness. It's really okay. I was afraid there would be missed or delayed shifts with the new wider spread, but I really haven't noticed that. I HAVE been careful to shift with a bit of authority.

I would have admitted it if this maiden voyage had been disappointing. But it was good, really. I'll keep it. DB

Wheels Of Steel

Whenever components are stretched beyond manufacturer spec I'm always more curious to know if the component decays quicker over time. 10-speed Campagnolo 53/39 front with 11-34 in back for example.

10 Wheels

You came for advice, received it,and enjoyed the new change to the bike.

dsbrantjr

"Surprisingly, the new cassette didn't require replacement of the chain."

I would suggest that you slowly and carefully make certain that your chain is long enough to shift into the large front/large rear combination without straining your derailleur. Turning the cranks by hand with the bike in a stand is ideal.

Even if you do not intend to shift to this combination, if you forget and your chain is too short you can do some severe damage to your derailleur and possibly your frame.

HillRider

The crank and chainrings don't care what's in back. If the rear derailleur is capable of clearing the largest cog and has adequate "wrap" capacity, everything should last as long as any other combination.

Duane Behrens

The penultimate poster convinces me I'll replace the chain (and re-size as necessary) rather sooner than later. The last poster eased my mind a bit re premature wear on the derailleur. Thank you both.

It seems as if 53x39 front and 12-25 (10 speed) in back have been the standard for some years, but are now giving way to 50x34 and 11-28. And possibly 11-speeds.

So, just to see where we've come in the last 30 years, I went out to the garage to count the teeth on an old Nishiki road bike I'm restoring. The results surprised me:

Front chain rings: 52 x 40
Rear 6-speed cassette: 14-16-18-20-22-28

So the chain rings are similar to what we refer to as a "standard" today. But look at the jump from the second largest to the largest rear cog!

well biked

I wouldn't use the term "standard" in regard to this. There are some different things available now, in road groups, that weren't available before, but that's more about choice (and the demise of the triple crank on road bikes) than a new "standard." On new road bikes, there are still plenty of bikes that come stock with 50/34 and 11(12) x 25. Also 11 x 28, 12 x 30, even 12 x 32, etc etc. All within spec and within road groups. 53/39 w/ 12 x 25, too........ Bottom line: there's no standard. Just lots of possibilities.

djb

Duane, I would highly recommend reading this page on the Parks site:

https://www.parktool.com/blog/repair-...-length-sizing

its good to learn how to properly size a chain, its very straightforward to do the test and see if you are pushing it with the 5 teeth diff. I used this or another similar tutorial last year when changing a friends bike from a 11-26 to a 11-32 (the rd could handle it fine, but had to put on a longer chain, it was fairly easy to evaluate using the tutorial)

Duane Behrens

I know how to size a NEW chain (big and big + 2 links), but have never tried to measure stress loads on an existing one. So thanks a bunch - you betcha!

djb

your welcome, the Parks site and others are great resources to figure stuff out, along with some youtube vids that can be a great visual help as well (although the Parks site is certainly one I would trust more than some of the youtube vids out there)
I have used an existing chain from a 12-25 to a 11-28, but as mentioned, you certainly dont want to screw around with a too short a chain and any possible much more expensive boo-boos with wheels or such due to a too short chain.

HillRider

Your Nishiki has what was then known as "Alpine" gearing and those huge jumps between cogs were necessary to get a fairly wide overall gear range with only 2x5 or 2x6 chainrings and freewheels. My '85 Bridgestone 400 came with 52x42 chainrings and a 6-speed freewheel geared 14,16,20,24,28,32. Talk about GAPS.

The increase in cog count from 5 or 6 up to 10 or 11 allowed relatively large tooth count spreads with out leaving impossibly wide gaps between cogs. For example a modern 12x27 10-speed freewheel is a "straight block" (1 tooth difference between adjacent cogs) for the first 6 cogs from 12 through 17 and only 2 tooth differences for the next 2 cogs.