Road Cycling - Seek advice about changing cassette, chainring

Hi, gang!

I have a Fuji Roubaix-Pro with Shimano 105 components.

The cassette is 12-23 and the chainrings are 39 and 53.

I almost never use the top two or three gears and I need a lower gear for climbing a few short but steep hills.

I bike shop owner told me a 25-tooth rear cog was about as large as my 105 rerailleur could handle, even though it is rated for a 29.

I'm thinking of buying a 13-25 replacement cassette.
* Will I need a new chain? I've had the bike since late May and ride about 10 miles a day.
* Will I need a LONGER chain?
* Will replacing the cassette require readjustment of the shifter?

Up front I'm thinking about getting a smaller large chainring. A 52-tooth is all I see offered by Nashbar.
* What is the dimension they talk about in the catalog, for example 52/130? I assume it's a measurement between holes on the crankset.
* Which holes are they talking about?

Thanks for any advice,

Condor

Hi,
this may sound crazy, but I think you could throw a
XT rear derailleur on, and get as big a cassette
as you feel like.

Originally posted by condor
Hi, gang!

I have a Fuji Roubaix-Pro with Shimano 105 components.

The cassette is 12-23 and the chainrings are 39 and 53.

I almost never use the top two or three gears and I need a lower gear for climbing a few short but steep hills.

I bike shop owner told me a 25-tooth rear cog was about as large as my 105 rerailleur could handle, even though it is rated for a 29.

I'm thinking of buying a 13-25 replacement cassette.
* Will I need a new chain? I've had the bike since late May and ride about 10 miles a day.
* Will I need a LONGER chain?
* Will replacing the cassette require readjustment of the shifter?

Up front I'm thinking about getting a smaller large chainring. A 52-tooth is all I see offered by Nashbar.
* What is the dimension they talk about in the catalog, for example 52/130? I assume it's a measurement between holes on the crankset.
* Which holes are they talking about?

Thanks for any advice,

Condor Duno how this happent. Brainfart?...NM

The 105 rear derailleur is officially rated for a 27-tooth large cog, with a 29-tooth total difference.

If you had the money, a triple crank, bottom bracket, and triple-compatible 105 derailleurs would be a really good solution. If that's a bit much, then I vote for a 12-27 cassette and a new Sachs PC-59 or PC-69 chain (color being the difference, the 69 is all silver instead of silver/black).

Unless your bike came with more chain than necessary, the chain will probably need to be longer in order to wrap the big-to-big combination, and getting a new chain with the cassette ensures that you don't get skipping from components whose wear levels don't match.

The 130mm measurement is the diameter of an imaginary circle that passes through the centers of the five chainring bolts. Your crank uses 130mm BCD (bolt-circle diameter) so look for rings of that BCD, if you really want to make that change. If you have hills to climb, then you have hills to descend, and I would hate to give up my high gear for no good reason (my Fuji had a 53 x 11!). Try a cassette and chain to start with, is my advice.

Originally posted by condor
Hi, gang!

I have a Fuji Roubaix-Pro with Shimano 105 components.

The cassette is 12-23 and the chainrings are 39 and 53.

I almost never use the top two or three gears and I need a lower gear for climbing a few short but steep hills.

I bike shop owner told me a 25-tooth rear cog was about as large as my 105 rerailleur could handle, even though it is rated for a 29.

I'm thinking of buying a 13-25 replacement cassette.
* Will I need a new chain? I've had the bike since late May and ride about 10 miles a day.
* Will I need a LONGER chain?
* Will replacing the cassette require readjustment of the shifter?

Up front I'm thinking about getting a smaller large chainring. A 52-tooth is all I see offered by Nashbar.
* What is the dimension they talk about in the catalog, for example 52/130? I assume it's a measurement between holes on the crankset.
* Which holes are they talking about?

Thanks for any advice,

Condor . As is not untypical the LBS guy is full of stinky applesause...just assuming your RD is 9 speed, it is speced for a 27 large tooth and will probably shift a 30, as specs are conservative.If your 105 is 8 speed, the RD large cog spec is 28 teeth, and it would shift a few more. For lower gears, you can stick on a cassette with bigger large cogs,27 for 9 speed and 26 for 8(road cassettes) Whether you need a new or longer chain depends on how much bigger you go and how your chain was sized originally.It is something you have to check after changing cogs. As long as the new cassette is the same speed as the old,no derailer adjustments ned to be made, except maybe the 'B' tension to accomodate the bgger cog. You could not use a 9 speed cassette with 8 speed shifters or vice versa anyway, even tho the hub will accomodate an 8 or 9 speed cassette.Changing the big front chainring is something of a waste of time and money for lower gears as low gears are small chainring and big cogs in the rear. BCD is bolt circle diameter. Yours is 130 and you have to match it.You could change your big ring to a 50 with no issues.The smallest front ring you can use is a 38. If you need even lower gears you can stick on a mtb cassette with a 32 or 34 large cog and a mtb RD to shift it.

Thanks, y'all.

:)

You can get chainsets with a BCD of 110 which is really useful for less athletic or slower riding without dropping your pedalling cadence..
I use a Stronglight 80 chainset, which is even smaller, but takes rings from 28 up to 50. I set up a commuter bike with a 36/48 and found it ideal.
MTB chainsets are generally too small for road riding, but OK for heavily loaded touring.

Check your chain for stretching. Shouldn't be a problem given what you've said, but it's usually a good idea to replace chains when you replace cassettes. You should have chain pins at every inch. If it's stretched, go ahead and replace it, too, or it'll wear your new cassette down quicker and your shifting will suck. Like I say, probably not necessary for you, but something to check.

Originally posted by ImprezaDrvr
but it's usually a good idea to replace chains when you replace cassettes. You should have chain pins at every inch applesauce and stinky applesauce. If chains are replaced at the proper time one can often go thru several chains per cassette,depending of course on some variables. Chain wear is checked over a foot of length. No way to meaningfully measure what is going on with 1" of chain, and the pins are actually every 1/2". A foot of new chain measures exactly 1'. Recommendation is to change it when it measures 12 1/16" c-c of pins or edge to edge of links. waiting till the of recommmended 1/8" of wear usually trashes the cassett.In that case,change the cassette too.

My bad, pokey. You're right, I was smoking crack.

You'd have to agree that it's something to check out, though.

Originally posted by ImprezaDrvr
My bad, pokey. You're right, I was smoking crack.

You'd have to agree that it's something to check out, though. ........................ My nemisis is cheap whiskey and sour applesauce. I try and not touch the stuff before noon. Your heart was in the right place.

I did this recently to one of my bikes. Changed from a 11-23 (53/39 chainrings) to 12-27. The only thing I changed was the cassette. No problems. :beer: