Bicycle Mechanics - replacing a 12-25 with a 12-27 cassette. will it work?

Hi,
I'm considering replacing my Shimano 105 12-25T cassette with an Ulgetra (got a deal on Ebay) 12-27T cassette.

My bike is a Shimano 105 triple (52-42-30T), so I assume the rear derailleur should be able to handle the 27 cogs (according to the specs)

Will it going to be a straight swap? or would I need adjust rear derailleur? would I need a longer chain?


Thanks in advance!

You can swap it no problem, it'll fit.

You might need a longer chain, but the RD might also be enough as you're only going up two teeth.

The cassette will go on fine - I changed a 12-23 to a 12-27 just a few months back (on a 105 double). If you're putting it on the same wheel, there should be no change to the indexing of the shifts so don't touch the H- and L-screws on the derailleur.

You may need to adjust the B-screw on the derailleur, but mine happened to be ok when I swapped. You might need a little bit more length in the chain, but it sorta depends on whether your existing chain has any extra on it now. I put a new chain on when I changed the cassette, but the jump from 23-27 is obviously bigger than what you're doing.

thanks y'all..

Would I need a special tool to undo the lock ring or is there a "generic" tool I could use?

Thanks again..

You'll need a chainwhip and a lock-ring removal tool, as well as a big spanner/shifter.

I use this chainwhip (http://www.parktool.com/tools/SR_1.shtml) and this lockring removal tool (http://www.parktool.com/tools/FR_5G.shtml).

If you think you'll change the cassette back and forth every now and again, it's worth buying the tools. If it's only going to be a once-off thing, get your LBS to do it. They won't charge much to change it over.

I have 53/39 and a 12/23 rear cassette on road bike. Shimano 105. What would be the least expensive way to get lower gearing. It's ok for rolling hills, however need something a bit lower for real grades.
I did the NYC Bikeathon today and had to use my mountain bike.

geo

NJ

I have 53/39 and a 12/23 rear cassette on road bike. Shimano 105. What would be the least expensive way to get lower gearing. It's ok for rolling hills, however need something a bit lower for real grades.
I did the NYC Bikeathon today and had to use my mountain bike.

geo

NJ
Least expensive is what I did - change the 12-23 for a 12-27. You'll probably need a new chain, since the 12-27 will require a few more chain links than a 12-23. Should be less than $100 for the cassette, chain, and either tools to complete the job yourself or labor charge at LBS.

Another option is a compact crankset, which will be closer to $200 including installation if you buy one that doesn't require a new bottom bracket. Compact crankset has 50/34 chain rings.

IMHO, go for the cassette change first. Makes a big difference.

How much lower do you think that you need to go?

You could install a 12/27 cassette and a new, longer chain and get a hillclimb gear that will satisfy most most hard core riders. That's the cheapest solution.

If you want a slightly easier gear, you can install a mountain bike cassette and derailleur along with a new chain. That's second cheapest.

A compact crank with the cassette you have now will give you a gear that's about the same as using a 12/27 cassette. If you use both the crank and the bigger cassette, it'll give you one more big step toward easier hill climbing.

You could install a triple crank. That'll give you the greatest gear range, but you have to buy a lot of stuff to make it look and ride like a factory triple crankset bike.

I have 53/39 and a 12/23 rear cassette on road bike. Shimano 105. What would be the least expensive way to get lower gearing. It's ok for rolling hills, however need something a bit lower for real grades.
I did the NYC Bikeathon today and had to use my mountain bike.
geo

NJ

It would be worth a try to change to a 12-27. You may not need any additional chain, just check to make sure that when in the big chainring and 27cog the chain is long enough that the rear derailleur does not reach it's forward limit of travel. And, of course, measure your chain to see if it is worn enough to replace. If it measures 12 1/16th" over a 12 link interval then it is more than ready for a replacement.

There is a significant difference between a 23 and a 27.

Al

Least expensive is what I did - change the 12-23 for a 12-27. You'll probably need a new chain, since the 12-27 will require a few more chain links than a 12-27. A longer chain is not always a given,depending on how the original was sozed.

A longer chain is not always a given,depending on how the original was sozed.
Hence the word 'probably' in my post.

Mine needed a new chain when I changed from 12-23 to 12-27. I could have left the old one, but if I ever were to shift into the 53-27, I woulda been in trouble!

Oh wow! thats an old post..:) (June '04)

Since then I replaced the cassette, rode a few hundred miles on it and sold the bike.... :) My current bike has Campy... :D

How much lower do you think that you need to go?

You could install a 12/27 cassette and a new, longer chain and get a hillclimb gear that will satisfy most most hard core riders. That's the cheapest solution.

If you want a slightly easier gear, you can install a mountain bike cassette and derailleur along with a new chain. That's second cheapest.

A compact crank with the cassette you have now will give you a gear that's about the same as using a 12/27 cassette. If you use both the crank and the bigger cassette, it'll give you one more big step toward easier hill climbing.

You could install a triple crank. That'll give you the greatest gear range, but you have to buy a lot of stuff to make it look and ride like a factory triple crankset bike.

I had bike in at LBS to check out rear wheel which is out of true. They are going to replace the wheel under warranty. I am going to switch to the 12-27 as it wont cost me any labor charge. Will see how it goes. Yesterday, I did the NYC Bike Tour and used my MTB as it was raining. It has plenty of gears, but it is too slow for me.
Geo

My $.02, I switch between an 11-25 and a 12-21 without any problems.