Ultegra or 105 cassette

Bellypopper

Hi all

I have just purchased a new (secondhand) road bike. I want to change the cassette to a 27 tooth from the 25 that is already fitted. I already have a new 27 tooth 105 cassette. Is there any reason why I cannot replace the ultegra that is fitted with the 105?

Thanks
Russ

pinarellokid

unless the ultegra is worn why would you want to??

if its worn and funds are limited it will all still work smoothly,, but not be as smooth and crisp as an ultegra change

Bellypopper

Thanks.. The reason I want to change is that I am 48, unfit, and need the lowest gearing possible..... :oops:

gozzy

Switch it, keep it, then when you're fitter you can switch it back.

Focus-rider

i asked a similar question a few days ago apart from the fact mine is reversed, im going from a 12/27 105 cassette to a 12/25 ultegra. I was told by a nice chap on here that its a simple like for like swap but to just remember to include all spacers that are currently there.
Im finding that im either doing less hills or im getting fitter and not needing the 27 tooth much any more. I dont think im getting fitter, im just riding the same roads som much that im wearing them down and making them flatter.

rothers_bikeo

Check your chain length. If it's been sized correctly for the 25 (big-big, no rear derailleur, 2 spare links) then it will be too short for the 27.

arlowood

Bellypopper wrote:

Thanks.. The reason I want to change is that I am 48, unfit, and need the lowest gearing possible..... :oops:

If you really want to get some extra gearing to help with the hills then why not consider the Tiagra 12-30 cassette. Cheap to buy at about £20 and it will be a simple swap over job. You may need to extend your chain length but that's not the end of the world.

6 months ago, I swapped from an Ultegra 11-28 to the Tiagra 12-30 without having to do anything in the way of chain lengthening or swapping derailleurs. I'm 68 BTW and at that time I needed the extra gearing on some of the steeper hills. 6 months on and my fitness has improved to the extent that I never need to resort to the 34/30 combo but it is comforting to know it's there

buckmulligan

rothers_bikeo wrote:

Check your chain length. If it's been sized correctly for the 25 (big-big, no rear derailleur, 2 spare links) then it will be too short for the 27.

This.

If you're switching cassettes, you may as well get a new chain to use with it and size it properly. If you use a chain thats too short and stray into a big-big combo, you run the risk of bending your rear derailleur into your spokes and then it's real trouble!

lef

BuckMulligan wrote:

rothers_bikeo wrote:

Check your chain length. If it's been sized correctly for the 25 (big-big, no rear derailleur, 2 spare links) then it will be too short for the 27.

This.

If you're switching cassettes, you may as well get a new chain to use with it and size it properly. If you use a chain thats too short and stray into a big-big combo, you run the risk of bending your rear derailleur into your spokes and then it's real trouble!

Not this.
If the chain is correctly sized for a 25 it should be okay for a 27. Install the 27 and if the derailluer is over stretched when big big then yes you may need a new chain but that would mean your chain was already a little short. - see the images in the below link for what is okay and what is too short. Going from 25 to 27 would not normally have this effect on the derailluer, and before someone cuts in to say you shouldn't be going big big, no you shouldn't but the bike should allow for it all the same.
http://www.parktool.com/blog/repair-hel ... gth-sizing