32 tooth cog - do i need a bigger chain

Spaceman7t2

Hi All, First post.

I have a Pearsons upandatem and also recently built up an old trek usps, love the look of trek bikes.

On the upandatem, i have been running out of gears and the shop said they have started to fit 32 tooth cogs now for that very reason.

So i fitted a new cassette with 32 tooth cog and the chain wont make the final shift, so my question is;

Longer chain or different shifter ?

Help and thank you in advance for your help. shane

drlodge

What do you mean by "the chain wont make the final shift"?

You will almost certainly need a longer chain, however it will be long enough to engage bottom gear (smaller chainring, largest 32T sprocket) hence why I don't know what you mean by the above phrase.

Assuming you replaced an n speed cassette with a larger 32T n speed cassette, the largest sprocket should be in exactly the same place.

By "different shifter" do you mean "different rear derailleur"? What's the rear derailleur on it now?

Spaceman7t2

Hi drlodge, grateful for your time. I will have a go at most things on a bike but i do get stuck sometimes.

What i mean is that the rear derrailiur is fully extended as in almost parralel to ground so the chain cannot shift to the largest cog on the cassette.

Both 10 speed and the rear derarailiur is Tiagra.

So its sounds simply like a new chain, which is not so bad news.

mrb123

Spaceman7t2 wrote:

Hi drlodge, grateful for your time. I will have a go at most things on a bike but i do get stuck sometimes.

What i mean is that the rear derrailiur is fully extended as in almost parralel to ground so the chain cannot shift to the largest cog on the cassette.

Both 10 speed and the rear derarailiur is Tiagra.

So its sounds simply like a new chain, which is not so bad news.

Are you trying this with the chain on the big ring at the front? If so, that is a gear combination you should avoid in any event, although you still probably need a longer chain.

If the rear derailleur is fully extended when you're in the small ring at the front then your chain sounds like it was too short to begin with, never mind the 32 cog!

drlodge

Per the post above - if the rear derailleur is at full stretch when on the 32T, I would assume you're also on the big chainring? This is a photo of my 32T cassette whilst on the small chainring. On big-big, the rear derailleur is at full stretch but it can just stretch to the extent required, as otherwise the rear end would get ripped to shreds. On small-small, there is still some tension in the rear derailleur spring.

The problem you may face even with a new chain, is that there is insufficient take up in the rear derailleur for the difference in teeth. I have 34-50 chainrings and 11-32 cassette, so that's a difference of (50-34)+(32-11) = 37T. I got round this problem by using a Road Fairy http://gearmechhanger.com/S14-Alpe-DHuez-Road-Fairy

Spaceman7t2

Are you trying this with the chain on the big ring at the front? If so, that is a gear combination you should avoid in any event, although you still probably need a longer chain.

If the rear derailleur is fully extended when you're in the small ring at the front then your chain sounds like it was too short to begin with, never mind the 32 cog![/quote]

I did at first, but when on smaller inner ring it was running ok. It does make sense what you said about on the big chain ring, but think an extra couple of links would bewortwhile.

appreciate your comments and help , shane

Spaceman7t2

drlodge wrote:

Per the post above - if the rear derailleur is at full stretch when on the 32T, I would assume you're also on the big chainring? This is a photo of my 32T cassette whilst on the small chainring. On big-big, the rear derailleur is at full stretch but it can just stretch to the extent required, as otherwise the rear end would get ripped to shreds. On small-small, there is still some tension in the rear derailleur spring.

The problem you may face even with a new chain, is that there is insufficient take up in the rear derailleur for the difference in teeth. I have 34-50 chainrings and 11-32 cassette, so that's a difference of (50-34)+(32-11) = 37T. I got round this problem by using a Road Fairy http://gearmechhanger.com/S14-Alpe-DHuez-Road-Fairy

it did seem to change ok only bering affected as far as i could see by the length of the chain, must get a new chain.

thanks again - shane

dj58

OP, don't forget that you will also need to screw in the B-Tension screw on your Ultegra RD to achieve the required clearance between the top guide pulley wheel and the 32T cog.