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Not the Slowest
12-13-2012, 02:48 PM
Currently using 50/34 in the front and 12/25 in the back
If I swap the 34 for a 36 would I need to change the chain length?

Thanks Rob

norcalbiker
12-13-2012, 02:56 PM
Not sure, but probably not.
I just recently change 34/50 with 25 on the rear to 28 with no problem at all.
Now I am not sure if 25 to 28 rear is the same as 34 to 36 front.

Does this make sense to you?

Louis
12-13-2012, 02:59 PM
I doubt it. And if it was done properly the first time, certainly not.

Even if it was not done properly, if you avoid slack-chain situations (little front, little back) you'll still be fine, and bigger in front would not aggravate this. Little front, big back should be no problem at all, since presumably big front, big back has already proven to be OK.

On further reflection, I'm 100% sure you'll be fine.

flydhest
12-13-2012, 02:59 PM
Almost certainly not. The big-ring-big-cog combo is one way people get the length on the chain. The bigger small ring will be smaller than the big ring, so it will be the equivalent of using one of the intermediate gears you are using now in terms of the take up the derailleur has to do.

You should be fine. If you were going to a smaller chainring, you might want to check if the chain would be too long.

christian
12-13-2012, 03:03 PM
No, you won't, because you're effectively reducing the required effective range of the rear derailleur.

Your initial required derailleur capacity/wrap was: (50-34) + (25-12) = 39 teeth
Your new required derailleur capacity/wrap is: (50-36) + (25-12) = 37 teeth

The way you set chain length best is to wrap small-small and ensure you have a small amount of tension in the rear derailleur. In your case, you will now actually have more tension in the r.d. in small-small, and you've reduced the capacity required. You're fine.

If anything, you could potentially add one link, but not required.

oldpotatoe
12-13-2012, 03:06 PM
Currently using 50/34 in the front and 12/25 in the back
If I swap the 34 for a 36 would I need to change the chain length?

Thanks Rob

Nope. If it's correct now then you have enough chain for big-big combo. PLUS hopefully no droopy chain in small/small..so adding a 36t won't make a difference.

Ralph
12-13-2012, 04:28 PM
No, you won't, because you're effectively reducing the required effective range of the rear derailleur.

Your initial required derailleur capacity/wrap was: (50-34) + (25-12) = 39 teeth
Your new required derailleur capacity/wrap is: (50-36) + (25-12) = 37 teeth

The way you set chain length best is to wrap small-small and ensure you have a small amount of tension in the rear derailleur. In your case, you will now actually have more tension in the r.d. in small-small, and you've reduced the capacity required. You're fine.

If anything, you could potentially add one link, but not required.

When calculating rear derailleur wrap.....I believe you calculate the difference then add. Thus....50-34= 16 difference plus 12-25=13 difference. So the rear derailleur needs to be able to handle a 29 difference. And most new short cage RD's will handle that (barely). Using a 36 just makes it easier.

christian
12-13-2012, 04:38 PM
When calculating rear derailleur wrap.....I believe you calculate the difference then add. Thus....50-34= 16 difference plus 12-25=13 difference. So the rear derailleur needs to be able to handle a 29 difference. And most new short cage RD's will handle that (barely). Using a 36 just makes it easier.Yes, correct. Formula good; mental math bad.

Not the Slowest
12-13-2012, 10:24 PM
Who needs google when I have You guys.

Thanks all

monkeybanana86
12-14-2012, 02:09 AM
I went from a 36 to 34 last night and had to take out a link. Big big was good but small big wasn't. But since you're going up I think you should have no problem since it would be like having your chain on the previously small front ring and on a cog one or two next to largets in the back.

monkeybanana86
12-14-2012, 02:12 AM
Who needs google when I have You guys.

Thanks all

haha so true. and you get an answer in almost the same time as you would with google

Black Dog
12-14-2012, 07:50 AM
When google has a bike question it comes here for an answer! :banana:

aoe
12-14-2012, 02:05 PM
The way you set chain length best is to wrap small-small and ensure you have a small amount of tension in the rear derailleur. In your case, you will now actually have more tension in the r.d. in small-small, and you've reduced the capacity required. You're fine.


For my learning...why is this method better than the Sheldon method for chain length?

Don49
12-14-2012, 02:13 PM
This is my go to thread for chain length, I have it bookmarked: http://forums.thepaceline.net/showthread.php?t=118937