Rear derailleur, again!

[Nebulous]

Okay guys - I have a mid compact ultegra set-up 52/36 up front and 11-28 at the rear. Looking for a lower gear for hilly stuff. Going to buy a mid-cage rear mech, an 11-32 cassette and a new chain. Local Evans has them all in stock and is open today. What do I need to do with the new chain? Add a link? 2?

I do occasionally, especially when tired, find myself in big / big. I had an expensive mistake in the past on my old bike doing that when the hanger broke and the rear mech wrapped itself round the spokes and chipped the frame. I'd prefer not to risk that again.

 

[gbb]

This is the trouble with compacts IMO. To reduce the need to run poor combinations, can you up the small front to say a 37 or 38 or would that leave you short on really steep stuff. I don't know your terrain of course.

 

[raleighnut]

Wrap the chain around the big-big combination (without the chain going through the derailleur) and add a pair of links, that'll give you the correct length to break the chain to.

 

[rusty bearing]

I must admit I have my own way. small cogs on back and front. Cut and join chain so that it just pulls the rear mech enough that it doesn't catch it. Done this way the chain is at the maximum possible length. Not failed me yet. Occasionally been able to take an extra link out if needed.

 

[Sea of vapours]

Use a chain length calculator such as this one.

Provided you know the chainstay length (or can measure it accurately) it's a reliable method and arguably easier than wrapping the chain, adding links, etc. Clearly there's a simple formula behind that calculation which is described under point 6 of Park Tool's chain sizing page.

 

[Smokin Joe]

Use a chain length calculator such as this one.

Provided you know the chainstay length (or can measure it accurately) it's a reliable method and arguably easier than wrapping the chain, adding links, etc. Clearly there's a simple formula behind that calculation which is described under point 6 of Park Tool's chain sizing page.

Well said.

That link has been posted countless times by myself and others yet people still persist in advising all sorts of Heath Robinson mumbo jumbo for getting the correct length.

 

[Nebulous]

Use a chain length calculator such as this one.

Provided you know the chainstay length (or can measure it accurately) it's a reliable method and arguably easier than wrapping the chain, adding links, etc. Clearly there's a simple formula behind that calculation which is described under point 6 of Park Tool's chain sizing page.

Thank you. Using the Park tools formula - chainstay is 405 mm or 16 inches, giving a chain length of 54 inches. That seems very straightforward.

The mech appears to no longer be in stock, so I'm not getting it until tomorrow afternoon. It only gives me one additional cog, an extra 4 teeth - so it is going to be an expensive bottom gear! Next weekend's 300k has over 4000m of climb and I've been struggling on the steeper stuff late on in rides so it could be worth it.

 

[tommaguzzi]

why not just change the small front ring to a 34? or is that too big a jump for the chain to get back on the 52? if a 34 works its a lot cheaper simpler solution.
if not why not just go fully compact 34/50. do you really need that big 52 ring.

 

[Ajax Bay]

why not just change the small front ring to a 34?

Front derailleurs are designed to work best with a maximum of 16 teeth difference - hence either 50-34 or 52-36. With the widespread availability of 11t smallest sprocket, no non-pro can really benefit from 52 as opposed to 50 on a road bike. But the OP has 52-36 and probably doesn't want to change both chainrings.
Fitting a 32t largest sprocket (vice the current 28t) will give the OP 14% more gearing / shorter gear. Going from 36 to 34 chainring will only improve the gearing by 5%.

 

[raleighnut]

Front derailleurs are designed to work best with a maximum of 16 teeth difference - hence either 50-34 or 52-36. With the widespread availability of 11t smallest sprocket, no non-pro can really benefit from 52 as opposed to 50 on a road bike. But the OP has 52-36 and probably doesn't want to change both chainrings.
Fitting a 32t largest sprocket (vice the current 28t) will give the OP 14% more gearing / shorter gear. Going from 36 to 34 chainring will only improve the gearing by 5%.

So how about triples with a 22 tooth difference (52-42-30)

 

[Ajax Bay]

how about triples with a 22 tooth difference

Triples work best with a special FD (eg FD-4503) - the inner plate is deeper to achieve the shifts. They work best with 10t difference between the large and the middle chainrings (eg 52-42). The middle to small difference is less critical (so you can comfortably go 52-42-28) but that challenges the RD wrap capacity with a cassette with more than 15t difference.

 

[Nebulous]

I changed it and got it all working. Using the Park tools formula and the big / big plus two links (one inch) both produced the same result, 54 inches. Strangely enough the chain that came off was 54 inches as well. It had done over 1000 miles, so changing it didn't cause any harm. 206 miles yesterday with 4200 metres of climbing. It was very hard anyway, but would have been even more difficult with a biggest sprocket at 28 teeth.