chain help for change of cassette

chatlow

I've just bought an R8000 11-30 cassette to replace my 105 11-28. Hoping the extra 2 teeth will help me up some tricky hills coming up next weekend. Running with a mid compact chainset or my main bike (propel) and compact crank on my P2 TT bike.

The ratios are as follows:
11-28 (11,12,13,14,15,17,19,21,23,25,28)
11-30 (11,12,13,14,15,17,19,21,24,27,30)

I have only just bought a 105 chain and it was cut to the correct length for the 11-28 setup. Question is can I use this same length? My thinking is that for all the lower gears (up to 21 sprocket) it will be fine as the same setup as before but would the running and shifting be poor with the lower gears when in the big ring?

The RD looks okay in the big-big combo not that I would ever use it and the b screw is further into help with the lowest gear on both bikes - again looks fine. I'm just wanting the best shifting and smooth running as possible for both setups, so would I benefit with longer chains?

Thanks

keef66

If it's OK in big / big then I suspect you'll be fine. Check the Shimano tech docs for the groupset if you want reassurance.

I always like to have my chains as short as possible for decent chain tension at the small / small end of things, while still permitting big / big just in case I ever end up ham-fistedly selecting it.

drlodge

Can you use a chain cut for a 28T cassette with a 30T cassette? It depends.

Most people and videos will tell you to size a chain when on big-big as keef66 says above, downside to this is that the chain will then not be long enough if you put on a bigger cassette. Only 1 way to find out, and that's try it (on a bike stand) and see if the chain is long enough.

Personally I like to size a chain on small-small so its as long as possible, then I check on big-big too. If you have a small cage derailleur and 11-30 cassette, chain length is going to be marginal at best and 1 link too big or small and you're in trouble.

shirley_basso

Can you put the inner ring from the TT bike onto the Propel? 34-52 should shift fine and will almost certainly shift fine if running di2.

chatlow

thanks for the replies - I agree with them all. So I just checked the small-small combo with the TT bike (so 34-30) and the chain was just about okay, but any longer and it would be rubbing the lower jockey. I am guessing this is the best length to work with both different setups?

Unable to swap chain rings over as P2 uses oval, so if I did increase the chain by 1 link then I could go buy a 36 oval ring but it's a pricey change! Although now I wondering about mid-compact on the P2 (dammit) BUT that said, I'd have thought the current length of the propel chain, being a new bike, would be ideal as done by the shop so I'd be increasing it by 1 link just for a select few 52/>24 sprockets and the others 52/<24 might be running a slightly loose chain then...

chatlow

In a nutshell: is there any point increasing the chain by 1 link if it's only for the 21,24 and 27 sprockets (when in the 36 chainring) because it will be running with less tension on all other combos?

drlodge

You mean when in the 52T chainring I assume...yes, as if you accidently put it into a big-big gear with the chain not long enough it will likely destroy your bike and take you with it.

chatlow

drlodge wrote:

You mean when in the 52T chainring I assume...yes, as if you accidently put it into a big-big gear with the chain not long enough it will likely destroy your bike and take you with it.

Sure - but the big-big combo isn't as bad as I'd expected, see below. Would you agree it's okay?

Thanks

keef66

That's what my son's recently purchased Cube looks like. He CBA to use the small chainring, and we live up a hill, so that's the gear he usually parks it in.

I've given up nagging him about cross-chaining and unnecessary noise and drivetrain wear. I'm just waiting for the howl of protest when he finds out how much Ultegra chain rings are...

drlodge

chatlow wrote:

drlodge wrote:

You mean when in the 52T chainring I assume...yes, as if you accidently put it into a big-big gear with the chain not long enough it will likely destroy your bike and take you with it.

Sure - but the big-big combo isn't as bad as I'd expected, see below. Would you agree it's okay?

Thanks

100% fine, not as bad as my Rourke with 34-50 and 11-32 cassette.