New Cassette or new chain rings

[ciderdrinker]

Afternoon all,

I know it's been discussed before but couldn't find this specific question answered, so was hoping for opinions please!

I'm upgrading my starter aluminium road bike to a shiny new carbon one. The bike I ordered was, all factors considered, the best deal for me, but comes with what I would not have ideally chosen, which is: 52-36 11-30. But I knew that when I ordered and have the budget to change things if needed.

I'm currently running 50-34 11-32 and live in a hilly area. I use the 34/32 combination occasionally, but probably 95% of my riding I don't need it.

So the first question is, how different will 36/30 feel to 34/32? Baring in mind i'm shaving at least 2kg off the bike weight too.

I guess the obvious answer is...go try it, I will! But i'll ask you anyway in advance.

Second question, if I were to change a few things - do people recommend I change the chain rings to 50-34 and keep 11-30 or change out the rear derailleur (it comes with short cage) and cassette for 11-32 keeping 52-36 up front?

Are there pros and cons to either option? Price is roughly the same for parts, approx £80/100.

Thanks in advance for you help.

[Brucey]

you don't specify what parts you have; if they are shimano 11s 'road' parts then the right RD should handle a 34T sprocket (eg CS-HG700-11 11-34T). For 10s or 9s the options would be different. You may or may not need a different RD depending on the exact model. If you want specific answers then you have to ask specific questions.

34/32 is ~13% lower than 36/30. So about 13% different.

2kg is likely to be 2-3% of the all up weight, so 2-3% difference there when climbing.

cheers

[willcee]

Hi what i would do and did and i have one on sale on here at this moment is change your 34 from the older machine and fit it to the new machine its maybe half an hours work at most... depends on the shimano chainsets are both 4 bolts and that they are both shimano.. will

[Jamesh]

I find 50 / 34 a big drop which often means a double shift typically on a hill.
So I would go for the bigger cassette if possible.

Cheers James

[bgnukem]

The drop between 52-36 and 50-34 isn't much different. Given an 11T top sprocket if it were me I'd go for something like 48/34 which still gives a 117 inch top gear which is high enough for most people, but closes up the gap between chainrings slightly and gives a bottom gear only 6.7% higher than the current one.

Or better still, use the larger cassette and get the same bottom gear.

[mattsccm]

Am I right in thinking that 52/36 chainsets are fairly new and that most if not all use a 110mm bcd as a 130mm only goes down to 39 normally? You could swap the rings probably to try things or if the chainset manufacturers are the same its just a 5 minute job plus any mech moving.. I find that a 34/30 combo is fine for me.

[ciderdrinker]

Thanks for all the replies, really helpful.

It is the new Shimano 105 R7000 - 52/36 crankset. 11-30 11 speed on a 105 R7000 SS RD (short cage, so max 30 tooth on the cassette)

To the two people that suggested, and have, changed the inner 36 chain-ring for a 34, how has that functioned and worked out for you? I'm a little concerned about the jump between 52 and 34 and the fact it is a bit of a bodge(?!). Any problems with it?

That would be the simplest and cheapest change, as it's a £27 and quick job.

Thanks again

[Brucey]

I would be surprised if your RD couldn't be pushed to 32T large sprocket but you are in danger of running out of total capacity too. Fitting a 34T chainring with the 52T one will result in some kind of imperfection in the shifting but it'll probably be tolerable.

If you can increase the clearance between the guide pulley and the sprockets by ~4mm (using the adjusting screw) you can fit a 32T sprocket. However you will

a) probably want to increase the total capacity of the RD and
b) accept that the precision of shifts on the smaller sprockets will be slightly reduced.

a) can be addressed by fitting GS side plates e.g.

https://www.sjscycles.co.uk/gear-spares/shimano-105-rdr7000-outer-plate-fixing-bolt-gs-type-y3f398060/
https://www.sjscycles.co.uk/gear-spares/shimano-105-rdr7000-inner-plate-gs-type-y3f316000/

this costs a mere £17 in parts and gives a mech with a good total capacity (about 39T) but it isn't quite a GS mech; the angle of the parallelogram is different I think.

Just in case it isn't obvious you will likely need a longer chain so check for this carefully.

Oddly enough the setup you will end up with is one small tweak away from what I might choose, which would be a (custom) 13-32T cassette with the 34-52 chainset. The SS mech with GS side plates would be ideal for this setup.

cheers

[willcee]

Interesting comments on the shifting on the 52/34. I'm quite hard to please on anything especially my own kit and believe me i never had any issue on the front with that large teeth difference,.. I would question the need to change twice on any hill that warranted my actual use of a 34/32.. I was taught to change before you really needed it and keep the revs up.. will

[Brucey]

good modern OEM chainrings are in matched pairs; the idea is that when you shift, the chain is nicely in mesh on the receiving chainring teeth as well as the departure chainring



this results in better, quicker shifts during which you can still apply some pressure rather than none, and return to full pressure more quickly too. It is like 'HG for the chainrings' if you like. It reduces the incidence of the chain sitting on the tops of the teeth and then moving/settling under load after the shift is meant to be complete.

However narrower (more finicky?) chain aside you shouldn't be much worse off with an unmatched pair than you would be with old-school chainrings. Hence my description of likely 'imperfection' with this combination; it'll most likely work, just not as well as a matched pair; all that R&D effort is wasted, giving the development engineers sleepless nights if only they knew what you are doing.....

cheers

[willcee]

Brucey , I know what you say is true, yet this conversation was had just last week when myself and my cycle companion stopped mid ride and were deep in cycle lore.. he like me had many years experience riding back then, at 11 y.o. from campag 5 sp then 6,7 and so on and the chat came around to our first 10 speed set up. I had old school stuff he says that changed every bit as well as these new fangled rings with the spurs on them, just went straight cleanly up and down with no issues, I had to agree as I had experienced the same and I put it down to stronger rings and stiffer front derailleurs then we got into indexing and he like me likes zero indexing front.. not that I need it now
as I 'm single ring on the E machine.. will

[Brucey]

it all helps but the crucial thing with modern 'matched pairs' is that the pins and gates are timed correctly so that the chain stays in mesh as illustrated during the shift. Random chainring alignments with no defined shift point (e.g. no pins or gates) or unmatched pairs results in slower less accurate shifting.

To get the timing right between the chainrings usually means that the pairing is marked on the chainring (eg 34/50 on both chainrings of a matched pair) and the apparently featureless inside chainring still needs a timing pip on it to ensure that it gives the best shifts possible. If you have a (5-bolt) setup like that, you can try running the inside chainring with a different timing and you will notice that the front shifts are that bit worse.

cheers

[ciderdrinker]

I think i'm with Brucey on this one, as money is not a deciding factor, i'd rather stick with Shimano's chosen pairings, 50-34 or 52-36. I guess if I need the 34 inner, i'm not going to miss 52-11.

General feeling seems to be more about changing the chain ring in some form rather than RD/cassette, so I think that's what i'll do if I need it. Both chain rings are interchangeable with some FD adjustment.

Thanks again for the advice.