Big cassette.

[si_c]

Assuming that you also have a Shimano Crankset, swapping the 50-34 chainrings out for something smaller might be of interest. Absolute Black do a set of oval (if you can live with that) chainrings in a 46/30 size which would fit a Shimano crankset. They're not particularly cheap, but they do look nice, I have a set on my Domane.

Possibly worth considering as swapping out a cassette / adding a Wolftooth or equivalent and shop time would probably be a comparable price. You'd need to adjust the front derailleur height a touch to compensate for the reduced chainring size but that's the hardest part of it.

 

[gavroche]

I understand steep climbs but with a 34 at the front and a 42 at the back, assuming you're struggling and doing a low cadence - say 60, your speed will be under 4mph - less than park walkers. At that pace better practice your track stand

What is your typical cadence up a climb? Do you have a target speed?

I do a 6% gradient on a 34/30 at 6 mph So not the best climber and I believe some of the hills on the C2C are quite a bit steeper so my best gears will be 34/32 then: struggle at first and then walk I say.

 

[Peter Salt]

I do a 6% gradient on a 34/30 at 6 mph So not the best climber and I believe some of the hills on the C2C are quite a bit steeper so my best gears will be 34/32 then: struggle at first and then walk I say.

You can fit an 11-34 cassette without any modifications. That would give you a 1:1 ratio.

 

[Dogtrousers]

You can fit an 11-34 cassette without any modifications. That would give you a 1:1 ratio.

I think (but I'd have to look it up) that the older 5800 series 105 GS rear mech went up to 32T but the newer 7000 series 105 GS mech goes up to 34T.

That's the Shimano certified largest sprocket. The real world largest sprocket may be a bit bigger.

So if the existing RD is an RD-R7000-GS then it can definitely handle 34T. If it's RD-R5800-GS then it can probably handle 34T.

All subject to my wonky memory being right.

 

[gavroche]

I think (but I'd have to look it up) that the older 5800 series 105 GS rear mech went up to 32T but the newer 7000 series 105 GS mech goes up to 34T.

That's the Shimano certified largest sprocket. The real world largest sprocket may be a bit bigger.

So if the existing RD is an RD-R7000-GS then it can definitely handle 34T. If it's RD-R5800-GS then it can probably handle 34T.

All subject to my wonky memory being right.

I have been told mine can go up to 34 but is it worth the expense for the sake of 2 teeth?

 

[Blue Hills]

I have been told mine can go up to 34 but is it worth the expense for the sake of 2 teeth?

as others have suggested, I think it best to do this job yourself - then you can tinker as you go along and test everything carefully before you ride off/put any strain on the system.
As others have also stated, Shimano IS very often conservative about the capacity of mechs. Bike shops wll have to follow these guidelines.
I recently put a rear cog on a bike with a 36T big tooth and a capacity which is I think strictly beyond what Shimano state. All works fine.

(I had to put a new rear mech on my build to get the thing to work - initially I plonked a mech on which matched my Hewitt set-up which the Hewitt purchase docs had said had a 36T big tooth on the back. Didn't work smoothly/properly which mystified me. Much tinkering with B screw. Then I checked the Hewitt and found that the cassette they had put on only had a 34T. Luckily I hadn't ridden my new build much before I discovered this)

 

[Dogtrousers]

I have been told mine can go up to 34 but is it worth the expense for the sake of 2 teeth?

The expense in this case is a new cassette and chain.

That's a question only you can answer. Your money, your legs.

I can say that from my point of view I made that change (32->34) and found it a noticeable improvement and I wouldn't go back. But that's just my opinion, and my legs.

However, when I did that I was replacing a completely worn out drivetrain, one broken shifter, knackered chainrings and BB and so on so from an expense point of view it was money I was going to spend anyway.

 

[T4tomo]

It sort of depends whether you are carrying a lot of gear or not (supported or unsupported ride) as to how low you need to go. but i will say you will notice a 2 tooth difference. Also being rated to 34 mean you could fit an 11-36 on it as Shimano are conservative and a 4 tooth diff is defo noticeable and 34:36 ratio should be fine.

to get a bigger a bigger sprocket than 36, If you are 10spd you could dip into MTB parts and fit Deore or similar RD and larger cassette, but if you're 11 spd that wont work (shifter incompatible), you'd need to go down the wolf tooth route, as with a double, even the gravel RD's wont go above a 34 (officially and 36 get away with unofficially).

 

[si_c]

I have been told mine can go up to 34 but is it worth the expense for the sake of 2 teeth?

Perhaps not, Sunrace do an 11-36 cassette which from experience will fit without any extenders (perhaps needing a slight adjustment of the B-Screw) which would be a 12% reduction in gear.

I see @T4tomo got in before me.

 

[presta]

The chain ring is 50/34.

That's a chainring difference of 16t, so if you use an 11-42 sprocket with a difference of 31t, that gives a total difference of 47t. Moving the mount by extending the gear hanger won't change total capacity, which is 40t maximum for any of the 105 range:

 

[Dogtrousers]

That's a chainring difference of 16t, so if you use an 11-42 sprocket with a difference of 31t, that gives a total difference of 47t. Moving the mount by extending the gear hanger won't change total capacity, which is 40t maximum for any of the 105 range:

That, I think, may be the answer to the question of why shops won't do it. Not because the big sprocket is so big, but because in higher gears on the little ring you're going to get slack in the chain that the mech can't cope with.

 

[Ridgeback Roller]

That, I think, may be the answer to the question of why shops won't do it. Not because the big sprocket is so big, but because in higher gears on the little ring you're going to get slack in the chain that the mech can't cope with.

That's the conclusion I came to when I wanted to lower the gearing on my Roubaix in advance of a cycling holiday in the Pyrenees. I had a SPA sub compact 46/30 chainwheel in my parts bin, so it was just a case of swopping over a square taper BB ( luckily the Roubaix has a threaded BB rather than press-fit) and tinkering with the derailleur height, which turned out had to be at it's lowest possible allowed by the mounting. I also fitted a 34T cassette. It's all worked well, fears of spinning out on 46/11 haven't really materialised , but that could be a problem for stronger riders. An unexpected bonus is that I find I stay in the big ring much more when cycling locally, which is rolling downland countryside. A slight downside is that the SPA set up isn't the prettiest , being essentially a triple minus the outer ring- however I wouldn't go back. a couple of photos.

 

[Dogtrousers]

@Ridgeback Roller a subcompact is on my list of things to try one day, especially as I spend probably more time in the small 34 ring than I do in my big 50. But my current chainset is still going strong so that experiment will have to wait.

 

[DCBassman]

If I keep the mixte going, considering a 50-34 for the front, or lower. Not sure that original Suntour mech will work well below that, but a 46-30 would be great if it could. 12-36 9-speed at the back.
The Scott roadie has a factory triple, although I've messed with that too. It has 50-39-30 to 11-34 8-speed, and that handles hills ok. Just a shame that the rider doesn't...

 

[GilesM]

If you go with your current chainset and fit an 11/40 cassette you will have some very big gaps between gears, okay off road, but on the road, it won't be fun, I would suggest fitting a MTB chainset, a Shimano 38/28 would give you a good low gear with the 11/32 cassette, and still a top gear of 38:11 which is a 93inch gear, if you spin out on that, freewheel. I fitted a 36/26 chainset to my other half's roadbike with an 11/32 cassette, it works really well and fairly small changes between each gear. If you don't want to go so small with the chain rings, I have a 46/30 on my road bike with a 15/28 cassette, perfect for me as I love the very close ratios, but a 46/30 with an 11/34 cassette would still give a very low gear, <24inch, should get up most things on that.