Tech Gearing question

Karl

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I would like to use Shimano road shifters (105s) on my rim brake bike. Also want to set it up as a 1x system with (optimally) a 30t chainring and an 11 speed 10-42 cassette. The second best setup for me would be to run a double with 30/46 chainrings and an 11 speed 11-42 cassette. Looks like, if I want to stay with Shimano road shifters, I'm SOL. So far the only solution I've found is if I use the Absolute Black oval 30/46 double. It would work but not so interested in the oval rings (and not jazzed by the looks of the chainring). Anyway, any ideas, suggestions?
 
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Winston Leg-Thigh

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I would like to use Shimano road shifters (105s) on my rim brake bike. Also want to set it up as a 1x system with (optimally) a 30t chainring and an 11 speed 10-42 cassette. The second best setup for me would be to run a double with 30/46 chainrings and an 11 speed 11-42 cassette. Looks like, if I want to stay with Shimano road shifters, I'm SOL. So far the only solution I've found is if I use the Absolute Black oval 30/46 double. It would work but not so interested in the oval rings (and not jazzed by the looks of the chainring). Anyway, any ideas, suggestions?
I've got FSA chainsets on both my bikes. One is 46/30 (11-30 Sora) and the other 46/36 (11-36 105). No problems with either and I don't think there'd be a problem with 11-42 if I used a wolftooth road hanger or something similar.
 
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OreoCookie

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Looks like, if I want to stay with Shimano road shifters, I'm SOL.
Why should disconnecting the left shifter and replacing the two chain rings with a single one not work? Yes, you are either left with a “dead” shifter or you will have to get a non-matching brake lever. But in principle this should work just fine. There are plenty of youtube videos out there, explaining the process. It looks very straight-forward, all you need are the tools to remove the crank (so if it is a Shimano Hollowtech crankset you will need a torque wrench and a tool to remove the plastic preload nut and locktite).
 

Karl

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@Winston Leg-Thigh That looks like a good possibility. Was looking at the FSA cranks then, and their mountain cranksets look like they have the 30/46 I'd like. Do the chainrings have any issues with using a shimano HG chain?

@OreoCookie Going from 2x to 1x is easy enough. Done it already on another bike. The issue is, if I use a 105 34/50 crankset, afaik, it won't allow a lower t chainring than 34t (except for the Absolute Black I mentioned).
 

Karl

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Wondering if there would be any reason a Deore XT M8000 1x crank with a 30t chainring wouldn't work with Shimano 105 (r7000) shifters and rd. From what I can tell, it should be OK. (Would prefer to stay with Shimano vs. FSA if it would work.)
 

kiwisimon

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@OreoCookie Going from 2x to 1x is easy enough. Done it already on another bike. The issue is, if I use a 105 34/50 crankset, afaik, it won't allow a lower t chainring than 34t (except for the Absolute Black I mentioned).
Or you could use a 48T sprocket with the 34T chainring and have an even lower gearing. Might need to check RD capacity.
 

OreoCookie

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@OreoCookie Going from 2x to 1x is easy enough. Done it already on another bike. The issue is, if I use a 105 34/50 crankset, afaik, it won't allow a lower t chainring than 34t (except for the Absolute Black I mentioned).
I don’t think the issue is the crankset, but clearance with your frame. The person who made the video I linked to made explicit mention of that. However, I’d just change the rear cassette instead. To be honest, a 30 tooth chainring is more mountain or touring bike territory, so a frame made for drop bars probably wasn’t designed with such small chain rings in mind. Of course there are exceptions which are meant to take subcompacts (e. g. 46/30).

As @kiwisimon suggested, though, the simpler solution would be to choose a larger front chain ring and couple that to a larger cassette in the rear. Out of curiosity: how have you decided on the gearing you will need? I found this gear calculator 1000x more useful than the infamous Sheldon Brown one.
 

Cactaur

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For the price of the super compact absolute blacks, you could get a whole new GRX crankset with chainrings. Front derailleur would need changing tho but thats relatively cheap.
 

Karl

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Or you could use a 48T sprocket with the 34T chainring and have an even lower gearing. Might need to check RD capacity.
If I stay with 105, the largest cog the 105 GS can manage (according to Shimano) is a 36, although I'm running a 40 on one now.
 

Karl

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For the price of the super compact absolute blacks, you could get a whole new GRX crankset with chainrings. Front derailleur would need changing tho but thats relatively cheap.
The GRX would be a great solution except, I believe, they don't make brifters for rim brakes and the GRX rd doesn't work with 105.
 

Karl

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I don’t think the issue is the crankset, but clearance with your frame. The person who made the video I linked to made explicit mention of that. However, I’d just change the rear cassette instead. To be honest, a 30 tooth chainring is more mountain or touring bike territory, so a frame made for drop bars probably wasn’t designed with such small chain rings in mind. Of course there are exceptions which are meant to take subcompacts (e. g. 46/30).

As @kiwisimon suggested, though, the simpler solution would be to choose a larger front chain ring and couple that to a larger cassette in the rear. Out of curiosity: how have you decided on the gearing you will need? I found this gear calculator 1000x more useful than the infamous Sheldon Brown one.
I'm not, by any stretch of the imagination, a speedster. So, I don't need much on the top end. A 30t chainring with a 10-42 would give me enough speed on the high end and still get me below 20 gear inches on the low end (which is what I'm looking for, given my knee issues). Keeping a 34t chainring means moving up to a 46 or higher cog to stay below 20 gear inches, but that requires a mountain bike RD and it is my understanding the 105 shifters don't work with the XT M8000 rd.

Thanks for the tip on the gear calculator. I like it. :tup
 

Cactaur

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Thought you just wanted to change the chainrings? Just get the grx crankset tho you do need a new FD. Also only the heavier but cheaper rx600 come with 46-30 out of the box. Unless you want to go full 105 for completion sake.

5800 is compatible with grx RD.

If you want xt you’d need something like a wolftooth tanpan to modify the cable pull. Maybe the Roadlink as well but you have no issues on the 40t.
 
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bloaker

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If... you were willing to go sram, exact actuation 10sp is compatible regardless of purpose.

My fargo was set up that way with sram road shifters and brakes but mtb crank and derailleurs.
 
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joewein

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Correct, a 30T ring won't work with a 105 crank, as the inner chainring uses a 110mm BCD, which limits it to at least 33T though in practice you will only be able to find 34T and larger.

I use a Sugino OX601D sub-compact crankset with 42/26T - same 16T difference as a 50/34 Compact or 52/36 Mid Compact so you can use a regular 105 or Ultegra FD but it helps if it's band-mounted so you can lower the FD to sit closer to the smaller rings. At the rear I'm using a 6800 11-32 cassette and RD 6800-GS, for a 21 inch low gear. I have not had any compatibility issues with 11 speed. I use an FD-CX70 front derailleur, mostly because my frame is set up for top pull, not around the BB. 32 at the rear is the official largest cog size limit for RD-5800-GS and 6800-GS whereas RD-R7000-GS and RD-R8000-GS also handle up to 34T. There are many different chain ring sizes available for the Sugino, so combinations like 40/24 or 44/28 will also work, depending on your cassette and you desired gear range.

I wrote about using large cassettes on road bikes in this blog post last year and about low gearing for road bikes about 4 1/2 years ago.
 

OreoCookie

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@joewein
Great blog posts, you should have posted those earlier and I could have saved my breath. And I am in total agreement about gearing (which is why 1x is even more of an option to people who do not race). One question: what about clearance issues with smaller cogs?
 

joewein

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Steel frames should be OK, but some carbon frames are very bulky around the BB and a small ring would not fit around that.

On gravel / adventure bikes it is often the other end of the spectrum that causes problems, i.e. larger tooth count inner or outer rings that would collide with the chain stays on bikes that can handle wider tires. For example, my NFE doesn't take 52 or 53 outer rings.
 
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Karl

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If... you were willing to go sram, exact actuation 10sp is compatible regardless of purpose.

My fargo was set up that way with sram road shifters and brakes but mtb crank and derailleurs.
I lean toward Shimano, mostly because I'm very familiar with it and it works well for me. OTOH, SRAM offers more options for gravel/adventure gearing. Would like to try SRAM sometime before committing to buying a groupset.
 

Karl

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I use a Sugino OX601D sub-compact crankset with 42/26T - same 16T difference as a 50/34 Compact or 52/36 Mid Compact so you can use a regular 105 or Ultegra FD but it helps if it's band-mounted so you can lower the FD to sit closer to the smaller rings. At the rear I'm using a 6800 11-32 cassette and RD 6800-GS, for a 21 inch low gear. I have not had any compatibility issues with 11 speed. I use an FD-CX70 front derailleur, mostly because my frame is set up for top pull, not around the BB. 32 at the rear is the official largest cog size limit for RD-5800-GS and 6800-GS whereas RD-R7000-GS and RD-R8000-GS also handle up to 34T. There are many different chain ring sizes available for the Sugino, so combinations like 40/24 or 44/28 will also work, depending on your cassette and you desired gear range.
Thanks, Joe. Really helpful.
 

kiwisimon

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I've used SRAM since I gave up on Campy about 12 years ago. I like it and generally it plays well between groupsets and on and off road flavors.
 
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