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It Is Impossible

Old 05-27-20, 07:41 AM
  #1  
Paul Barnard
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It Is Impossible

I have been itching to build or buy a gravel bike. I want a double crankset and brifters. I want my lower gear inches to be below 20 (non-negotiable) and the upper close to or above 100. Gravel bikes are built on a road bike chainline. It seems that every time I start mentally assembling my drivetrain that some incompatible or less than ideal variable pops up. What am I missing?

Let me give you an example. I wouldn't mind buying a Lynskey or Litespeed Gravel bike with the 2x10 GRX drivetrain. They can be had for under $3000 and that's about as much as I would want to spend. The stock gearing is 46/30 11-36. The GRX derailleur is a long cage listed with a max 36 tooth cassette and a 41 inch chain wrap. A long cage can run a 42T cassette as far as I can tell. If there were a ramped and pinned (outer) 40T chainring that would work with the GRX crank, I'd buy it and a 10 speed 11-42 cassette and live happily ever after. I am assuming in this scenario the GRX derailleur would work well.

Building would open up more options for me, but I always arrive at some level of incompatibility as I start piecing things together. There are mountain cranksets that give me the chainring options I want, but then I end up with a chain line issue on the road bike ideal chainline on gravel bikes. Then once I get into an MTB crank I am working an FD that needs road pull ratios. Those FDs are profiled for larger rings. I prefer mechanical discs FWIW.

Best I can tell I am chasing a unicorn.
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Old 05-27-20, 08:36 AM
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Get a 3X9.
22-32-42/4
12-27 cassette.
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Old 05-27-20, 08:53 AM
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Not your first choice but 12 Speed Etap Sram Eagle will work with with Sram road E road shifters.

That could probably give you a 36 or 38 x10-50.

It would also mandate hydraulic brakes and 1x. It could also blow your budget.
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Old 05-27-20, 08:54 AM
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You just need to look for a different color unicorn. Probably a 1x 12 speed will be your best bet. Sure you loose a few gears in between, but do you need them? SRAM Eagle with 10-50 cassette and say a 38 or 39 front chain wheel.

Problem with 2x trying to get that range is going to be your rear DR trying to take up the slack of a wide ranging cassette or if you narrow the cassette range and have a wide range on the front, then same thing. And I think you even have to worry about the chain snagging the big ring when in the small small on a crank set with really large differences in chain wheel size when you are in the wider stacks of 10 or more cogs on the back. But someone else is going to have to say if that's a thing to worry about. I'm only imagining it currently.
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Old 05-27-20, 09:16 AM
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I had much the same goals regarding gearing. Fortunately, I don't enjoy drop bars and brifters. I changed to butterfly handlebars, but there are a variety that would accept mountain shifters and brake levers.
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Old 05-27-20, 09:28 AM
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If you were flexible on maybe not using brifters, the Rohloff hub drivetrain would
be able to meet your drivetrain requirements.
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Old 05-27-20, 09:55 AM
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Originally Posted by Bill Kapaun View Post
Get a 3X9.
22-32-42/4
12-27 cassette.
Triples work for me, too.
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Old 05-27-20, 01:23 PM
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Originally Posted by Paul Barnard View Post
Best I can tell I am chasing a unicorn.
If you have boxed yourself in then you need to change your constraints.
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Old 05-27-20, 03:46 PM
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Reminds me of the old Peanuts strip where (IIRC) Linus is telling Charlie Brown, "It is better to light a single candle to curse the darkness."

Since I've been looking for a stock gravel bike with similar gearing to O.P., I feel like Lucy yelling, "You stupid darkness!"
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Old 05-27-20, 03:51 PM
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Don't worry about chainlines, the difference between road and MTB chainlines is meaningless in this case. Road and MTB cassettes are in exactly the same place. The only reason MTB uses a wider chainline, is for tire and chainring clearance.

If you are not opposed to SRAM components, I know for certain that the SRAM Rival front derailleur will shift an XT crankset with 38/28 chainrings. You could use a SRAM Rival 22 mechanical shifters with a GX 10 speed MTB rear derailleur. Both are Exact Actuation and will work together.
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Old 05-27-20, 04:45 PM
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Originally Posted by DeadGrandpa View Post
I had much the same goals regarding gearing. Fortunately, I don't enjoy drop bars and brifters. I changed to butterfly handlebars, but there are a variety that would accept mountain shifters and brake levers.
I thought I should add that I run a 46/30 crankset and a SRAM 10-42 cassette, which on 700x40c tires is a pretty good gearing range. Brifters won't let you do this except on 9 or 10 speed. 11 speed brifters won't work. But I'm an age where I don't enjoy the drops. Jones bars work great.
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Old 05-27-20, 05:18 PM
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Originally Posted by dsbrantjr View Post
If you have boxed yourself in then you need to change your constraints.
Or give folks who might know more than me the opportunity to enlighten me.
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Old 05-27-20, 05:22 PM
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Originally Posted by dsaul View Post
Don't worry about chainlines, the difference between road and MTB chainlines is meaningless in this case. Road and MTB cassettes are in exactly the same place. The only reason MTB uses a wider chainline, is for tire and chainring clearance.

If you are not opposed to SRAM components, I know for certain that the SRAM Rival front derailleur will shift an XT crankset with 38/28 chainrings. You could use a SRAM Rival 22 mechanical shifters with a GX 10 speed MTB rear derailleur. Both are Exact Actuation and will work together.
Now we are getting somewhere. Tell me more about the Rival 22 shifting the 38/28. Your bike? Was it smooth? Set up easy? Finicky?

I have a 1x11 MTB that has a horrid chainline that I can't correct. I don't want to do another build like that.
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Old 05-27-20, 05:23 PM
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Originally Posted by DeadGrandpa View Post
I thought I should add that I run a 46/30 crankset and a SRAM 10-42 cassette, which on 700x40c tires is a pretty good gearing range. Brifters won't let you do this except on 9 or 10 speed. 11 speed brifters won't work. But I'm an age where I don't enjoy the drops. Jones bars work great.
What rear derailleur are you running?
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Old 05-27-20, 05:33 PM
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Originally Posted by Paul Barnard View Post
What rear derailleur are you running?
It's a SRAM GX long cage.
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Old 05-27-20, 05:35 PM
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Originally Posted by Paul Barnard View Post
Now we are getting somewhere. Tell me more about the Rival 22 shifting the 38/28. Your bike? Was it smooth? Set up easy? Finicky?

I have a 1x11 MTB that has a horrid chainline that I can't correct. I don't want to do another build like that.
It was a gravel bike that I built for a friend. He wanted to run 2.1" tires, so I built the frame with a 73mm bottom bracket and used the XT double crankset. The only experience I have with the shifting was building the bike in the stand. It shifted as well as my 48/34 SRAM Apex crankset with the same Rival front derailleur. He has been riding that bike for about 2 years now and has never complained about the shifting. (I should note that it was Rival 2x10 on that bike, but I don't see any reason that the Rival 22 shifter wouldn't work just as well.)

What is the issue with the 1 x 11 MTB chainline? If you need it further out, you can just switch to a boost chainring.
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Old 05-27-20, 05:37 PM
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And the shifters are SRAM X9 for the front derailleur and SRAM X0 for the rear. I currently use butterfly handlebars but can switch to other mtb handlebars.
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Old 05-27-20, 05:56 PM
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Originally Posted by dsaul View Post
It was a gravel bike that I built for a friend. He wanted to run 2.1" tires, so I built the frame with a 73mm bottom bracket and used the XT double crankset. The only experience I have with the shifting was building the bike in the stand. It shifted as well as my 48/34 SRAM Apex crankset with the same Rival front derailleur. He has been riding that bike for about 2 years now and has never complained about the shifting. (I should note that it was Rival 2x10 on that bike, but I don't see any reason that the Rival 22 shifter wouldn't work just as well.)

What is the issue with the 1 x 11 MTB chainline? If you need it further out, you can just switch to a boost chainring.
I need it further in. It is centered on the 3 smallest sprocket. I bought a new chainring that was supposed to fix it, but it didn't. When I am in granny gear it is really crossed up good.
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Old 05-28-20, 05:12 AM
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Originally Posted by Paul Barnard View Post
I need it further in. It is centered on the 3 smallest sprocket. I bought a new chainring that was supposed to fix it, but it didn't. When I am in granny gear it is really crossed up good.
It sounds like you are already running a boost chainring, which is 3mm outboard from a standard offset chainring and shouldn't be used with a 135/142 rear hub. The standard offset (6mm) chainring should work fine with a 135/142 rear hub, as long as you have chainstay clearance for the ring.
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Old 05-28-20, 09:49 PM
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Originally Posted by Paul Barnard View Post
Best I can tell I am chasing a unicorn.
You could also just be seeing things that aren’t really there.

Originally Posted by Paul Barnard View Post

I have been itching to build or buy a gravel bike. I want a double crankset and brifters. I want my lower gear inches to be below 20 (non-negotiable) and the upper close to or above 100. Gravel bikes are built on a road bike chainline. It seems that every time I start mentally assembling my drivetrain that some incompatible or less than ideal variable pops up. What am I missing?
Thought experiments are just that...thoughts. Aristotle convinced the whole world that two weights would fall at different rates and probably set science back 700 years based on “thought” experiments. He didn’t do the experiments so he didn’t know that he was wrong and everyone went along with him.

Quite thinking (so much) and start doing. The wisest words every spoken to me by one of my colleague’s...and words I have lived by for nearly 40 years...is that “you can always talk yourself out of an experiment”. The limits on bicycle gear trains are very conservative. I’ve pushed the limits on my drivetrains for a long time and have seldom found even the limits of possibility.

For example of the limits and how far they can be pushed, I’m currently using a 46/34/20 tooth crank with an 11-36 cassette being shifted by a Shimano Sora front and Shimano 8 speed XTR rear derailer. I have added a road link to accommodate the 36 tooth cog. I also have a 44/32/20 crank with an 11-36 cassette on a couple of mountain bikes and never had shifting or capacity issues.

Originally Posted by Paul Barnard View Post
Let me give you an example. I wouldn't mind buying a Lynskey or Litespeed Gravel bike with the 2x10 GRX drivetrain. They can be had for under $3000 and that's about as much as I would want to spend. The stock gearing is 46/30 11-36. The GRX derailleur is a long cage listed with a max 36 tooth cassette and a 41 inch chain wrap. A long cage can run a 42T cassette as far as I can tell. If there were a ramped and pinned (outer) 40T chainring that would work with the GRX crank, I'd buy it and a 10 speed 11-42 cassette and live happily ever after. I am assuming in this scenario the GRX derailleur would work well.
​​​​​​​
It looks like the crank uses 110/80mm chainrings. The 80mm BCD seems to come in 26 tooth count. That brings the low dow to 20 gear inches with the 11-36. Alternatively, why not just use an 11-42 without modification of the crank. If it doesn’t work, get the 40 tooth ring.

Originally Posted by Paul Barnard View Post
Building would open up more options for me, but I always arrive at some level of incompatibility as I start piecing things together. There are mountain cranksets that give me the chainring options I want, but then I end up with a chain line issue on the road bike ideal chainline on gravel bikes. Then once I get into an MTB crank I am working an FD that needs road pull ratios. Those FDs are profiled for larger rings. I prefer mechanical discs FWIW.
​​​​​​​
Chain lines are easily adjusted with modern external bearing cranks. Just move the spacers around as needed to adjust the chainline. I run mountain triples on road bikes all the time. I just have to move some spacers from one side to the other.

As for the front derailer, the curve of the derailer isn’t as much of a problem as some would have you believe. Road fronts do just fine with the curvature of the mountain cranks. I’ve been running strictly road front derailers with 46 tooth chainrings shifted by STI shifters for years without issue.

Experiment. If it doesn’t work, you are out some time and maybe a few parts. If it does work, you have something you want and can use.
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