Building a Resource for Crank and Chainring Clearances

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I’m working on chainring check tooling for my framebuilding fixture - The Creator Frame Fixture.

I started to build a G-Sheet last night as a master repository of published chainring and crank arm clearance data. Sram, Shimano, White Industries, Wolf Tooth, etc. I suspect others have done very similar work before and I’m re-building the wheel. I did a search here and found some threads containing references to crank and chainring clearance, but I didn’t see a master resource anywhere.

If there is such a resource, please let me know

Otherwise, I’ll try to make mine worth a damn and publish it on my website and link that here.

Frustratingly, many of these published data points are defined differently or are seemingly conflicting. I’m trying to put the data together as simply as possible.

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Good idea Joe! I’d be happy to work with you and provide info on my cranks and all their different widths. Chainrings, especially 2x is a mess and there isn’t great documentation on actual ring location.

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I’ve made a Fusion drawing with a couple of crank/chainring combos that I 3D printed to fit my CS mitersetup. The file is a bit of a mess as I have just added stuff going along, but the crank/chainring templates so far are working IRL:
BB blok CS fixture.f3d (1.4 MB)

20220420_200458
20220420_2004581908×4032 1.62 MB

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As an update here:

I have found this Wolf Tooth chainring diameter chart to be helpful and close to other MFG data.

It’s super fascinating how linear the diameter jumps are! +4mm on radius for every +2 teeth. Almost perfectly across the 24-52t range. You see the same thing with other MFG charts.

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On Chainline, I think this sheldonbrown.com chart is a great bird’s eye view of the situation.

https://www.sheldonbrown.com/chainline.html#standards

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My biggest struggle is crank arm inner width- basically chainstay clearance. I can usually find Q-Factor but if it is not a Sram crank I can rarely find the inner crank width/distance.

If anyone has that info, it would be hugely helpful to share.

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Hey Joe -

I’ll add a sympathetic “good luck”. I compiled this data for all the major cranks a couple of years ago. I would share the spreadsheet, but it’s in serious disrepair at this point. Here were my conclusions…

  1. You only truly need to know two/three/four (1x/double/triple) X/Y coordinates for any given crank. The different manufacturer’s provide a bunch of different dimensions, most of which are just clutter. The important ones are circled below in pink. (L3/W3; L4/W4; L5/W5). This is a page from a SRAM tech manual, but all the drawings include these points. (Sure, you may occasionally run into a situation where a chainring bolt or the middle of the crank arm affects clearance, but if you’re building to that tight a clearance you probably already have–or should have–the crankset on-hand.)

CrankDims
CrankDims1706×1014 74.5 KB

  1. Yes–as you mention–chainring diameter is linear and consistent. This shouldn’t be surprising… There are several “chainring diameter calculators” and charts out there.

  2. Similarly, crank arm length is pretty consistent. Take the arm length and add 15mm and you’ll get very close to that L5 dimension for most cranks.

  3. Published “Chainline” isn’t a very helpful dimension, for a bunch of reasons. You really do need the technical drawings from the manufacturers’ frame fit specs.

  4. There’s a lot of overlap between manufacturers’ similar cranks, and then are some frustrating outliers. I’m sure Campy EKAR has bitten a lot of builders… Take a look at the drawings and you’ll immediately see why.

  5. Don’t even try to account for power meters, crank boots, etc. Again, if someone is dealing with those items and pushing clearances, they should have them on-hand.

Here are most of the drawings, if anyone is having trouble finding them:

SRAM Road/Gravel:
https://www.sram.com/globalassets/document-hierarchy/frame-fit-specifications/road/2023-road-frame-fit-specifications.pdf. Cranks starts on Page 34

SRAM Mountain:
https://www.sram.com/globalassets/document-hierarchy/frame-fit-specifications/mtb/2023-mtb-frame-fit-specifications.pdf. Cranks start on Page 16

White Industries Square Taper:
https://www.whiteind.com/support/technical-documents/crank-drawings/

White Industries M/G/R30:
https://www.whiteind.com/support/technical-documents/mr30-crank-and-chainring-dimensional-drawings/

Shimano:
Shimano-Cranks2020.pdf (550.0 KB)

Campagnolo:
Campy_CX.pdf (2.6 MB)
Campy_Record.pdf (2.9 MB)
Campy_EKAR.pdf (3.0 MB)
Campy_Potenza.pdf (3.0 MB)

Most of the others… RaceFace/Ingrid/Etc… all have drawings available too. They’re usually in the “Support” section of each individual crankset’s product page. Yes, even most of the manufacturers can’t seem to put all of their specs in one spot! (Thank you, thank you White Industries… You might be the only one.)

In the end, I ditched this effort… Instead I determined the narrowest clearance and longest crank arm dimension for each “type” of crank (Road Double, Gravel 1x, etc.) regardless of brand, and we just built our frames to those specs. And if someone specified “Sram/Shimano Gravel 1x” to us and then they slapped a EKAR crank on the frame and wondered why things didn’t clear, well…

Sincerely, good luck! I’ve been hoping someone smarter like you would do this at some point and keep it all neatly organized. If you can do it in a universally discernible way and keep it up to date, you’ll deserve a huge thanks.

PS. If anyone out there uses Adobe InDesign, I made a tool to easily produce 2D chainstay overview drawings. It includes the major cranks on different layers. You can hide/show the cranks and rear hub spec, and print out a full-scale drawing to use during a build. Chainstay length is accounted for by taping the two sheets of paper together using the scale. It’s hokey, but it works great. Then you just draw the tire in by hand and you’re good to go. Here’s a sample. I can’t seem to attach an InDesign file here, but if you’d like a copy shoot me an email.

ChainstayWorksheet-Sample.pdf (34.1 KB)

Blandford-5137
Blandford-51371867×2800 567 KB

-Chris

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That’s a lot of good specific information and also practical wisdom - what is noise, what will commonly bite you, etc.

So far things feel much simpler to me since beginning to study this. End of crank arm isn’t something I can practically accommodate with the tool I’m trying to make at this time so I’ve left that research for later. The chainrings themselves aren’t that intimidating if you break it down.

It shouldn’t be surprising that a linear increase in tooth count produces a nearly perfect linear increase in diameter. I guess I was half-thinking it was an exponential relationship (such as area of a circle) and so it was surprising to me. It’s basically circumference and only when you get into super low tooth counts that you see any weird jumps. And those are because it’s the pitch diameter of a polygon, not the actual circumference of a perfect circle. I assumed the polygon thing was somehow coincidentally canceling out the exponential part of things almost perfectly across the size range we were looking at. Which in hindsight doesn’t make much sense, haha.

Very cool to see that Illustrator tool!

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Aw, gotcha. Yah, I suppose it is a little odd in that way. Something about teeth and wrapping and… yikes… that’s way more geometry than I absorbed in 8th grade. Ha.

Yah, if you keep it to a chainring checker (and not a true “this-crankset-with-all-these-different-variables” checker) that should make it doable. I hope you can get it done. As far as I know, there is not a master reference. There definitely should be.

-Chris

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Adding to the confusion: I have a client with a GX crankset on his fully. I built the frame to fit a 34 oval snugly, but no issues with clearance after 2000kms. Because he kept wearing out the DUB BB’s I got him a Hope BB with DUB adapters. Turns out this moves the crankset quite a bit to the non driveside, giving about 1mm clearance for the chainring. Also not a lot of room in the width so in the end I turned down the non driveside DUB adapter to get enough room. One of those 10 minute jobs that took 1.5 hours before everything worked…

Thanks for the Shimano specs! While Sram is kind enough to publish it all I have not even been able to get them from Shimano Benelux directly even…

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I made a template for shimano GRX cranks. Trying to decide what dimensions to use is a bit tedious. I decided to go with the biggest chainrings that the crank would fit. I suppose someone might later decide to put a compact crank on one of these frames and be disappointed. Along the same lines, maybe we should just find the worst clearance problems of any crank and make the “worst case” template.

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Yeah, ain’t that the whole debacle. Optimize for what you intend to actually do with the bike, or generalize for future optionality.

That was the issue I faced in trying to adapt my Sidewinder chainstay yoke to “Gravel Bike” applications. I would rather optimize for single chainring applications, but commonly folks will still run doubles in that application and for that use case you’d like a significantly different profile. I’ll release something one of these days, but choosing which side of the fence to walk isn’t always easy.

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Agreed! Unfortunately, I have found third-party (non shimano/sram/campy) BB specifications to be all over the place. There is a ton of variation in outer bearing width (OBW). The length of the threaded cup can also vary between 12-14mm, which causes issues with internally routed brake lines.

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