[Standards] Road and Gravel Drivetrains - Cranks and BB's

Chainlines

The gravel/road world has a confusing set of chainring and chainlines standards.

Standard Brand Chainring Bx Sx By Sy Cx Cy Q-factor Chainline
Road SRAM 48-35t 98.3 73.4 47.7 39.9 190 60 145 45
Road SRAM 46-33t 94.3 69.4 47.7 39.9 190 60 145 45
Road Wide SRAM 43-30t 88.2 63.3 50.2 42.4 190 62.5 150 47.5
Road 1x SRAM 46t 96.6 x 43.3 x 190 60 145 45
Road Wide 1x SRAM 42t 88.5 x 45.7 x 190 62.5 150 45
Road Semi Compact SHIM 52-36t 107.1 76.1 46 37.8 192 57 146 43.5
Road Compact SHIM 50-34t 103 72.1 46 37.8 192 57 146 43.5
GRX 2x SHIM 48-31t 99 66.1 48.5 40.3 193.4 60 151 46.9
GRX 2x SHIM 46-30t 95 64 48.5 40.3 193.4 60 151 46.9
GRX 1x SHIM 42t 88.7 x 46.7 x 193.4 60 151 49.7
GRX 1x SHIM 40t 84.6 x 46.7 x 193.4 60 151 49.7
EKAR CAMPY 44t 92 x 43 x 189 57.5 14.5 45.5

BB Standards:

Standard Nom. Width Type Typ. OD Comments
BSA 68mm Thread 1.5in Most common BB standard. No internal cable routing possibilities.
T47 EB 68mm Thread 2in Sram does not make a DUB T47EB BB at the moment. Used by NMW, Meriweather, …
T47 IB 85.5-86.5mm Thread 2in T47 IB is becoming the threaded gravel and road standard
PF30 68mm Press 2in Most common pressfit standard
BB86 86.5mm Press 1.5in Also known as “Shimano Pressfit” standard. No one makes a BB shell for this anymore. The industry seems to have moved to PF30
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52-36 is Road Mid Compact or Road Semi Compact

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Thanks for the correction, that is a great segway to a road sub-compact (~46-30t) discussion

I think this is a pretty good standard: road Q factor with large gear ratio. Unfortunately Sram, Shimano, and Campy don’t have this option, so there is little documentation on it

As far as I know, there are a few options:

However, these cranks don’t list their Q factors, or if they do, they are really wide (for example, the White Q is 163mm). That really puts them in the gravel 2X category rather than Road Sub-Compact

I would love to hear people’s thoughts and opinions on these Sub compact cranks.

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I’ve used white ind square taper (44/30), and modified sram road cranks with praxis sub compact chainrings (46/32).

On a road-ish gravel bike, or even ‘winter’ road bike, pairing a 11-32 cassette with sub compact road cranks is an amazing combo. Reasonable cadence jumps, enough gears for steep climbs and most descents.

For customers I’ve set up sub compacts with 11-42 cassettes. Can’t speak for how it rides, but holy moly that’s a lot of range.

I posted Easton Q-factor info in another thread - 150-155mm depending on spindle choice.

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Maybe I’m missing something but 30mm spindles fit just fine in BSA shells.

I say this because none of the big drivetrain companies (Shimano, Campy, SRAM) support 30mm spindles in BSA shells. 30mm spindles and BSA BB’s are all aftermarket upgrades.

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I understand that, but my point is that those are not drivetrain manufacturers. The level of testing and validation an aftermarket company goes through vs a drivetrain producer is not the same.

The main driver for SRAM to release a 29mm spindle instead of 30mm is to make it backward compatible with BSA. How much of that is a business decision vs actual engineering is up for debate. But that is what their official technical position is, and I agree with their assessment.

All the information I provided is directly from the respective manufacturer’s documentation. Since none of the manufacturers support a 30mm spindle with BSA, I gave it a “poor compatibility”.

 

Just seems like an odd thing to mention. It doesn’t really matter because those same drivetrain manufacturers offer solutions for BSA.

I know you’re biased to T47. It seems great for certain applications, like titanium and internal routing. Otherwise, for steel good old BSA is hard to beat.

I ask this as a forum user, not a moderator: Let’s not waste our energy debating BB standards. Everyone has their own preferences, experiences, and biases. I removed the “poor compatibility” from the BSA comments.

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Big yes to subcompact cranks and the 46-30t combo. Rode a Sugino XD wide-low double on my touring bike for years and the cranks are still going on a mate’s commuter. That was with an 11-32 cassette. For older bikes it’s a hard setup to beat for range at good value. I would say most riders would be better of with that kind of gearing.

My current preference is for a Rival 1x mech and a 10-42 cassette (XG1150 - all steel). Yes there’s a slight reduction in range—from 446% down to 420%—but I prefer the simplicity of the 1x setup and the chain retention of a proper clutch mech. That and the fact that my gravel bike now uses the same drivetrain spares as my MTB (1x11 GX).

As far as cranks go I’m using the WI G30 cranks on the above bike. They’re great looking cranks but I have a few issue with them. I mentioned in the MTB drivetrain thread that I’ve cracked a couple 30mm BB cups for BSA shells in the past. That was on this bike. I think a 30mm spinle in a BSA shell requires a step up in the shape of the external cup that is more prone to failure than the equivalent design for T47. Also the 1.5mm hex WI uses to cinch down the preload collar really sucks. A 1.5mm hex is not included on most multi-tools and a loose one is super easy to lose. It also fills up with dirt way to easily. I recently set up some of their cranks on a mate’s MTB with a bunch of Wheels MFG spacers and a 30mm wavy washer and that’s been a good work around so I’ll probably do the same on my bike eventually.

Oh and one crank option you’re maybe missing is the Sugino OX2-901D. I’m assuming they still make them as they’re listed on the site but I know availability has been hit and miss in the past. They’re 24mm spindle, 145mm Q-factor and have a option for 110/74 BCD so could tick a lot of boxes.

There’s also the Middleburn R01 (square taper) and R02 (24mm) which are now being manufactured by BETD. 1x and 2x spiders are available IIRC.

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I would be remiss if I didn’t share an internet friend’s beautiful Nerd Crank Database. Developed specifically to help fellow bike geeks find suitable subcompact crank combos!

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Glad to see a lot of subcompact fans. and some good options. I think the gearing in gravel and Q factor in gravel biking is not talked about enough. This might be another fun project to look into: A modern, <$200 sub-compact crankset w/11 and 12s compatibility.

To me, the huge advantage of a road bike is:

  • narrow Q factor
  • smaller steps between gear changes

When you start slowly taking that away, I would rather ride a mountain bike :sweat_smile:

I get a lot of requests to design gravel yokes that don’t make much sense in my opinion. A compact double (50-34) and a 700x50mm tire should not be on the same bike! Tires have gotten larger in diameter (less mechanical advantage), terrain steeper, but the gearing for gravel bikes are still thought of in road bike terms.

Comparing Tire Size and Gearing

Here are some charts to visualize the gear ratios.

  • High-low = 40x26 (2x mountain bike gearing)
  • Sub Compact = 46x30

High and Low range:

Lowest Gears Compared:

Highest Gears Compared:

That is my conclusion as well. BSA + 30mm spindles are just too tight to get enough room for the cup, spindle, seals, etc… Contrary to what people think, I am actually not a huge T47 fanboy, especially for gravel bikes. A lot of our customers want to use those cool CNC cranks, which are all 30mm spindles (which I also am not a fan of), so T47 is the least constraining option. It also seems like the industry (Cervelo, felt, trek) has chosen to go with the T47IB standard, so you can find a Praxis T47 BB and more importantly a $16 tool at any Trek store.

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Just chiming in for Canadians about Praxis stuff.

Don’t buy it.

There is only one Praxis distributor in Canada (Great Western). They don’t stock the 28mm bearing for the NDS (the bearing that always dies). You have to purchase an entirely new BB because Great Western doesn’t offer the bearing by itself, even though Praxis designed the BB cups to have replaceable bearings (like Wheels MFG cups). The proprietary 28mm bearing is so stupid. It’s literally a 30mm bearing with a sleeve reducing it to 28mm.

Praxis also doesn’t allow you to purchase directly from their website if you’re in Canada, they refer you to your LBS who will order from Great Western. Last time I worked at a store that stocked Trek (a year ago) we couldn’t order the bearing from Trek, we had to go through Great Western. I’d also prefer not to give my money to Trek… for many reasons (cop bikes, that awful ‘thank you for dying for us’ video that Jon Burke put out, etc,) but everyone has different values.

I’m still a huge fan of friction for front D (and rear D honestly, but I know that’s not everyone’s bag).

I have a bike that uses a GRX 46/30 crankset, GRX front derailleur, friction bar end shifter for the derailleur, and Sram Rival Hydro rear D + brifters, with an 11spd 11-46 cassette. Dropper post is actuated by left shifter. I really love mixing and matching like this. I use this bike for bikepacking / off road touring. Conquering loose shale rocks on a steep climb while fully loaded is a great feeling.

I actually prefer the wider Q of ‘gravel’ cranksets. I like bombing descents fully loaded and the wider stance makes me more planted.

Here’s a +1 for Path Less Pedaled inspiring me to think creatively about drivetrain configurations.

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Hmmm, I don’t love the road/MTB binary but if we’re to simplify things like that it seems as though the current gravel trend is bike just “road bikes with wide tyres”. I reckon things are going to change as these bikes are developed properly and hopefully some standards will follow.

Note: Personally I hate drop bars for mixed surface rides and think that XC bikes from 10 years ago make better gravel bikes than most of what is being produced now. I have seen the term ATB for these kind of bikes which I prefer!

Same! Wide Q has never been an issue for me. The wider stance of a MTB crank is great for rougher roads and standing climbing. I’ve done a 200km day on a fatbike crakset with 228m Q. I find you do need a steeper STA and a higher hand position (flat/riser bars) to open up the hip angle and make a wide Q work though.

Yep this is my experience. The 30mm spindle standards seems to have been developed for carbon fiber and aluminum bikes and T47 is the best work around for steel construction. On a MTB the extra weight/size of T47 doesn’t bother me—I actually think they kinda suit a bike with a 44mm HT—but for a lighter weight gravel/ATB build I think a BSA shell and a 24mm crank is a much nicer choice.

That’s a great list of options. Thanks for sharing!