Help me understand BB30 vs. GXP on SRAM Force 22 crankset

[NHAero]

Building on what Mark McM has written about how he is using a Force 22 crankset with a removable spider to fit a 42-28 chainring set from a SRAM MTB crankset:

I have a frame with a 68mm BSA threaded BB. The GXP BB uses external bearings. The BB30 BB on my CAAD10 uses bearings internal to the BB shell, and the cranks are right up against the BB, very little space, and they have significant flare outward to clear the chainstays.

SRAM makes the Force22 cranks in both BB30 and GXP. Does the GXP version have a longer axle, and, do the crank arms have less flare such that the Q factor ends up the same with each version?

I hope I'm clear about what I am asking...it's hard to figure this out from looking at pictures of separate component parts.

Thanks!

[jtbadge]

The Force 22 "BB30" crankset has a spindle the same length as the GXP, which is much longer than a standard BB30 crankset. When installed in a CAAD, you will need 10-15mm of spacers (I forget exactly how much) along the spindle taking up that extra length.

This pic shows the difference in spindle length (but on FSA cranks). Shorter is BB30, longer is the BB386 standard that the Force 22 BB30 cranks use.

https://bikerumor-wpengine.netdna-ssl.com/wp-content/uploads/2011/12/FSA-SLK-Light-Pressfit-BB30-BB386EVO-comparison05.jpg

[kppolich]

Building on what Mark McM has written about how he is using a Force 22 crankset with a removable spider to fit a 42-28 chainring set from a SRAM MTB crankset:

I have a frame with a 68mm BSA threaded BB. The GXP BB uses external bearings. The BB30 BB on my CAAD10 uses bearings internal to the BB shell, and the cranks are right up against the BB, very little space, and they have significant flare outward to clear the chainstays.

SRAM makes the Force22 cranks in both BB30 and GXP. Does the GXP version have a longer axle, and, do the crank arms have less flare such that the Q factor ends up the same with each version?

I hope I'm clear about what I am asking...it's hard to figure this out from looking at pictures of separate component parts.

Thanks!

What bike are you putting these cranks on?
What is the BB type on that bike (68mm threaded, BB30, Other)?

A nice SRAM document to review is here on page 42:
https://www.sram.com/sites/default/files/techdocs/gen0000000005175_rev_b_frame_fit_spec_2017_road.pd f

[kppolich]

Q Factor is the distance between the outside of one crank arm to the outside of the opposite crank arm.

https://www.cyclingweekly.com/news/latest-news/what-is-q-factor-and-does-it-make-a-difference-187403

I happen to have both cranksets at home and grabbed my caliper. Looks like the same Q factor for both GXP and BB30 to me. ~1mm could be my error.

Force22 GXP: 148mm Outside to Outside
https://farm8.staticflickr.com/7822/46097528975_dd5fe7fb34_c.jpg

Sram Quarq BB30: 149mm Outside to Outside
https://farm8.staticflickr.com/7901/46097529065_7098b06005_c.jpg

Compared:
https://farm5.staticflickr.com/4881/46097528965_86f333fb11_c.jpg

[Jaybee]

If you have a 68mm BSA threaded bottom bracket, get the GXP.

[NHAero]

Looking to do this on my stainless steel Anderson, with a threaded 68mm BSA BB shell. Wanting to do the hack Mark McM outlined, in which a SRAM XX 120/80 spider with 42/28 chainrings is fitted to a Force 22 crankset. Before I spend the money, I want to make sure it will work and will yield a normal road chainline and reasonable Q factor.

What bike are you putting these cranks on?
What is the BB type on that bike (GXP or BB30)?

[NHAero]

Very helpful, thanks very much!!!


Q Factor is the distance between the outside of one crank arm to the outside of the opposite crank arm.

https://www.cyclingweekly.com/news/latest-news/what-is-q-factor-and-does-it-make-a-difference-187403

I happen to have both cranksets at home and grabbed my caliper. Looks like the same Q factor for both GXP and BB30 to me. ~1mm could be my error.

Force22 GXP: 148mm Outside to Outside
https://farm8.staticflickr.com/7822/46097528975_dd5fe7fb34_c.jpg

Sram Quarq BB30: 149mm Outside to Outside
https://farm8.staticflickr.com/7901/46097529065_7098b06005_c.jpg

Compared:
https://farm5.staticflickr.com/4881/46097528965_86f333fb11_c.jpg

[kppolich]

Looking to do this on my stainless steel Anderson, with a threaded 68mm BSA BB shell. Wanting to do the hack Mark McM outlined, in which a SRAM XX 120/80 spider with 42/28 chainrings is fitted to a Force 22 crankset. Before I spend the money, I want to make sure it will work and will yield a normal road chainline and reasonable Q factor.

I don't see any issues.
GXP Threaded BB
GXP SRAM Crankset
the 42/28 rings are small, so there isn't a risk of them running into the chainstay/frame. Usually that's the trouble with bigger rings and running into the stays.
Chainline might be an issue with the little ring up front (28) and anything on the high end of the cassette (11-12-13) but that should be common knowledge with cross chaining and such.

[kramnnim]

SRAM removable spider 30mm spindle cranks all have the wide spindle that will work with BB386, BBRight, BB30a, BSA30 and regular BB30/PF30. The crank arms are straight, just like the GXP arms. They are basically the same as GXP cranks except the spindle is 30mm instead of 24mm.

The SRAM 30mm cranks that don't have removable spiders only work with 68mm BB30/PF30 frames, they have the very flared crank arms that step out to clear the stays.

You can use the BB30 Force22 cranks with your BSA threaded frame if you get BSA30 cups. They're just like your GXP cups, but have a bigger diameter bearing to allow for the 30mm spindle.

[kramnnim]

...make sure you get the correct spline pattern spider to match the crank arms, SRAM's original removable spiders were attached with three bolts, some now use 8 bolts but maybe those are only used with Quarq spiders...?

[yinzerniner]

SRAM removable spider 30mm spindle cranks all have the wide spindle that will work with BB386, BBRight, BB30a, BSA30 and regular BB30/PF30. The crank arms are straight, just like the GXP arms. They are basically the same as GXP cranks except the spindle is 30mm instead of 24mm.

The SRAM 30mm cranks that don't have removable spiders only work with 68mm BB30/PF30 frames, they have the very flared crank arms that step out to clear the stays.

You can use the BB30 Force22 cranks with your BSA threaded frame if you get BSA30 cups. They're just like your GXP cups, but have a bigger diameter bearing to allow for the 30mm spindle.

Just an FYI, the SRAM Red Exogram cranksets in BB30 can also work with 73mm wide shells (ie BB30a) if you remove the preload adjuster. You'll have to eliminate the play via trial and error and some thin spacers with the wavy washer, but'll work fine once that's done.

[NHAero]

Lots of information from you folks, thank you. Some more questions:

- What does wide spindle mentioned below mean? I want to keep the chainline tight as possible - my goal is to use the large ring in all but the largest cog, and the small ring only for the largest cog up through the middle (6th) cog - almost as a 1x set-up with a granny bailout gear. So if a wider spindle means that the chainline grows, that's the wrong direction.

- Is there a preference for any reason between the GXP and the BB30 version, assuming the threaded 68mm BB shell?

- Is there any reason that the 11 spd Shimano shifter and front derailleur won't play nice with the SRAM Force 22 crank with the 42/28 rings? Currently using a CX70, which is 10 spd, and 44/33 TA rings on an old Sugino AT crank and it all works fine.


SRAM removable spider 30mm spindle cranks all have the wide spindle that will work with BB386, BBRight, BB30a, BSA30 and regular BB30/PF30. The crank arms are straight, just like the GXP arms. They are basically the same as GXP cranks except the spindle is 30mm instead of 24mm.

You can use the BB30 Force22 cranks with your BSA threaded frame if you get BSA30 cups. They're just like your GXP cups, but have a bigger diameter bearing to allow for the 30mm spindle.

[kramnnim]

By wide spindle, I mean wide enough to work with an 86mm BB shell. Which is the same width as GXP.

I guess it would be better to call that a normal spindle, and to call the ones that only work with 68-73mm shells "narrow."

[kramnnim]

The 30mm version is stiffer and maybe a little lighter than GXP?

The BSA30 cups would need a different tool for installation

GXP doesn't require a wavy washer or spacers like the 30mm

GXP is harder to find used.

GXP require larger boxes to ship. (lol)

30mm do not work with Trek frames that use BB90

[bikinchris]

I didn't go through all of this figuring. I just got a very lightly used XX crankset with 42-28 rings for my frame.

[NHAero]

Chris, I'm an engineer and suffer from Overthinking-itis. As I've fooled with this on the two bikes (the Anderson all-rounder, and the Litespeed MTB converted to a dropbar 26er) the issues I'm trying to resolve together are:
- the 11 spd Shimano shifter will shift the front derailleur so that the chain doesn't rub the chain guide in some gears
- the chainline is 44-45mm so the larger of the two chainrings works with all but the largest cog
- The larger chainring doesn't touch the chainstay
- the Q factor of the crankset isn't too wide

I have old Sugino AT cranks on square taper BBs on both bikes. The 45T chainring barely misses the Litespeed chainstay, which are wider than the Anderson.

It seems that Mark McM's hack with the Force 22 crankset is the best path because it has a road chainline. In your approach, what is the chainline of the XX crankset in place? AFAIK MTB chainline is 47.5mm and that's why I've been leaning towards the Force 22 solution.

Thanks very much for sharing your experience!


I didn't go through all of this figuring. I just got a very lightly used XX crankset with 42-28 rings for my frame.

[Mark McM]

I see there's already lots of good information here already, so I'll just add a few comments:

As mentioned, SRAM's labeling of their "BB30" road cranks is a bit misleading - while they use the same 30mm spindle diameter as BB30 cranks, the spindle is actually quite a bit wider than true BB30 spindles, and are essential the same width as the GXP cranks. Consequently, the "BB30" cranks have the same Q factor (and U factor - crank width as the spindle) as GXP cranks. Both cranks use the same spiders and have the same chainline. (Note, however, that for SRAM MTB cranks, the GXP and "BB30" versions use different spindle widths - more below.)

As you know, MTB cranks have wider chainlines than road cranks. But also, GXP MTB cranks use longer spindles than GXP road cranks. So when a double chainring spider intended for a GXP MTB crank is installed on a road crank, the chainline is reduced, and the chainline becomes nearly identical to the standard road chainline. (Note: because GXP and "BB30" MTB cranks have different spindle widths, they also use spiders with different chainring offsets. Using a "BB30" MTB spider on a road crank will result in a chainline that is about 3mm wider than standard road chainlines, and closer to standard MTB chainline width)

The propensity for the chain rubbing the big ring when cross-chained in the small chainring and small sprockets is reduced with smaller chainring sizes, so a 42-28 chainring combination may have less rub than, say, a 50-34 chainring combination.

I don't know whether the Shimano shifter/derailleur will shift the 42-28 well, as those are smaller chainrings than the (road) derailleur is designed for (for my setup, I used a Campagnolo derailleur and an Ultrashift shifter, which is not indexed). And for the most part, you can't mix-and-match Shimano road and MTB front derailleurs. However, SRAM double MTB cranks do use the same 8mm chainring center-to-center spacing as their road cranks, so the road derailleur may indeed work.

I mentioned this before, but another factor that may come into play is that the Force 22 crankarms are angled outward from the BB, which means that the clearance between the derailleur cage and the back of the crank arm diminishes as the derailleur is lowered (for smaller chainrings). This can be mitigated by offsetting the chainrings inboard with chainring spacers (both chainrings are mounted to the inner face of the spider, so both can be offset inward with spacers). Since the outer chainring is attached with a bolt that threads directly into the chainring, longer bolts may be required if the chainrings are offset with spacers. Of course, this narrows the chainline also, but it sounds like you had wished to do this anyway.

[NHAero]

So helpful, thanks Mark, your insights and experience here has been absolutely invaluable.

I see there's already lots of good information here already, so I'll just add a few comments:

As mentioned, SRAM's labeling of their "BB30" road cranks is a bit misleading - while they use the same 30mm spindle diameter as BB30 cranks, the spindle is actually quite a bit wider than true BB30 spindles, and are essential the same width as the GXP cranks. Consequently, the "BB30" cranks have the same Q factor (and U factor - crank width as the spindle) as GXP cranks. Both cranks use the same spiders and have the same chainline. (Note, however, that for SRAM MTB cranks, the GXP and "BB30" versions use different spindle widths - more below.)

As you know, MTB cranks have wider chainlines than road cranks. But also, GXP MTB cranks use longer spindles than GXP road cranks. So when a double chainring spider intended for a GXP MTB crank is installed on a road crank, the chainline is reduced, and the chainline becomes nearly identical to the standard road chainline. (Note: because GXP and "BB30" MTB cranks have different spindle widths, they also use spiders with different chainring offsets. Using a "BB30" MTB spider on a road crank will result in a chainline that is about 3mm wider than standard road chainlines, and closer to standard MTB chainline width)

The propensity for the chain rubbing the big ring when cross-chained in the small chainring and small sprockets is reduced with smaller chainring sizes, so a 42-28 chainring combination may have less rub than, say, a 50-34 chainring combination.

I don't know whether the Shimano shifter/derailleur will shift the 42-28 well, as those are smaller chainrings than the (road) derailleur is designed for (for my setup, I used a Campagnolo derailleur and an Ultrashift shifter, which is not indexed). And for the most part, you can't mix-and-match Shimano road and MTB front derailleurs. However, SRAM double MTB cranks do use the same 8mm chainring center-to-center spacing as their road cranks, so the road derailleur may indeed work.

I mentioned this before, but another factor that may come into play is that the Force 22 crankarms are angled outward from the BB, which means that the clearance between the derailleur cage and the back of the crank arm diminishes as the derailleur is lowered (for smaller chainrings). This can be mitigated by offsetting the chainrings inboard with chainring spacers (both chainrings are mounted to the inner face of the spider, so both can be offset inward with spacers). Since the outer chainring is attached with a bolt that threads directly into the chainring, longer bolts may be required if the chainrings are offset with spacers. Of course, this narrows the chainline also, but it sounds like you had wished to do this anyway.

[Mark McM]

One more observation about Force 22 cranks:

SRAM documents state that Force 22 cranks have a Q-factor of 145mm, but as seen earlier in this thread, measurements appear to show that width of the cranks is more like 148mm. Why the difference? SRAM is fudging a bit. As it turns out, the pedal mounting surfaces are inset into the crank arm faces by about 1.5mm (3mm total for both sides), so the actual pedal mounting faces are 145mm wide. I use Speedplay pedals, which have quite a bit of lateral adjustment. I prefer as narrow a stance as possible on the pedals, so I adjust the cleats to space my feet as far inboard as possible. So if, for example, I adjust the cleats so my shoes just barely avoid scraping against Campagnolo cranks (145.5mm Q factor at the pedals, slightly narrower for the rest of the cranks), my shoes will scrape against SRAM Force 22 cranks.

[NHAero]

Are there strong preferences for a particular brand of GXP BB for a 68mm threaded shell? It seems as though the choices are either SRAM at about $30, then there are brands such as Wheels Mfg and Token for about $80, or Chris King, BBInfinite, and the like for over $150.

Are the SRAM versions low quality? I'm thinking of how fairly low cost Shimano square taper BBs have served me so well over the years, hard to tell from the Phil Wood units I have in some bikes.