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Discussion Starter · #1 ·
I'm trying to figure out which BB i need for a simple BSA73 frame, with 148mm boost rear spacing. SRAM's chart is pretty extensive, but what the heck is "MTB" and what is "MTB WIDE"? It doesnt say anywhere on the PDF or their website.
Is MTB=135 and WIDE=148 ?!
or is MTB=148 and WIDE=SRAM AXS WIDE ?!
Or is it something else?
Man, they really chose the most generic name for that...
Appreciate any insight

(PS-there's a chain guard but it's on ISCG tabs and not BB mounted, so i dont think it should affect the chainline or spacers)
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ForaBot's answer is created from summarizing the responses in this thread.

According to the information provided by members of the community, SRAM's "MTB Wide" refers to a bottom bracket with 148mm boost rear spacing. This bottom bracket is designed for bikes with a 55mm chainline to allow for additional clearance at the bottom bracket for wider tires and suspension linkage. The cranks for this bottom bracket have "DUB WIDE" etched on their spindles. It is recommended to order a SRAM spacer kit along with the bottom bracket to ensure that the correct spacers are included.
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Discussion Starter · #3 ·
MTB Wide = 148 and is what you need. The only real difference is the spacers that come with the BB.
Thanks.
Hmmm, are you ABSOLUTELY sure that MTB wide = 148?
I just ran into this thread a minute ago and it says differently, now i dont know what to think
specifically this reply "
I have a 73mm shell width, running 148mm (boost spacing) with a threaded BB and recently asked Sram what "Wide" is. Sram's response, "MTB Wide is a specific spindle that will be marked on the spindle itself."
Sram said 148mm spacing would be "MTB" per their charts. "
 

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I still can't figure out exactly what MTB wide is, SRAM has done a terrible job of documenting it and all other posts I find are equally confused. It is definitely not just wide = boost and regular = non-boost. Because a regular crankset/BB with a 3mm offset chainring is the correct setup for boost, whereas a 6mm chainring is for non-boost. Maybe wide pushes a further chainline for even more tire clearance?

The only thing I can find is an article that says Road Wide is a new standard made to increase tire clearance. https://bikepacking.com/gear/sram-force-axs-wide/

The BB is the same between them, just different spacer setup. You'd buy the BB that matches the cranks you have, then install spacers according to the manual.
 

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Discussion Starter · #5 ·
Yeah, but each kit comes with different spacers, so i can't order the correct kit without knowing which spacers I need! This is so bewilderingly stupid of them.
I also ran into some comments saying MTB Wide is some new crank spindle width, but I can't seem to find any such cranks, let alone in the MTB category (so why does this definition even exist in the MTB Bottom Bracket compatibility chart?!)
I found this chart - the funny thing is, this chart doesnt even mention the "MTB Wide". But the 148boost kit is the one ending in *.000 which is the normal (i.e - "MTB") version. I can only assume it's an earlier chart before they threw in the extra confusion.
Seriously, screw them. They parade it as "not a new standard", but then somehow make it even more complicated than all existing standards.
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since 4/10/2009
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Looking at both charts together (with the second one frustratingly missing MTB Wide and 73 Ai applications), I am wondering if MTB Wide is supposed to be their fitment for bikes that use a 55mm chainline. That's a touch wider than regular boost, but also not as wide as super boost.

Bikes like my older Guerrilla Gravity Pedalhead (it seems their revised frame uses a 52mm chainline now), the Yeti Arc, and I'm sure others.

Of course, I have no proof because this SRAM documentation is absolute trash.
 

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Discussion Starter · #7 ·
Looking at both charts together (with the second one frustratingly missing MTB Wide and 73 Ai applications), I am wondering if MTB Wide is supposed to be their fitment for bikes that use a 55mm chainline. That's a touch wider than regular boost, but also not as wide as super boost.

Bikes like my older Guerrilla Gravity Pedalhead (it seems their revised frame uses a 52mm chainline now), the Yeti Arc, and I'm sure others.

Of course, I have no proof because this SRAM documentation is absolute trash.
Yeah, perhaps. But its all speculation.
Their documentation would be great if only it didn't miss some critical definitions like these. They omitted just enough to turn it from great to absolute unusable hieroglyphics
 

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SRAM MTB Wide refers to cranksets with a 55mm chainline designed for boost 148 rear ends. They achieve this chainline by using the same 3mm offset chainring as normal boost cranksets, but paired with a longer spindle. A normal BSA 73 DUB BB for boost 148 rear end uses a 4.5mm right side spacer. A MTB Wide BSA 73 DUB BB uses a 3mm left side spacer and 7.5mm right side spacer to account for the longer spindle. You can see an example of a MTB Wide crankset in the link below:

 

since 4/10/2009
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SRAM MTB Wide refers to cranksets with a 55mm chainline designed for boost 148 rear ends. They achieve this chainline by using the same 3mm offset chainring as normal boost cranksets, but paired with a longer spindle. A normal BSA 73 DUB BB for boost 148 rear end uses a 4.5mm right side spacer. A MTB Wide BSA 73 DUB BB uses a 3mm left side spacer and 7.5mm right side spacer to account for the longer spindle. You can see an example of a MTB Wide crankset in the link below:

why is it so hard for SRAM's own documentation to include the chainline? honestly, that would solve a lot of problems right away.
 

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It's fairly new and only applies to a handful of new bikes, so they probably just haven't got around to updating all their documentation.
I don't buy it. the chart that OP posted would have been the perfect spot to put it. They updated the chart enough to mention "MTB Wide" and put it under the 73mm bb section, but then ignored details about what it actually is? Lazy is what that is.
 

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Discussion Starter · #12 ·
So, basically, for a "normal" 148 rear end i'd need the MTB version?
Also, when they say "chain guide" - are they referring only to ISCG/BB mounted bashguards which push the cups out, or also to Direct Mount guards? I dont see how a direct mount chain guard should affect the bottom bracket...
 

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Discussion Starter · #13 ·
I don't buy it. the chart that OP posted would have been the perfect spot to put it. They updated the chart enough to mention "MTB Wide" and put it under the 73mm bb section, but then ignored details about what it actually is? Lazy is what that is.
Agree. Lazy and incompetent. Their charts are extensive enough that them leaving something so critical out isn't just because they had not time to revise them
 

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Does it even matter what version someone would buy?
Threaded bb cups are all the same just with different spacers for 68 and 73mm width.

And the dub cranks are also the same, the only difference is the offset of the chainrings.
6mm offset =142mm ( 49mm chainline, non boost )
3mm offset = 148mm ( 52mm Chainline, Boost )
0mm offset = 157mm ( 55mm Chainline, superboost )
 

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Discussion Starter · #18 ·
Does it even matter what version someone would buy?
Threaded bb cups are all the same just with different spacers for 68 and 73mm width.

And the dub cranks are also the same, the only difference is the offset of the chainrings.
6mm offset =142mm ( 49mm chainline, non boost )
3mm offset = 148mm ( 52mm Chainline, Boost )
0mm offset = 157mm ( 55mm Chainline, superboost )
Of course it matters - the different kits come with different spacers (although even that's hard to tell which, because most online stores dont specify which spacers). So, in order to know which kit to buy, you must know which spacers to get, which depends on whether you're MTB or MTB WIDE.
Again, how dumb it is to call something "MTB"... it's like calling a car part "FOR-CAR".
 
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