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PostPosted: Fri Oct 18, 2013 3:25 pm 
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I saw this recently:

BB30 Force22 crank on 73mm BSA frame
Image

It seems like there are many spindle lengths between all of the different models of OEM and aftermarket cranks. Not to mention differences in 'usable spindle length' due to the type of preload device used. Checking to see if the arms clear the chainstays is easy enough with the SRAM frame fit info and the chainline can be manipulated quite easily in most cases too, but there doesn't seem to be much data on spindle length to make this kind of hack easy without trial and error. purchase/measure/return error? It sounds like some combos may only work on 68mm wide shells and not 73mm wide shells etc.

I think a few people have posted about this in the road section (often to do with GXP vs BB30 when buying a powermeter) and maybe a few others have done it on an MTB but surely there are some other MTB weenies who've got similar combos? If so post your setup :thumbup:


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PostPosted: Sat Oct 19, 2013 9:38 pm 
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Its hard to tell from the photo, but I'm not convinced it's showing what you say it is. Unless a typical Sram BB30 install involves a ~10mm spacer run between EACH arm and the BB, it's just not going to fit. And even if it did, the bearing seats on the axle wouldn't be positioned correctly (they'd be designed for bearings 73mm apart on the outside, but with the BSA73 you'd have bearings ~75mm apart on the inside.

OTOH, I have (and seen plenty of others too) been able to install a Cannondale Hollowgram BB30 crank on a BSA frame, but it requires a special axle with wider bearing seats, and no lip.

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Posted: Sat Oct 19, 2013 9:38 pm 


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PostPosted: Sun Oct 20, 2013 2:42 am 
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I don't think it's possible to put a "BB30" crank on a BSA MTB BB shell.

What the picture shows I believe is either a GXP frankencrank on a BSA shell, or a BB30 frankencrank on a BB30 shell.

I'll explain.

Since a BSA shell is smaller diameter than a BB30 shell, and a BB30 crank is larger diameter (30mm vs 24mm), there is no room in the shell for bearings for a 30mm crank. Therefore the bearings have to be external. For the spindle to be long enough it would have to handle a total BB width then of about 95mm (73+11+11).

I'm not seeing any 30mm spindles long enough to do this.

Plus, why would you bother? The end result would be no better than a regular GXP setup.

Better photos would have shown for sure what this is, but I suspect it's a 30mm spindle setup on a "BB30" shelled frame, with a modified road crank.

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PostPosted: Sun Oct 20, 2013 3:25 am 
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Look guys, it works but there are lots of variables which is why I asked people to come out of the woodwork and show there setups. Here's a post from the road forum, but same deal as to how it generally works with the SRAM cranks:
grover wrote:
If you're interested in using a powermeter the NEW RED Quarq BB30 crank will work with these cups in your BSA 68mm frame. It is similar in contruction to the S975 but uses the new graphics and chainrings (and quarq). The reason it works is that instead of preloading the bearings with a wavy washer (standard red/force) there is a threaded collar and sleeve. This takes up more room, when removed you have room for the external bb30 cups...just use a wavy washer to preload the bearings.

AFAIK the Force22 crank is basically the same arms/spindle used on the RED Quarq crank - I was just surprised there was enough room for the extra 5mm width of BB shell. It's also easy to tell that the Force22 crank is a BB30 version because the crank bolt is on the drive side.


bikerjulio wrote:
I'm not seeing any 30mm spindles long enough to do this.

With S-Works cranks it works great, but only 68mm shells. And yeah, a fair few SRAM models.
bikerjulio wrote:
Plus, why would you bother? The end result would be no better than a regular GXP setup.

This is Weight Weenies right? A BB30 version of the SRAM cranks with THM cups and a wave washer will weigh less than the GXP version.


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PostPosted: Sun Oct 20, 2013 10:12 am 
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Mr Google returned this http://www.cannondale-parts.de/epages/61764971.sf/en_US/?ObjectPath=/Shops/61764971/Products/KP094

So it appears a 132mm BB30 spindle is needed, and it will work.

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PostPosted: Sun Oct 20, 2013 11:58 pm 
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I'll have to take your word for it that the threaded collar on the new Sram BB30 cranks is wide enough to make space for an external bearing cup (and that there's a similarly wide spacer on the drive side that can be removed also). But this doesn't address the question of whether the bearing seats will be in the correct place. Its typical for a crank spindle to be ~0.1-0.2mm undersized in diameter over most of its length, and the spec diameter only in two places where each bearing is meant to sit. This allows the spindle to be inserted easily into the BB without being a tight slip fit throughout it's length. Assuming the Sram BB30 cranks are this way, it wouldn't work well to use external bearings, even if they fit because there'd be play between crank and BB that would lead to movement, wear, and noise. (Unless for some reason they made the seats extend to the ends of the spindle...)

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PostPosted: Mon Oct 21, 2013 11:16 am 
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Can a Rotor BSA to BB30 bottom bracket not allow for the installation of SRAM cranks or do the spacing issues still apply?

http://www.velotechservices.co.uk/shop/ ... 7416001655


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PostPosted: Mon Oct 21, 2013 3:25 pm 
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That BB is a part of a solution, but a 73mm shell with this BB has an outside-to-outside measurement of about 93mm, whereas a normal BB30 is 68 or 73mm outside to outside. So unless the crank spindle has plenty of space on the BB30 setup, and actual full 30.0mm bearing seats that extend under where the bearings will now be...

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PostPosted: Mon Oct 21, 2013 6:29 pm 
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Makes sense!


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PostPosted: Tue Oct 22, 2013 3:03 am 
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Not sure why you think this cant work dwaharvey?
Image
I'm just interest to know what some of the usable spindle lengths are on the SRAM cranks because they vary a great deal.


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PostPosted: Tue Oct 22, 2013 5:53 am 
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Good photo... that does look like they've extended the bearing seats all the way to the spindle ends (rather than just where the bearings are intended to sit). I doubt that's the case for every BB30 crank, but certainly for this one, if the spindle is longer than 93mm then I'd agree it should work (and actually better than on a BB30 frame since the bearings have a wider stance). Probably requires the larger Q-value (168mm) crank (to save cost I would assume the arms are the same between the 156 and 168, and its just that the 168 has a longer spindle).

I think there's still the question of whether the proper chainline, and equal arm-positioning is possible with the BSA installation, even if the spindle is long enough. For instance, with my Hollowgram SiSL2 installation on BSA, I have a 9mm spacer on the NDS, and only a 1mm spacer plus wave-washer on the drive side (it uses a 132mm modified cannondale spindle). Only way to know is to try I guess...

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PostPosted: Tue Oct 22, 2013 6:09 am 
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a mtb bsa shell will be 68mm, right? and an HT2 bb will be spaced to make it 73mm face to face. is a road bsa shell will be 73mm with no spacers? for some reason i thought that a road spindle would be too short for a mtb, but i don't know why...

If this is just about using road cranks on a mtb frame, PF30 and BB30 mtb shells will be 5mm wider so you need just need a bb30 or pf30 frame and a crankset more spindle. in theory, a bbright/bb30/pf30 compatible road crank should work - to get the crankset to be bbright compatible they just add extra spindle and then to get them to work on a narrower PF30 or BB30 frame, you just use more spacers. can someone confirm?


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PostPosted: Wed Oct 23, 2013 8:30 pm 
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Mentok: you have it totally backwards... MTB standard BSA is 73mm (some use 68mm like Moots), Road standard BSA is 68mm. Road spindles are typically too short because they don't put the chainring far enough out to clear the wider MTB chainstays (or give proper chainline), and/or have the crank arms clear the chainstays also...

As to why to do this... are the Force 22 crank arms lighter than XX1 arms (seems unlikely the spindle would be longer than XX1 BB30 crank...)? Also, if weight-savings and larger spindle diameter are ultimate goal here, why not go for the new Race Face Next SL or Cannondale Hollowgram SiSL2 since those are designed to work? My Cannondale setup (Zipp BB, 132mm lipless axle from R2-bike, Leonardi racing spider) was 110g lighter than a Sram XX1 GXP setup, and almost certainly 60g+ lighter than a botch-job Sram BB30 setup...

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PostPosted: Thu Oct 24, 2013 3:49 am 
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@dwaharvey; thanks for the correction. i've been riding various bikes with 24mm spindle cranks for the better part of a decade and i only learnt recently that there was a 5mm difference between road variants, as there is for bb and pf30 standards :\ whoops.


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Posted: Thu Oct 24, 2013 3:49 am 


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PostPosted: Thu Oct 24, 2013 4:05 am 
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@dwaharvey - I think 'botch job' is a bit of a harsh term - by that reasoning, you're just as 'botched' for using SiSL cranks and a Lefty with the wrong BB shell and head tube. Just remember, the SiSL cranks are not designed to fit your bike, they fit because of a 'custom' spindle :thumbup:

As to why? It's simply a cost thing. If you hunt around you could get the entire setup (arms, BB cups, chainring/spider or spiderless setup - all new) for less than what just new SiSL crank arms can sell for. The new NextSL cranks are cool, but again, could end up costing almost twice as much as a 'cobbled together' SRAM setup. Ideally if you've got a PF/BB30 or 68mm BSA frame and live in the States, the S-Works are actually the best buy. Lighter than SiSL/NextSL yet costing only slightly more than SRAM. If you live elsewhere it becomes much less of a bargain :roll:


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