Author Topic: New 29+ Frame (CS-496) build  (Read 1086 times)

carbonazza

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New 29+ Frame (CS-496) build
« on: February 24, 2017, 12:27:21 PM »
We are starting the build of a 496 frame with a friend as a 29+
It is my first boost, so I start this build post with some doubts  :)

  • We will put an SRAM Eagle on it. Does it need the boost version of the crankset or is the frame already takes care of the 52mm chainline?
    The groupset was bought complete, but I'm wondering the crank need to be exchanged.
    The BB is BB92, and the width of the BB shell is... 92mm !
     
  • It will be my first set of boost wheels too...
    cmh sold me his 29" rims(42mm/36mm wide)
    They finally landed in Belgium ( they transited in a friend's luggage from Phoenix AZ to Europe recently  :o ).
    From what I understood the 3mm offset goes:
    • to the right of the front wheel
    • to the left of the rear wheel
    Is it right? Does someone has a good article dealing with the specifics of building asym wheels?
    Anything special I need to take care about?



Carbon_Dude

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Re: New 29+ Frame (CS-496) build
« Reply #1 on: February 24, 2017, 12:59:20 PM »
I can tell you the crankset is not boost specific, that is taken care of with the chainring.  You would need the proper Boost chainring that has the correct offset.  As for the wheels, I've always just had wheels that were pre-built with 12x148 hubs rear, 15x100 front.
2017 Trek Stache 9.8 (29+)
2016 Specialized Stumpjumper FSR Carbon Comp 6Fattie (27.5+)
2016 Trek Stache 9 (29+) w/upgrades (Sold)
2014 -036 Full Suspension Chiner (Sold)
2013 -057 Hardtail Carbon Chiner (Sold)
Atlanta, GA

carbonazza

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Re: New 29+ Frame (CS-496) build
« Reply #2 on: February 24, 2017, 02:58:57 PM »
The confusion comes that SRAM is providing both GXP versions... Boost and not.

To confuse us even more there are two kind of rings available, with 3 or 6mm offset.
As the offset goes inside, more offset means a smaller chain line.
And finding online resources about this is not easy.

SportingGoods

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Re: New 29+ Frame (CS-496) build
« Reply #3 on: February 28, 2017, 11:42:25 AM »
I can confirm the info from Carbon_Dude, in a SRAM Eagle Boost group, the "Boost" is taken care of by the chainring. The cranks are standard. You can give it a try or just replace the chainring with the Boost version.

bxcc

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Re: New 29+ Frame (CS-496) build
« Reply #4 on: March 06, 2017, 01:20:11 PM »
We will put an SRAM Eagle on it. Does it need the boost version of the crankset or is the frame already takes care of the 52mm chainline?
The groupset was bought complete, but I'm wondering the crank need to be exchanged.
The BB is BB92, and the width of the BB shell is... 92mm !


The others are correct. The standard offset it 6mm, boost is 3mm, and BB30 cranksets use 0mm offset. If you have a BB92 bottom bracket, definitely get the 3mm offset. With the BSA stuff, you can shift a GXP crank inboard by using a non drive side bb spacer so you can essentially use a 0mm offset ring with one NDS spacer and still be good. But with the BB92 bb, you can't do that. So you really should get the right offset chainring.

As far as the crankset itself goes, you just need a GXP BB92 bottom bracket. It will need to be pressed in but otherwise, all Sram GXP cranks will work once it's installed. My daughters bike has a BB92 bottom bracket and a Sram Stylo GXP crankset that was previously installed on my SS with BSA bottom bracket.

I am big fan of the Sram GXP setup. For me, it has been perfect and I have 5 bikes at home with cranksets that are completely interchangeable. Well, sort of, my daughters is a bit short at 150mm.

Carbon_Dude

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Re: New 29+ Frame (CS-496) build
« Reply #5 on: March 06, 2017, 01:31:05 PM »
Speaking of crankset, this past Saturday, I upgraded the cranks on my Spec SJ 6Fattie from a set of GX-1000 aluminum cranks to a set of XO Carbon cranks.

Both cranks are PF30/BB30.  When I did the upgrade, the new carbon cranks came with a different drive side spacer, looks like about a 3mm wide spacer.  The stock GX1000 cranks had a 6mm drive side spacer.  At the time I wasn't sure if I should keep the 6mm spacer on our install the 3mm spacer that came with the carbon XO cranks.  Turns out the answer was to install the new 3mm spacer with the new carbon cranks.

For the chainring, I just moved over the direct mount 28T stock SRAM ring from the GX cranks to the XO cranks.  The XO cranks came with a spider that I needed to remove in order to install the direct mount ring.  Now I have a spare set of BB30 GX cranks to sell on eBay.

It's all very confusing but if you are aware of all the differences, you will get the Boost Spacing sorted out.
2017 Trek Stache 9.8 (29+)
2016 Specialized Stumpjumper FSR Carbon Comp 6Fattie (27.5+)
2016 Trek Stache 9 (29+) w/upgrades (Sold)
2014 -036 Full Suspension Chiner (Sold)
2013 -057 Hardtail Carbon Chiner (Sold)
Atlanta, GA

carbonazza

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Re: New 29+ Frame (CS-496) build
« Reply #6 on: March 06, 2017, 07:48:08 PM »
Thank you all. I guess I finally got it now ???
The difference between the boost and non boost version of the SRAM crankset is probably just the 32T ring that come with it. That has either a 3 or 6mm offset.

bxcc

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Re: New 29+ Frame (CS-496) build
« Reply #7 on: March 07, 2017, 07:34:21 AM »
Thank you all. I guess I finally got it now ???
The difference between the boost and non boost version of the SRAM crankset is probably just the 32T ring that come with it. That has either a 3 or 6mm offset.

Correct.
The BB30 has a different setup with spacers and such. The BSA and BB92 both use the same GXP cranksets just different BB's. One easy way to tell the difference between GXP and BB30 cranksets is that GXP spindles are on the drive side arm and BB30 spindles are on the non drive side arm.

carbonazza

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Re: New 29+ Frame (CS-496) build
« Reply #8 on: March 07, 2017, 02:50:30 PM »
The BB30 has a different setup with spacers and such. The BSA and BB92 both use the same GXP cranksets just different BB's. One easy way to tell the difference between GXP and BB30 cranksets is that GXP spindles are on the drive side arm and BB30 spindles are on the non drive side arm.

Easy to remember!
Isn't 24mm for GXP and 30mm for BB30/PF30 an always true difference too?
I made a mistake to buy a Next SL 30mm spindle to fit a BB92( spindle on the non drive side :) ), the bearings are too thin and non standard. I will never do that again.

SportingGoods

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Re: New 29+ Frame (CS-496) build
« Reply #9 on: March 08, 2017, 02:18:04 AM »
Correct, GXP is always 24/22 mm (non-drive side is 22 mm, drive side is 24 mm), never 30 mm.

Considering the quality of GXP I really see no reason to use 30 mm cranks. Can anyone really feel the difference?? And as you mention, 30 mm axle in BB92 results in smaller bearings; not suitable.

And now that I have experienced most of the range of bottom bracket types (BSA, BB30 and BB92), my preference really goes to BB92.