2021 Stumpjumper

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2021 Stumpjumper
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flag johnovey
O+
Posted: Mar 22, 2022 at 11:16 Quote
Looks like that chainring is too far inboard, & needs to be spaced out.
Wrong offset on the ring, maybe?
flag AndrewFleming
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Posted: Mar 22, 2022 at 11:17 Quote
schralped wrote:
I recently purchased a new 2021 Stumpjumper Alloy Comp (NX build) from my LBS. I wanted to put a 34T ring on it so the gearing would be close to my previous set up.

The bike was designed around a 30T and it's a single pivot, so I wouldn't mess with it. Were you spinning out with the 30T on downhills?
flag ScaryGuiTarS
Posted: Mar 22, 2022 at 11:18 Quote
I can't see WHY there'd be any problem running a 32t on a Stumpy? That's actually common. I have a ab-black 32t on my 2019.

What about the "boost" sizing? Isn't there about 30mm or so offset on boost sizing? Could that have anything to do with it"
These bikes are all "boost" but not all 32t chainrings are.


~JSV
flag schralped
Posted: Mar 22, 2022 at 11:21 Quote
newbermuda wrote:
I had no problem with fitting a 34t chainring on my stumpjumper s-works but the rear end is a bit different than the aluminum one. Do you have a plastic spacer between the bottom bracket and the cranks/chainring? mine came like that and 34,32, and 30t rings have all been fine.

There looks like there is something between the ring and the BB, maybe like 3mm thick.
photo
flag schralped
Posted: Mar 22, 2022 at 11:25 Quote
AndrewFleming wrote:
Were you spinning out with the 30T on downhills?

I never actually rode the bike with a 30T. I was coming from a 1x11 setup with a 34T and it was working well for the trails I usually ride. I asked the bike shop and they said they could install a bigger chainring when I bought the bike.
flag schralped
Posted: Mar 22, 2022 at 11:31 Quote
johnovey wrote:
Looks like that chainring is too far inboard, & needs to be spaced out.
Wrong offset on the ring, maybe?

ScaryGuiTarS wrote:
What about the "boost" sizing? Isn't there about 30mm or so offset on boost sizing? Could that have anything to do with it"
These bikes are all "boost" but not all 32t chainrings are.

How would I tell? It is offset towards the bottom bracket slightly. The LBS told me that they could try the 34T with a different offset, but with the "correct offset" the 32T was the biggest that would fit. So I'm guessing the offset is right.
flag AndrewFleming
O+
Posted: Mar 22, 2022 at 11:39 Quote
schralped wrote:
AndrewFleming wrote:
Were you spinning out with the 30T on downhills?

I never actually rode the bike with a 30T. I was coming from a 1x11 setup with a 34T and it was working well for the trails I usually ride. I asked the bike shop and they said they could install a bigger chainring when I bought the bike.

Well, personally, I would leave the 30T on it. The suspension was designed around the 30T and with it being a single pivot, it's best to not mess with it as that will change it's pedaling efficiencies. Plus, unless you are spinning out on the 30T, there's really no reason to go with a bigger ring.
flag lyzyrdskydr
Posted: Mar 22, 2022 at 11:39 Quote
Spacer setup looks correct, I would double check that the chainring has the proper 3mm boost offset. That's a pretty common area to get scuffed up but in the pictures the chainring looks like it's really close to the chainstay.

The shop could've accidentally installed a 6mm offset one which would bring the ring too far inboard. The offset should be printed on the backside of the chainring

As noted by others the suspension performance is effected by chainring size, a larger ring will make the suspension a bit more active but will also increase pedal bob when unlocked
flag ScaryGuiTarS
Posted: Mar 22, 2022 at 11:45 Quote
lyzyrdskydr wrote:
Spacer setup looks correct, I would double check that the chainring has the proper 3mm boost offset. That's a pretty common area to get scuffed up but in the pictures the chainring looks like it's really close to the chainstay.

The shop could've accidentally installed a 6mm offset one which would bring the ring too far inboard. The offset should be printed on the backside of the chainring

As noted by others the suspension performance is effected by chainring size, a larger ring will make the suspension a bit more active but will also increase pedal bob when unlocked

Yeah ok THAT'S what I was thinking. Isn't that the boost offset 6mm or 3? What did I say 30? Anyway that's what I meant, and all of these bikes are boost.

And even though these bikes were designed around 30t chainrings, I still can't see why a 32 is NOT an option? I guess it would make more sense having trouble w/a 34 or oval or something but I can't image no other riders are running a 32?

~JSV
flag AndrewFleming
O+
Posted: Mar 22, 2022 at 12:15 Quote
ScaryGuiTarS wrote:
And even though these bikes were designed around 30t chainrings, I still can't see why a 32 is NOT an option? I guess it would make more sense having trouble w/a 34 or oval or something but I can't image no other riders are running a 32?

32T is an option, but the bike won't pedal as well as it will with the 30T. One of the best outcomes of 1x drivetrains, is that they made single pivot bikes relevant again as long as the pivot and the chain ring are in alignment. So, stick with the ring that the bike was designed for and you'll get the best performance. Plus, why move up to a 32T if you're not spinning out on the 30T?
flag ScaryGuiTarS
Posted: Mar 22, 2022 at 12:24 Quote
I'm not really disagreeing w/you about that. I ride a 2019 carbon FSR w/my 32t anyway so my frame's different. The only point I was chiming in on was that I couldn't see WHY a 32t even on a 2021 would be scraping the frame like that was?

Whether that SHOULD be on the bike it seems odd to have that problem. The mounting, installation, or sizing must be off in some way.

~JSV
flag dundundata
Posted: Mar 22, 2022 at 13:16 Quote
I just installed XT cranks with 34t xtr chainring, close but it has space. There's a 2.5mm spacer on the drive side bottom bracket. I would def fix that before riding again, your shop sounds clueless.
flag Daray
O+
Posted: Mar 22, 2022 at 16:51 Quote
To me it looks like a chain suck problem- probably need a chain guide to help
flag schralped
Posted: Mar 23, 2022 at 20:04 Quote
lyzyrdskydr wrote:
Spacer setup looks correct, I would double check that the chainring has the proper 3mm boost offset. That's a pretty common area to get scuffed up but in the pictures the chainring looks like it's really close to the chainstay.

The shop could've accidentally installed a 6mm offset one which would bring the ring too far inboard. The offset should be printed on the backside of the chainring

As noted by others the suspension performance is effected by chainring size, a larger ring will make the suspension a bit more active but will also increase pedal bob when unlocked

Yeah, I checked and it's a 6mm offset. I guess the chainring or chainstay is flexing under load or something because it doesn't touch when I'm just pedaling. Either way, it's still the wrong spec.

Thank you all for your help and advice! Now I should be able to get this sorted out.
flag Mikelb01
Posted: Mar 28, 2022 at 11:08 Quote
Not sure if anyone on here would be interested, but I'm selling a Carbon fiber clevis that the rear of the shock mounts to from an S-Works Stumpjumper 2021-22. This could be a nice little upgrade for a Comp, Expert or Pro frame...https://www.pinkbike.com/buysell/3270797/

 


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