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Chainring / Chainstay Clearance

2838 Views 10 Replies 5 Participants Last post by frdfandc, Nov 5, 2021

NWA_Tre

Discussion Starter · Nov 2, 2021

So let's say you're working on the proper chainline for an 11 speed drivetrain on a boost 148 rear. In getting to the ~50mm chainline, the chainring is within 3mm of the chainstay. Does that make you uncomfortable? How much finagling of the chainline do you do in order to feel better about the chainring/chainstay clearance?

Currently got a Specialized Fuse 27.5 second-hand. Bike is designed to be able to run plus tires, so the stays flare out a good bit. The gently-used crankset I got off eBay (NX Eagle boost) had a 6mm offset 32t ring (not what SRAM recommends for boost, but IDK why the guy had it on there). Even with adding a 2mm inside spacer to the BB (and the 4.5mm recommended outer spacer) the 6mm offset ring is very close to the stay. Thing is, the chainline looks to be pretty good. Now, I've ordered a 3mm offset 30t chainring, which I know will take me out from the chainstay some, but will also move the chainline out...

What's the happy medium you've arrived at in this scenario?

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frdfandc

· #2 · Nov 2, 2021

Use the 3mm offset ring for a boost setup. Use the 6mm ring for non boost setup. This will keep things in check providing everything else is boost fit.

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Bicycle Rider

· #3 · Nov 2, 2021

Regardless of published spec, locating the chainring as far inboard as possible is usually best ( chain tension is higher while climbing, in the larger cogs out back right - try to optimize for them).

I have put chainrings as close as 1mm from chainstay - but that was a very stout steel frame, and the nearest point of contact was a beefy steel plate yoke. You’ve already got it set up- take if for a spin and do some climbing sprints and a typical drop or two. If you haven’t flexed anything to the point of contact (paint rub), you’re good to go IMHO. I think you only need to worry about flex—— in the event of bent ring /catastrophic failure, it hardly matters if you started with 1mm or 8mm of clearance.

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NWA_Tre

Discussion Starter · #4 · Nov 2, 2021

frdfandc said:
Use the 3mm offset ring for a boost setup. Use the 6mm ring for non boost setup. This will keep things in check providing everything else is boost fit.

Yes, I know 3mm is the ring for boost. And only the 4.5mm outboard spacer for the BB. However I know this will still have the chainring close to the stay, and I think the chainline is going to be a little biased to the smaller cogs. Wolf Tooth recommends a chainline about 2mm biased to the smaller cogs, which is odd because others want it biased to the larger cogs...

Bicycle Rider said:
Regardless of published spec, locating the chainring as far inboard as possible is usually best ( chain tension is higher while climbing, in the larger cogs out back right - try to optimize for them).

I have put chainrings as close as 1mm from chainstay - but that was a very stout steel frame, and the nearest point of contact was a beefy steel plate yoke. You’ve already got it set up- take if for a spin and do some climbing sprints and a typical drop or two. If you haven’t flexed anything to the point of contact (paint rub), you’re good to go IMHO. I think you only need to worry about flex—— in the event of bent ring /catastrophic failure, it hardly matters if you started with 1mm or 8mm of clearance.

Yes, flex is my main concern with being close to the stay, however I also want a good chainline...

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NWA_Tre

Discussion Starter · #5 · Nov 2, 2021

Curious, too: has anyone used a small (1-2mm) spacer behind the 11sp cassette, like we did with 9/10's, in order to get a more optimal chainline...when moving the chain ring inward wasn't an option?

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Mounttesa

· #6 · Nov 2, 2021

NWA_Tre said:
Curious, too: has anyone used a small (1-2mm) spacer behind the 11sp cassette, like we did with 9/10's, in order to get a more optimal chainline...when moving the chain ring inward wasn't an option?

Yeah every little bit helps. Just make sure there's enough thread engagement on the cassette and enough high-limit adjust on the RD.

I have a 0.5mm spacer on now. Tried 1mm but felt like I was too close to maxing out my RD high limit.

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TylerVernon

· #7 · Nov 2, 2021

It would be bike specific. I have a close ring on one bike but it's also a stiff frame and never touches. Definitely a concern and something I look for when doing a build.

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NWA_Tre

Discussion Starter · #8 · Nov 2, 2021

Bicycle Rider said:
You’ve already got it set up- take if for a spin and do some climbing sprints and a typical drop or two. If you haven’t flexed anything to the point of contact (paint rub), you’re good to go IMHO.

I may wrap some tape around the stay 3 or 4 times and check it out.

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NWA_Tre

Discussion Starter · #9 · Nov 2, 2021

Wolf Tooth said:
You might ask, "Wait a minute. The center of 11 speed cassette is ~44mm from the centerline of a bike. Why isn't that used as the chainline?" Well, for proper shifting on a 1x setup you want to be at least ~2 mm to the outside (towards the small cogs) otherwise the chain will catch on the next bigger cogs when pedaling in the smaller cogs.

Boost Chainline and 1x Boost Chainring Selection

Boost Chainrings, Chainline and 1x Boost Chainring - science, explanation, and selection.

www.wolftoothcomponents.com

Thoughts? (actually 47mm with boost, plus the 2mm they recommend above is 49mm chainline. Wolf Tooth says 49-50mm is ideal unless you run plus tires and have tire/chain clearance issues.)

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NWA_Tre

Discussion Starter · #10 · Nov 5, 2021

Rode the bike yesterday and it was good. Probably going to a 30t chainring for the climbs, for now, lol. I'll keep the 32 for a backup and when I get stronger. I really rarely use 11th gear. I'll use a CS protector and probably something super thin near the chainring and I'll monitor wear, but so far even the 32t didn't look like it contacted the chainstay, even with standing sprints.Chain line is ok. I don't love it, but there's not much I can do. It's quiet and shifts perfect.

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frdfandc

· #11 · Nov 5, 2021

NWA_Tre said:
It's quiet and shifts perfect.

Then your chain line is perfect.

Sent from my moto e6 using Tapatalk

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