Chainring clearance possibilities

[Jad]

I'm trying to find more space between my 42t chainring and the chainstay (clearance is a hair under 2mm and I'd like more). This is on my all-road bike with a 68mm bb shell. Right now I've got a Rival 1x GXP crankset with a Sram chainring. It's offset toward the frame, but I'm not sure by how much.

I have considered using a dub wide crankset, which would push everything 2.5mm out on each side. But I'm wondering if there's a way to do this without changing where the pedals are.

Does anyone know of any 0 offset (flat) 1x chainrings? I've been looking, but finding it difficult to identify.

[Dave]

Can't you use spacing washers behind the ring mounting bolts?

[Mark McM]

If I'm picking up the clues correctly, you are using a 1x direct mount chainring? Then I guess you probably want a Boost or Super-Boost chainring to increase chainring offset. Another option to increase chainring clearance is by using a 2x spider and mounting a chainring in the outer position.

[Jad]

Originally Posted by Dave

Can't you use spacing washers behind the ring mounting bolts?

Huh--I hadn't thought of that or seen that as something anyone's tried. Maybe with longer chainring bolts, spacers could work? Seems like the way the bolts sit it might be tricky.

Originally Posted by Mark McM

If I'm picking up the clues correctly, you are using a 1x direct mount chainring? Then I guess you probably want a Boost or Super-Boost chainring to increase chainring offset. Another option to increase chainring clearance is by using a 2x spider and mounting a chainring in the outer position.

Thanks--the ring is 110 bcd with 5 bolts. If there were a 110bcd 42t Boost/SuperBoost chainring that was offset away from the frame, that might work, but I'd worry that it might be offset outboard too much? I think if my current chainring is offset inward at least 3mm (not sure), a zero offset chainring (if such a thing is available) might be just the ticket.

[Mark McM]

Wait, so your chainring is mounted to a 5 arm 110mm BCD spider? Is is currently mounted to the inner our outer position? If on the inner position, couldn't you switch it to the outer position? (And no, there really arent Boost or Super-boost 110mm BCD chainrings. Boost and Super-boost offsets are usually applied to spiders or direct mount chainrings.)

[Jad]

I wish there were a farther outboard mount (which I could get by mounting a double setup, as you suggested), but this is a Rival 1 (1x) gxp crankset. There's only one chainring position. I think the 1x crankset puts the chainring/chainline a bit in between where an outer and inner ring would be on a double.

[Mark McM]

Is this the crank you have?



If so, then Dave's suggestion above is a good one - just install chainring spacers between the spider and the chainring. (Note: You may need longer chainring bolts.)

[DeBike]

There really is nothing wrong with the barely less than 2 mm gap. As long as there is clearance, it’s functionally ok. If you go the ring spacer route, I assume for peace of mind, 3 mm extra is a lot. Maybe start with 1mm spacers. The offset is likely there for a reason, but if moving the ring outward affects that, I cannot say. It seems to me that cause extra flex in the ring. I am not familiar with Gxp, so I don’t know if a drive side bb spacer is doable, but that would move your crank and pedals outward.

[Dave]

I use 2.3 mm spacers with stock bolts. That's almost 3 turns lost, but it works.

[Jad]

That is the crankset I've got, Mark. The chainring bolt spacer idea is interesting. I do like my chainring to sit flush though...

Originally Posted by DeBike

There really is nothing wrong with the barely less than 2 mm gap. As long as there is clearance, it’s functionally ok. If you go the ring spacer route, I assume for peace of mind, 3 mm extra is a lot. Maybe start with 1mm spacers. The offset is likely there for a reason, but if moving the ring outward affects that, I cannot say. It seems to me that cause extra flex in the ring. I am not familiar with Gxp, so I don’t know if a drive side bb spacer is doable, but that would move your crank and pedals outward.

I hear you--I've flipped back and forth on whether the clearance will actually be a problem. In reading a bunch of takes on it (here and in other forums), I've seen that under 2mm is on the edge/too close or that as long as the ring is not touching, there's nothing to worry about. I certainly don't think my uphill sprint is world class/metal-bending. So you're right--it would be for peace of mind.

Originally Posted by Dave

I use 2.3 mm spacers with stock bolts. That's almost 3 turns lost, but it works.

Ah, ok--what spacers do you use?

[Dave]

Wheels Manufacturing makes some spacing washers, but I use washers that I've modified to work. I have the tools to drill holes larger and/or ground down the diameter to work. I have machinist skills. Regular washers often vary significantly in thickness too, so each one has to be measured to get a group that varies by only a few thousandths of an inch.


I've also made aluminum washers from aluminum sheet, using a hole saw to start, then using the plug that's normally trashed as a washer.

[Brian Smith]

Originally Posted by Jad

That is the crankset I've got, Mark. The chainring bolt spacer idea is interesting. I do like my chainring to sit flush though...



I hear you--I've flipped back and forth on whether the clearance will actually be a problem. In reading a bunch of takes on it (here and in other forums), I've seen that under 2mm is on the edge/too close or that as long as the ring is not touching, there's nothing to worry about. I certainly don't think my uphill sprint is world class/metal-bending. So you're right--it would be for peace of mind.



Ah, ok--what spacers do you use?

Peace of mind without totally destroying chainline

[Jad]

Originally Posted by Dave

Wheels Manufacturing makes some spacing washers, but I use washers that I've modified to work. I have the tools to drill holes larger and/or ground down the diameter to work. I have machinist skills. Regular washers often vary significantly in thickness too, so each one has to be measured to get a group that varies by only a few thousandths of an inch.


I've also made aluminum washers from aluminum sheet, using a hole saw to start, then using the plug that's normally trashed as a washer.

I do not have machinist skills/access, but what you're able to get together sounds great. Custom setup!

Originally Posted by Brian Smith

Peace of mind without totally destroying chainline

Thanks for that; .6mm could work well if they fit well...


I still wonder if there are zero offset 1x chainrings. Some (like Raceface maybe?) look like they might be "flat," but hard to tell relative to the x-sync rings. Maybe I'll get in touch to ask.

[martl]

i'm sure you have your reasons for the spacing, and it seems you got a good solution approach for it as well

just my 2ct about chainring clearage:

- chainring clearance is a function of the crankset/BB in combination with the frame. With modern style cranksets with fixed axle, there is literally no wiggle room unless one goes to the chainring mount itself and uses washers, as has been suggested. SRAMs technical manual allows for some adjustment using 0.5mm washers on the BB NDS in certain combinations only.

- some of my older bikes have super minimal clearance without having caused any issues, ever. My Mike Appel runs on maybe 3mm clearance quite happily, and both modern frames and crankset combos are waaaaay stiffer/less bendy than that Columbus SL without gusset and a Campagnolo Record BB.



- i was under the impression that having a clearance that is near to the width of the chain (or bigger) is a recipe for chainsuck. Am i wrong?

As for the "Washers at the chainring" solution: I don't know if i would go that way as:

The way a bolt connection works is by applying pressure between the two connecting surfaces, creating friction. This is what keeps the two parts connected. More surface = more better - more force can be transmitted.
Using washers removes much of that friction and transfers power as a shear force through the bolts, which they are not designed for. And the forces/the torque at that point is huge!

[Mark McM]

Originally Posted by martl

- chainring clearance is a function of the crankset/BB in combination with the frame. With modern style cranksets with fixed axle, there is literally no wiggle room unless one goes to the chainring mount itself and uses washers, as has been suggested. SRAMs technical manual allows for some adjustment using 0.5mm washers on the BB NDS in certain combinations only.

Some modern cranks/BBs have more lateral adjustability than others. For example most 30mm spindle cranks (and also SRAM's 29mm DUB spindles) use spacers and either a wave washer or a bearing pre-load collar. This typically allows the cranks to be shifted left or right by a few millimeters. Unfortunately, the OP is using a GXP crank, and due to the way the spindle mounts to the left BB cup, there is no lateral adjustability with this system.

Originally Posted by martl

- i was under the impression that having a clearance that is near to the width of the chain (or bigger) is a recipe for chainsuck. Am i wrong?

Chainsuck is more related to the shapes and engagements of the chain and chainring teeth. Chainring clearance has no effect on whether a chainsuck will occur - however, the less chainring clearance there is, the more likely chainsuck will result in the chain getting wedged between the chainring and chainstay and gouging the chainstay.

Originally Posted by martl

As for the "Washers at the chainring" solution: I don't know if i would go that way as:

The way a bolt connection works is by applying pressure between the two connecting surfaces, creating friction. This is what keeps the two parts connected. More surface = more better - more force can be transmitted.
Using washers removes much of that friction and transfers power as a shear force through the bolts, which they are not designed for. And the forces/the torque at that point is huge!

I wouldn't worry about this. Chainring bolts are more than strong enough to handle drive torques. There are many cranks which are designed to have their inner chainrings mounted on top of spacers (and these spacers can be 4mm - 5mm thick). One example of this is Sugino XD cranks, although there are many more designed this way. There are also several crank designs in which the inner chainring is bolted on top of stand-offs which are about the same size as a chainring washer - this includes SRAM X series MTB cranks, Campagnolo 4 arm cranks, Shimano GRX cranks, etc. As long as the OPs chainring bolts are long enough, they should have no problem adding a millimeter or two of spacers under the chainring.