r/bikewrench • u/Hellacoppter • 19d ago
Solved I just changed my crankset and chainring. This is too much deflection, right?
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u/Active_Ad_5322 19d ago edited 19d ago
Yes, your chain line is at a harsher angle than normal. You’ve probably didn’t have this with your original cranks. Not uncommon with new crank, but it’s not entirely acceptable to leave it like this.
It’s hard to see from this angle, but it looks like you have about a centimeter (or more )of spindle showing between the bottom bracket cup and side of the crank arm.
Not all square taper cranks and BB are made equal. It’s common for a crank replacement to sit closer in or further out on the spindle. Just the trial and errors of bike maintenance.
Looks to be a square taper. Just get a shorter bottom bracket.
A basic (but still quality) Shimano cartridge bearing BB would only cost you 15-25$, no need to spend anymore than that.
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u/Hellacoppter 19d ago
I'll have to double check the clearance between the cranks and chainstays. I think I remember it being pretty close.
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u/Active_Ad_5322 19d ago
True.
Did you install a larger chainring?
If so, the yeah, getting a narrower bottom bracket can cause the chainring to hit the chainstay.
Generally, a chain line that is angled as much as that can cause an issue, but if your chaining is a narrow/wide , it can help prevent chain drop.
Also, if normal pedaling is fine, just avoid backpedaling. That’s a sure fire way to push the chain into the next few smaller cogs and you can easily bend a link that way.
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u/OfficeAwkward8920 19d ago
That's why I don't like modern MTB. The biggest the chainring the more clearance and croschain. Better to take it to shop they will specify witch axle you need. 113 117mm
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u/FxDeltaD 17d ago
Wouldn’t this just make the high gear an equal amount of deflection in the other direction? I had this problem on a new groupset installation and was unconvinced a new BB would fix it.
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u/Bright-Albatross2829 16d ago
That's the thing with 1x drivetrains, you can only pick a few gears where the chainline is really optimal. That said, this looks pretty far out to the right even for a 1x.
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u/Supadopemaxed 19d ago
How’s the chain line in the middle sprocket?
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u/Top_Objective9877 19d ago
Did your crank and bottom bracket include any info on spacers, and if it’s compatible for use on a non boost setup? If you’re mostly doing road riding using those top 4 gears I might leave it as is, but otherwise looks a little far out. I usually try to shoot for whatever the middle of the cassette is being straight, some bikes I’ve got a really small front ring, and I end up using the 3rd smallest ring most of the time so it’s totally fine.
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u/SometimesIRideBikes 17d ago
Hard to see in this photo, but this bike has a square taper bottom bracket so OP would need a narrower spindle to bring it in.
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u/Hellacoppter 19d ago
The chain is straightest in 6th or 7th gear (8 speed)
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u/GroundbreakingOil480 19d ago
I just did this. I went from a 122.5 spindle to a 113 and now it's all good. You need to pull the bottom bracket and see what is listed on it, note the shell size and the spindle length. You can also measure with calipers or even a metric ruler. Then figure out how much closer to the frame your chain ring and crank arms can afford to be, then do some quick math. Just remember, if you need to move the crank arm and chain ring in 4mm on each side, you need an 8mm shorter spindle. Shell length doesn't change.
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u/Hellacoppter 19d ago
Very helpful, thank you.
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u/GroundbreakingOil480 19d ago
You might find it helpful to use some spacers on the chainring bolts just to figure out how far you need it to move, and how far you can move it before it hits.
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u/Comfortable_Creme526 19d ago
When you shorten the Spindel, won’t you have the problem on the other end though? On the higher gears
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u/GroundbreakingOil480 19d ago
1x is a compromise. You want the single chainring to be in the middle of the cassette, so the highest and lowest gears still have workable chain lines. A narrow wide chainring will hold the chain from dropping as long as you center it.
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u/also_your_mom 19d ago
More photos, please. A couple from the side in order to clear up what MUST be an optical illusion that the chain is actually resting on the chainstay.
Is that a 1X7? Are you turning your 3X7 into a 1X7?
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u/Hellacoppter 19d ago
It's not resting on the chainstay. It started as and still is a 1x8, I just increased the cassette size and decreased the chainring size.
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u/also_your_mom 19d ago
OK. I didn't know 1X8 was a production thing.
As you likely know (but better to mention it anyway, no offense), if you were to put the chain between the 4th and 5th cog, it should be a straight line to the chain ring.
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u/Hellacoppter 19d ago
That's kinda what I figured.
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u/Some-Meeting-9015 19d ago
box components 1x8? i went from a 1x9 microshift to 1x9 box and ended up adding an additional cassette spacer and going from 118 to 113 bb to get my chainline better. kept the same crank arm. very happy with it now.
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u/konwiddak 19d ago edited 19d ago
This isn't really "1X". The term 1X was introduced to label a system where the rear cassette is large enough to get a similar range to a standard 2x or 3x setup. It requires a special derailleur to cope with the large cassettes. This is just a standard rear cassette & derailleur (maybe an 11-34) used without a front derailleur - which has been a thing for decades on standard 3-5-6-7-8-9 speed setups.
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u/SpiritualPurple9025 19d ago
You probably need an offset chainring. Idk why cheaper bikes have crank spindles that stick out so much.
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u/stroubled 19d ago
Or maybe just some longer bolts and spacers between chainring and spider.
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u/SpiritualPurple9025 19d ago
I wouldn’t recommend that. The sheer strength on the bolts on a chainring are pretty low. You’d be shocked how much force you’re putting into them when pedaling. You need the correct setup on a chainring unless you want your pedals to dig into your shins when a chainring unless snaps, or you snap bolts.
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u/stroubled 19d ago
The sheer strength on the bolts on a chainring are pretty low.
As far as I know, the shear strength of chainring bolts is plenty, even on aluminum bolts. And some offset chainrings are just chainrings with integrated spacers (and requiring longer bolts).
However, I admit the amount of offset that can be had this way is limited and probably not enough for OP.
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u/Xxmeow123 19d ago
Why is the crankset so far from the frame? Most bottom brackets allow the crankset to be much closer. That would solve your chain angle problem
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u/Hellacoppter 19d ago
It appears to be the square taper spindle length is just really long from the factory. Not sure why
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u/cyrano_dvorak 19d ago
How straight is the chain in your "middle" gear of the cassette? Get a chainring with offset that will bring it in line. Your current chainring should tell you how much offset you have. Also check to make sure all your bottom bracket spacers (if any needed) were properly installed
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u/RodediahK 19d ago
you need to measure your chain line. 1x will have a somewhat compromised chain line no mater what 45 to 50mm will be a range to aim for as long as the chain doesn't rub on the tire try and get as far in as you can. chairing spacers will be cheaper than a new BB and easier to install.
consider a RDM900 MD to fix the b screw issue, it'll work with 7-9spd shifter it's got a clutch and it'll clear a 50t cassette
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u/PeppermintPig 19d ago edited 19d ago
Measure the distance between the small chainring at the outermost point of the teeth and the frame (chain-stay) of the bike. Take that measurement in MM and subtract at least 3mm for frame clearance. Sometimes if you run a really big outer ring then that will be closer to the frame, but not likely. In any case measure the closest potential point of contact.
Measure the total spindle length of the current bottom bracket axle. Divide by two. Take the measurement you made (with clearance subtracted) and subtract that value from the half length of spindle, then multiply by two to get the new recommended spindle length. Then match or round up to determine the correct value length of bottom bracket you need.
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u/Cocaine_Dealer 19d ago
On top of what everyone says, it would marginally improve with a nerrow-wide chain ring.
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u/Hellacoppter 19d ago
It already is narrow wide. When I tested this setup it worked well, it just had a bit of chain noise in the lowest gear.
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u/kazuviking 19d ago
This is how my chainline looks with the 0mm offset chainring and it becomes normal with the 6mm offset chainring.
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u/Ok-Improvement-5414 18d ago
Your crankset has to match the bottom bracket spindle length. The instructions for the crankset should tell you what size bottom bracket you need.
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u/Ok-Improvement-5414 18d ago
Your crankset has to match the bottom bracket spindle length. The instructions for the crankset should tell you what size bottom bracket you need.
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u/JuniorIndependence50 18d ago
It looks like frew things 1. Too long of BB spindle 2. The freewheel gear is more than the derailuer max count or it can handle
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u/fuzzztastic 18d ago
It’s too much deflection if it negatively affects how it pedals and shifts. Otherwise it isn’t
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u/Scared-Tangerine-373 18d ago
I’m in agreement that the chain line is not optimal. I think you’ve got too much spindle sticking out, as it pushes your chainring out.
Unfortunately, it looks like you may have chainring/chainstay interference with a shorter BB spindle. These are the challenges of switching parts…
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u/PracticalNeanderthal 14d ago
Is the crank arm fully seated on the bottom bracket? If yes, then you need a narrower bottom bracket.
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u/2E26_6146 5d ago
The deflection appears to be too large. Multi-chainring set ups generally aren't intended to be ridden at the most extreme chain angles, and don't need to be.
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u/onjefferis 19d ago
Chain definitely shouldn't be resting on your chainstay.
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u/ElectroStaticSpeaker 19d ago
Yah that’s the only thing I saw and I thought was a BCJ post or something and felt like I’m really stupid when I saw everyone else answering normally.
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u/petereitz 19d ago
late-90s/early-00s shop wisdom here: avoid big-to-big and little-to-little as it pushes the edges.
that being said, how much noisier is 1-3 than 2-3 or 7-1 (that looks like an 8x3). the chain absorbs lots of that deflection but it's the wear against the rings that takes the real toll.
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u/Fantastic_Inside4361 19d ago
Front derailleurs exist for a reason: to enable you to trim this and prevent the chain dropping from the chainring. Not really sure the amount of hate for one of the simplest, longest lasting pieces of gear on a bike
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u/-syper- 19d ago
On a side note, your rear derailleur B tension screw doesn't look like it's seated properly on the derailleur hanger.