# Front Big Chainring Straightness



## gofast2wheeler (Oct 13, 2011)

I was wondering if the big ring on double crank should be perfectly straight when it travels in a circle. When I pedal and look at the space between front der. The ring moves in and out, sways, ever so slightly. Is this normal, due to pedaling flex in frame or natural curve in ring to promote better shifting like the rear cogs are pitched, or could the ring,crank sider or BB be bent. Any advice would be appreciated before I go to bike store to test ride another bike to see if that does it as well.

Thanks,
Mario


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## Dave Hickey (Jan 27, 2002)

It could be an illusion.. The ramps on chainrings can give the appearance of a wobble....I've noticed it on a couple of my bikes...Cassettes can give the same appearance...


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## Peanya (Jun 12, 2008)

And some cheap rings won't be flat. I had a 2200 crankset where you could see it wouldn't spin in a straight line.


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## gofast2wheeler (Oct 13, 2011)

Didn't think about that. If you look at your cassette the tooth on the same cog though are not in perfect alignment, they seem to be pitched . Crank Chorus 9SPD Taper.


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## kbiker3111 (Nov 7, 2006)

Sometimes they'll bend. If its older it might be worth a look.


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## nightfend (Mar 15, 2009)

I've seen some slightly warped 105 big chainrings in the past. Higher quality rings don't seem to have this problem.


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## AndrwSwitch (May 28, 2009)

The chain ring should be perfectly planar. Nothing in real life is perfect, but a badly bent chain ring can have problems with shifting, dragging on the derailleur cage, and throwing the chain. It can also be frame flex. I'd say if it's not a new problem and you're not experiencing related problems, it's fine.

Something to check is if your chain ring does this when the bike is on a work stand, or only when you pedal under load. That isolates it to the chain ring or spider being warped or something flexing. There's not a lot you can do about flex, but a warped chain ring is fixable.


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## Drew Eckhardt (Nov 11, 2009)

gofast2wheeler said:


> I was wondering if the big ring on double crank should be perfectly straight when it travels in a circle. When I pedal and look at the space between front der. The ring moves in and out, sways, ever so slightly. Is this normal, due to pedaling flex in frame or natural curve in ring to promote better shifting like the rear cogs are pitched, or could the ring,crank sider or BB be bent. Any advice would be appreciated before I go to bike store to test ride another bike to see if that does it as well.


Some of the newer bottom bracket designs (ISIS, FSA Power drive on their integrated spindle cranksets, etc.) require the crank arm(s) to bottom on a shoulder, may not be square until that happens, and getting that to happen may require installation at the upper end of the torque spec.


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## Kerry Irons (Feb 25, 2002)

*Getting straight*



gofast2wheeler said:


> I was wondering if the big ring on double crank should be perfectly straight when it travels in a circle. When I pedal and look at the space between front der. The ring moves in and out, sways, ever so slightly. Is this normal, due to pedaling flex in frame or natural curve in ring to promote better shifting like the rear cogs are pitched, or could the ring,crank sider or BB be bent. Any advice would be appreciated before I go to bike store to test ride another bike to see if that does it as well.


This wobble is likely either a slightly off spider arm, or a slightly off chain ring. Either/both is a very common thing (I won't say problem, because in most cases, it has no effect on performance).

Assuming that your BB is OK (i.e. not loose - it's extremely unlikely that it's bent), you have to straighten your spiders and/or chain rings. If it's a CF crank, then only your chain rings can be straightened. Hold a small screwdriver or other short, pointed object against the seat tube so that the tip just grazes the crank spiders as they pass. If the spiders are bent, you can even them out as follows:

Place the bike on its side with the crank supported on a block of wood at the axle. With another block of wood or a stout dowel placed at the end of the offending spider(s) give it a whack with a hammer. Check for change in alignment. If you got no change, hit it harder next time. Repeat until all the spiders are even. You may need to bend them away from the frame (brace the right crank on the block of wood) or toward the frame (brace the left crank).

Once the spiders are even, check the chain rings with the same technique except put the point of your screwdriver at the teeth of the rings (most likely the big ring only if the spiders are even). Straighten the chain ring by placing a large adjustable wrench over the ring with the jaws adjusted for a slip fit over the ring. Bend gently, and check alignment. Repeat until you've got it right.

Even with the chain rings dead straight, you still will get some deflection due to pedaling forces, but that should greatly improve your situation.


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## gofast2wheeler (Oct 13, 2011)

Thanks for the responses, they are all valid and very good. Will definitely check while not pedaling, and if it still does it will definitely try to straighten it by the methods suggested. 

Thanks.


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## GRAVELBIKE (Sep 16, 2011)

The problem could also be with the mounting tabs on the crank/spider.

Many chainrings will have some radial/lateral run-out. The best rings I've encountered have been from Specialites T.A. Virtually zero run-out.


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## gofast2wheeler (Oct 13, 2011)

Update, crank does do it ever so slightly while off ground and no chain and just turning with hand. I don't think it is anything to worry about, will leave alone. But what got me started on this was when I turn my crank while on bike at around 17mph or a good head wind causing more force to be apllied to pedals I get a vibration in my pedals. I can pedal thru it then it stops, but have been trying to figure out the cause. Things looked at so far, new pedals, loosened BB same, exchanged BB same. I gues the only thing would be rear wheel and hub. It always does it at same spped or force but can always pedal thru it (faster) to get past it. Any ideas. Would a bent BB cage cause this.


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## malanb (Oct 26, 2009)

happens to my old bike 2007ish drive train fsa, that shite got bended


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## wilmamiller32 (Oct 31, 2011)

This is my first time I visit here.


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## cierrecart (Oct 31, 2011)

I was worried mine was when on the trainer till I realized it was just my carbon frame flexing a bit.


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