F red

How much chainring wobble is acceptable on a new unused crank? Bought a new Sora 9 speed crank to replace my Tiagra 9 speed crank, and it wobbles and chain rubs noticeably more. I'm unsure how much of it is due to simply being lower quality.

FBinNY 

IMO (strictly opinion) any new crankset should have runout of less than 2mm TIR (from one extreme to the other). Better cranksets should have runouts of less than 1mm TIR.

F red

Interesting. The old Tiagra crank definitely had less than 1mm, I know my Campy stuff as virtually no detectable wobble. 2mm sounds like something you might find on a Walmart bike. Any more than that and the chain would probably rub the FD no matter what.

Kimmo

Sounds pretty shabby.

I have a Sora 9s triple crankset on a bike with no visible runout, and I can barely get the chain to rub intermittently if I press on the shifter and backpedal.

F red

I haven't actually measured it, but it is one of the new external BB Sora 9s triple cranks.

I estimate it to be a little over 1mm. I just know I was able to set up the FD without any chainrub at all in any gear with the square taper Tiagra cranks, but there is some chain rub cross chaining the last 2 cogs. The frame is a little flexible around the BB, so it is even worse when riding.

RubeRad

How much runout is typically due to imperfect chainrings, vs flex under load? Would that flex usually come from the bottom bracket, or the spider?

RubeRad

This is why indexed FD shifters are a bad idea. IMO, indexing only makes sense for the rear.

shelbyfv

You could loosen the chainring bolts and then tighten them in the proper sequence, just in case they were installed improperly. Otherwise, return it.

RubeRad

What's that now? Is it start anywhere, then move "across" (either two to the left or two to the right) in a star shape like car lug nuts? What difference does order make?

FBinNY 

I would be very surprised if any tweaking of the bolts made a difference The relative strengths of the chainring and spider are too different. If there's runnout, either the ring itself is warperd, or much more likely, the spider is a bit off.

shelbyfv

AFAIK, just the star shape and going around a few times, as opposed to cranking one down and moving to the next. Edit- FB's comment makes sense but I would try anyway since it's cheap....

F red

Thanks for the responses.

I did do start tightening and put some other chainrings on, so I'm inclined to think the spider is a bit bent or the axle is off. I would probably agree that it makes very little difference since the spiders can easily bend the chainrings.

FastJake

Honestly I doubt the spider is off. I bet it's the rings. If so, you can try bending them to not rub, but if they are that bad I would probably just return the crank instead. It should essentially have no discernible runout as far as rubbing on the FD. If it does, something is wrong.

F red

I have put two sets on chainrings on, including the old chainrings that worked with the old crank fine, and both have rubbing issues. Seller insists 1-2mm is completely normal for a new crank and it really isn't worth sending it back for the price I got it at. I could see 1mm due to poor manufacture, but 2mm seems excessive for a new crank, and on the verge of needing repair to me.

gilaasepeda

Did you put spacer? Seems similiar to my problem

cycle_maven

I bought an external bearing Sora crank, and darned if I can see any wobbly at all on mine if I just spin the cranks. Any rubbing under load is strictly flex, not sure if it's BB flex or crank flex.

I would take off the chainrings and see if it's the spider or the chainrings by using a dial indicator on the flats of the spider and by laying the chainrings on a glass tabletop to check for flat. File and bend as necessary.

Kimmo

+1, but Shimano and SRAM are kinda stuck with it since they don't have a mouse ear to push the barrel in the other direction. A travesty that Campy should mess with their micro-ratchet.

Kimmo

Oh wait, here's a thought - you could rotate both rings around and see if you can get it straighter that way; there are four other places they could be. Although the timing of front shifts may be less opportune as a result.

But obviously, don't rotate the rings relative to each other or you'll kill the shifting.

That's crap. Up to 0.5mm for anything half-decent like Sora is more like it IMO.

F red

It wobbles on the stand, and it rubs in more gears when standing on the pedals.

That's what I was trying to figure out. The lowest I have is Tiagra, so I really was unsure how bad Sora is supposed to be.

caloso

Agree. I have 10-speed Chorus shifters on my Ridley and the micro-ratchet is the greatest thing ever.

cycle_maven

Wobbling on the stand is completely unacceptable. Something's bent. The only difference between Sora and, say 105, is that Sora is painted and 105 is anodized. Maybe a slightly better finish, but Shimano doesn't tool up for 4 levels of crank- they just spend less time on the cheaper ones. Drop forges and dies are pretty darn expensive, and if you can use the same forge for 4 different cranks, then you're way ahead. The first hollowtech cranks were the top of the line Dura Ace, then they did cost reduction to Ultegra, then 105, then Tiagra and Sora.

Continuity

How bad an idea is it to use spacers to compensate for chainring wobble?

F red

On the subject of Campy FD trim, my Chorus chainrings run perfectly true, and I have my FD set up so there is no chainrub in any gear except small-small, which is because the chain is rubbing against the big chainring.

F red

Well either the spider is off or the axle is off. The chainrings aren't perfectly flat, but I took them off and taped a stick to the FD. Couldn't figure out how to measure but I set it up to scrape the chainring mounts. 2 were more out toward the pedal side, and 2 were more in toward the BB side, in the same problem areas as the chainring wobble.

Obvious it is a lot less than 1mm, and around 1mm at the teeth.

Also want to check there is no way BB alignment can affect wobble on the stand. In my head, that is how it works.

F red

Figures out how to take some measurements, although if the arms are radially bent, it will be off. Pressed one jaw of the caliper flat to the mount surface and measured to the other side of the seat tube.

1 0.19mm
2 0.00mm
3 0.04mm
4 0.20mm
5 0.24mm

So only about 0.24mm off at the crank. Not sure how that compares to normal, and if I should be bending the spider or the chainrings.