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Chain skipping when pedaling hard in lower gears.Shimano Acera drivetrain

26602 Views 13 Replies 9 Participants Last post by  eicca
I have a brand new K2 Sidewinder from Sports Authority. I've only ridden it around 3 times for no more than 5 miles total so far. When I'm in the lowest 2 gears and I push hard on the pedals, the chain slips momentarily. I've had the local bike shop adjust it the best they can with no avail. I had another Sidewinder (the same bike) with the same issue & returned for another one but still the same syptom. I doubt that it's due to any drivetrain/chain wear since the bike is brand new.

Is chain slippage a common thing in the lower gears?
Are there any known problems with the Shimano Acera setup?
Any thoughts of anything else that could be checked or adjusted?

Any help wouuld be greatly appreciated. I wanna eventually get out & ride the thing without any problems.

Thanks in advance.

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Um, what ring are you on up in front? Check the teeth on both the front chainrings and the cassette, do any of them look funny? Does the chain skip when on any of the other front rings on the same rear cogs?

Also, being honest and not snobbish, it's an acera level spec? You can't expect it to behave the same way as XTR.
Are you cross-chaining when this happens? Well, just to make sure we are on the same sheet of music here - when you say "2 lowest gears", to me that means the 2 biggest (most teeth) cogs in the back. So, up front, you should be in either the middle chainring or the smallest chainring (granny). If you are in the Big Ring up front when you are in any of the 3 "lowest" gears in back (again, the bigger cogs), then you are cross-chaining. This can cause skipping, and is all-around bad ju-ju for your drivetrain. Don't cross-chain, whether it's big-to-big or small-to-small.

Other things to check are limit screw adjustment, and proper chain length perhaps, but I assume the "real" LBS you brought it to did those things at a minumum. However, a second opinion (different LBS or more experienced wrenching riding buddy) can't hurt.

Good luck!

Cheers, Chris
I guess I threw you off a little. I mean the 2 smallest cogs in the rear & the smallest ring in the front. So that would be "small-to-small" right? Is this "cross-chaining"? Tell me more about this cros-chaining thing you speak of.:) Is this an expected symptom for the way I'm riding? Is it due to the quality of my drivetrain (Shimano Acera)? When the kid in the store (around 130 lbs) tried to repeat the slippage, he couldn't. But when I (around 210 lbs) dig into it, it starts to skip. The guys in the LBS adjusted the derailleur, checked the chain, & a couple of other things to no avail.

Good point. I understand that it's the "el-cheapo" of Shimanos but nevertheless I still want to get to the bottom of the problem or at least better understand what's going on & learn a thing or two in the process. I'm pretty much a novice. I figured I'd work up to better components as I get more into riding.

It sounds like I can just chalk this up to cross-chaining & low quality components. Would a different setup (such as an XTR) correct this problem? Is there anything else I could try?

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Ja, OK, let's say you have a 3x9 drivetrain - 3 chainrings and 9 cogs on the cassette. In general, most of your trail riding is done while in the middle chainring. On most stock setups, your chainline is such that you can use safely & routinely use all 9 gears in the back when in that middle ring, no problems. However, when you are in the Big Ring (literally the biggest chainring) up front, you should ideally try to stay in the 3 smallest cogs in back (smallest in diameter, least amount of teeth). Likewise, if you are in the granny ring up front, you should try to stay within the 3 biggest (closest to your wheel) cogs in the back.

This will ensure that you have a properly straight chainline. Stand behind your bike and look at your chainline from the cassette up to the chainrings. It shouldn't "angle" too much either towards or away from the bike. Standing there, you can picture when you are doing big-big or small-small, the chainline is at a hefty angle - hence the term "cross-chaining". Not good. Your goal when shifting is too keep that chainline as "straight" as possible. Cross-chaining is hell on your drivetrain; it puts a lot of undue stress on the chain, and it wears down the teeth on your cassette and rings alarmingly fast.

On a 3x9 drivetrain, there aren't really 27 completely unique gearings - closer to half that number, in fact. That's one reason why 2x9s and 1x9s (or single-speeds, haha!) are increasingly popular. In theory, you can use all 27 gears, but in practice, you definitely shouldn't. Your drivetrain will explode in short order.

Also, you are pretty big dude, so that adds stress to the drivetrain - that itself isn't a big deal, but it doesn't help either. Here are some tips to consider: When you shift gears, do NOT do it "under load" (in the middle of a heavy pedal mash). Either pause your pedal stroke for the split-second when you shift or just unweight your pedal stroke during the shift. Also, anticipate shifts ahead of time - trying to downshift while struggling to grind up a hill is going to end badly. Remember that your derailleurs are just brute-force mechanisms - they don't operate well under a heavy load (or hard pressure, or however you want to think of it). Higher-end systems (XTR or X.0) are indeed much more forgiving and consistent, but nothing's bomb-proof.

Cheers, Chris
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Agree w/Chris130...sounds like you could be crossing up your drivetrain. You should never be in the smallest cog in the front and the smallest one in the rear. As was pointed out, most of your riding will be done in the middle chainring, while your steepest uphills will be in the small (granny gear) chainring, and your fastest downhills will be in the big ring in front.

You're safe to use pretty much all 9 of your rear cassette in the middle chainring, but should dfinatly stay in the lower (bigger ring) half of your cassette if you are in your granny gear, and stay in the upper (smaller rings) half of your cassette if you are in the big ring up front.

If you find yourself in your smallest front and smallest rear, chances are you should have shifted to the middle ring up front long before you get into that combination. Short term use isn't bad (to get you out of a sticky spot where you are NOW) but you should try to shift into a better chainline as soon as you can.

You'll find that whatever gear you are pedalling in now will be the equivalent of the same gear (roughly) if you went up one chainring and down two cogs, or down one chainring and up two cogs...or vice versa.

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I see this is a old thread but I wanted to chime in. I have the same Shimano Acera setup accept it's on a Motobecane Trail Elite which I recently purchased to replace my warn out Huffy mountain bike. I weight 250 lbs and have the same identical problem described by jcarter. I am not cross chaining. The chain jumps/slips on two of the smallest rear sprockets when its under load.

I noticed that the teeth on the gears are cut at weird angles and wonder if it might be contributing to the issue for heavy riders. Some teeth are shorter then others too. I never had this problem with the old Huffy.
the teeth are cut that way to help shifting. It's normal, strange as that may be. It sounds more like a derailure adjustment or alignment issue. Have you taken it to an LBS, or are you fairly confident in your wrenching ability? I'd adjust the shifter's barrel adjuster a quarter turn and see if that helps. And make sure your limit screws are adjusted right so the chain doesn't come off while messing with the derailure.
My bike does the same thing, but only after putting a brand new chain on. It slips when on the smallest two cogs and pedaling hard, both on middle and large front rings. The cassette should last for four chains, and I'm only on number two. It still shifts fine and everything, all aligned properly. The rear mech is a Deore Shadow.
Thank you for the reply. The limit screws are set properly. The derailleur hanger is new (unbent) and aligns properly over the gear once shifted. Playing with the barrel adjuster makes it worse either direction from center. The cassette is new with the bike.
new chain slipping but old doesn't

i have the acera drivetrain also with the slipping only when I installed a new sram pc870 and pc850 chain. it doesn't slip with the original equipment kmc chain. The specifications of the chains appear to be identical. i see that the outside of the link are actually cut different. would that matter?
Wanted to provide an update. After further tinkering, I was able to decrease the slip frequency by lowering the height of the derailleur to the cassette. This allowed for a sharper angle when switching gears and more stability in gear. I plan to tinker a bit more to see if I can eliminate the slipping altogether.
Wanted to provide an update. After further tinkering, I was able to decrease the slip frequency by lowering the height of the derailleur to the cassette. This allowed for a sharper angle when switching gears and more stability in gear. I plan to tinker a bit more to see if I can eliminate the slipping altogether.
Interesting. Mine skips where the RD is furthest from the cogs for sure, but I can't get it any closer than it already is.
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