velospace is about bikes and the people who ride them marketplace photos random forums














  1.  
    So about three or four times so far while I've been riding, my chain slips off my cog and goes between the cog and the hub. I've had a bunch of people look at it and say it shouldn't be doing that for any reason. But I found out that my chainring is really lopsided, since the tension gets really tight, then really loose when you spin the cranks, probably making the chain slip off. Is this a common problem with cheap cranks and what should I do about it?
    I'm thinking new crankset instead of just a new chainring...
  2.  
    If your chainring is out of true, you can just replace it with another of higher quality. If you're worried about having the same issue again, get a ring made of steel. You could replace the crank arms, but they have nothing to do with your chainring being out of round unless they or the BB were installed incorrectly. Also, depending on when you bought the bike, these parts could still be under warranty.
    • CommentAuthorBen Hittle
    • CommentTimeFeb 18th 2010
     
    It most likely sounds like your chainring is bent or not exactly round. You could just get another cheap chainring like an Origin8 or something for like $30 and hopefully that would fix it. But those Truvativ's that come on the Kilo TT's are pretty crappy, you could invest in some Sugino Messenger cranks but that's going to be a lot more money.
  3.  
    Yeah, I was looking at Omniums + BB for 180 so it's really tempting...
    I just don't want to cheap out on the drive train, since I've already had to pull the New York stop because of the slips.
  4.  
    Well, if you're going to buy a new crank, at least see if your existing messed up part(s) are under warranty, return them, sell the replacements, that money can then go to a new crank.

    The Omniums are great. And that's according to me and everyone else who has them and has bothered to post on VS. They carry a good rep.
  5.  
    So I've heard. According to bikes direct, I got a full factory warranty with Truvativ (I think?). I'll give them a call and see if I'm still covered.
    Are Omniums are comparable to 75s? They're only like $50 more than messengers too.

    Oh, and thanks for the responses.
  6.  
    I prefer the Omniums over 75's because they are easier to install/deinstall, they are lighter, just as stiff and are cheaper.

    In terms of quality, I think Messengers are far below Omniums and 75's.
  7.  
    So the extra $50 would be wellllll worth it :)

    I just gave SRAM a call, and they said I just have to take my bike to a lbs and have them call SRAM and they'll send me a new one or something. I'll probably do what you said suicide_doors and get me some Omniums. Now I have something to look forward to besides my chain slipping off.
  8.  
    Having a chain come off on a brakeless track bike is probably one of the most dangerous things. Having your drivetrain set up properly and with good communities is well worth it.
  9.  
    Yeah, S75s are on their way out. They sell for far too much used to be worth buying when you have the Omniums with a BB for $175 new.
  10.  
    I love my 75's :D.Ive never used Omniums so i dont know but i did use Sugino Messengers. Definite difference between both 75 and Messenger. so im guessing the Omniums will also.
    • CommentAuthorSkidMark
    • CommentTimeFeb 18th 2010
     
    Maybe try to get the chainring to be a little more concentric on the spider like this:

    "One at a time, loosen up each of the stack bolts on the chainwheel, and tighten it back just finger tight. Spin the cranks slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. The rotate the cranks some more, finding the new tightest spot, and repeat as necessary.

    This takes a little bit of practice, until your hands learn how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

    Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt."

    Sheldon Brown
  11.  
    I don't think it's a concentric chainring problem, but I'll give it a try over the weekend. I still think it's just ovalized...
  12.  
    Posted By: SkidMarkMaybe try to get the chainring to be a little more concentric on the spider like this:

    "One at a time, loosen up each of the stack bolts on the chainwheel, and tighten it back just finger tight. Spin the cranks slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. The rotate the cranks some more, finding the new tightest spot, and repeat as necessary.

    This takes a little bit of practice, until your hands learn how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

    Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt."

    Sheldon Brown


    As much as it pains me to call Sheldon Brown's encyclopedic knowledge into question, this is the only piece of his advice I've never understood. With the stack bolts installed even completely loose the chainring will move on the spider like .01mm at most. With my Campy chainset, the chainring actually snaps onto the shoulders of the spider because the tolerance is so tight. Unless Sheldon was talking about setting up a chainset that's astoundingly poorly made I can't figure out what he was getting at with this.

    The only possibility that comes to mind if the crankset is so mis-machined that the chainring is eccentric is that the spider might be eccentric as well. Perhaps you could try rotating the chainring to a different position on the bolt circle?
  13.  
    I might also recommend Soma Hellyer cranks (unlike most other Soma products)

    I have ridden Omniums and Sugino 75's, and then I bought a pair of Hellyer's for my commuter. I love them, and they come with a beautiful finish on them.
    • CommentAuthorClinton
    • CommentTimeFeb 19th 2010 edited
     
    new sram cranks?
  14.  
    Posted By: LuvCumsInSpurtsI might also recommend Soma Hellyer cranks (unlike most other Soma products)

    I have ridden Omniums and Sugino 75's, and then I bought a pair of Hellyer's for my commuter. I love them, and they come with a beautiful finish on them.


    How much did you get the Hellyer's for? If there isn't a big price difference between the Omniums I think i'd still take the Omniums for peace of mind and overall what people say.

    And I don't quite understand Sheldon Brown's advice either...
  15.  
    The Omniums are still easier to install, and with less tools. The bottom bracket and bearings are also less maintenance.

    Those Soma cranks are really no different then all the other mid-range cranks on the market, such as Sugino RD, IRO, Pake, Origin 8, Lasco, etc etc etc. Many of these cranks are actually made by the same company, with different logos on them. Some places just have custom chainrings made.
    • CommentAuthorMancha150
    • CommentTimeFeb 19th 2010
     
    Incredibleting: I would say definitely get the omniums if you are new to bikes and want to do a lot of this maintenance stuff on your own. I had never been really good at bike maintenance before I got my bowery, and when I learned that frequent checkups and adjustments were key to keeping everything problem free (especially on a cheap bike like mine), these cranks really came through. I only need two tools to install or remove the crankset and BB, and doing so is very user friendly. The BB area is also much easier to clean. Not to mention these cranks feel great and are very, very stiff. I have not tried the 75s, but if you are using the bike as a commuter, I dont think you would notice much difference (if there is any) between the two, and it seems that the omniums are much more practical.
    • CommentAuthorSkidMark
    • CommentTimeFeb 19th 2010 edited
     
    There is no way to machine a chainring oval but it is very easy to machine one eccentric. It would also be very easy for a spider to be machined eccentric. In a worst case scenario the two tolerances stack up, probably enough to make a chain loose tight loose tight. I know the difference between chain too tight and chain too loose at the axle is around 1mm on my bikes.

    Also if you are mixing brands, this can create a gap between the spider and the chainring, and it would be very easy to bolt it down so it's eccentric.

    I used to do Sheldon's procedure on my BMX's and it does work. It also worked on my beat-up Deore LX cranks and almost-trashed Vuelta chainring. What also sometimes works is rotating the chainring 1 bolt hole over until the problem lessens.

    Comparing the quality of Truvativ's low end crank to that of a Campagnolo crank is just not fair.

    Also if anyone has a Soma cog and this chain issue, it could be the cog. A lot of them are machined eccentric.
 
\



velospace | about, FAQ & policies | contact | blog | status | site map
© 2005-2011 velospace. All Rights Reserved.