When I'm climbing a steep hill, usually standing, always pressing hard, and always in my lowest gear (or is it highest?) my front chainring "slips out-of and around" the chain. It feels as if I'm pushing so hard that the teeth of the chainring simply push their way out of the links of the chain. When this happens I instantaniously have no resistance on the pedals, I always loose my balance, usually have to dis-mount, and sometimes fall. It also makes a lot of noise, so that when I do fall everyone sees it !!
Here are some stats for your evaluation:
Bike is a Trek 1500, Alum frame w/ Ultegra rear &105 front.
I'm 6'1", 200 lbs and ride 2,000 mi/year
Replacing both the chain and the front chain ring at the same time did NOT solve this problem.
Granny gear ratio is 30 x 12.
Front derailer is properly adjusted (I think). No rubbing or delayed shifting.
This only happens in my lowest gear when I'm pressing down the hardest.
What's the problem and how do I fix it? Ride!Urb - Good catch! Sorry for the error. Granny = 30x26. Cross-chain is not the probelm. If you're in a 30x12 gear, you mean that you have a triple crank and you're in the smallest ring up front.....and that you're in the smaller cog (12 tooth) in the rear....right?
If that's the case, you're definitely not in your lowest gear (that should be something like 30x26 or so.....it'll be the largest cog in the rear).
AND if that's the case, then you're in a *bad* combination that you *shouldn't* be using really.....it creates a cross-chain condition where the chain is flexing a lot and running diagonally across the width of the gears. It's very tough on the metal of both chain and gears.....very easy to break chains this way and it wears out the gear teeth rapidly (and makes a lot of noise!).
My guess is that if this is the case, the angle of the chain is severe enough that under hard pedaling pressure it's flexing the ring or just at a bad enough angle to derail on its own. It's a good way to get hurt, too.....as I'm sure you can imagine! If you find yourself needing this gear, it'd be better to shift to the middle ring and a larger gear in the rear -- to help the chain run more in a straight line instead of an angle.
Check out www.sheldonbrown.com for some great articles on gears, shifting, and combinations. It's something every cyclist should know, and it makes riding much more efficient (and fun!).
EDIT: Damn. LOL Back to the drawing board. I don't think chain length would make this happen even if it were drastically long. Has anyone checked to see if your crankarm or the spider is bent.....or the bottom bracket spindle? Looking from overhead and focusing on the front derailleur cage, you can notice any wobble in the ring or crank/bb system while you rotate the pedals backwards. You said you have a new ring, so I doubt it's bent, but that's the obvious place to check. Also, look at it carefully....if you're really mashing down, it's possible that the ramps are already toast? I've seen guys ruin a ring in a single race....mashers! I also kinda doubt that the ring would flex that much (especially in that gear combo), but maybe a steel ring would minimize that. Shimano and Truvativ make some good steel rings that still shift well.....many of the other steel rings on the market are plain stamped rings for singlespeed and downhill use. My only other guess is frame flex, but you'd have to really hammer for it to flex enough to affect things to the point of derailling a chain. That's it, I give up.....but I'm curious! Post back if you figure it out, please. And you must have some hellish steep hills up there! :o) might want to get it checked out Given that you've already addressed the obvious stuff (chain, derailleur, worn ring), my next thought is your size. I'm 6'2 and 200lbs and I've definitely noticed that when im cranking hard I put a lot of stress on my gearing. We are heavier than what they are technically designed for. I ride campy gearing, so I don't know what it is for you, but I know for mine the max recommended weight is 180lbs. I readily admit I'm grasping at straws here, but it may just be that you're putting so much force on the pedals you are bending something just enough to let chain slip loose. Assuming none of your parts wiggle when you pedal hard.
You chain might be too long. Have it it checked ang cut to proper size. Okay the clue could be in the info, if you are climbing on your granny ring up front(30) yet you have the sprocket at the back on the smallest(12) then that could be a reason why because you have an angled chain. You should be on the 30 at the front and say a 25 or 27 at the rear keeping the chain line as straight as possible, in reverse you wouldn't want to be on your 52 ring with your 25 at the rear(or whatever it is) this just causes extra lateral pressure on the chain. Have you checked your cassette sprockets?
Another reason could be chain tension, correct chain length, chain quality.
I weigh 15stone 5/215lb or 97.5kg and only recently had a chain slip but that was down to a lot of pressure from a standing start and you,said you have changed your drivetrain I do not think that human leg power is responsible for this slips out because you do not develop when cycling more then 1 hp anyway . Cross chain ? Well there is one old rule .To cross chain is OK , but just 3 gears maximum on cog compare to crank . Keep this rule in your mind when shifting . go to a bike shop Wow, that sucks! My best guess is you are flexing the frame to the extent the front derailleur is derailing the chain. Under normal circumstances the chain does not rub the front derailleur and all seems cool. When you apply your weight and ox like strength to the pedals, you flex the frame, the derailleur makes enough contact with the chain to screw you.
First off, though, I'd very carefully check out the bike frame for a crack or cracks. A cracked frame will allow excessive flexing that can cause derailment of the chain and other problems.
Assuming your frame is OK, next check the alignment of your front derailleur. If the front derailleur is somewhat misaligned if could also cause derailment of the chain especially if your frame is flexing. The front derailleur should be pretty much parallel with the chain. However, it is better for the back end of the front derailleur to be rotated slightly out than in.
Also, check the low (L) limit screw to be sure the front derailleur only comes in enough to just allow the chain to shift to your inner chain ring and not rub. If the limit allows the front derailleur to move too far to the inside, it may be derailling the chain when the frame flexes.
If neither of these adjusments help, I'd put the the bike on a trainer and see if it is possible to recreate the problem. On a trainer, you can get someone else see if they can tell what's going on.
Anyhow, this sure sounds like a miserable problem. Sure hope this helps. |
