Well, when it comes to bike mechanics, i am a real dummy, so I thought I might ask the ST community some advice.
I have just installed a new set of chainrings on my road bike, and since then, when I apply some kind of pressure on the pedals (say, more than 250 w, unless I pedal extremely smoothly, which is not a bad exercice in itself, but not really suited to the demands of road racing) the chain slips over the rear cogs. It does not change cogs but slips over them. I do not want to mess the whole drive train.
I did some search on the net: Sheldonbrown explains that this might be due to the RD cable guide under the BB not being greased enough, causing the cable tension to change when applying more power on the bike (I ride a titanium litespeed that is not over-rigid, excellent climbing bike) I regreased it but to no avail.
Then I tried to tweak the RD tension adjuster while riding: no success.
I know that one has normally to change its chain when installing a new cogset. In my case, both the chain and the cogs were installed new in February, alhough the chain has been riden a bit more than the cogs as this weel is indoor-trainer dedicated.
Could it be that my lockring has not been locked tight enough: I guess I would have had such problem much sooner then, although the new rings are oval ones (osymetric) and the old ones were round, so the power transfer curve may not be quite the same.
At the end of the day I think I will eventually get my bike to my Lbs, but if anyone had a clue of what the problem might be, I would sleep a lot better…
without seeing it in person I can’t guess what it is…think about it no more, take it to the bike shop!
Need more info, is the chain skipping? is it every pedal stroke or every third stroke? is it every gear combo? little ring and big?.
This could be just a derailler adj or you might have some drive train adj to make, because the new chainrings are not ligned up with the casset like the old ones were.
You could just have a burr on one tooth that is catching the chain as it tries to leave.
Here’s your diagnostic checklist: Is the rear wheel in the frame straight with the quick release skewer properly tightened? Is the cogset lockring tight and the cogset correctly installed (spacer behind last cog, etc.)? Are there any stiff links in the chain? Is your crank tight on the bottom bracket spindle? Are all the chinring bolts correctly torqued? Are the chainrings straight (i.e. not bent)? Is your cogset and chain of comparable wear, i.e., do they have about the same amount of miles on them? They may have “worn together” and are reaching the end of their normal wear lifespan.
My recommendations are: Take it to a trusted LBS and describe the problem. Tell them you performed the above diagnostics. Ask them if they feel you may need a new chain- always replace components from cheapest (starting with chain) to most expensive (possibly ending with cogset).
I think that stuff will either fix the problem or go a long way to discovering what it is. Good luck!
Thank you guys for your input, and thank you Tom for sharing your professional advice.
I hate to look/sound too dumb in my LBS. Your check list will go a long way ensuring they have a serious look at my bike!