Road Cycling - why? when hammering hard @ easiest gear, der. hits spokes.

I was climbing a steep hill the other day and discovered when a stood up and hammered hard at full power, bike rockin' and all, I can hear my der. hit my spokes(or vice versa?) everytime the hammer my right foot, at the same time the bike is leaning to my left...

But if I apply "normal" power, this doesn't happen..

Is it my frame flexing, or is it my wheels?

By the way, I am using a Cr-Mo frame with 36h rims.

Ok, if it is frame flex, it would tighten/loosen my shift cables w/c would explain der movement, right?

Have you checked to see if your derailleur hanger is bent?

I would say that your limit screw adjustment is off. However Im not sure why it happens when cranking hard gears.

Bikes are not completely rigid, to check, lean bike over a little while standing on one side and put your foot on the crank at the axle and push on the axle:
see how much the BB deflects? (Some of this is in the wheels of course but not all.) That is what happens when you stand up and
grind up hills. The chain line changes. The wheel will sometimes let you know they are under stress by little pings from the spokes in the rear. Net result is the derailleur moves a little closer to the wheel. So yes, it is frame flex. Do check the limit to be sure the cage isn't a little over too far and adjust it in a bit consistent with continued good shifting. Steve

It could be a combo of several things........slight frame flex......limit screw adjustment......slightly bent hanger. You can't do much about the flex, but you can certainly fix the other likely culprits.

I had the same problem when climbing steep hills when the chain was on the innermost cog. The answer was an adjustment to the L limit screw. Tighten it slightly so that the derailleur doesn't hit the spokes, but also allowing the chain to rise up cleanly and completely.

Rich

Originally posted by Bikesick
Have you checked to see if your derailleur hanger is bent?

no, the hanger is perfectly ok.. checked the alignment..

thanks.

It must be frame flex + crappy adjustment by yours truly.. :)

i have adjusted the limit screws.. I'll try this out tommorrow..

thanks everyone..

If you check your rear wheel I'll bet you'll find that it's laced wrong. The pulling spokes belong on the outside of the spoke cross, this causes the spokes to sqeeze inward when torque is applied to the crank pulling them away from the derailure, if the pulling spokes are on the inside of the cross, the spokes will pull to the outside when you apply power brining them closer to the derailure and possibly hitting it. This will be more pronounced on a loose wheel and only contact in the lowest gear (the largest cassette cog), I find many bikes have improperly laced wheels from the manufacturer. Do yourself a favor, don't turn any derailure adjusting screws unless you fully understand what they do. If you don't understand the spoke issue, have a wheel builder look at your wheel to see if it's laced the way it should be.

i don't think that its the frame flex. cro-mo does have nice flex (stiff, but not too rigid)
check the non-drive side spokes. is the wheel dished properly?

Its not the wheel it is your low limit screw. The triple rears have more problems when the screw it loose.

Generally, people say that the low limit screw should be adjusted so that it is open as much as possible without allowing the chain to fall into the spokes. Nice in theory, but it can cause the kind of situation you have.

You can analyze the situation more by rubbing chalk on the inside of the derailleur at the lower jockey wheel. I have found that even if you think that there is only a problem when you're hammering, you will find that the peoblem exists all the time--you just don't hear it because it is so slight. Just spin the wheel and see which spokes have chalk marks on them. If it's only one or two, you might want to check their tension. If it's most of them, I bet it's the L screw.

Rich

spokes? wheels? it might be.. But it would be unlikely that a wheel builder would make that mistake, right? By the way, the wheels were built.

Anyway, I'll have the wheels checked by my wheel builder today for loose spokes, dishing, etc..

On the issue of how many spokes get hit by the der.. Almost all
had specs of paint knocked off by the der..

Or am i just pushing too hard gears? As posted in another thread, I climb steep hills with my 42-23 (my easiest gears) @ 45-50rpm..

I'll be taking-note-of/printing out all your thoughts on the matter and show it to mechanic... it'll help, im sure..

thanks.

i talked to some others about it. check your frame for cracks. steel can stress. check the rear stays,etc.

i am totally serious. if you swear your derailluer hanger isn't bent, then it might me a stress crack in the frame.