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Is bike flexing ?(9 posts)

Is bike flexing ?noupi
Sep 24, 2001 3:11 PM
I just bought a Trek 2200 and have put on about 400 miles,
It has a triple on it and I noticed that with the chain on the middle FR and the smallest in the rear when I am sitting
it runs smoothly and there is about 1 1/2 to 2 MM space
between the chain and the front derai.( outer edge)
But if i get up to power up a small hill when i am pushing
down on my right leg the chain rubs on the derailler...
I am just starting biking 50 years old 5,9 175 pounds
So its not a over power thing :-)
Opinions would be appreciated
Sounds like the F derailleur needs a little adjustment. -NMTig
Sep 24, 2001 3:17 PM
On second thought...Tig
Sep 24, 2001 3:20 PM
You may not want to cross the chain over that much from the middle ring to the small 12 cog. Then again, I've never used a triple on a road bike. OK, I'll shut up some more!
re: Is bike flexing ?Lone Gunman
Sep 24, 2001 3:55 PM
The front deraileur has a trim adjustment. It is a half shift that will move the deraileur to the right just a shmidge and clear the cage. I swear that my FD works part index and part friction. I will sometimes get the rub you describe and push on the shifter, not get an audible click and the rubbing stops. You also have an adjustment barrel on the down tube at the cable boss which you could tighten a bit to see if that works. Tighten is a counter clockwise turn of about 1 revolution or so. Also 400 miles could be a little cable stretch. The trim feature works differently than the rear click/index type shifting in that it has several positions other than 1 for each chainring. But try the partial shift thing when in the 42x12 and see what you get. I spend alot of time in that range, no problems here. One way to tell if you have stretch in the cable is to shift to the 30xbiggest cog and see if there is any slack in the cable. If so, loosen the allen screw and pull the cable taunt without moving the derail position and retighten.
re: Is bike flexing ?jacques
Sep 24, 2001 5:00 PM
Noupi - Your bike bottom bracket shell is indeed flexing, but that's perfectly normal - they all do to some degree or another. All the replies are right on the mark, and you should be able to get rid of the chain rub.

Sometimes a bottom bracket flexes excessively from left to right because of the rider's pedaling style. Power applied to the right crank when it is in the six-o-clock position will not translate into forward propulsion, but will flex the bottom bracket to the left. As your pedaling style gets more efficient, this flex will become less and less. The mental trick is to consciously stop applying power to the crank at about the four-o-clock position, with the opposite leg starting to apply power at or slightly before that very instant.

This is not an an over-power thing, as you recognized. It's just power applied past the point of usefulness. I used to do this for years until someone spotted it corrected it.
re: Is bike flexing ?noupi
Sep 24, 2001 6:11 PM
Thanks for the replies :-)
Jacques, I will try your suggestion.
Did it take you long to pedal that way automatically ?
re: Is bike flexing ?jacques
Sep 25, 2001 1:14 AM
Noupi - interesting question . . . there are still times (usually at moments of stress, like attacks or difficult climbing) when I catch myself "bending metal" instead of bringing those cranks around smoothly. But basically, it took about three months of constant self-correction before the muscles started to turned on and off automatically at the right times.


make sure the drive side crank bolt is torqued correctly (nm)terry_b
Sep 24, 2001 6:27 PM
re: Is bike flexing ?davidl
Sep 25, 2001 6:44 AM
Hi Noupi -

I'm 57 and ride a triple. The bike is probably flexing some, which doesn't hurt, but you need to know about "crosschaining". You do not want to crosschain. You do not want to use the extreme gears on any chainwheel/cog combination - for example, do not use the smallest chainwheel and the smallest rear cog [and probably the next two either]; do not use the middle chainwheel and the smallest rear cog, do not use the largest chainwheel and the largest rear cog. It just wears out your driveline quicker [chain rubs against the sides of the chainwheels, cogs,and everything wears funny and faster], and transfers power less efficiently. You do not want extreme chain angles under power. Throughout your gears you probably have acceptable combinations that are close enough to these extremes that you can use them instead of the extremes without overstressing your driveline. That way you do not have to set your derailleur stops as wide, and do not have the trim problem you described, and do not overstress and wear the driveline parts.

When they advertise the 27-speeds, they don't tell you it's really 23 or 24 - but that's really enough. Try it out.