Rear derailleur - relative position of upper and lower jockey wheels

[beanzontoast]

Having just about completed the revamp of my 30+ year old Galaxy (new bb, Stronglight Impact Triple, front derailleur, gear cables and outers, HG30 rear cassette, sram chain with powerlink) I'm left with one thing to tidy.

I've fitted the chain using the 'biggest front, smallest rear, through both derailleurs, then aim for a line through the centre of both jockey wheels meeting the ground at 90 degrees' method. To achieve this, I only had to take one link out with the gears in this configuration, and now a line through the upper and lower jockey wheel meets the ground at a right angle. However, what I've found is that when I change into smallest front and smallest rear, the chain sags.

If I was to remove another link, with the 'biggest front, smallest rear' selected, the lower jockey wheel would be pulled further forward and end up closer to the cranks than the upper one, i.e. no longer making that 90 degree line with the ground. It looks a bit odd in that position too, and I'm not sure whether it's meant to run like that.

Any advice welcome.

 

[GrumpyGregry]

have a look in the Park tools site here

 

[beanzontoast]

Hmm... that kind of suggests I'd get away with taking one more link out. Just had me thinking because I don't recall seeing many bikes with the derailleur in that 'bottom-leading' position.

 

[swee'pea99]

Two things: 1) you shouldn't ever have it on the small front + small back, and 2) if you get it too short, then have it - deliberately or thru' carelessness - on the big front + big rear, the back wheel can suddenly lock solid. I know this because I once bought a 2nd hand bike that suffered from this, and found out about it the interesting way...

 

[beanzontoast]

, and 2) if you get it too short, then have it - deliberately or thru' carelessness - on the big front + big rear, the back wheel can suddenly lock solid. I know this because I once bought a 2nd hand bike that suffered from this, and found out about it the interesting way...

Yep - I'm aware of the 'combination to avoid' thing. I was just investigating the look of the chain on different combinations (statically - not while riding) and the look of this one really caused me to pause.

Sorry about your 'unplanned lack-of-rotation' event
Think I'll err on the not too short side then!

 

[GrumpyGregry]

I've got (n+1)-1 bike in the shed and umpteen mates bikes being ridden with the chain sized as per Park Tool. Never had a problem with any of them. Follow the instructions and it will be sweet as a nut.