Hi, bought a new Quarq elsa power meter crank with sram chain rings and the LBS can't seem to be able to figure out why I'm getting so much chain rub agains the inner large chain ring when in the small chain ring up front and when in 1st or 2nd cog in the rear. I know I shouldn't be in small in front and 1 in the back and a little rub against the inside of the front big ring is acceptable but the 2nd rear cog shouldn't have any rub/ grinding on the inside of the front big ring..This rub/grind would either happen or not in #2 cog but it was a 50/50 chance = often... Also once and a while shifting from 1 to 2 in the rear would send the chain off the inside of the front ring (dropping the chain) , even happen when I brought it back to the shop in the stand. The tech couldn't figure that one out.. What they did try was to add 3 very slim spacers to the crank to move the rings out , didn't help.. also took the 1mm spacer out behind the rear cassette in a attempt to lesson the angle of the chain , That didn't work either.. Anybody have a similar problem or have a solution ... BTW my bike is a 2012 cannondale evo with pressfit BB30 with ultegra DI2..

Find a friend taller than you and stand with him between you and the sun in the evening. The bigger the difference in your heights, or the closer you stand to him the sooner you'll be in his shadow. You don't have to wait until tomorrow sunset, you can imagine the situation.

That's the essence of your problem. The chain is the light from the sun, the smaller sprockets are later in the evening, and the chainrings are you and your friend. If the rings are close together, the outer will "shadow" the inner as the chain comes from an outside angle, and it'll rub the outer as it passes.

Note that the angle is made greater if the chainrings are moved inboard, or the cassette (or sprocket) outboard.

On most 10s and 11s bikes the chain will rub when coming from the outermost sprocket. Because of chain line or chainring separation some will rub when coming from the outer two as yours does.

Most people live with it, since there's no real reason to be riding the small/small pair. Or you can move the chainline out at the cranks by moving the BB spacers (on some cranks). If it really bothers you you can increase chainring separation with spacers made for the job.

BTW- I'm a bit confused, bothered, or disappointed that your LBS mechanic couldn't tell you this. IMO, any mechanic smart enough to tie his shoelaces should know and understand this phenomenon, or at least dope it out by observation.

The chain drop to the inside can be stopped with a "chain watcher". The Third Eye's Chain Watcher, N-Gear's jump Stop , Deda's Dog Fang and, most expensive, K-Edge's Chain Catcher will form a barrier inside the smaller chainring and keep the chain from derailing to the inside. They also help protect the frame from damage by the chain. Good insurance and even the pros use them.

Yes I understand but the 2nd cog ??? and what about when I change gears from 1 to 2 in the rear and it sends the chain off the inside of the front small ring to the frame **********???

The shift process sends a wave down the chain, similar to what you do when you try to flip a snagged garden hose or rope over an obstruction. If the chain is brushing the outer ring, the wave can "bounce" off the ring and push the chain over, or a vertical wave interferes with the one tooth at a time engagement on the inner ring, allowing the chain to snag on a tooth, ride the tip and then derail.

You can add a chain watcher and maybe should, but the key is to address what causes the shadow by separating the rings, or moving the crank out, whichever is practical.

Have seen this problem many times with customers (and my bikes, but since I understand and accept things it's not an issue for me). The solution is to shift into a combo that doesn't have the issue.

Before tight ring spacing, uber short chain stays and lift pins made this chain rub worse we would just tell our customers to avoid that combo. It was generally understood that a 10 speed was really a 7 or 8 speed at best in real life. Now the culture of riding is established by racers and real life isn't spoken much or accepted by the masses.

Yes, you can respace the ring further apart or shift the chain lines but these options will have their cost. Like so many aspects of shifting, gear size and selection simple behavior goes a long way to "fixing" the problems. The OP's shop probably didn't want to say as much. Was it Pogo who said "we have seen the enemy and they are us"? Andy.

What problems do you see happening spacing out the crank rings as a unit ??? and why is it that the 4-5 guys I know with the same Quarg are not having the problem I'm having.. Thank you for your insight ..

dh- I'll reply here to your PM to me, allowing for more readers to share in this issue. I do get a bit testy about people expecting bikes to be perfect. Bikes never have been and never will be IMO.

You say you didn't have this chain rub issue with the OEM crankset. Do you still have it? If so take careful measurements of chain line, ring diameter difference, ring spacing and lift pin "heights" on the Quark. Then remove the Quark crank and reinstall the OEM one and repeat the measurements. What differences do you find? Is the OEM crank made by the company that also makes the rest of the gear system? If so then they got the various dimensions right (and the Quark doesn't).

As i mentioned before the short chainstay lengths that are so in vogue make this issue worse. (never knew of a race lost or hill not climbed due to a couple of CMs more stay length...) As rear ends have gotten wider the small cassette cogs have also moved further outward, again worsening this issue. As the difference between the ring diameters grows (BITD it was 12 teeth, now 16+ teeth is common) this issue worsens (as Francis said).

I have to admit i don't think I've seen a chain have inside the rings drop off (over shift) with a well adjusted ft der and with good shift technique (when the chain is on the smallest cassette cogs). As the cross chaining angle is pulling the chain to the outside the tendency is to not have drop off happen. I will say that the very fast down shift release and movement of the Shimano STI controlled ft der is much more susceptible to inside drop off in general. hence the recent and growing use of chain watchers/catchers mounted inboard of the inner ring. perhaps one of these will be the solution to your drop off issue.

In my world if this drop off issue was a frequent issue I would handle the down shift need by using the rear der and not the ft. This would also have the added benefit of getting the chain run FAR more straight and the chain rub issue would also be gone.

BTW as a matter of terminology the small cassette cogs are usually called 9 and 10 (in a 10 speed system) and the large cogs (the low gears) are usually called 1 and 2. Most of us are smart enough to understand what you are referring to but your switching the terms around could be confusing to some.

dh- I didn't answer your question about spacing the entire crankset further out from the frame. Since current cranksets don't have the ability to change the BB axle length (as with traditional tapered square BBs can) as you move the RH side outward the LH side moves inward. The LH arm's fit onto the axle can be challenged. The clearances between the LH arm and the LH chainstay can reduce to less then needed. Depending on the shell and bearing's design this ,movement might need spacers behind the RH bearing in the shell. But the LH bearing might not be able to also be moved to the left and the way the axle and bearings fit will be lost. Some cranksets require the LH bearing to sit against a shoulder on the axle for proper assembly. As the rings are moved outward the chainline does too (this being your short term goal) but then when you're in the large cassette cogs (low gears) the chain will then be further off line. You will approach the chain angles that typical cross chaining have. Don't be surprised if the chain drop off issue worsens when using the Low gears and shifting off the big ring.

So as i have tried to explain moving the crankset outward does have it's concerns.

As Francis suggested respacing the rings further apart would be the easiest way to gain chain rub reduction. But then the lever controlled ft der movement might not be enough to keep ft cage/chain rub down. Andy.

Picked up the bike today and it was just as it was when I dropped it off, (rubbing and grinding in the 2 small cogs but they said thats the best they could do . I also talked to a Quarq rep and he said all you can do is add spacers to move the crank outward and the shop did with 3 spacers (the rep said the most u could use is around 4-5 ) But anymore might create problems on the big big rings. So veridic is just don't use the 2 small cogs while in the small in front . I never really used them that often anyway ... Thanks for all the replies they where very helpful in me understanding everything .. Thank You