Steve_sr

Hello,

As the title says I am looking to shift a custom road triple crankset possibly with a CX70 FD. As they say the devil is in the details...

FD - CX70 10S cyclecross
Crankset - Ultegra FC-6603 with 24-38-46 rings. The rings are TA and are pinned.
Shifter - Ultegra 6603 STI

After spending waaay too much time online I have been able to pull the following tidbits out of the ether...

• Jan Heine and others on this forum have confirmed that the CX70 FD has enough throw to shift a triple. Jan indicated an issue with STI caused by lack of pins on the chain rings. My pinned rings may or may not fix this.
• Rivendell supposedly used the CX70 FD with a half-step triple which would have fairly close middle/big rings. It is unknown what they used for shifting. Knowing Rivendell it was probably friction.
• I have seen various places where the CX70 should be able to handle the 22T capacity even though it is only rated for a 16T (double configuration). This is likely rated for maximum jump between rings instead of total capacity (cage size).
• Cable pulls should be compatible as the CX70 is a road (cyclecross) FD and the 6603 is also a road shifter?

What is lacking is any real data points that anyone has ever tried or had success with this configuration. Now it is your turn! Any thoughts on why this setup either would or would not work? Please be gentle!

BTW, I have considered a triple MTB FD but apparently the cable pull is different than road... Don't know by how much.

Thanks,
Steve

masi61

With the 46/38/24 chainrings, I would say your choice of the FD-CX70 is probably a better option than the Ultegra 6603 FD, But with the 6603 indexing shifter you are going to want to get into set up for proper indexing. I say go ahead and give it a whorl then report back here your results. I suspect it will work, but getting it to index perfectly may not be intuitive. The FD-CX70 might be for a compact double but not a compact triple. If you have the orange gauge block that these ship with you will need it here. It you don't possess the orange gauge block you can use a 5mm Allen key for the set up. The idea is, that when you first pull a new inner front cable you want the FD to initially be between the "granny" ring and he middle ring. This allows you to use the barrel adjuster to set your trim stops and it prevents the cable from getting too tight when you shift to your "big" chainring. Good luck and please keep us posted on how this works for you. I feel like there are still many, many applications where triple cranks are relevant be they road, trekking, gravel, commuting or whatever you want to call it.

veganbikes

CX-70 was a fantastic derailleur. I am using it on my touring bike with a similar ratio (24/36/48) but mine is friction shifting so I cannot make any promises to indexing but I wish they still made that derailleur. I would happily scoop up a couple more but at the time I didn't think about it and wasn't as spare conscious as I am now not that I have had problems but incase I want to use it for a future build.

Steve_sr

The 6603 FD rear cage is too tall and runs into the middle ring if the outer cage is set correctly for the big ring.

I saw a link to the 5mm allen trick but the link was broken. Where is the allen positioned? I am assuming that this has something to do with the swing position and not the vertical height on the seat tube. Would the orange gauge block be relevant with this oddball ring setup?

KCT1986

Possibly a older 9 speed, FD-6503 or 5503/04 may be an option. These were designed for a 52/42 combo, so 10T instead of the 13T of later models. The cage is slightly different from the FD-6603.

See the difference in the inner cage shape.

rccardr 

That CX 70 will definitely shift the triple flawlessly…when friction shifted.
Many here will be interested to find out how it works with STI shifters.
Not me personally, but…others.

masi61

The 5mm Allen key is positioned between the parallelogram arms when they are pressed outward against the spring to make a sufficient opening for it. Then you can tighten all the slack out of the cable while the triple shifter is in the lowest position. Then you can test the indexing and trim stops as you pedal and shift into the middle, big chainrings and back down. Hopefully whatever ramps are on your chainring set will speed the upshifts and downshifts without too much drama. I have learned on my 7803 Dura Ace triple crank bike that I shift with a 6603 Ultegra front derailleur and Dura Ace 7703 front indexing shifter - to shift early, and to try to give the shift a full 360 degrees of rotation under reduced pressure before really laying the power down. Generally all this works but indexed triples I think are naturally a bit tricky. I wax my chains and for some reason my downshift from the middle 39 chainring to the 30 tooth granny pops so strongly that my waxed chain doesn’t flex sufficiently (sometimes) so I will drop the chain at the base of a hill. More embarrassing than anything if on a group ride.

Steve_sr

Yes, I just became aware of the different ring sizes of the 9 speed vs 10 speed triples. The FD-6503 might be a good alternative as well for this combination.

I just did some quick calculations and there is only a .156" radius difference between a 38T and a 36T middle ring. So if there was cage interference with this setup raising the FD a bit might fix it.

I was out riding my now ancient 1992 Trek 950 MTB today and thinking... This bike has a 46-36-?? triple on it with indexed shifters and it shifts the front flawlessly with no help from any ramps or pins. So what has changed over the years to require all of these fancy chain ring shapes and pins?

70sSanO

People and expectations. I can shift flat rings with STI, but it takes some technique.

What I can’t do is just force it over and have it climb onto the next ring seamlessly.

People want to just shift immediately without that slight pause that was used decades ago. And in some ways I can’t blame them.

John

Steve_sr

Thanks for the tip! So does this do the same thing as the gauge block that comes with the FD?

I gave up on waxed chains a long time ago. I now use my own proprietary blend of equal parts 90W gear oil, chainsaw bar oil, and mineral spirits. The secret to chain life is to get the chain pristine clean either with solvent or ultrasonic cleaning. Then apply the chain lube and let the mineral spirits flash off overnight. Next day wipe any excess off the chain and go ride. Wipe the chain as necessary between rides.

Now the most important thing is to NOT add any more lube until you can thoroughly clean the chain again. Adding lube in between just washes road grit into the pins and wears out the chain in short order. This gets really critical on trails with granite screenings (dust). I made it coast to coast on less than one chain using this method.

masi61