elpedro

Hey gearheads,
I’ve turned my early 90s Trek 520 touring bike into a steel gravel crusher. Have kept the bar-end friction shifters, went from 7-speed to 9 with a nice Shimano 11-34 cassette which has been awesome. However now I’m experiencing some chain suck issues with the front, which is the original 7-speed half-step+granny setup: 50-44-28, shifted by a Deore DX FD. That’s too much range up front anyway so I’d like to drop down to a double and get away from 7sp.

What double crankset should I put on there? I’m thinking 46-34 would be great but road or mountain, 9 or 10-speed? Will these work with my FD?

andrewclaus

Are you familiar with chainline? See Sheldon Brown's website if not. You may need to stay with a road double to match your chainline, and you might need to change the bottom bracket. And you may have changed the chainline when you changed the rear wheel to 9-speed.

As long as the chainline is right, the derailleur will work. That's one of the frequent problems with an incorrect chainline.

I had the chain suck problem with the 1983 Trek 520 that's my daily rider now. I rescued it from the landfill a few years ago. I volunteer at a non-profit shop in Golden, so I had access to a lot of salvaged parts.I had to go through several combinations of cranks, bottom brackets, and spacers before I got the chain line to work.

Did you reset the rear dropout spacing? Your old wheel was probably 126 mm, the new is probably 130.

pdlamb

Did you change your chain? A worn chain has caused chain suck for me more than once...

elpedro

Solid point. Probably only had about 500mi on the current chain. But I did read on Sheldon that a 7 speed crankset is prone to suck a 9 speed chain and it has happened more than once to me with different chains.

elpedro

Definitely planning to replace the BB with a double-specific one, but it sounds like a road crankset would be kinder to the chain line. Thanks.

I am pretty lucky: 132.5mm rear spacing, fits a 50mm tire and the chain stays are longer than most. The 1991 frame is a keeper.

squarenoise 

Check out the New Albion Crankset in 46/34. It says 11 speed, but works with 9,10,11. I have the Triple version and really like it.

oldbobcat

In my experience chain suck indicates badly worn chainrings. Check both.

rccardr 

46/34 is easy. Any Deore crankset from the 80’s would work set up as a double with the rings of your choice.
Bottom bracket of 115mm should do the trick.
I’ve done this exact setup on at least a half dozen bikes with a 9 or 10 speed 11-34 or 12-34, shifts very nicely.

70sSanO

According to MOMBAT, a DX will run as low as 26t and high as 48t. It also works with Rapid Fire.

If you want to change the crank, your first step is to determine your high/low chainrings that you use now. If you use the 28t, in lower cogs, then 34t might not be low enough. If you ride in the 44t most of the time and use the 11t cog enough, but never use the 50t, you can go to a 44/28, or 46/30, or whatever covers what you currently use.

John

Camilo

Not what you're asking, but have you considered staying with a 9 speed (or 10 speed) triple, something like a 48-50t big ring and a 28-30 small ring? I ran something like that for many years on my original "gravel bike" (a cross bike with road crank and MTB cassette gearing). Gave me great shifting, lots of both high and low gears for everything from fast pavement rides to moderate single track. My current double gravel bike has a very similar range to what I had, but with a much larger cassette.

But it sounds like you don't need the gearing range I do. So I'd suggest any 50 or 48-34 9 speed road double if that suits your gearing needs. My 9 speed triple FD worked on a double crank, but FDs are so cheap, you might as well get a double.

Of course, get a BB specific to your new crank.

Duragrouch

OP: Why limit the range? Go with a 50/34 double, that'll reduce your number of duplicate gears. My favorite is "hollowtech II style", comes in 5x110mm BCD (34T won't work on 130mm BCD), and it's a road crank so has low Q-factor (lateral pedal spacing), has pretty straight crank arms. Crank, rings, and "ISO External" BB bearings, all for $65 on amazon, though not currently available there, but I do see on ebay for the same price. Chainline was perfect (for my 7 speed cassette), I think 43.5mm. That crank and bearings have been a VAST improvement.

choddo

Does GRX have the same chainline as road cranks? Great rear mech too, clutched and can handle a wide range, do the lot.

Duragrouch

I don't know, but this may help: I used to be confused, thinking there were more variables than there were, on "common" setups. What matters is:
- Bottom bracket shell width; Half of the width is the spacing from the bike centerline to the right shell face.
- Centerline of the cassette cogs, for the best average angle of the chain from the chainrings to the cogs. This is (from bike centerline):
(Outer Locknut Distance/2) - (half the total cassette thickness) - (distance between smallest cog (not hyperglide lockring) and right inner dropout).

Now, there are many variables to the above, but, within more "standard" configuations, such as:
- 135mm OLD
- 8 speed cassette
- 8 speed triple crank
Those components are designed to work with each other, meaning the chain center of that triple crank (so the middle chainring) is designed to line up with the cassette center. What I didn't look for in the past was, "What bottom bracket spindle length is this crank designed for, assuming X bottom bracket shell length?" Because there will be a recommendation if you dig for it.

On my generic hollowtech II style double crank, there is no choice of BB spindle length, the spindle (tube) is permanently bonded to the right crank arm, so it better be correct length. It was designed for a 68mm wide BB shell, and installed, that chainline was dead perfect (I think actual number is 43.5mm from chainring center (between the two rings) to bike/shell centerline. Some cranks this style say they can accomodate 68, 70, 73 mm shell widths, and will include spacers to go under the drive side external BB bearing if you have a 68 or 70 shell, to achieve the same crank position as 73.

So ask those questions for the crank, see what the specified chainline number is, based on what bottom bracket shell, and see how that matches up with your cassette. But if fairly common size OLD and BB shell, and the same "family" of parts (like Shimano Deore 8-speed), chances are, the parts are gonna line up.

It gets more weird if, say, you are using a right crank arm that is a triple, but only running a single on the innermost position, to get a very low gear; In that case, the chainline will be off, it's not used as intended. Doesn't mean it can't be used, but you'd need to adjust for that, space the crank out further.

choddo

Thanks. It was more of a suggestion for the person asking but GRX is hollowtech 2, 1x or 2x, 10 or 11spd afaik which is why I thought it might be worth consideration.

t2p

GRX cranksets (FC-RX600 and FC-RX810) have 47mm chainline - requires specific FD (FD-RX400 or FD-810/815 for example) - but in some cases an existing / road FD can be used with some tweaks

t2p

note - GRX FC-RX810 crankset is Hollowtech II - but FC-RX600 is also a two piece crankset but is not Hollowtech II

t2p

good 2x option for some applications :

MTB crankset with the small ring removed

one old school example pictured above - Shimano 563 LX crank with 44 / 29 chainrings (94 mm bcd)

a more current example could be a two piece SLX M660 crankset with outboard bearings (can also be good candidate for 1x)

choddo

Ooo thanks, didn’t know that.

cyccommute 

Chain suck is less due to worn chains and more due to damaged chainrings. Look for a burr on the ring and file it smooth.

elpedro

Very good question. The range i have right now is a bit too much. The bike was originally equipped with a touring 14-25 cassette on rear, so my current 11-34 means that the extreme ends of the range aren't very useful especially considering the bike is repurposed from heavy touring to gravel riding. I find having the front triple equates to too much shift fiddling on technical gravel and a double would significantly reduce that while preserving the range I need.

So many fantastic replies and knowledge here, I'm grateful for all responses and learning a lot about measuring chain lines and bracket to width build up an optimum personalized setup.

elpedro

That is a very nice looking choice and I love the ability to move to 10 speed easily on my current wheelset or 11 speed on the next set. Thank you.

elpedro

A couple of good suggestions here on the amount of chain wear, and considering the gravel usage that is entirely possible on these original chain rings. I'll check it out.

Duragrouch

I love that the new wider-range 2Xs, 16 tooth drop, work almost as good as a 3X, which is a problematic fit for my 20" wheel folder. And with a big wheel bike per this thread, I could see not needing a 50 high, so going with 46. But even with my 50/34 11-30 (7sp), I have 5 duplicate gears in the middle of the range (an advantage of 1X, no dupes, but a tough fit on my bike). My point being, having as wide a spread on a 2X as possible, reduces duplicate gears. Unless a 46/34, 12 tooth drop, shifts that much easier? My 16 tooth drop shifts fine. Unless the 46 provides half-steps? I haven't run the numbers. I hate dupes, would love to go 1X, but other limitations hold sway.

t2p

can provide limited experience on this one Ultegra 6800 46/34 bike that was changed from 50t big ring (top pic) to 46t ring (bottom pic)

the front shifting was good with the 50 - but noticeably better with the 46 … it ‘snaps’ quickly up to the 46 from the 34 and also back down quickly … this is the best front shifting 2x bike I have

might also be due to the shorter chain length (links were also removed)

the 50t ring does look better though

Duragrouch

Good to know! My 50/34 upshifts great, even with "dented" steel rings with no lift pins. The crank was supposed to come with aluminum rings with lift pins, that the seller later sent, so I have a set of those to try when the steel ones are worn, should be even better, though I don't know how. Occasionally I'll drop the chain on an upshift, the lift pins will probably allow me to adjust the front derailleur in a bit to prevent that.

I hate 4 arm assym shimano cranks with the fire of a hundred suns. Just me. I know, lighter. And that was just based on style, before the delamination issue on some. I will forever be a 5-arm man, used to be 130mm BCD, but I'm loving the 5x110mm 50/34, should be less duplicate gears than with only 10 teeth difference on my old 130 road crank. And fortunately as I have seen on here, shimano did make a hollowtech II in a 5 arm road triple, I do love the hollowtech system and bearings, some advances truly make sense. But it doesn't pay to buy a crank with used chainrings, so I hope the aftermarket makes the above in a hollowtech II, 5x110x74mm, if I ever replace the crank on my roadie. Probably not, I'm in the townie mode, and perhaps, touring mode at some point.