WGB 

Is the issue of cross chaining specific to granny gears?

For the past 30 odd years I'd only ridden bikes with doubles and I'd never personally encountered this phenom before today. I'd heard of it and when I was showing off my new-to-me Panasonic PT-4500, people casually mentioned I should be careful of cross chaining. Initially I dismissed it as a real issue but after I read a few online horror stories about rear derailleurs being driven into spokes I became a bit more cautious.

This bike shifts excellent on the stand and seemed to have no issues shifting to the large-large configuration. In the small-large configuration, chain slack is noticeable. Since I had no plans to use either configuration I wasn't concerned. Chain was checked with a checker and seems not to be stretched.

It has a 50/44/28 front with a 6 speed Shimano MF-Z712 14-28FW. Chainring teeth seem ok (not sharks' teeth).

After I took it for a round the block cruise there were only a few minor adjustments required. I was then fine riding for about 30km, mostly doing flat riding. I had one sharp uphill but I just rode it using the middle chainwheel due to heavy traffic.

On the way home I decided to try out this half-step (granny) gear thing on a very slight uphill slope. Prior to downshifting to the small chain ring, I was using the middle chain ring. I was in the center of the the six speed rear (either 3rd or 4th cog). I believed that as long I didn't use an extreme (largest chainring with largest rear cog or smallest chainring with smallest cog) I would be fine.

Immediately, the chain locked up. I was travelling relatively slowly and because I was wary of any potential shifting issues, I immediately kicked free of my SPD pedals and was able drag my feet. The RD did not jump into the spoke as I feared might happen but the chain remained kinked and jammed in the process of changing from the middle to the smallest chainwheel, if that makes sense. It remained tightly jammed, even after I stopped and I had to use force to separate the chain from the chainwheels.

I have reinstalled the steel dork disk, in case of the derailleur jumping inwards too far in the future.

My questions are:

Isn't cross chaining only a danger with the large-large configuration? I had no need to use the large chainring during my ride and only used it after this issue appeared. I had no trouble with changing from the middle ring to the large ring and then back. I did again remain in the middle rear cogs (again either the 3rd or 4th gear). I noticed no hesitancy with those shifts.

When I change from the middle to the small chainring I notice a slight jumping. Is there normally a jump with these type of chainwheels?

What is the recommended method for shifting with this configuration? Assuming everything is working properly, what rear cogs should you be using when moving from one chainring to another?

I can install a new SRAM 830 chain if that is recommended.

Photos for posterity

I did completely strip to bare frame and forks.

As bought and in my hotel room
Seat, bell and that rack are gone as is the foam bar padding. The bar padding had paint on it.



as a work in progress
The worn Brooks is just so I have something to ride (it has only front brake pads as I wanted to have Kool Stop Salmons and ran out). I haven't taped the bars as I want to switch them for wider bars. There are plugs installed to prevent injury.
Wheel is spinning in photo as I was trying to duplicate this issue on the stand

79pmooney

Did you shift both derailleurs at the same time? 44 to 28 up front is a big drop. Best to do that, then shift in back. Otherwise you are trying tro shift in back while the chain and its slack are doing wild things.

Also, could you see where the chain came off? Or where it jammed? Those details often are the clue to what happened and what is needed to prevent it from happening again.

HTupolev

I'm a little confused by the sequence of events. Your concern seems to be that the chain/derailleur will jump into the spokes on the rear wheel, but here you're saying that it was stuck between your chainrings?


What do you mean by "jumping"?

davester

Sounds like you got "chain suck" and the chain refused to release from the middle chainring. There are a whole bunch of reasons that chain suck can occur, and it is quite common with large jumps between chainrings, which is what you have. What shape is your chain in? Have you measured it to see if it is beyond wear limits? This is a common reason for chain suck. Either buy a chain wear checker or go to Sheldon Brown's website where he explains how to assess chain wear using a ruler.

Prowler 

I think I have that same drive train on my 1987 Voyageur. I’ve done many miles on that bike, including 450 miles full touring load, and have had no problems. And I’ll, at times, shift with wild abandon dropping to Granny and back. It would seem that fundamentally there is no design issue. So no ideas for you from here.

old's'cool

Could the jumping you notice be due to Biopace chainrings?

pastorbobnlnh 

My two cents: Try the new SRAM 830 chain.

rccardr 

And size it properly (I always use big/big plus a link).
There should be no issues with this drivetrain once properly adjusted, it's good stuff and like Prowler says it should shift like buttah.
Park Tool website has excellent instructional videos if you need them.

WGB 

Thank you all.

@79pmooney I saw it jam but didn't mark it as a specific spot. I had only changed the front shifter when it happened. Were you recommending I shift both front and rear simultaneously? Not sure how that would work?
@HTupolev I'd assumed that the jamming was a consequence of cross-chaining. By jumping I actually mend a slamming or sudden shift.
@davester Chain seems ok (​​​​​​Chain was checked with a checker and seems not to be stretched). It might be chain suck, though teeth seem smooth. I will inspect each one again. I fully stripped the bike and rebuilt it and that included the cranks.

I will install the new 830 and see if I see an improvement. I will also get a 2nd opinion on my front shifter adjustment!

Edit: I wondered about Biopace but was focused on the (what seems to me to be a) massive jump between middle and small chainrings.

Thank you

majmt 

I’ve noticed that before.

nlerner

Are the spacers used with the 28t ring the right size? Sounds like you have too large a gap if you’re getting chain suck.

WGB 

@Nlerner
Are the spacers used with the 28t ring the right size? Sounds like you have too large a gap if you’re getting chain suck.

I didn't even consider that! It's a used bike and as has been bluntly pointed out to me there's a reason why Biopace didn't last. Perhaps a PO installed the wrong spacers and I just cleaned and reinstalled them. Perhaps if I went to different crank set (I have an NOS Tourney from back in the day). It was also suggested I need a wider chain.

SJX426 

Here is another possibility, The FD didn't move the chain far enough or fast enough to catch the teeth on the small ring. Check chain line
My tandem is a 7V block with a triple. I have to shift authoritatively and accurately to get it to move without sucking between the rings. It is frictions so a bit more challenging. I should check the chain to see if is too narrow.
P1010339 on Flickr

WGB 

Thank you all.

I switched chains just now.

I installed a KMC 8.1 instead of the SRAM. After all, the Kmc box said "Anti-drop design. Wider. Thicker. Safer."
And it promises a quieter ride.

The old chain was stamped "Narrow" so wondering if that's an issue.

I will try to get a second opinion on my derailleur adjustment. Currently it's shifting very smoothly. I'll road test it with my shoes not clipped in...!

​​​​​

79pmooney

No, I was not recommending doing both at once. (I've had bikes set up triple where I could but I've also stopped more than a few times when I've tried double shifts with 42-28 jumps.

Another thought - is your chain narrower than anticipated for your crankset? In other words, do you have a cranset designed for an old 5-speed or 6-speed freewheel that can use the old (1960s and '70s) 3/32" chains? Are you now running a 6,7,8-speed chain? That 6,7,8-speed chain is narrower. Runs just fine, maybe better over the freewhaal and crankset but - being narrower, it might be able to fall into the crankset gap(s).

If this is the case, a narrower crtankset would be the easy fix. (Might well require a new bottomn bracket also.) If only the 44-28 gap is the issue, perhaps you can find narrower spacers for the inner chainring or cut down the ones you have. This could cause "overthrows" by the front derailleur; easily stopped using a chain watcher. (There are at least three brands. They all work.) Or you could install quides on the inside of the middle chainring to push the chain out away from the gap. I've done this. Takes ingenuity and patience. (In my case, to make a very narrow, long crank arm triple to have absolute mi9nimum Q-factor for my ailing knees. Ancient very low Q cranksets arte hard to find in 9-speed or narrower formats.)

Just scanned down the thread. See that you are running 7-speed in back and an 8-speed chain. That you're going wider with the KMC. Good. But even the KMC might be wide for that crankset. Ride it and keep your eyes, ears and mind open.

WGB 

I went for a quick 30km. Bad idea as hottest day so far this year.

No real issues so might just have been the chain (though old chain wasn't stretched). I did try fast shifting and from middle to large, no issues. Large to middle no issues and small to middle also no issues. Dropping fast from middle to small resulted in the chain coming off to the inside. I expect the chain watcher/chain catcher idea of @79pmooney might be a very good one. I did look on line for a 6 speed chain but perhaps no one makes them anymore as I didn't see any. The spacer idea maybe another route I need to travel. I'm going to look into that as well.

Thank you

Drillium Dude 

One other "always check" item when troubleshooting drivetrain/shifting issues: find and eliminate any stiff link(s) in the chain. A stiff link can cause all sorts of issues.

DD

Sierra

If you had the crankset apart for cleaning, make sure that you got the granny ring back on the right way.
I got the chain jammed between the middle & granny rings on a bike of mine with the half step + granny triple.
It turned out that when I had reassemble the crankset, I installed the granny ring flipped side for side.
It made for a slightly wider gap between the middle & granny rings.
I turned the granny ring around and no more issues with it.

Jeff Neese

If your chain came off to the inside of the crank, that's just a limit screw. You don't need any extra gizmos. There are plenty of 6-speed chains. I use Shimano HG71, although they all come with quick-links now so I have to buy the pins separately. KMC makes them too. 6-7-8 speed chains are the same. Things start to get narrower with 9 speed and up.

SHIMANO HG71 6/7/8-Speed Chain
KMC Z8 Chain, 116 Links, 6/7/8 Speed

You're right to avoid crosschaining in regular riding, but it certainly should "work". On any build I complete, it's a requirement that I can shift into and use all gear combinations, including large-large and small-small, and I test that both on the stand and on the road. I don't ride cross-chained but I make sure nothing bad happens if it gets that way by accident.

It sounds like you bought a new chain so hopefully that will work better. The old "large-large + 2 links" has always worked for me when it comes to sizing.

There is no reason to have a dork disk on a properly-working bicycle. Both front and rear derailleurs have limit screws, inside and outside. Watch some videos.

mountaindave 

The good news is that you’re sorting your shifting issues. The bad news is that this drive train, as set up, will not function as a half-step. The bike either came that way (spec’ed by somebody who didn’t understand HS+G) or the FW was replaced by a PO who didn’t understand HS+G.

The freewheel is actually very nicely spaced - steps in the 12-16% range are very comfortable for most people. If I were you, I’d ditch the 44t chainring and go with a 40t or 38t ring for a nice, classic triple setup. Read on if you need some edjumacation on half step drive trains.

The goal of a half-step drive train is to have twice the gain ratio in each shift of the freewheel as the shift of the chain ring. For example, my setup is 50/45 x 14-17-21-26-32. The gain ratio of the chain ring shift is 11%. The gain ratio of each sprocket of the freewheel is twice that: ~22%. (In reality it varies slightly with each sprocket, but you get the idea).

What I tell my wife is that I have a high and low gear for each shift in back and that all the options are unique - there’s no overlap in gearing.

Your setup, however, is fraught with overlap. Your gain ratios in the freewheel almost precisely match the gain ratio in your two largest chain rings: 13.6% chainring gain and 12.5%-16.7% in the freewheel. Instead of having 12 unique gears, you have only 7 unique gears as five are repeated.

You’d need a 14-38 5 speed FW to make a 50/44 chain ring combo work - which doesn’t exist. Hence, my recommendation to go to a standard triple. It’s easier and simpler than converting over to some other half-step drive train. You might even find a biopace ring on the ‘bay!

WGB 

@mountaindave - Interesting that you say this as the suggestion I had was that someone had switched out the cranks.

I had been thinking of moving the 44t to the outside and installing a 40t or 38t as a center. That would make a "compact triple" of say 44/38/28 or 44/40/28. Surely having a maximum of 12 teeth for a drop is much easier to adjust for? Many doubles are 53/39 or similar.
Just wondering what negatives would come with this set up? I do have a spare standard triple and can easily install it instead.

I can't see why I'd need a 50 for a touring bike (why would I need to go downhill rapidly with all the touring weight)? Perhaps there is something I'm missing?

mountaindave 

No negatives at all. In fact, you could replace the outer chainring with a “bashgaurd” (aka pant-cuff-saver) and you would have a very nice compact double: most road FDs are designed to handle a 16t gap like 28-44. With careful shifting, one can expand the gap to, say, 26-50…

Looking closely at your picture, it looks like you have a mountain or alpine FD, one designed for mountain triples, not for half-step+granny. In the ‘80s Shimano made two variants of their triple FDs and are labeled on back. If it has a sticker or a stamp in the metal that says half-step, it should work. If not, it is likely a standard mountain triple. The inner plate of a mtn triple FD drops down too low to properly pick up the chain from the middle chain ring to the outer chain ring of a half-step crank. It can cause the chain to bind or the FD must be raised up significantly to avoid hitting the middle chainring which in turn tends to cause the chain to ride on the back of the FD… it’s a big mess. I have only one such half-step-specific triple FD. The rest of my half-step+granny bikes use Suntour road FDs with a tight curve to follow the smaller chainrings better. (On a desktop, check out my Trek 710 photo link in my sig).
Again, you’re missing nothing. You seem to know your capabilities and limitations.

sd5782 

Playing with the gear calculators is loads of fun. I am kinda addicted to it. It visualizes things you may change. My touring bike has a 42 outer ring, but has a 12-28 in back. You can see that it gives a higher gear than your 50 with the 14-28. Playing with this let’s you plan your rings to suit you. Very fun.

ehcoplex 

On the subject, here's a pretty nifty online gear calc version. Note you can hit the 'compare' button and add a second setup.

WGB 

Iirc it had a sticker that said either half step or similar but sticker came off in the ultrasonic.

Ps for mtbikerjohn
You did very well on that Kellogg. The paint job alone are the price of the bike!