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Steel frame flexing and shifting

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Steel frame flexing and shifting

Old 07-15-19, 08:03 PM
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gvv1980
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Steel frame flexing and shifting

I did find a lot of responses on phantom shifting and that likely this phenomena caused by flexing of a steel frame under force of rider going uphill. What I couldn't find is any viable solutions for it. Is it just a nature of steel bikes and cannot be fixed or someone has a checklist of things that I need to go through and if not fix it forever, but minimize effect of flexing?

Thank you
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Old 07-15-19, 08:28 PM
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If possible, look into using lower gearing and spinning up the hills more. This should result in torquing the rear end less, so less flexing, therefore less ghost shifting, rear brake rotor rubbing, etc.
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Old 07-15-19, 08:44 PM
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Originally Posted by Metaluna View Post
If possible, look into using lower gearing and spinning up the hills more. This should result in torquing the rear end less, so less flexing, therefore less ghost shifting, rear brake rotor rubbing, etc.
It will also be easier on your knees and better for your cardiovascular system.
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Old 07-15-19, 09:14 PM
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Isn't that caused by cable stops? Would going to full cable housing help?
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Old 07-15-19, 09:18 PM
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Originally Posted by gvv1980 View Post
I did find a lot of responses on phantom shifting and that likely this phenomena caused by flexing of a steel frame under force of rider going uphill. What I couldn't find is any viable solutions for it. Is it just a nature of steel bikes and cannot be fixed or someone has a checklist of things that I need to go through and if not fix it forever, but minimize effect of flexing?

Thank you
Exactly what bike are you asking about? Sure, bicycle frames flex, some more than others. My 1973 Raleigh Professional was flexy compared to some other bikes back then, but I never experienced "phantom shifting". There are steel bikes that are extremely stiff, my steel Bertrand touring bike is the stiffest bike that I own. Steel bikes are not necessarily flexy. Stop blaming the material your bike is made of. Your phantom shift problem is not the fault of frame material
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Old 07-15-19, 11:07 PM
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The only time I get Phantom Shifting on my Carbolite steel frame is if the screws securing the DT shifters have loosened.
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Old 07-16-19, 12:44 AM
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Switching back to indexed downtube shifters solved my ghost shifting problems. With friction shifting I'd get ghost shifting when standing to climb or sprint. Part of the problem was the mediocre friction mode on my bike's Suntour Accushift lever. It's fine in index mode.

No problems with Shimano bar-end shifters in friction mode on my other steel bike with flexy frame. The shifters have detents to hold the desired position.
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Old 07-16-19, 03:23 AM
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Just don't stand up while climbing. It 's useless unless you depend on winning races.
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Old 07-16-19, 04:27 AM
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Originally Posted by gvv1980 View Post
I did find a lot of responses on phantom shifting and that likely this phenomena caused by flexing of a steel frame under force of rider going uphill. What I couldn't find is any viable solutions for it. Is it just a nature of steel bikes and cannot be fixed or someone has a checklist of things that I need to go through and if not fix it forever, but minimize effect of flexing?

Thank you
Cable guides should be installed and cables / housing routed properly. RD properly tuned, RD hanger aligned (if needed). Wheels aligned and securely fastened in the dropouts. Do double check all that.

BB cable guide pic - that usually helps with "ghost shifting":



Can't imagine there being so much flex that even with a cable guide in place you get phantom shifting... though, could be wrong, considering how tight the 9+ geared sprockets are (for example, if that is the case) packed together.
Old Shimano 10 speed road RDs (pre Tiagra 4700) should be mostly sensitive to this: RD moves a lot for minimal cable movement, while sprockets are very close to each other.

With a proper setup, you should be able to ride however you like up hills - your strength being the limiting factor.

Having said all that, do check if it happens only when riding severely cross chained.

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Old 07-16-19, 07:14 AM
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I had a Peugeot in the late '80s that would want to shift chainrings when climbing out of the saddle, a 'feature' for which these bikes were known. As I recall, the solution was to avoid climbing out of the saddle.
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Old 07-16-19, 07:47 AM
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Originally Posted by gvv1980 View Post
Is it just a nature of steel bikes and cannot be fixed.........
Thank you
Might be the nature of your steel bike, but not all steel bikes. At least that is if phantom shifting is what you are talking about.

The springiness of steel is one of the qualities that makes many steel bikes ride so well on pavement that others hate to ride on. But not all, different steels, different sizes of the same steels and small differences in tube geometry can make a big difference in whether a steel bike is more springy or less. Also, a lot of those old really light for their day steel bikes had a very low rider weight. Though I'm not sure your bike is one of those.

While using lots of muscle on a bike can be part of your issue, there are still some cable routing and cable binding issues that might be part of the problem. And maybe just a slight DR mis-adjustment or bent hangar.
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Old 07-16-19, 08:09 AM
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The route cause of frame flex induced shifting is that the cables don't run through the tubes' centers and that the shift lever will migrate bit by bit with each cycle of flex. I've mentioned this for years and back when screwed and glued AL frames were just coming onto the market came up with the proof test.

Detach the rear shift cable from the der and secure it with masking tape to the stays. Take a short piece of inner cable with a head on one end. Thread it through your der's casing stop/adjuster so the cable head is nestled inside the stop. With your hands shift the der into a central cog and while holding it there secure the cable to the anchor bolt. You can use the cable adjuster to trap the der directly under the cog, effectively creating a single speed. Now go out and ride in the way that would have caused the ghost shifting. You won't get any because the cable is no longer tugging on the shift lever. Andy
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Old 07-16-19, 10:56 AM
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Originally Posted by gvv1980 View Post
I did find a lot of responses on phantom shifting and that likely this phenomena caused by flexing of a steel frame under force of rider going uphill. What I couldn't find is any viable solutions for it. Is it just a nature of steel bikes and cannot be fixed or someone has a checklist of things that I need to go through and if not fix it forever, but minimize effect of flexing?
How old is the bike?

Back in the days of Delrin bodied Simplex Derailleurs we used to get that a lot. The period appropriate solution would be a Suntour VGT derailleur.
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Old 07-16-19, 08:12 PM
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Originally Posted by alcjphil View Post
Exactly what bike are you asking about? Sure, bicycle frames flex, some more than others. My 1973 Raleigh Professional was flexy compared to some other bikes back then, but I never experienced "phantom shifting". There are steel bikes that are extremely stiff, my steel Bertrand touring bike is the stiffest bike that I own. Steel bikes are not necessarily flexy. Stop blaming the material your bike is made of. Your phantom shift problem is not the fault of frame material
I have 1985 Peugeot PGN-10. The steel flexing as a cause was mentioned more often that other when I was looking through old threads. Now, reading your and other responses, will go to back to double check cables, guides, and rear derailleur setup.
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Old 07-16-19, 08:16 PM
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Originally Posted by Bike Gremlin View Post
Cable guides should be installed and cables / housing routed properly. RD properly tuned, RD hanger aligned (if needed). Wheels aligned and securely fastened in the dropouts. Do double check all that.
Will do. Thank you.
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Old 07-16-19, 08:20 PM
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Originally Posted by Andrew R Stewart View Post
Detach the rear shift cable from the der and secure it with masking tape to the stays. Take a short piece of inner cable with a head on one end. Thread it through your der's casing stop/adjuster so the cable head is nestled inside the stop. With your hands shift the der into a central cog and while holding it there secure the cable to the anchor bolt. You can use the cable adjuster to trap the der directly under the cog, effectively creating a single speed. Now go out and ride in the way that would have caused the ghost shifting. You won't get any because the cable is no longer tugging on the shift lever. Andy
Interesting solution. I will try it for my next hilly ride. Thank you.
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Old 07-16-19, 08:26 PM
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Originally Posted by Retro Grouch View Post
How old is the bike?

Back in the days of Delrin bodied Simplex Derailleurs we used to get that a lot. The period appropriate solution would be a Suntour VGT derailleur.
I have original 6 speed Sachs-Huret Rival rear derailleur paired with Sachs downtube friction shifters on 13-24 freewheel on 1985 Peugeot PGN-10.
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Old 07-16-19, 10:19 PM
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Originally Posted by gvv1980 View Post
Interesting solution. I will try it for my next hilly ride. Thank you.
My trick is a test, not a solution. And I sure wouldn't set up my bike this way for a hilly ride Andy
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Old 07-16-19, 10:24 PM
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Originally Posted by Metaluna View Post
If possible, look into using lower gearing and spinning up the hills more. This should result in torquing the rear end less, so less flexing, therefore less ghost shifting, rear brake rotor rubbing, etc.
Originally Posted by dsbrantjr View Post
It will also be easier on your knees and better for your cardiovascular system.
Originally Posted by Kovkov View Post
Just don't stand up while climbing. It 's useless unless you depend on winning races.
PFFTT!

Standing to climb is fun and it's a great workout. No harder on your knees than walking up stairs.

If your bike can't stay in gear, get it fixed.
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Old 07-17-19, 04:08 AM
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Originally Posted by gvv1980 View Post
I did find a lot of responses on phantom shifting and that likely this phenomena caused by flexing of a steel frame under force of rider going uphill. What I couldn't find is any viable solutions for it. Is it just a nature of steel bikes and cannot be fixed or someone has a checklist of things that I need to go through and if not fix it forever, but minimize effect of flexing?

Thank you
Run a full length outer cable, bar to rear DR. That will separate frame flex from shifting.
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Old 07-17-19, 03:58 PM
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Originally Posted by Andrew R Stewart View Post
Detach the rear shift cable from the der and secure it with masking tape to the stays. Take a short piece of inner cable with a head on one end. Thread it through your der's casing stop/adjuster so the cable head is nestled inside the stop. With your hands shift the der into a central cog and while holding it there secure the cable to the anchor bolt. You can use the cable adjuster to trap the der directly under the cog, effectively creating a single speed. Now go out and ride in the way that would have caused the ghost shifting. You won't get any because the cable is no longer tugging on the shift lever. Andy
That doesn't sound like a very complete test, since the cable on the derailleur is no longer subject to flex between stops on the frame.

To test whether frame flex can cause ghost shifts by tugging on the cable (without budging the shifter), it seems like you'd need to use a long shift cable and anchor it at the location where downtube shifters or the downtube cable stops go. Then, if it does cause ghost shifts, you could also fiddle with the adjuster at the derailleur to test how prone the bike is to ghost shifts when the derailleur is at various degrees of off-centerness below the cog.
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Old 07-17-19, 09:27 PM
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Please excuse 30 years ago thinking form getting of your modern experiences. Back then as indexing was just coming onto the market and the whole stiffer is THE WAY had yet to be fully established (and Cannondale was still getting panned for their ride quality), the narrower spacing cog sets combined with shift enhanced profiles shift levers with "soft" positioning ghost shifting was a much more common issue then today. Customers would ask for a tune up on their bike and expect that the "fault" that caused power shifting would be corrected. But the base issue was their equipment, frames that flexed more then before and shifters that migrated with each pedal stroke. We did what we could think of back then.

Such was my test for what caused the ghost shifting. What I was after was that the equipment (and the rider's stressing the bike) was the cause when the equipment wasn't up to the task of the rider's "strength". I needed to show customers that our shop's mechanical skills weren't at fault. That when the shifter lever friction setting was really tightened down the ghost shifting went away. But that the resulting shift lever's reluctance to move smoothly was lost wasn't my liability.

The removal of the frame flex from the picture showed that my explanations were correct and the customer understood that I wasn't going to make an acceptable difference without a major cost (new frame of gear system).

Fast forward to today's situation with indexed shifters being the norm and (overly) stiff frames ruling and we find this situation rather different. Both in how common it is and how the current riders view the options/choices/aspects. If In were to suggest (and I did a few times, only to learn my lesson as to what a customer was willing to listen to...) full length casing I would have been associated with department store Huffys, the type of bikes with full length casings back then.

With out context past understandings are mistakenly thought of as incomplete. For many it's hard to forget what we currently accept as fact was once unknown. Andy
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Old 07-17-19, 11:03 PM
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I can't believe nobody's gone and referred to St. Sheldon's article on this.

Originally Posted by Sheldon Brown
The usual cause of the problem, though, believe it or not, is the cable guide that the derailer or hub shifter cable uses to get around the bottom bracket. As you pedal the bike, the frame flexes from side to side. This causes the gear cable to get tighter and looser with every other pedal stroke.

If the bottom-bracket cable guide has too much friction, it can act as a one-way clutch, pulling the cable down from the lever, but not allowing it to retract on the opposite pedal stroke. In many cases, greasing the cable guide is all that is required.

In one particularly bad case, that of a large, strong racer with an old steel bike, I had to use more heroic measures. I installed a Sturmey-Archer pulley that clamped onto the bottom of the seat tube in place of the original cable guide. This eliminated the problem.
I couldn't have said it better myself. This does explain above posts. Plastic cable guides help because they lower friction. Same with having a nice smooth rust-free cable. Tightening the shifter also helps because if the shifter is tighter than the grip the cable has on the bottom bracket guide, it won't move the shifter. Putting a fixed run of cable there is like completely locking the shifter in place. The cable gets tighter and moves the derailleur, then it slackens up and gets pulled back by the spring in the derailleur. No net movement in either direction.

So grease your cable, check for rust (even that powdery corrosion that occurs on galvanized cables), and go buy a Sturmey Archer pulley if you still can't make it stop.

My Vitus 979 is really bad. Nuovo Record levers and an alu cable guide under the bottom bracket, with an old Campagnolo cable. Sometimes it works to my advantage. Sometimes not. I keep it like that for a good laugh.
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Old 07-17-19, 11:17 PM
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Originally Posted by Andrew R Stewart View Post
Please excuse 30 years ago thinking form getting of your modern experiences.
I didn't mean to offend, and I'm not thinking of this in the context of modern bikes. I'm younger than SIS, but not all of my bikes are.

I'm genuinely interested in what specifically happens with ghost shifting. It seems like it must have something to do with cable tension changing as frame flexing, but what's not clear to me is whether that's entirely due to shifter motion, or if the fluctuations in cable tension also have a significant effect directly on the rear derailleur even when the shifter isn't yielding.
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Old 07-18-19, 04:31 AM
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The Sheldon Brown article linked above explains it pretty well. Older Shimano 10 speed groups, for example, only move the rear shift cable 2.3mm per shift. So it seems plausible to me that you don't need shifter slippage to get a phantom shift if enough other factors combine in the right direction, e.g. slight RD misadjustment, sticky cables, flexy frame, grinding pedaling style etc.
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