Tandem Cycling - Chainring Issues and Findings - Granny Gear

OK

So we have been experiencing some problems with our bike for the past month and a half.

Here were the initial issues:
1) Clickity-clack noise while exerting strong effort (hill climbing) but not limited to any specific gears or chainrings
2) Skipping when in the lowest gear on steep grades. The pedals just drop out from beneath your feet in a loud *POP*

The derailleurs were adjusted perfectly, and the shifting was crisp and had no issues. The noise was not chain rub, but a weird crunching kind of noise. It did not have any perceivable effect on performance.

The skipping was under high pedal pressure, no shifting involved, and perfect chain/derailleur alignment.
The first time we encountered the skip was on a very short section of close to 20% on El Toyonal/Lomas Cantadas on the Berkley Hills Death Ride that I posed a pic from a few months back. It was just one skip, but almost sent us to the ground since it was out of nowhere with full pedal pressure applied. Then again on the same ride on a short section of over 20% on the path that goes to the summit of Vollmer Peak in the Berkley Hills. I ended up adjusting the B-tension screw on the RD to get it closer to the cog, and didn't experience the skip after that for a while. Then on one of our training rides for Everest Challenge , it skipped on a short steep off-road section, but not on Qumiby's sustained 13%. But, then we did all of Everest Challenge without any skipping. However, after Everest Challange, on the local rides, the skip would happen at-will with hard pedal pressure on anything over maybe 15%. Making the bike almost unridable around here. (Example: a hill with average 8% may have a more than a couple sections with an instantaneous 15%).

SO...
Here was my course of action, laid out below:

So first I replaced the chain. I got the KMC x10SL based on good reviews.
Results:
- Around 75% of the crunching noise went away.
- Skipping still there

So, I figured it must be the SRAM Red cassette. I had Ruth look down to see what happens when the pedals skipped on a 20% grade down the street from us, and she swore the chain never jumped off the cassette. So, I thought maybe the splines were busted. I looked things over... The hub splines and the cassette splines were both fine. So I figured, maybe the Open Glide (missing teeth) on the Red Cassette just wasn't working for the tandem.

So we swapped the Red OG-1090 Cassette with a new Force level PG-1070. This Cassette is Power Glide rather than Open Glide. So it does not have any missing teeth. It was still pretty light, so not a big issue in the weight dept.
Results:
- 100% of the crunching noise GONE!!!
- Skipping still there... WTF

So obviously the clickity noises and the skipping were not caused by the same issue. Hmmm...

I had Ruth watch the chain on the steep hill again. She still swears the chain never skips off the cassette.
OK I thought, maybe it's the freehub pawls not catching. I read that if too much grease exits some overly packed bearings it can muck up the pawls.

So I took apart the rear hub, sure enough quite a bit of grease had made its way around the pawls. I de-greased all the springs and pawls, and coated it with light oil, per White Industries' recommendation.
Result:
- Skipping still there :(

Only one thing left now is really the chainring. This chainring was nearly new, only 1000 miles or so on it.
The chainring was a Specialites TA 28t chainring. I called up my knowledgeable LBS (Slough's in San Jose) and talked to the tech I know there. He said he was almost certain it was the chain skipping on the chainring. He said he knew a bigger guy who did some hard touring miles, and had the same issue with a TA granny gear after like 1200 miles. Everything I read on TA was good, so I was surprised.

I looked at the tooth profile of the TA ring. Sure enough, the teeth are pretty short, and the U shaped valleys between them were quite shallow. Not too much from wear, but just the shape of the teeth.

So I ordered a Salsa 28t to try out, since they are no-BS teeth profiles for single speed use. I also swapped to my old FSA 30t that I was using when these cranks were on the Santana to test in the mean time.
Results:
- Went out for a tough ride with no skipping!
- Still No clickity noise!

So I installed the Salsa 28t ring last night, and those teeth are TALL and the valleys between are steeper on the sides. We might do a night ride tonight, and we can test if the salsa ring solves our problems. My friend brought over two different 28t rings, a Sugino, and some beefy one. Both had more prominent tooth profiles than the TA, but less so than the Salsa.

I think we have finally fixed this issue, but more to come after we try the Salsa.

How about the freehub? I had a similar problem. Took the freehub off and the pawls were gunked up and not moving freely. I cleaned and lubed the pawls and the problem was gone.
Just a thought.

Used TA exclusively way back when in the '70s/'80s on our Assenmacher tandem; never had an issue with them.
Does sound like you've got your problem solved!

How about the freehub? I had a similar problem. Took the freehub off and the pawls were gunked up and not moving freely. I cleaned and lubed the pawls and the problem was gone.
Just a thought.

Oops, I just saw you did that already.
Good to know about the small chainring teeth.

We use a Specialties TA Zelito 26t for our grany chainring...have about 7000 miles on it since install and so far so good...we climb more than the average team but not a fraction of what you and Ruth do... and needless to say we don't make your kind of power.
Hope you have it solved...it sure sounds like you have found the limit of that puppy.

Bill J.

We use a Specialties TA Zelito 26t for our grany chainring...have about 7000 miles on it since install and so far so good...we climb more than the average team but not a fraction of what you and Ruth do... and needless to say we don't make your kind of power.
Hope you have it solved...it sure sounds like you have found the limit of that puppy.

Bill J.

Yeah, it's weird. I thought TA was really good stuff too (why I bought it to begin with).

We didn't have to lay down tons of power to get it to skip either. We just had to be a on a really steep hill, press down, and POP!

We use a TA 26 and never had any skipping on grades above 15%. Perhaps it's the match between the chain and the chainring? We've been using DuraAce.

We use a TA 26 and never had any skipping on grades above 15%. Perhaps it's the match between the chain and the chainring? We've been using DuraAce.

Could be, but it did the same thing on 2 different chains

FWIW I run Dura Ace chains as well...But...I use the CN 7701 for my 9 speed setup not the narrower and lighter CN7801 or CN7900 needed for 10 speeds.

Bill J.

Thanks for posting. It is always good to have ideas as to where the skipping could be coming from. The chain skipping is hard on rear wheels.

Had this happen when our Co-Motion was brand new. 30t chain ring would spin right inside the chain. Horrible feeling when you're trying to get up a steep grade. Took awhile to figure it out, but when we did, you could actually stand next to the bike with the brakes applied and step hard on the pedal and make it happen. Shop had a campy 31t laying around that fixed us right up.

Are you sure it's not a timing chain tension issue?

If you're really torquing up front, your timing chain will lose tension on the bottom and may partially derail on the stoker's ring, leading to the pop. This is especially likely if you're using smaller timing chainrings.

Are you sure it's not a timing chain tension issue?

If you're really torquing up front, your timing chain will lose tension on the bottom and may partially derail on the stoker's ring, leading to the pop. This is especially likely if you're using smaller timing chainrings.

In a recent picture of them climbing, there was a lot of slack in the timing chain on the bottom. There may be enough flex in the frame under heavy load to, as you say, partially derail the chain off the granny.

Are you sure it's not a timing chain tension issue?

If you're really torquing up front, your timing chain will lose tension on the bottom and may partially derail on the stoker's ring, leading to the pop. This is especially likely if you're using smaller timing chainrings.

It definitely not skipping on the timing chain. It is on the drive train side of things. We are both simultaneously loosing the pedals, and never coming out of sync.

FWIW, we have tightened the timing tension since that picture of us climbing Marin St.

Besides. It had zero issues with the FSA 30t ring the other day. If it were the timing chain, wouldn't the problem still exist.

Also, as far as framer flex. There is not very much. This thing feels much more solid than the Santana. Besides, the RD will account for flex, just like it accounts for different gear combos.

OK

Only one thing left now is really the chainring. This chainring was nearly new, only 1000 miles or so on it.
The chainring was a Specialites TA 28t chainring. I called up my knowledgeable LBS (Slough's in San Jose) and talked to the tech I know there. He said he was almost certain it was the chain skipping on the chainring. He said he knew a bigger guy who did some hard touring miles, and had the same issue with a TA granny gear after like 1200 miles. Everything I read on TA was good, so I was surprised.

I looked at the tooth profile of the TA ring. Sure enough, the teeth are pretty short, and the U shaped valleys between them were quite shallow. Not too much from wear, but just the shape of the teeth.

So I ordered a Salsa 28t to try out,
So I installed the Salsa 28t
I think we have finally fixed this issue, but more to come after we try the Salsa.

Did you buy the Salsa 28T from your Knowledgable LBS? The local LBS don't make a living answering questions. They like other small businees make a living by building long term realtionships with people who buy things from them.

Crap we have 3200 miles on our sprockets, mostly the middle/big ring. No skipping yet... We replace the chain when the tire is replaced (about 1000 miles).

It definitely not skipping on the timing chain. It is on the drive train side of things. We are both simultaneously loosing the pedals, and never coming out of sync.

FWIW, we have tightened the timing tension since that picture of us climbing Marin St.

Besides. It had zero issues with the FSA 30t ring the other day. If it were the timing chain, wouldn't the problem still exist.

Also, as far as framer flex. There is not very much. This thing feels much more solid than the Santana. Besides, the RD will account for flex, just like it accounts for different gear combos.

I am not sure about that...you may or may not know how much your frame flexes and whether it is significant or not. However, my point is that the granny gear during flex may turn slightly i.e. not parallel to the rear cassette gears. If the teeth of the TA chain ring are not "deep" enough, the chain may slip when the granny is not parallel. Conversely, if there is zero flex and the chain is cross chain and the teeth are not deep enough or worn, the chain may slip or the chain just slips because they are warn.

What strikes me about this problem is that pro racers produce more torque / power individually than you and Ruth can produce together and the red cassette works for them.

The problem with the rear cassette clicking and the front chainring skipping seem odd to me. I hope the front gear replacement fixes the problem and you can go back to your red rear cassette.

We hope to see you on the Low Key Hill Climbs,:thumb:

Did you buy the Salsa 28T from your Knowledgable LBS? The local LBS don't make a living answering questions. They like other small businees make a living by building long term realtionships with people who buy things from them.

Chichi.

No I didn't buy the chainring from them.

BUT, I do buy plenty of stuff from this particular LBS, and use their services for whatever labor I don't do at home. They are my go to LBS.

I was planning to take the bike in for service, if this didn't work. The call was more, like this:
Me: "hey ____, I think I have to bring my bike in, I can't figure this out... *explains situation* ...
Them: "... try the chainring."
Me: OK, if it doesn't work, I'll bring it in.

The only reason I didn't buy it from them, was that we have a lot of stuff going on right now (busy), and the shipping was more convenient. I am pro LBS, and get plenty of stuff there.

Good to hear the more Calfee work being concentrated at one shop the more expert they will become.

I belive they have 4 or 5 Calfee tandem regulars

What strikes me about this problem is that pro racers produce more torque / power individually than you and Ruth can produce together and the red cassette works for them.

The problem with the rear cassette clicking and the front chainring skipping seem odd to me. I hope the front gear replacement fixes the problem and you can go back to your red rear cassette.

We hope to see you on the Low Key Hill Climbs,:thumb:

Here's my take:

1)
If we are talking about the cassette/hub:
I actually doubt that a 140 lb pro rider going up an 18% grade in a 39x26 or whatever is putting down more torque at the rear hub than a 300+ lb team in a 28x28.

For a given torque at the crank, a gear ratio of 28x28 (1:1) provides 50% more torque at the rear hub than a 39x26 (1.5:1). A pro rider of lightweight, or even a strong recreational rider will spin out (redline) a such a low gear, since there is just less load on the system.

Think of it this way. The heaviness of a tandem+team is like virtually increasing the grade versus a lightweight solo rider. I don't doubt that many teams out there are putting their bikes through more stress than the average pro rider.

2)
There have been many complaints about the noisiness of the RED cassette online in various forums. There is most likely a GOOD reason why SRAM switched the Force cassette from openGlide to powerGlide for 2009/2010. Wouldn't you think?

The RED cassette, apparently, handled the power/load just fine. It also shifted fine. So I am not saying it did not work. However it was noisy, and now with the powerGlide Force cassette, it's not. The shifting is smoother too.

Also, the problems with the RED cassette may have to do with many things. Number one, I am using Campy levers, RD, and a shiftmate. it could be that maybe the RED cassette needs to be dialed in within a micron or something to not make any noise. It was noisier in some gear combos than others. Also, the chain's vertical angles at which it approaches/departs the cassette and amount of wrap is certainly different on a triple (28t granny) equipped tandem, than it's intended implementation.

3)
The 2010 Force cassette has made things smoother/quieter. To me so far, that is worth the extra 61 grams. (178g for RED v. 229g for Force).

The XX 10s mountain cassette does not have openGlide. I will probably look into that 11-32, and going back to a 30t ring, once it is available at a cheaper price. Then I will save the 28t ring for events like Everest Challenge.

The XX 11-32 is 208g. Putting it right in between the Red and Force 11-28 at 30g more than the 11-28 Red.

Bike worked great today with several steep sections. New Salsa 28t ring worked perfectly.

Shifted fine too, no difference in the shifting vs. the TA ring.