jnbrown

When I look at FSA's web site it gives a chain line of 46mm for their tandem cranksets.
This is the standard chain line for a road triple.
Since a tandem has 145mm rear spacing vs 135mm for a single, it seems the chain line would be off by about 5mm.
Am I missing something here?

Also since FSA no longer makes 170mm fronts I am thinking of just buying a standard road crankset reversing the sides and installing helicoils to reverse the pedal threads. I would have to find a shop that could install the helicoils and there obviously could be some risk involved. Does this seem like a reasonable idea? Calfee tells me their BB shell is 68mm and in theory it should work.

TandemGeek

No, that's pretty much it... which is why it's not unusual to find your chain kissing the big chain ring when it's in the middle ring and smallest one or two rear sprockets. Many folks incorrectly assume the chain is hitting the derailleur cage and causing the rubbing noise, but it's more often than not the big chain ring. Granny chain ring alignment beyond the middle of the cassette is also pretty awful. But, on the bright side, being cross chained in the big chain ring and your tallest rear sprockets doesn't usually create a problem.

Absolutely. The only risk would be having someone recut (tap) the existing threads or doing the Helicoil installation without a bench press and the skills needed to properly set up and do the work.

I could be wrong, but I believe R&E has been doing this exact procedure to create Campy cross-over cranksets for many moons.

jnbrown

I would do it myself and feel better about it but the tap kit costs $125.
I have a machine shop and mechanical engineers at work.
Have not found a LBS that can do it yet. R&E who are they?

jnbrown

Just found a LBS that will do it for $25 per side. I think it's a go.

WebsterBikeMan

R&E pops up fairly early if you do a search on Custom Tandem Bicycle (which, I'm guessing, is how I found them). They're based in Seattle, and they sell non-custom as well. As far as I can tell they generally sell direct to the public, bikes they build themselves. We considered them but went with Bilenky, partly due to geographic proximity.

jnbrown

So instead of the Gossamer I could use Ultegra SL and save some weight (maybe 75g) on the front.
Might look weird having Ultegra front Gossamer rear, I don't know.

TandemGeek

R&E Cycles, Seattle, WA (www.rodbike.com)
Founded by Angel Rodriguez and Glenn Erickson who sold the shop many years ago. It's now owned by Dan Towle and in addition to selling the home-grown Rodriguez brand, they bought-out Bushnell Cycles a few years back and also sell under the Trillium brand. Dennis Bushnell is their master frame builder. They have a full machine shop, on site frame shop, on site paint, etc....

Butcher

This idea may cause people to cringe but the cheapest way is to swap pedal axles and use a small amount of locktite. Not the heavy duty type but the low to medium strength. It works and I did that without any issues for a couple of years now. I truely believe that the reverse pedal threading is just old technology that worked back then but is not needed now.
A cheap way to see if the chain angle change is worth it, is to install shims on the drive side to allow the BB to move to the right. If it works then you can get the correct BB length.

jnbrown

I had that same thought, but I am not sure if you swap axles on Keo pedals. I found instructions issued by Look for replacing defective spindles. The spindle has a thread on it that fastens to the pedal body and I think the thread is left or right on each side just like the threads that go into the crank so I don't think you can swap them.

zzzwillzzz

thanks for the info, i was wondering if that would work. and with my speedplays i wouldn't even have to swap pedal axles. i'm headed out to the garage now, i must have some old 7400 dura-ace 172.5 cranks in my boxes of old parts, i've been wanting to swap out the 175s front cranks for a couple of years now but never saw the right deal.

PMK

As a thought, you may just want to try to tap the cranks and not run inserts. I have read of several that ride MTB tandems that had new opposite rotation threads cut into the crank arm and have ridden many miles off road with no issues.

It appears if done properly, the opposite thread forms will form an "X" shaped pattern leaving plenty of material to secure the pedal spindle.

With the need to purchase two taps, the taps or old pedal spindles (if true) could be used to align the crank arm for rethreading. Once clamped, the proper tap could replace the aligning tool and threads easily cut as true as the originals.

PK

jnbrown

Or maybe you can swap them but then the spindles will have a tendency to loosen from the pedal body just like the pedal from the crank. Look says to apply locktite so enough or stronger locktite might solve the problem. Its probably worth a try before doing the Helicoils.

Butcher

Campy Record pedals have threaded collars that are threaded the same direction on both pedals. That's what allowed me to do it. Since I have two right side Campy cranksets on the stoker side I had to find two right side spindles. Got lucky on eBay with a right side only pedal with worn out bearings [Record too!].

Ritterview

Have you ruled out the Lightning crank? You could get exactly the crank arm length you want for both captain and stoker, and save a pound over the FSA. This has an aluminum spindle, the production stoker's tandem crank will have an a titanium spindle.




This one is the tandem prototype. It has weight weenie carbon spyders that are going to be switched out for standard aluminum. Note the spacers between the Gates ring and the spyder, which were required to obtain chainstay clearance. I haven't used this yet, so I can't tell you if the crank is any good yet.

I don't know what Lightning will charge for the production tandem crank, that is something you might want to discuss with Tim Brummel at Lightning.

A pound is a lot to save on a tandem with one component choice. It is probably more than the difference between a Tetra carbon frame and an aluminum frame.

jnbrown

My bank account has ruled it out at $1500.

I am looking at Gossamer rear and Ultegra SL front to save a bit of weight and I like Ultegra better.
I think it won't look that bad.

sprinter

I think you may be. I know that the web page states a 46 mm chain line, but if you go to the tech support page and look at the "tandem crank service instructions" you'll find the chain line for the tandem crank sets are 48mm with both crank spacers on the left (135 mm hub width), 50.5mm with 1 spacer on each side and 53mm with both spacers on the right side (145 mm hub width). Also, I think standard road hub spacing is 130mm.

My calfee was built with 130 mm spacing so I use the 48mm chain line. It's not perfect on the low end except in the 30 t, but it works.

slattekd

It would be very helpful if someone will provide a bit more of the basics on the subject of chain line measurements being discussed here which I am having some difficulty following. New to the tandem world, I am looking for a "chain line 101" explanation. Perhaps it already exists in the archive?

TandemGeek

https://www.sheldonbrown.com/chainline.html

https://www.parktool.com/repair/readhowto.asp?id=110

Chain lines on tandems that use extra-wide rear spacing such as 145mm or 160mm are always sub-optimal as cranksets and front derailleurs are designed for bikes that use 130mm (road) or 135mm (off-road) rear spacing.

The wider rear spacing moves the cassettes further away from the centerline of the bike and changes the relationship between the chain rings and rear sprockets, such that instead of the chain running in straight line from the middle chain ring to the middle of the rear cassette, they tend to run towards the larger sprockets.

To correct the chain line means moving the cranks further away from the frame (increasing the chain line, or the distance between the center of the frame to the center of the middle chain ring on a triple) which, as you'd expect, either off-sets the cranks to the right creating an asymmetrical relationship between the rider's hips and their foot placement on the pedals OR requires a very wide rear bottom bracket spindle to keep the symmetrical relationship of the hips and foot placement.

At the same time, the chain line for the front cranks becomes limited by the maximum travel distance of the front derailleur. In other words, while you can push a chain out out to 57mm to replicate the chainline on a mountain bike on a 160mm rear spaced tandem, the front derailleur probably won't extend that far out.

In fact, Santana's tandems with their very wide 160mm rear spacing finally adopted a special adapter called the "Far Out" front derailleur clamp that works with a bolt-on front derailleur. It allows Santana to use a 129mm rear spindle and very wide chain line by moving the front derailleur's mounting point away from the frame.

Bottom Line: Tandems that use 145mm or 160mm rear spacing typically have sub-optimal chain lines or make other compromises (like using a wide bottom bracket spindle) to try and correct for it. There's always some type of a trade-off and owners simply need to figure out which is the lesser or two evils... recognizing that even the lesser of the two evils is still a compromise.

jnbrown

Well after some research and measurements I can say the following:

The chain line on my Santana with 160mm rear spacing is about 50mm. At first this seems way off. But the Cassette on the Hadley hub is pushed in further to the center than normal. The end result is the chain line is off by about 5mm and I have never noticed it being a problem.

Regarding the Gossamer instructions, I don't know why they recommend 53mm for a 145mm hub. This seems too much to me. My estimate is closer to 50mm. This is somewhat dependent of the position of cassette on the rear hub, which is a number that White Industries does not publish. FSA also don't say what the chain line is for the right side (timing) chainring. If I use an Ultegra crankset on the front with 43.5mm chain line I am concerned about a mismatch to the Gossamer on the rear. If I can mount the 42T chainring on the outside that will help. Even if it was off by up to 8mm I don't think that would be a problem as the length of the timimg chain would tolerate it fine.

TandemGeek

Just curious: What year is your Sovereign? Does it have the Far-Out front derailleur clamp?

jnbrown

It's a 1996. It has an XTR clamp on derailleur.
Works fine with barcon shifter.
I have octalink bottom brackets, I know I had to get the extra wide ones.

TandemGeek

Yeah, I was thinking you must have made some changes from the original configuration on a pre-STI Santana.

We had a '95/96 Arriva which would have come with same original equipment as your Sovereign: Kajita square taper BBs, Deore XT cranks, the awesome XTR derailleurs of that vintage (Blue steel connector plates) and Edco hubs with 8 speed & barcon shifting.

After adopting STI shifting and 9 speed Santana needed to 'fix' the shifting issues that were created by the extra cog and that's when the chain line got adjusted with slightly wider BB spindles, the Hadley hubs and that's when the Far-Out derailleur hanger was introduced.

Again, tandems and chain lines are a bit of a mess if you're a purist and fan of narrow Q. I've always used 108mm up front and 108mm or 111mm in back for Debbie on our tandems which, as you'd expect, creates the aforementioned interference issue with chain rub on the big chain ring when the chains in the middle ring and on the smallest two cogs. I believe Co-Motion specs 118mm rear spindles which remove a lot of the interference. As previously noted, Santana has used very wide 127mm and 129mm spindles to get their desired chain line (and to deal with their wider 73mm bottom brackets).

jnbrown

So back to my question:

Does anybody see any issues with pairing a Gossamer rear with Ultegra front crankset?

TandemGeek

Sorry, I thought you answered your own question, i.e., "Even if it was off by up to 8mm I don't think that would be a problem as the length of the timimg chain would tolerate it fine."

The length of the sync (aka, timing) chain does, as you note, tolerate off-set pretty well. Moreover, you can always bias the front cranks left or right using spacers on the bottom bracket and/or by sliding the eccentric a few mm right or left IF you ever experience a problem with rear timing ring / sync chain derailment.

jnbrown

It was really a theory and something I thought I heard before. I have never actually run a timing chain with an offset. I guess I could test the theory by just sliding the eccentric over on my current tandem like you said.