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-   -   I'm confused about chainline on Co-Mo Speedster (https://www.bikeforums.net/tandem-cycling/1238978-im-confused-about-chainline-co-mo-speedster.html)

sapporoguy 09-17-21 11:26 AM

I'm confused about chainline on Co-Mo Speedster
 
I'm confused about what the chainline on our Speedster should be. FSA's service page suggests it should be 53mm. Using Sheldon Brown's rear-chainline measuring formula, I get about 48.5mm chainline on the rear wheel.
Do I want the front chainline to be 4.5 mm to the right of the rear chainline? That would make the granny gear happier, I think, judging from the analysis on Sheldon Brown's page. Or do I want to place the BB spacers to bring the crank chainline closer in line with the rear at the cassette? What do you do?

Bike: 2205 Co-Mo Speedster Co-Pilot, 145mm rear-hub spacing
Crankset: FSA Gossamer MegaExo triple on FSA MegaExo BB-7000 tandem BB
Wheel: DT Swiss Hugi hub (same as a 540, I think) 40-spoke + Shimano Alivio 9-speed 12-36 cassette

-Here's the FSA crankset service page (or click on it here at bottom from Co-Mo site in case this link doesn't work) with a chart showing 53mm chainline for a 145mm hub
-Here's Sheldon Brown's page on chainline. Partway down is "Chainline Measurement-Rear"; this formula results in about 48.5mm for me at the cassette.

Rick 09-17-21 08:31 PM

What is causing this confusion.

sapporoguy 09-17-21 11:04 PM


Originally Posted by Rick (Post 22235056)
What is causing this confusion.

All the questions I put at the top of the post.

Rick 09-18-21 12:01 AM

For the chainline to be different than the manufacture set it up for. Somebody had to either put a rear hub with different spacing or Spindles front or rear that are longer or shorter. I replaced the wheel set on my bongo and ordered in Phil Wood Tandem hubs that had the same spacing. They were also dishless. When I bent the front spindle standing on the pedals going up to Sundance I replaced the spindle and bearings. I measured the amount of crank spindle coming out of the eccentric. I made sure during re-assembly to have that same amount of spindle hanging out. So what is the cause of your confusion. If nothing is different than stock on the chainline I would check with the shop were it was purchased or the manufacture.

jim_pridx 09-19-21 10:23 AM

If I'm building up a bike from scratch, I like to set the middle front ring (assuming triple) so that it's nearly perfectly in line with the middle cog of the rear cassette. If it happens to be a 10-speed cassette, I'll shoot for lining up the 4th cog starting from the inner cog, primarily because we tend to use the easier gears more than we do the higher gears. I generally use Sheldon Brown's and the manufacturer's guidelines as ballpark figures only, for it's not very often that I can get the chainline perfectly in line with those figures. I can usually get close but rarely perfect. Once I've established the center line for the rear spacing, though, I'll install the spindles that have the length to get me closest to the chainline figure that I've established for that particular bike. If I'm off by two or three millimeters, I consider that to be close enough to where I need to be.

Rick 09-19-21 09:34 PM


If I'm building up a bike from scratch, I like to set the middle front ring (assuming triple) so that it's nearly perfectly in line with the middle cog of the rear cassette. If it happens to be a 10-speed cassette, I'll shoot for lining up the 4th cog starting from the inner cog, primarily because we tend to use the easier gears more than we do the higher gears. I generally use Sheldon Brown's and the manufacturer's guidelines as ballpark figures only, for it's not very often that I can get the chainline perfectly in line with those figures. I can usually get close but rarely perfect. Once I've established the center line for the rear spacing, though, I'll install the spindles that have the length to get me closest to the chainline figure that I've established for that particular bike. If I'm off by two or three millimeters, I consider that to be close enough to where I need to be.
If you were using a square taper BB. It is possible with a Phil Wood BB. Some of the newer BB types can be trickier. Finding all the correct parts to set it up may be problematic do to parts shortages.

sapporoguy 09-20-21 12:40 AM


Originally Posted by jim_pridx (Post 22236624)
If I'm building up a bike from scratch, I like to set the middle front ring (assuming triple) so that it's nearly perfectly in line with the middle cog of the rear cassette. If it happens to be a 10-speed cassette, I'll shoot for lining up the 4th cog starting from the inner cog, primarily because we tend to use the easier gears more than we do the higher gears. I generally use Sheldon Brown's and the manufacturer's guidelines as ballpark figures only, for it's not very often that I can get the chainline perfectly in line with those figures. I can usually get close but rarely perfect. Once I've established the center line for the rear spacing, though, I'll install the spindles that have the length to get me closest to the chainline figure that I've established for that particular bike. If I'm off by two or three millimeters, I consider that to be close enough to where I need to be.

Thanks, from OP here. This is very helpful. I bought this tandem used about 5 years ago, so I have no idea what the chainline was in 2005 or whether anyone alterted it since. I've subbed out the majority of the components other the the frame--not quite building from scratch, but in that direction. I sent Co-Mo an email to see if they had a recommended chainline; will see what they say. But in any case I'm going to try to line mine up with the middle cog as a baseline and then tweak from there. The spacers on the FSA crankset will let me come pretty close.

jim_pridx 09-20-21 06:07 AM


Originally Posted by Rick (Post 22237438)
If you were using a square taper BB. It is possible with a Phil Wood BB. Some of the newer BB types can be trickier. Finding all the correct parts to set it up may be problematic do to parts shortages.

Yeah, no doubt! I'm not experienced enough with newer systems to have a full grasp of what's available out there, but assuming that the OP can find the correct parts, the same basic principle would apply. But man, this "parts shortage" thing is insane! Earlier this year I had to set up my wife's new fat bike with shorter cranks, and because I couldn't find the right parts, I had to cobble up a temporary system that that'll work for her until I can obtain the correct parts.

sapporoguy 09-20-21 11:11 AM

I emailed FSA with my questions above and they replied quickly:

"With such a difference in chain lines you will most likely have chain rub in the extremes and poor shifting. They should be as close to equal as possible for best performance. The crank/BB does come with spacers that allow for an adjustable chain line from 45mm to 53mm depending on your frame and spacer position."

Will post Co-Mo's reply when they respond.

Carbonfiberboy 09-20-21 12:40 PM

So do you have shifting problems or is this just worry about a tech spec? If you don't have problems, my advice is to ignore that measurement and just ride the bike. You do want the chainline to be the same at both BBs for the sync chain.

sapporoguy 09-20-21 01:12 PM


Originally Posted by Carbonfiberboy (Post 22238252)
So do you have shifting problems or is this just worry about a tech spec? If you don't have problems, my advice is to ignore that measurement and just ride the bike. You do want the chainline to be the same at both BBs for the sync chain.

The rear shifting feels not so crisp compared with the rear shifting on our older Santana, which has an almost identical drive train, including the RD. We rode the Co-Mo on our 3,800-mile crosscountry this summer, so it's not like it won't shift. But when we got on the Santana again after we got back this month, I noticed how much crisper and more decisive the shifting was on the Santana.
So I'm going through everything to try to narrow down the issue. Replaced cables, new chain, new cassette (all of which it needed anyway) adjusted indexing.
The left-side timing chainline is equal front-back, although it's a "beltline" on that side, as I swapped in a Gates system mid-trip this summer.

Carbonfiberboy 09-20-21 04:17 PM


Originally Posted by sapporoguy (Post 22238302)
The rear shifting feels not so crisp compared with the rear shifting on our older Santana, which has an almost identical drive train, including the RD. We rode the Co-Mo on our 3,800-mile crosscountry this summer, so it's not like it won't shift. But when we got on the Santana again after we got back this month, I noticed how much crisper and more decisive the shifting was on the Santana.
So I'm going through everything to try to narrow down the issue. Replaced cables, new chain, new cassette (all of which it needed anyway) adjusted indexing.
The left-side timing chainline is equal front-back, although it's a "beltline" on that side, as I swapped in a Gates system mid-trip this summer.

Did your Santana have the same tubing arrangement as the CoMo, same guide placement, same brifter and RD? I improved the shifting on our CoMo by using Alligator ILINK housing. I also installed the Gates system. It seems to me that chainline measurements tell you which cog would be directly behind which ring and not much else. We probably ride with a perfect chainline 5% of the time, if that. It's different on a SS or fixed bike, but even there the frictional increase would be very minor. Try messing with the housing. I feel a difference whether the RD housing goes above or below the skewer fitting. Doesn't take much. There's also the BB guide.

reburns 09-20-21 04:27 PM

Have you checked RD hanger alignment?
 

Originally Posted by sapporoguy (Post 22238302)
The rear shifting feels not so crisp compared with the rear shifting on our older Santana, which has an almost identical drive train, including the RD. We rode the Co-Mo on our 3,800-mile crosscountry this summer, so it's not like it won't shift. But when we got on the Santana again after we got back this month, I noticed how much crisper and more decisive the shifting was on the Santana.
So I'm going through everything to try to narrow down the issue. Replaced cables, new chain, new cassette (all of which it needed anyway) adjusted indexing.
The left-side timing chainline is equal front-back, although it's a "beltline" on that side, as I swapped in a Gates system mid-trip this summer.

I have found that small changes to rear derailleur hanger alignment can have a noticeable effect upon shifting crispness.

sapporoguy 09-20-21 04:36 PM


Originally Posted by Carbonfiberboy (Post 22238619)
Did your Santana have the same tubing arrangement as the CoMo, same guide placement, same brifter and RD?

The cable layout is pretty close to the same: housing from shifter to near the top of downtube, from there naked cable all the way to mid-chainstay, housing arching to RD. Same Shimano bar-end shifters on both. Jagwire Pro cable/housing on both. The Co-Mo RD is an XTR, the Santana is an older XT. One thing I need to do is swap the bar-end shifters; one's older than the other.
To be clear: I realize tweaking the chainline isn't likely to create miracles. It's partly an academic exercise: to just understand the concept and to get it as close to the theoretical optimum-compromise position. But I also know from decades of tinkering with machines that when you get lots of little things in a process as close to "correct" as possible, the entire system tends to work better.

sapporoguy 09-20-21 04:40 PM


Originally Posted by reburns (Post 22238631)
I have found that small changes to rear derailleur hanger alignment can have a noticeable effect upon shifting crispness.

Thanks. You mean like a bent hanger (bent inward or outward) and/or how the derailleur is attached to hanger? I have a hanger-alignment tool that showed good alignment before our long trip, but I should use it again now to check.

Carbonfiberboy 09-20-21 05:54 PM


Originally Posted by sapporoguy (Post 22238645)
The cable layout is pretty close to the same: housing from shifter to near the top of downtube, from there naked cable all the way to mid-chainstay, housing arching to RD. Same Shimano bar-end shifters on both. Jagwire Pro cable/housing on both. The Co-Mo RD is an XTR, the Santana is an older XT. One thing I need to do is swap the bar-end shifters; one's older than the other.
To be clear: I realize tweaking the chainline isn't likely to create miracles. It's partly an academic exercise: to just understand the concept and to get it as close to the theoretical optimum-compromise position. But I also know from decades of tinkering with machines that when you get lots of little things in a process as close to "correct" as possible, the entire system tends to work better.

The XTR M952 is a very nice bit of equipment. Weird that the bar-ends aren't crisp. On my bar-end bike, I don't use indexed ones, don't quite see the point. I just adjust for silence.

reburns 09-20-21 06:46 PM


Originally Posted by sapporoguy (Post 22238653)
Thanks. You mean like a bent hanger (bent inward or outward) and/or how the derailleur is attached to hanger? I have a hanger-alignment tool that showed good alignment before our long trip, but I should use it again now to check.

Yes, thatís what I mean. Youíre all set if you have an alignment tool, just check for parallelism with the wheel in all directions: top-bottom, fore-aft. It wouldnít be surprising if during a loaded cross-country journey that the rear derailleur might get a bump or two.

Rick 09-20-21 07:06 PM


Thanks. You mean like a bent hanger (bent inward or outward) and/or how the derailleur is attached to hanger? I have a hanger-alignment tool that showed good alignment before our long trip, but I should use it again now to check.
I would also make sure that the shift housing and end caps are not causing binding. Tandems are affected more than singles due to there longer cable runs. When I setup shift or brake cables I use Jagwire Lined End Caps.

sapporoguy 09-20-21 07:29 PM

Thanks for all the ideas. I shall try them all! I may even swap the RD from the Santana over to the Co-Mo to see how that is.
I still use the index position on the right bar-end because I often can't hear or feel those gears way back there when in friction mode!

Meanwhile, here's what Co-Mo says about my original question:

"Yes the chainline recommended for a 145mm rear hub used with a triple ring crank would be 53mm. This can be challenging to calculate since it starts in the middle of the seat tube. I would start with the spacer orientation as outlined in the FSA tandem crank instructions, two spacers on the drive-side. With the chain on the middle chain-ring on the crank and also in the middle of the cassette, you can use your sight line to see how straight the chain is and then adjust the spacers from there."

jccaclimber 09-20-21 11:56 PM

My bet is on cable routing or the shifters. I recently swapped out a 15 year old 8sp bar end shifter for a 9sp one and was surprised at just how much crisper the new one was. After disassembling the old one I think corrosion from sweat was the main destructive action, not 15 years of shifting, but it was something I didnít expect.
Seemingly small differences in cable routing and housing condition will also make a substantial difference in shifting and even braking feel. If one bike has slick cut cables and the other standard or corroded, that will also make a difference.

sapporoguy 09-21-21 10:07 AM


Originally Posted by jccaclimber (Post 22239139)
My bet is on cable routing or the shifters. I recently swapped out a 15 year old 8sp bar end shifter for a 9sp one and was surprised at just how much crisper the new one was. After disassembling the old one I think corrosion from sweat was the main destructive action, not 15 years of shifting, but it was something I didnít expect.
Seemingly small differences in cable routing and housing condition will also make a substantial difference in shifting and even braking feel. If one bike has slick cut cables and the other standard or corroded, that will also make a difference.

Good points. I once spend hours messing with the indexing adjustments before noticing the RD cable wasn't slipping through the housing at the rear very well; pulled the cable and it was kinked inside the housing--new cable/housing fixed it.
My next step after getting the bike back together is to swap over the new bar-end and see. Then I'll refresh the cable/housing, perhaps trying out Yokozuna this time.

LV2TNDM 09-21-21 11:21 PM

Try "crossing" your cables while you're at it. I've never liked how so many bike makers send the right derailleur cable to the right cable stop, causing all sorts of binding and sharp curves. And with today's hidden cables, the binding is even worse. It also mars the head tube as the housing rubs it over time. With a tandem, you can effectively run the right cable to the left housing, send it down to the left BB cable guide, and THEN cross it to the the right cable guide under the stoker BB. Do the same, but opposite, with the left shifter cable. This creates much smoother derailleur cable/housing curves and less friction. I do this on every bike I can. Some cable stops on single bikes don't allow it. But you can almost always do it on a tandem.

The other thing that's required is grinding the cut cable housing ends. Quality housing cutters will cut well, but still leave sharp, non-square edges. I grind them totally flat and square to reduce any sort of compression or "wiggle" where the ferrule abuts the housing end. Just be careful to not melt the liner and outer plastic - use water if necessary to cool.

My rebuilt Co-Motion speedster shifts amazingly well with standard housing. I did add rubber sleeves over ferrules with tubes extending past the cable stop to keep the housing as clean as possible without going with Gore Ride On. Again, I'm really, REALLY pleased with its shifting, especially since it's a 2007 model. I'll add that both STI levers were basically gummed up so bad they didn't function. But flushing with Tri-Flow and lubricating with grease restored them to amazing function.

jccaclimber 09-22-21 01:18 AM

Similar to the above, but I no longer grind my housings after cutting. With shifter housing Iím typically happy with the cut, but I have good cutters. Brake or any other spiral housing I now file instead of grind. It leaves a slightly smoother edge, carries no melting risk, and is faster as I donít have to pull out the rotary tool. I have a small block of wood with a hole drilled in it that I put in a bench vise or clamp to a table that holds the housing for me to file.

Both properly executed perform equally IMO, but itís an option for those without a rotary tool or bench grinder.

Rick 09-22-21 09:52 AM


Similar to the above, but I no longer grind my housings after cutting. With shifter housing I’m typically happy with the cut, but I have good cutters. Brake or any other spiral housing I now file instead of grind. It leaves a slightly smoother edge, carries no melting risk, and is faster as I don’t have to pull out the rotary tool. I have a small block of wood with a hole drilled in it that I put in a bench vise or clamp to a table that holds the housing for me to file.

Both properly executed perform equally IMO, but it’s an option for those without a rotary tool or bench grinder.
I have used a file for this work also. I also use the Jagwire lined end caps. The extended tube coming out of them keeps friction down at cable stops. They also smooth out the sharp angles created by my extra wide Paul Klampers.

sapporoguy 09-22-21 10:08 AM

I do grind my housing ends and will take extra care this time. I like the idea of a wood block with a hole for filing.


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