cyclehealth

We have a 2003? Burley Duet, 9 speed triple. I replaced the Shimano FC-1057 crankset with 53-42-30 chainrings to a Sugino SD 600 with 46-36-26 chainrings. Chainline was 50 mm at the crank. Now it is 55 mm. When I held up the original Shimano to the new Sugino I could see that the spider on the Shimano sets the chainrings in further than what the Sugino does. Now the original Shimano FD-5503 (105) is not able to move the chain over far enough to engage the chain to the outer chainring. It also seems like it may not be the best choice for the smaller chainrings.


Chainline for the left side cranks both front and rear is 55 mm. Bottom brackets are square taper.


My idea is to purchase two bottom brackets that are 10 mm shorter than current BB's to move the new crankset inward 5 mm. And I think it would also move the left side cranksets inward 5 mm. There appears to be room to allow this.


I am also open to purchasing a new front derailleur if another would work better with the new chainring sizes.


Would love to hear about your experience and thoughts on this. I would really like to make the new crankset with the smaller chainrings work. We loved riding the tandem last year but are no longer young and could benefit from the smaller gearing.


Thanks for your help!

Leisesturm

5mm diff in chainline. Hmmm. Have you tried backing out the high limit screw on the FD all the way? Yes, a shorter BB spindle will help, but 10mm sounds like a lot. We had a Shimano 105 equipped Raleigh Coupe and I changed the 30T granny to a 24T and the FD handled the difference just fine. I changed the 42T middle ring to a 39T which actually makes more of a difference to a FD, and there is also not much of an issue. Before I spend money changing any more variables I would be looking at those limit screws. A new FD might work and you only need one. And you could make sure it is optimized for a compact crank gear range but you will spend who knows what. Last would be new BB's because you would probably want two (you don't 'need' two but its what I would do). The new unit BB's are common as salt and just as cheap, but you can spend more, much more, sky's the limit with those things. Something in the $25 ish range each should do you fine but I'm not sure you need to go 10mm shorter. 5 should do it.

cyclehealth

Yes, I backed out the limit screw to allow the FD to move outbound as far as it would go. It was not enough. I am willing to spend for a FD and two bb's if that would make for the best setup. My aim is to have a setup that is reliable and trouble free.

A FD I recently purchased for another project specifically said it required a 50 mm chainline. How many derailleurs have that requirement, I don't know? So I would be concerned with just bringing the crank set in 2.5 mm and then having to go and purchase yet another bb. Wouldn't it be wise to just purchase the bb's that would accomplish that the first time?

Carbonfiberboy 

Put the old crankset back in with an inner 26T, middle 39T 10-speed, and outer 53T B-type 10-speed ring The inner ring will be plain, no ramps etc. All problems solved.

cyclehealth

Thanks for your input. But one of the reasons for going with the new crank set was that I wanted to get away from the 53t chainring. When going downhill I get a tap on the back and a voice in my ear when we reach 30 mph. We are getting older and slowing down.

Besides, I purchased the new crank set just for this project so there is no going back now.

Carbonfiberboy 

The way forward look kinda complicated, though. So put on a 50 instead. You have lots of cogs in the back. We run a 34T cassette and spend a fair bit of time in the 53 X 26. My stoker used to have to close her eyes at 35. Now she keeps them open until 55.

Bornco

Hi

Would something like this help? https://www.jensonusa.com/Problem-So...SABEgIrg_D_BwE

or this https://www.ebay.com/itm/Santana-Tri...2038391?_ul=SV

Good luck, we ride smaller chainrings too

cyclehealth

The existing derailleur is a clamp on. Otherwise the "triple fix far out adapter for braze on" looks like a great idea.

cyclehealth

I just ordered a pair of 113 mm bb's to replace the existing 122 mm bb's. I will deal with the FD after if necessary

Thanks everyone for your input so far.

Will keep everyone posted with the progress.

Darth Lefty 

cyclehealth

The bike has trigger shifters.
No trouble with the timing chain line.

cyclehealth

Finally had a chance today to install the two new 113 mm bb's. It brought the chainline back to it's original measurement of 50 mm or very close to it. As Leisureturn mentioned I only had to change the one bb but decided to change both to keep the timing chain running in a straight line.
I was able to keep the original front derailleur. It works fine. No road test yet, it has been snowing here all day with more to come in a couple of days.
Many thanks to everyone for their help!

LV2TNDM

Different cranks require different spindle lengths. A 122mm spindle is really long and were used on earlier cranksets. Crank design changed and shorter and shorter spindles were utilized. You made the right choice by switching to 113. I don't think anyone here mentioned Q factor in this whole discussion. Even if you could have accommodated the F derailleur, your Q would have been too wide. Wasn't the right solution from the outset. Good job switching the BBs.

bakerjw

When I upgraded components on our Girodanno "Cheap Chinese" tandem, I had to toy with different square taper BBs when I replaced the crankset. After measuring the POS one that was in the frame originally, I got the right size and it worked fine. You should be good to go if you get a narrower set.

cyclehealth

Update: Wife and I are loving the new Sugino SD 600 with 46-36-26 chainrings. It is a much more practical sized chain ring set for us.

Road Fan

I agree with your idea to buy a pair of 10 mm narrower bottom brackets, that should correct the chainline. I think you really SHOULD correct the front chainline. But before you do that, check the clearances from the new crank arms to the chainstays and the new chainrings and chainring bolts to the chainstay. If any of those is less than 5 mm, you will absolutely have the crank hitting the frame. I don't know how much your frame flexes, but if you have a clearance of 8 mm before the fix, you should have 3 mm clearance. Is that enough? It depends on a lot of things. But I would certainly try to get your front chainline as close to your rear chainline as is practical.

I don't have much tandem wrenching or riding experience, but decades with my singles and those of my wife. She's going to be Rear Admiral, with me as Pilot.

Road Fan

I agree with doing this!