Timing chainring on spider: outboard or inboard position?
10-25-19, 05:09 AM
#1
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Timing chainring on spider: outboard or inboard position?
The timing chainrings on our Co-Motion and Santana are bolted to the spiders on the outboard position. I just got a replacement front crank (FSA Gossamer) for the Co-Mo on eBay, and the chainring is on the inboard position. (See pix.)
Anyone know if there's an advantage, inboard vs. outboard? I can imagine inboard would reduce chain tatoos, perhaps mean a bit less off-axis twisting of the shaft inside the bottom-bracket bearings? Maybe inside would put the chainring too close to chainstays on some models? Maybe no dif at all?
Old chainring, outboard on spider:
New chainring, inboard on spider:
Anyone know if there's an advantage, inboard vs. outboard? I can imagine inboard would reduce chain tatoos, perhaps mean a bit less off-axis twisting of the shaft inside the bottom-bracket bearings? Maybe inside would put the chainring too close to chainstays on some models? Maybe no dif at all?
Old chainring, outboard on spider:
New chainring, inboard on spider:
10-25-19, 06:47 AM
#2
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I would agree. If the chain doesn't interfere with something, inboard mounting would reduce twisting on the BB.
10-25-19, 07:03 AM
#3
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Agree with OldAcura.
Move the stoker timing chainring inboard as much as you can. Allow 3mm or more of clearance between the chainstay and the chain.
After that’s set, you may want to move the front timing chainring for a straight chainline. Note that the front timing ring might need to be in the outboard position.
Move the stoker timing chainring inboard as much as you can. Allow 3mm or more of clearance between the chainstay and the chain.
After that’s set, you may want to move the front timing chainring for a straight chainline. Note that the front timing ring might need to be in the outboard position.
10-25-19, 02:16 PM
#4
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Sapporoguy,
If at all possible, mount both timing chain rings on the inside. This will reduce the flex of the boom tube slightly. Our 2016 Santana Beyond came with them mounted like that and so did an earlier (2002) Santana we owned. There was a thread on Tandem@Hobbes about this many years ago that educated me to the stresses on the boom tube.
Tailwinds,
Charlie
S&S Santana Beyond
If at all possible, mount both timing chain rings on the inside. This will reduce the flex of the boom tube slightly. Our 2016 Santana Beyond came with them mounted like that and so did an earlier (2002) Santana we owned. There was a thread on Tandem@Hobbes about this many years ago that educated me to the stresses on the boom tube.
Tailwinds,
Charlie
S&S Santana Beyond
10-25-19, 08:30 PM
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10-25-19, 08:46 PM
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The cutout seat areas of the spider seem to me that they would provide support as far as placement and strength for the chain ring.
I wouldn't do it.
I once thought I was cool and went for colored bolt rings on my tandem. They sheared off so forget that, I am sticking to the engineering concepts for my own safety as well as my stoker.
I wouldn't do it.
I once thought I was cool and went for colored bolt rings on my tandem. They sheared off so forget that, I am sticking to the engineering concepts for my own safety as well as my stoker.
10-31-19, 02:46 PM
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FWIW, I just found these FSA Gossamer tandem crankset service instructions, which clearly show the chainrings on the *inboard* side.
See attached pdf.
See attached pdf.
Last edited by sapporoguy; 10-31-19 at 02:56 PM.
10-31-19, 06:38 PM
#8
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The FSA Gossamer crankset on our tandem came with both timing rings on the insides.
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11-02-19, 08:33 AM
#9
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Since no one cares about aesthetics here
, it seems that I have to take that part: Doesn't it look somewhat funny with all those precisely milled fitting areas at the outside of the spider and the chainring sitting on the inside?
With all chains right (Rohloff speedhub setup) my/our timing chain is inboards anyway. And since the rear spider is "fully equipped" with a single speed chainring for the drive chain outboards, I choose a nice (okay, somehow 80-s -looking
) bashguard for "captains spider". Problem solved. Even some protection for the front chainring during loading operations into trains and ferries included...
, it seems that I have to take that part: Doesn't it look somewhat funny with all those precisely milled fitting areas at the outside of the spider and the chainring sitting on the inside?With all chains right (Rohloff speedhub setup) my/our timing chain is inboards anyway. And since the rear spider is "fully equipped" with a single speed chainring for the drive chain outboards, I choose a nice (okay, somehow 80-s -looking
) bashguard for "captains spider". Problem solved. Even some protection for the front chainring during loading operations into trains and ferries included...
11-03-19, 09:07 PM
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,
I choose a nice (okay, somehow 80-s -looking) bashguard for "captains spider".
) bashguard for "captains spider".
11-04-19, 04:01 AM
#11
Junior Member
Et voilà! As said, stokers crank has no "aesthetical problem"
, it is fully equipped with the time chain ring and the drive chain ring. But captains crank looked a little like a “homemade solution” without that “bash guard”. So we carry about 80 extra grams not only for optical reasons, it even helps to protect the chain ring while carrying “The Lady” over steps or trunks that are in our way...
Last edited by lichtgrau; 11-04-19 at 04:05 AM.
11-05-19, 11:01 AM
#12
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Great solution! Adds to the bike's good looks.
11-05-19, 04:59 PM
#13
Clipless in Coeur d'Alene
These spider tab shims from Raceface do an ok job of providing some aesthetics and dispersion of point loading from crank bolt head lips. <-- yes, that was an intended funny.
https://www.amazon.com/dp/B00B5Y1YB4?tag=duckduckgo-exp-b-20&linkCode=osi&th=1&psc=1
The tab shims may be used either inside or outside of the spider and of course will depend on having sufficient crank nut & bolt length (for a typical 2 chainring setup). Here is a shot of the tab shims on the inside of our carbon spiders:
While we do have the timing rings on the outside of the spiders, the spiders are flipped so that the offset put the Gates CDX rings as close to the chainstays as possible while clearing the stoker's left side crank arm. Simply installing the rear timing ring on the inside of the spider did not meet that criteria.
Plus if the Gates belt was moved any further inboard it would rub the stoker's bottle cage that is mounted to the bottom tube.
The end result:
https://www.amazon.com/dp/B00B5Y1YB4?tag=duckduckgo-exp-b-20&linkCode=osi&th=1&psc=1
The tab shims may be used either inside or outside of the spider and of course will depend on having sufficient crank nut & bolt length (for a typical 2 chainring setup). Here is a shot of the tab shims on the inside of our carbon spiders:
While we do have the timing rings on the outside of the spiders, the spiders are flipped so that the offset put the Gates CDX rings as close to the chainstays as possible while clearing the stoker's left side crank arm. Simply installing the rear timing ring on the inside of the spider did not meet that criteria.
Plus if the Gates belt was moved any further inboard it would rub the stoker's bottle cage that is mounted to the bottom tube.
The end result:
Last edited by twocicle; 11-05-19 at 05:19 PM.
11-06-19, 08:46 AM
#14
Junior Member
Gosh, we love our „Rabbit Soulmate“ dearly and unconditionally, but compared to those carbon rockets it looks rather vintage...
