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  1. #1
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    Perfectly round timing rings?

    Do they exist?
    I've read that all timing chains have tight and loose sections but the T/A rings that came on my Santana seem really extreme in their variance.
    Read Mr Browns section about tapping them round. I'll do that as a last resort but first would like to find some that are maybe better quality which I hope means rounder as well as better finish.
    What do you use? Brand, size etc.?
    Thanks.

  2. #2
    hors category TandemGeek's Avatar
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    The only 'perfectly concentric' timing rings that I'm aware of are the ones made by daVinci. If I have time later on today I'll take a photo of one from the seldom seen backside so you can see the interface. In sort, you have a crank that's CNC's from an aluminum billet with a square spline and a chain ring CNC'd from aluminum flat stock and when you put them together there is zero slop.

    Of course, the down side is that daVinci's cranks are only available with a square taper spline interface. Being a lightweight team, that's never been an issue except when we foolishly tried to use a rear bottom bracket with a ti spindle: now that sucker would flex. No perceived flex issues with Shimano UN72 or other better quality steel BB spindles.
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    Last edited by TandemGeek; 11-23-07 at 09:16 AM.

  3. #3
    shut up and ride
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    our burley duet tandem has the basic shimano tandem cranks but the 40 tooth timing rings are much nicer than than the other chainrings. they look like dura ace chainrings and are very round, the chain tension is very consistent

  4. #4
    rebmeM roineS JanMM's Avatar
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    It's not that timing chainrings aren't perfectly round. It's that it can be difficult to mount them perfectly centered on the crankarm. Looks like the daVinci system takes care of that.
    If both rings aren't centered/concentric, then you end up with loose and tight chain sections.
    Last edited by JanMM; 11-23-07 at 01:06 PM.

  5. #5
    Senior Member Retro Grouch's Avatar
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    Quote Originally Posted by dvs cycles View Post
    I've read that all timing chains have tight and loose sections but the T/A rings that came on my Santana seem really extreme in their variance.
    Read Mr Browns section about tapping them round. I'll do that as a last resort
    I'd be willing to bet that the runout you're experiencing is due more to the chainrings being mounted non-concentrically on the crank arm spiders than to manufacturing varience in the chainring roundness.

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by Retro Grouch View Post
    I'd be willing to bet that the runout you're experiencing is due more to the chainrings being mounted non-concentrically on the crank arm spiders than to manufacturing varience in the chainring roundness.
    I'd tend to agree, particularly since you have Specialites TA rings and shimano cranks which both tend to be pretty-well made. I've seen a few sets of low-end cranks from Sugino and others that aren't as well made as they could be and if they weren't used for direct drive applications like a tandem sync chain or on a fixed-gear/single speed drive most folks would never notice.

    The only other thing I've seen that put a set of timing rings out of kilter was a bent bottom bracket spindle, but that was on a square taper and a low-quality one at that.

  7. #7
    Senior Member swc7916's Avatar
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    Quote Originally Posted by TandemGeek View Post
    Of course, the down side is that daVinci's cranks are only available with a square taper spline interface. Being a lightweight team, that's never been an issue except when we foolishly tried to use a rear bottom bracket with a ti spindle: now that sucker would flex. No perceived flex issues with Shimano UN72 or other better quality steel BB spindles.
    We had our new tandem equipped with a DaVinci crankset because it was the only way we could get 170mm captain cranks paired with 165mm stoker cranks. They are a beautiful crankset and those timing rings are really stout.

    On the issue of square taper cranksets/spindles: What are the disadvantages of them? I had ridden square tapers for years and never had a problem with them. They were the de-facto standard for decades and now they seem to be hard to find. You mention flex here, but is that because of the square taper or because of the ti spindle? Agreed, they are better than the old cottered cranksets, but how are the new splined ones better? Are they stiffer? Are they lighter? Were any compromises made to move the bearings outboard of the bottom bracket?

    I hope you don't mind all of these questions, but this whole issue of the new crankset/bottom bracket design has me confused and wondering: Is this for real, or is it just a fashion fad?

  8. #8
    hors category TandemGeek's Avatar
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    The bicycle industry has been fiddling around with bottom brackets as long as there have been bottom brackets, e.g., cotter pins, one-piece, square tapers (ISO & JIS), Octalink V1, ISIS, Octalink VII, ISIS II, Mega Exo, Gigapipe, etc... What a mess.

    Personally, and like you, all 10 bikes in our stable -- to include all three tandems with their daVinci cranks -- have either a JIS or ISO square taper bottom bracket: simple, durable, and at one time easy to find and inexpensive even for the better quality brands/models. Well, if there's one thing that the bicycle industry seems to have a disdain for it's the status quo. So, all that said, to your questions:

    1. What are the disadvantages of (square taper)?

    It requires a certain amount of knowledge to properly spec. one for a set of cranks (e.g., to JIS for most these days & ISO for Campy and some other cranks) and to service, to include understanding torque specifications and the like. In practice, square tapers are often times over-torqued by shade tree bike mechanics and many so-called "bike techs" who actually got paid to ruin cranks. Removing cranks with square tapers is also difficult because it requires you to either: a) own and know how to use a crank puller, or b) be resourceful enough to discover those wonderful little things called self-extracting crank bolts. Finally, there were way too many affordable, long-lasting square taper bottom brackets on the market in a wide variety of sizes which really put a cramp on bottom bracket product line margins for those making them as well as crank manufacturers. Remember, the bicycle industry does not like the status quo: it's bad for business.

    2. Are (Octalink, ISIS, etc) stiffer?

    Actually, I'm told that they are and I've seen data that suggests this is true. Of course, I'm not sure just how big a deal this is for the average cyclist or tandem team vs. Magnus Backstedt or Alessandro Pettachi. Of course, stiffer is relative in that the added stiffness traded off durability with the first generations of Octalink / ISIS (and even the second generation compared to the better square tapers), and they're still getting the kinks out of some of the outboard bearing designs.

    3. Are they lighter?

    Actually, no... They all appear to be in the same ball park when you have similar materials and price points. There are high-end and expensive BBs of all types that are svelte and low-end models that are porcine. The latest and most highly integrated models are hard to compare since the manufacturer have succeeded in making you buy their proprietary bottom brackets to go along with their proprietary cranks because the spindle is no longer part of the bottom bracket (hence, the weight of a Mega Exo BB is clearly lower than square taper or splined which do include the spindle) and is, instead, part of the crank. Anyway, if you're bored you can find a pretty comprehensive list of the various pre-MegaExo type bottom brackets and their weights here at the Weight Weenies Website.

    4. Were any compromises made to move the bearings outboard of the bottom bracket?

    IMHO, yes... The outboard bearing designs are perhaps the best example of how the bicycle industry's dislike for the status quo can sometimes get out of hand when an agreed to set of standards isn't put in place before companies go off and start spending big $$ on R&D and new product development. The very need for the outboard bearing is, in and of itself, a bit suspicious. At least one person who watches the industry even more closely than I do has suggested that the outboard bottom bracket designs are more about marketing and building moats around proprietary product features than they were about truly fixing the mess that was created during the Octalink & ISIS wars. The biggest problem -- noted by my friend -- is that these new Octalink and ISIS bottom brackets didn't look any different to the average consumer who never pulled apart their crankset where they could see and appreciate the changes.



    So, from a marketing standpoint, it's kind hard to grab consumer interest in your product's unique and distinguishing features -- never mind charging a premium -- when they are essentially invisible and indistinguishable from one another. The outboard bottom bracket designs changed all of that because they were radical-new designs that broke apart the status quo of the bottom bracket design. Of course, we now have four competing proprietary outboard bearing designs: like life wasn't confusing enough when you first discovered that English & Italian bottom brackets were threaded differently.

    5. Is this for real, or is it just a fashion fad?

    Octalink is for real. ISIS is on the verge of extinction, and there's no way that the overall bicycle industry can support having more than one outboard bearing design: three of the major designs aren't going to make it... who will be left holding. Time will tell.

    Bottom Line: With few exceptions, square tapers are more than adequate for the vast majority of cyclists. They have few REAL drawbacks for all but the strongest cyclists who have a compelling reason to eliminate all forms of drivetrain deflection, e.g., professional racers. Splined interfaces are a bit more idiot proof and help to preclude so-called "bike shop techs" or do-it-yourselfers from deforming square taper cranks by over-torquing during installation which may or may not be a good thing, i.e., it allows their lack of skill to go unnoticed a little bit longer similar to how threadless headsets no longer require as much "touch" to properly adjust compared to the older quill models. Good and skilled mechanics are a dying breed

    Long-live the square taper. Hey, I own a torque wrench and I'm not afraid to use it.
    Last edited by TandemGeek; 11-25-07 at 08:17 AM.

  9. #9
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    For me the biggest advantages of external bearings are more support for the spindle and a stiffer feel, at least that is my observation with my D/A 7800 on my single. Also once you have your crank with pipe spindle, all you need to replace are the bearings when worn. Your not even limited to Shimano for Shimano cranks or FSA for FSA. Even Ceramics for the hard core techies. I think that they are here to stay or Campy wouldn't have changed. They held on to Square taper way too long. Again, my opinion and I'm sure others feel different.

  10. #10
    hors category TandemGeek's Avatar
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    Quote Originally Posted by dvs cycles View Post
    . Also once you have your crank with pipe spindle, all you need to replace are the bearings when worn. Your not even limited to Shimano for Shimano cranks or FSA for FSA. Even Ceramics for the hard core techies.
    Don't disagree on the bearing replacements: however, the question becomes the economics. How often and at what cost will the bearings require replacement? Early on, and before the ceramic bearings were introduced, the service life of the bearings in the various outboard bearing designs was not all that impressive. I'm not sure average consumers have had these things in their possession long enough to establish the norms for ceramic bearing life but one thing is clear: ceramic bearings are a heck of lot more expensive than the $25 Shimano UN72 bottom brackets that they replaced and the UN72s would last for well-over 10k miles with minimal if any maintenance.

    Personally, I think Campy has once again done a good job of sitting back and bringing out it's Hirth joint design a few design cycles after everyone else and may have one of the best design. Shimano's design and quality also appears to be fairly solid, and the other designs from FSA, TruVativ, and RaceFace have been improved. But, therein lies the problem: everyone's locked into a different, non-interchangeable design and changing horses requires a complete change out of your cranks and BB: not just one or the other.

    However, what's troubling is that the bottom bracket design process hasn't stopped and there are still new designs in the pipeline that are looking to either enlarge, widen, or enlarge and widen the BB shell to accommodate more robust bearing and spindle designs.

    So, while it is true that current crank buyers of the various outboard bearing designs will likely have 3rd party sources for bearings in the future, they key components may have a finite life span from the OEM if and when either a new common standard is finally developed (Trek, Cannondale, and other large volume producers are pushing for this).

    Bottom Line: There's good enough, better and the best. When is good enough good enough and what are the implicit costs of better and the best long term? Time will tell which designs stand the test of time.

    Anyone have an U-brakes, self-energizing brakes, bio-pace rings, SunTour Microdrive components, Shimano airlines parts, or Mavic Zap or Mektronic systems?

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    Quote Originally Posted by swc7916 View Post
    We had our new tandem equipped with a DaVinci crankset because it was the only way we could get 170mm captain cranks paired with 165mm stoker cranks.
    Just as an FYI -- Thorn makes a huge variety of tandem crank lengths:

    http://www.sjscycles.co.uk/category-...insets-660.htm

    Here are stoker cranks from 140mm to 175mm, in 5mm steps:

    http://www.sjscycles.co.uk/product-T...Drive-1671.htm

    How about captain cranks from 150mm to 175mm?

    http://www.sjscycles.co.uk/product-T...Drive-1670.htm

    So many choices! And when I ordered our awesome 160mm square taper stoker cranks with ramped & pinned steel 74/110 28/38/48 chainrings, shipping to the US was super-quick. I'd order from them again without a second thought.

    Beware, though -- SJS Cycles sells tons of stuff that's decidedly uncool in the US. Fenders, racks, lights... a high-performance audax single weighing in at over 24lbs at a cost of US$1,800? Won't see that at PerformanceBikeMart, EVER!

    -Greg

  12. #12
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by dvs cycles View Post
    Do they exist?
    I've read that all timing chains have tight and loose sections but the T/A rings that came on my Santana seem really extreme in their variance.
    Read Mr Browns section about tapping them round. I'll do that as a last resort but first would like to find some that are maybe better quality which I hope means rounder as well as better finish.
    What do you use? Brand, size etc.?
    Thanks.
    Last year I fitted Middleburn rings and these are about the best I have ever come across. Straight out of the box- Fitted to the cranks and no discernable movement on the chain.
    How long was I in the army? Five foot seven.


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    Time for a change. stapfam's Avatar
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    Quote Originally Posted by gregm View Post
    Just as an FYI -- Thorn makes a huge variety of tandem crank lengths:



    Beware, though -- SJS Cycles sells tons of stuff that's decidedly uncool in the US. Fenders, racks, lights... a high-performance audax single weighing in at over 24lbs at a cost of US$1,800? Won't see that at PerformanceBikeMart, EVER!

    -Greg
    SJS are probably the best Tandem stockists for parts in the UK. Not cheap and they do carry a lot of old obsolete stock. so if you want a part for an old UK origin bike- give thenm a try. Have to admit that I do find that my LBS- although they do not carry Tandem parts- Can get me a better product at a cheaper price- Eventually.
    How long was I in the army? Five foot seven.


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    Quote Originally Posted by stapfam View Post
    Last year I fitted Middleburn rings and these are about the best I have ever come across. Straight out of the box- Fitted to the cranks and no discernable movement on the chain.
    Never heard of them before. Is that a UK local company?

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    "Anyone have an U-brakes, self-energizing brakes, bio-pace rings, SunTour Microdrive components, Shimano airlines parts, or Mavic Zap or Mektronic systems? "

    Ah yes the next great battle of Electric shifting is almost here.
    Both Campy and Shimano have proto-types out amongst the top teams as we speak.
    Campy looked closer in final product from the pictures I've seen.
    While I don't think on my single it would be anything to jump on, the tandem might be.

  16. #16
    hors category TandemGeek's Avatar
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    Quote Originally Posted by dvs cycles View Post
    Never heard of them before. Is that a UK local company?
    Yes, they are out of the UK: http://www.middleburn.co.uk/

    Alex Nutt (MTBTandems.com) is their Southeast US Distributor and they are VERY nice cranks as I've had the opportunity to fondle most of Alex's inventory. They're just a schooch heavier than the daVinci cranks and are only offered in square taper and ISIS.

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    The only 5 hole chainrings they seem to have are Downhillers and I don't see any bolt center space specs.

  18. #18
    Captain - 2nd in Command djsincla's Avatar
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    Of the three Santana I have owned I have not had an issue with Timing rings - I personally interested to know what year the bike is, how many miles are on your rings, and what brand are they?

    I'm currently using FSA on an 2007 S&S Ti-700.

  19. #19
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    There is no such thing as "perfectly round" or "zero runout". Only closer approximations.

  20. #20
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    Quote Originally Posted by djsincla View Post
    Of the three Santana I have owned I have not had an issue with Timing rings - I personally interested to know what year the bike is, how many miles are on your rings, and what brand are they?

    I'm currently using FSA on an 2007 S&S Ti-700.
    2007 Team Scandium. Shimano aluminum cranks. T/A rings. 2100 miles so far.
    Don't care for the finish on the rings and plan on replacing them with probably Dura-Ace or FSA.
    What size are your timing rings?

  21. #21
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    Quote Originally Posted by Retro Grouch View Post
    I'd be willing to bet that the runout you're experiencing is due more to the chainrings being mounted non-concentrically on the crank arm spiders than to manufacturing varience in the chainring roundness.
    This and similar replies are spot on. Modern machining makes it trivial to make chainrings sensibly perfect. That said, if the machine shop is 10 degrees warmer one day, then the rings made that day will be a little smaller than the ones from a cold day, and they will also vary a little if the end mill (cutter) was replaced just before that ring was made, or 100 parts prior.

    Therefore steps are taken to insure that the smallest rings are just a hair larger than the largest crank spiders...which means that average ones will be a bit sloppier, and you may end up with a worst case pair with .1 mm clearance. Due to the geometry (catinary) that much eccentricity will produce noticeable chain deflection mid span.

    The procedure Sheldon describes is NOT to bend the rings round, but to shift them on the spider arms. It doesn't necessarily make them concentric though....they don't need to be concentric, as long as the eccentricity of both the captain and stoker rings is clocked to the same phase, the sync chain tension will be constant.

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