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  1. #1
    Charles Ramsey
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    one again with the McCready wheel strenght formula

    here http://www.sudibe.de/articles/wheandhub.html is the classic formula for wheel strenght by Bill McCready of santana. I read about the benifits of reduced dish in articles by Frank Berto in the 70's In 1980 I stopped in the bicycle shop run by Ron Boi in chicago who was also a custom builder. His personal bike had an 18 spoke back wheel built with a crowsfoot pattern with campagnolo hubs and a special order 130mm over locknut campagnolo axle. The wheel had no dish and a suntour ultra six freewheel with an extra gear welded to the back of the largest cog. Mr Boi was an amature racer who weighed about 175 pounds. He reported no problems with that wheel. I tell people this and am accused of being a troll. Since then I have built all of my wheels with zero dish here http://share.ovi.com/media/currentre...resident.10016 is one. For full disclosure I am a tourist not a tandemist the back wheels carried 150 to 165 pounds. One the other hand I have put 70000 miles on these wheels and my beta testers have done an additional 10000 miles. I have broken one spoke the one with the N stamped on the head and cracked one rim a syncros XLT. I do however bend a lot of solid axles. I understand basic strenght of materials and I think I know where Mr McCready is comming from with his formula. First the easy part if you have a flange that is 22mm from the center line of the wheel and you usa a 10mm wider axle so that the flange is now 27 mm from the centerline of the wheel it will make the wheel stronger by a factor of 27/22 due to the sideways pull on the rim this is not the correct formula the correct formula involves vectors and trig but it is a good approximation. If you have a hub with 22mm from one flange to the centerline and the other is 32 mm from the flange this reduces the tension on one side of the spokes by a factor of 22/32 again this is not the correct formula but it is a good approximation. A few spokes on the bottom of the wheel loosten under a load you can actually see this on a highwheeler bike. If one half of your spokes have one half tension of the other half it effectively reduces your wheel strenght by one half. Use both of these formulas together (22/27)*(22/32)=.5601 this is the calculation for Mr Boi's wheel a standard wheel was only .5601 times as strong as his wheel with the wider dropouts letting him use only half as many spokes. The formula works for me it seems to work for tandemist.

  2. #2
    hors category TandemGeek's Avatar
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  3. #3
    MB1
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    Is a "Tandemist" a pair of cyclists riding in light rain?

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    Quote Originally Posted by TandemGeek View Post

  5. #5
    Dharma Dog lhbernhardt's Avatar
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    I find McReady tends to really overbuild stuff for no appreciable reason. We know that it's possible to build 18 or 20-spoke tandem wheels, but the strength (I think, and IANAEngineer) comes from the increased strength of the high-profile rim. The critical factor in a classic Campag hub with a 130mm OLD is the length of that axle, and I am not surprised that you have broken a number of axles. You can't even use 126 OLD on most threaded hubs without breaking axles. I have respaced all the old threaded hubs I use on my fixed gear bike to 120mm, and I will still occasionally bend or break an axle, although the frequency is certainly not as high as it used to be when I just ran the 126. (I weigh 175 lbs.)

    I'm currently using the Bontrager tandem wheels with 145 spacing, threaded for a drum brake, so the rear wheel must be pretty symmetrical. It's got at least 2000 km on it with a 320lb team, and so far so good. I really don't think you need 160mm spacing on a tandem; that's classical McReady overbuilding. for no good reason other than marketing/differentiation/consumer lock-in on the non-standard rear wheels.

    Luis

  6. #6
    pan y agua merlinextraligh's Avatar
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    Quote Originally Posted by lhbernhardt View Post
    I find McReady tends to really overbuild stuff for no appreciable reason....

    I really don't think you need 160mm spacing on a tandem; that's classical McReady overbuilding. for no good reason other than marketing/differentiation/consumer lock-in on the non-standard rear wheels.

    Luis
    I think you hit on the real reason in the end of your post
    You could fall off a cliff and die.
    You could get lost and die.
    You could hit a tree and die.
    OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.

  7. #7
    hors category TandemGeek's Avatar
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    Quote Originally Posted by lhbernhardt View Post
    II find McReady tends to really overbuild stuff for no appreciable reason. I'm currently using the Bontrager tandem wheels with 145 spacing,
    Who's this McReady guy?

    Anyway, Bill McCready's rationale for 160mm is what it is and has been debated to death.

    As far as overkill goes, have you checked the weight of your Bontragers? 2,245 grams, last time I checked.

    Santana's current Sweet 16's: 2,057 grams and Rolfs for 160mm rear spacing at 1,768 grams.

    So, are the Bontrager's that you're using over built for no appreciable reason?

  8. #8
    Charles Ramsey
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    I met Bontrager at a bicycle show in portland he is a very smart man however he tends to build things too light. The last two broken flanges I have seen have been on Bontrager reduced spoke wheels. Flange breaks on wheels with crossed spokes always break in pairs so there is a good chance your wheel will lock up when the tire hits the chainstay. The other broken flanges I have seen were a campagnolo record rear a specialized sealed bearing front and an XT front that was radially spoked it was broken at three spoke holes. Here http://felixwong.com/gallery2/images...e_parts-13.JPG is a third.

    I'm currently using the Bontrager tandem wheels with 145 spacing, threaded for a drum brake, so the rear wheel must be pretty symmetrical. It's got at least 2000 km on it with a 320lb team, and so far so good. I really don't think you need 160mm spacing on a tandem; that's classical McReady overbuilding. for no good reason other than marketing/differentiation/consumer lock-in on the non-standard rear wheels.

    Luis[/QUOTE]

  9. #9
    Dharma Dog lhbernhardt's Avatar
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    Yeah, you are right, sorry about the spelling, I'm usually more careful!

    I've never been concerned with the weight of the Bontragers, more with the price at which I was able to get them, which was appreciably less than Shimanos or Rolfs. The 200 to 500 gram difference (much of it in the few additional spokes, I imagine) can be made up with one small waterbottle filled from one-third to nearly full (yes, it's additional rotating weight, but who cares? I'm not racing the tandem.

    The point is that even if the Bontragers were overbuilt, they are still compatible with a standard rear tandem dropout. I don't need to stretch out the dropouts to 160mm, just like I don't need to find a 1 1/4" headset for the bike. And the overbuilding appears to be for the right reason - to reduce the chance of failure with a 320-lb team aboard. And I don't need a 160mm OLD wheel for that.

    Luis

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    Custom (or hand built) wheels with White Industries hubs, CX-Ray spokes and 32H Kinlin 27 or 30mm rims beats all of those on cost, weight, durability and on the road repairability. May sacrifice just a tad on the aerodynamics vs a low spoke count wheel. Its funny that they call wheels built with standard components "custom". Its really that they are the standard wheels and the name brand low spoke count wheels are the custom wheels.

  11. #11
    hors category TandemGeek's Avatar
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    Long live standard / conventional / custom wheels.

    Racing wheels are, well, racing wheels. If you ain't racing you have to ask yourself... why I am using these?

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    Even if you are racing does the tiny amount of difference matter?
    I never did like bicycle racing, one winner and everybody losers. I never won a race.
    Thats why I always enjoyed competing in running events, although there was a winner you are also competing aginst the clock and your last best time and actually I did win or place in a few races.

  13. #13
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    Quote Originally Posted by TandemGeek View Post
    Long live standard / conventional / custom wheels.

    Racing wheels are, well, racing wheels. If you ain't racing you have to ask yourself... why I am using these?
    I spent an afternoon with this guy last week, as he tweaked and fixed the wheels for our mixed (different front/back) rim-first-purchased used tandem. It was a wonderful experience.

    http://www.youngwheels.com/

    I'm convinced, that for our tandem;
    I'll probably never own a set of aero wheels.
    I'll never own a set of 16 spoke wheels.
    I'll never own a set of goofball spoked wheels.
    I'll have a drag brake as long as I have rim brakes on the bike.

    I will let him build me a set of 40 spoke Aeroheat 26" rims on my 110/145mm Shimano hubs in the near future.
    Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman

  14. #14
    Senior Member Homeyba's Avatar
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    Quote Originally Posted by jnbrown View Post
    Even if you are racing does the tiny amount of difference matter?
    I never did like bicycle racing, one winner and everybody losers. I never won a race.
    Thats why I always enjoyed competing in running events, although there was a winner you are also competing aginst the clock and your last best time and actually I did win or place in a few races.
    Racing is racing and seconds matter. It doesn't matter if you are on a bike, running, on a motorcycle or whatever! Why would you race if you didn't enjoy the competition and beating your opponent? Even if you and your opponent are racing for tenth place those seconds can really matter.
    It doesn't get harder, you just go slower.

  15. #15
    hors category TandemGeek's Avatar
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    Quote Originally Posted by lhbernhardt View Post
    Yeah, you are right, sorry about the spelling, I'm usually more careful!
    No worries. Sometimes folks simply don't know how to spell his name while others repeat misspellings so I tend to set it straight when I see the error. I do so because, despite our many differences of opinion, I still consider Bill to be a friend and someone whom I have immense respect for in that he has lived his dreams and done more for tandem cycling in the US than anyone else I know. Again, we differ on some things but, having spent a lot of time hashing out the rationale, I can appreciate his design choices and preferences. As for his marketing approach, I don't like it but, then again, I'm not his target audience either: it's marketing (period). However, give Bill credit for not second guessing or waffling: even where a decision or design may have been bad he simply sticks to message, makes what he believes to be improvements, and moves forward: he has sold a lot of tandems using this approach.

    Quote Originally Posted by lhbernhardt View Post
    I've never been concerned with the weight of the Bontragers, more with the price at which I was able to get them, which was appreciably less than Shimanos or Rolfs. The 200 to 500 gram difference (much of it in the few additional spokes, I imagine) can be made up with one small waterbottle filled from one-third to nearly full (yes, it's additional rotating weight, but who cares? I'm not racing the tandem.
    I'm not exactly sure what the back story is on the Bontrager tandem wheels, but the $850 MSRP wheels somehow ended up being blown out by someone at $500 or $550 a pair and that destroyed their resale value in the second-hand market: a boon for wheel shoppers looking for deal on wheels. The additional .5 lb of weight is somewhat negligible when you consider that some of the OEM 40h and 48h standard tandem wheels sold on base model tandems are closer to 2,700 grams... a full lb heavier than even the Bontragers. And, after all, Bontrager's RaceLite (there's that race word again) Tandem wheel was the first mass-marketed low-spoke count wheel to actually hit the streets. Santana announced it's Sweet 16s well before the Bontragers, but it took a long time to bring the wheels to the market and in the interim the Bontragers just showed up on the T2000 without any fanfare. Moreover, the first generation of Sweet 16's were also coincidentally around 2,200 grams; it was a few years later that they went to a lighter rim. So, yes... at the blow-out pricing they were being offered at the Bontragers were perhaps too good to pass up. However, I'm pretty sure Bontrager discontinued the tandem wheels so I'm not sure how deep the spare parts inventory is that owners can draw against IF they damage one of those wheels. That is, of course, one of the problems with integrated wheelsets: you must go back to the manufacturer for spare parts.

    Quote Originally Posted by lhbernhardt View Post
    And I don't need a 160mm OLD wheel for that.
    Turns out, most average teams don't either. However, back in 1992 when 130mm - 140mm was still pretty much the 'standard' and spoke breakage on tandems was still very common AND when 7 speed had given way to 8 speed and 9 speed was expected to be just around the corner, a wider rear axle was seen as necessary for tandems. 145mm, 150mm and 160mm were all put on the table and while many took the incremental, evolutionary step and adopted 145mm, Santana / McCready looked out long term in anticipation of 10, 11 and perhaps even 12 speed decided to go with his 'belt and suspenders' philosophy. That approach led to a 160mm wide hub as a hedge against a future need for something wider than 145mm that also gave him the zero-dishing and wide bracing angles that he saw as key to having a very robust rear wheel on a tandem. Remember, as an OEM selling to the masses, Santana wanted a rear wheel that could handle not just the heavier 400 - 450lb teams, but the 500 - 700lb teams handled by their triplets quads and quints, a segment of the market that they truly owned. This same belt and suspenders approach is what drives all kinds of more robust design features that you see on Santana's tandems: extra large chainstays, extra large headset, extra robust forks and very robust hubs, many of which Santana had a hand in developing. Now, the Achilles heel of the 160mm rear spaced wheels was the same that all wheels suffer from: quality escapes on spoke tension so, in reality, while 160mm rear wheels had fewer broken spokes than the previous 140mm wheels, that was also true of the 145mm wheels. Moreover, a poorly tensioned or dinged 160mm rear wheel would break spokes with the same frequency as a 145mm rear wheel that was also not evenly tensioned or dinged. I want to say that I must have replaced a dozen broken spokes on mid-90's Santana tandems at a time when Wheelsmith was building all of Santana's wheels... so much for theory. Instead, at the end of the day it all comes down to the quality of the build. And, the fewer spokes you use the more critical that build quality becomes.

    So, no... you nor I really 'need' all of that extra robustness that is inherent in every Santana, but then again... for the average tandem buyer all of that 'belt and suspenders' stuff is fairly invisible and simply makes a Santana tandem what it is: a very comfortable, easy to ride and durable machine. The same holds true for most wheels which, at least for a tandem that's not being used in a true competitive event, should be over-built to provide added safety margin needed to provide thousands of miles of trouble-free service AND that will get a team home even when they've had a bad day on the road and dinged the rim. In regard to the latter, it's a darn shame when you have a wheel that may or may not be repairable only because the parts are so unique that you become dependent on a sole-supplier for those parts.
    Last edited by TandemGeek; 10-24-09 at 06:40 AM.

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