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Thread: Cross winds

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    Cross winds

    I am interested in input on tandem handling in heavy cross winds. I have no problem countersteering in the wind but I hate fighting handlebars that are tugging back and forth.
    I will be changing the fork from 55mm rake to 44mm rake (for other reasons). Will this help significantly? Would a theoretical fork with NO rake handle completely neutral?
    Our rims are about 31mm deep with 24 fat bladed spokes. How would it compare to a 21mm Aerospoke with 32 round spokes - like Zonatandem's front wheel. Would the side profile difference be of any significance.
    Are there other mechanical factors?
    Ed

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    sch
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    The biggest factor from the wind point of view, is not the bike but the
    riders. Tandems have twice the 'sail area' that singletons do and in
    anything other than a straight head or tail wind the increased surface
    area contributed by two riders will be much more than any minor
    contributions from changes such as you mention. Trail on the fork
    will have some effect on handling but not as much as you want.
    Spoke area will not be enough different in the sizes cited. This assumes
    a typical wind, ie less than 10-15mph normal to the bike.
    Gusts and higher winds will have effects that go up with the 3d power
    of the wind velocity IIRC.

  3. #3
    hors category TandemGeek's Avatar
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    I will be changing the fork from 55mm rake to 44mm rake (for other reasons). Will this help significantly?

    If you're trying to improve straight line stability in crosswinds the shorter rake fork will increase, not reduce, the amount of steering input needed to keep your tandem tracking in a straight line.

    Remember, on a tandem, shorter rake makes the tandem more responsive to lean angle and countersteering inputs. Santana, Trek and others use 55mm of rake to reduce the captain's task load with respect to things like stoker movements and minor changes in lean angle whereas Co-Motion, for example, has always used 50mm of rake on it's steel forks for what has been characterized as more sport / race-oriented handling and responsiveness to leaning inputs... making their tandems "feel" more lively and reminiscent of a single road bike. Co-Motion and others have taken this a few steps further on their racing tandems by spec'ing forks with 45mm or 44mm of rake.

    Would a theoretical fork with NO rake handle completely neutral?

    For reference:

    55mm rake w/73* head tube = 4.9 cm of trail (Santana / Trek w/OEM steel fork)
    53mm rake w/73* head tube = 5.1 cm of trail (Cannondale)
    50mm rake w/73* head tube = 5.4 cm of trail (Co-Motion w/OEM steel fork or Trek w/OEM carbon fork)
    44mm rake w/73* head tube = 6.0 cm of trail (Calfee or Co-Motion w/Alpha Q fork)
    0mm rake w/73* head tube = 10.6 cm of trail

    Zero rake would obviously present a wheel/frame/toe clearance issue on any bike not specifically built for it and would be of no practical use on a road tandem. So, assuming a 73* head tube angle, it's probably a moot point. If, however, someone was so inclined to design a frame around a zero rake fork they could probably find a head angle that would create the necessary amount of steering trail to make the tandem handle to suit the team's needs.

    Our rims are about 31mm deep with 24 fat bladed spokes. How would it compare to a 21mm Aerospoke with 32 round spokes - like Zonatandem's front wheel.

    As mentioned in the other thread about wheels, this may be getting to the crux of your issue if what you're trying to address is how the lower number of paired, flat-bladed spokes react to crosswinds vs. a more conventional higher-count round spoke network. Again, from the other post I offered this in response to your follow-up question which introduced "easier to handle" as a criteria as well as your point of reference, a set of paired spoke wheels:

    That depends on your definition of "easier". That notional 48 spoke wheel might have a higher side loading and be experiencing more of a push effect from a crosswind; however, it probably exhibits less buffeting or "pulsing" than a Shimano Santana Sweet 16 or Rolf Prima Vigor (and perhaps your Bontragers?) since the loading is distributed on 48 small and round spokes vs. 16, 20 or 24 flat bladed spokes that are paired together in 8, 10 or 12 places around the rim.

    The latter may be the real issue you're trying to address -- the effect of crosswinds on bladed and/or paired low-spoke count wheels -- not simply the differences between a semi-box section 22mm deep rim and a 30mm deep rim with conventional and round spokes. In that vane, then yes... I have found the Rolf's to be 'twitchier' in a crosswind than our other 30mm deep wheels with more conventional, non-paired and higher count spoke networks, e.g., 36h Deep-Vs, 36h Fusion and our 24h Topolino AX3.0-Ts (which probably have as much spoke surface area with respect to crosswind loading as a pair of 40h wheels).
    If you remove the flat bladed spokes from the equation and are only comparing a set of wheels with 36 spokes that has a 30mm deep rim vs a 22mm deep rim then there will be a difference in wind side loading. However, the degree to which the additional side loading would be detremental to handling would seem to be pretty subjective based on rider sensitivity, i.e., some riders will know if their tires are 5lbs low on air, whereas others might not know they are 20 lbs off. The best way to find out would be to simply borrow a conventional front wheel and use it on your tandem. There's nothing "tandem specific" about a front wheel unless a team's weight demands something greater than 32 or 36 spokes, e.g., 350 - 450 lbs, respectively for non-technical terrain.

    However, bear in mind, from a performance standpoint having a low-side load doesn't necessarily equate to lower overall drag. The trick is balancing an acceptable level of low drag against any negative characteristics of the side loading, e.g., a tri-spoke or very deep aero wheel is still faster in a crosswind vs. a conventional or semi-aero wheel but can become too difficult to handle. It's all about trade offs.

    Therefore, if you really aren't interested in the very slight aerodynamic advantage your current semi-aero wheels afford to you there are a lot of really good reasons to set them aside for a conventional set of wheels. Getting rid of that slight twitchiness that you seem to be experiencing in crosswinds might just be one of those benefits. Others include lower overall ownership costs, ease of repair, replaceability of parts, no obsolescence issues, etc..

    Would the side profile difference be of any significance.

    It is, but as noted there's more to consider than just the rim's depth.

    You can find data on side force and drag coefficients that compare conventionally spoked wheels to the more aerodynamic wheels at these links.

    John Cobb's aero data:
    http://www.analyticcycling.com/DiffE...sc.html#Wheels

    The side force data is near the bottom and a GL330 is a box rim.
    http://www.zipp.com/_media/pdfs/technology/rimshape.pdf

    Rolf's wind tunnel data:
    http://www.rolfprima.com/techinfo_aero_results.php


    Are there other mechanical factors?

    Just remember, when you're trying to address crosswinds on a moving bicycle you need to look at the wheel from the perspective of how it is influenced by the apparent wind, not the true wind. For the folks who have learned to master sailboats or who fly aircraft, it's a pretty straight forward thing. However, for anyone who hasn't thought about how the difference HED cycling as an excellent article and a web-based tool that lets you experiment with different riding scenarios to see how wind velocity and direction are altered by the movement of the bike: http://www.hedcycling.com/technical/yaw-calculator.php
    Last edited by TandemGeek; 11-15-08 at 09:34 AM. Reason: Added HED cycling link on apparent wind

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    Senior Member ftsoft's Avatar
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    How much wind are we talking about here? I consider it dangerous to ride my single if it's over 35mph. Our tandem IS a little more sensitive to the wind than a single, but I wouldn't consider it a factor up to 25mph or so.

    Deep dish wheels can really make a difference. I sometimes ride Velocity Deep Dish wheels and they are MUCH more sensitive to the wind (I got blown off the road on TOSRV a few years ago).

    Overall, the momentum of the tandem makes up for a lot.

    Frank

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by ftsoft View Post
    Deep dish wheels can really make a difference. I sometimes ride Velocity Deep Dish wheels and they are MUCH more sensitive to the wind (I got blown off the road on TOSRV a few years ago).
    On your single or on your tandem? What type of spokes and how many?

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    Senior Member zonatandem's Avatar
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    Velocity/direction of wind and total team weight/size will make more of a difference than spoke shape/count or rim depth.
    Having said that, don't try a disc wheel in (cross)winds; especially in front of a tandem.
    Have actually been pushed sideways (more than a foot) on our tandem on a ride in Indiana. Don't know velocity of the wind, but telephone wires were 'singing' and only a handful of people finished that century ride.
    On single bike was blown over and crashed (5 broken ribs + punctured lung) in high wind situation when I crested a steep hill and wind blew fiercely through a saddle (opening between 2 mountains). Even got knocked out but considered myself fortunate as I just missed a 50 ft. dropoff.
    Cross winds can be dangerous . . . stick with tailwinds and downhills . . . if you can!
    Pedal on RWOgether!
    Rudy and Kay/zonatandem

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    Sorry, I was talking about my single with 16/24 bladed spokes. Probably another kettle of fish on the tandem, but even though it's pretty windy here the only effect I've noticed on the tandem is a slight wobble in the rear with crosswinds. That is with velocity Dyad wheels with 40 spokes.

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    Quote Originally Posted by ftsoft View Post
    How much wind are we talking about here? I consider it dangerous to ride my single if it's over 35mph. Our tandem IS a little more sensitive to the wind than a single, but I wouldn't consider it a factor up to 25mph or so.
    (I got blown off the road on TOSRV a few years ago).
    Frank
    25mph plus gusting gets tiring. I did a long ride in 40mph winds ok on the single but we only went several miles on the tandem before turning back. We have basically one day a week to ride so I hate to have to cancel.
    Do you understand how you got blown off the road? Why couldn't you just countersteer to stay in your lane? I'm still trying to understand how this works.
    Ed

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    Quote Originally Posted by zonatandem View Post
    Have actually been pushed sideways (more than a foot) on our tandem on a ride in Indiana.
    On single bike was blown over and crashed (5 broken ribs + punctured lung) in high wind situation...
    Pedal on TWOgether!
    Rudy and Kay/zonatandem
    What happens for you to get pushed sideways? Is it one step short of getting blown over (not steering quick enough and losing balance)?

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    Remember, on a tandem, shorter rake makes the tandem more responsive to lean angle and countersteering inputs.
    YESSSSSSS, steering by balance and quick maneuvering to counter the unpredictable and unseen wind forces!

    Would a theoretical fork with NO rake handle completely neutral?

    For reference:

    55mm rake w/73* head tube = 4.9 cm of trail (Santana / Trek w/OEM steel fork)
    53mm rake w/73* head tube = 5.1 cm of trail (Cannondale)
    50mm rake w/73* head tube = 5.4 cm of trail (Co-Motion w/OEM steel fork or Trek w/OEM carbon fork)
    44mm rake w/73* head tube = 6.0 cm of trail (Calfee or Co-Motion w/Alpha Q fork)
    0mm rake w/73* head tube = 10.6 cm of trail

    Zero rake would obviously present a wheel/frame/toe clearance issue on any bike not specifically built for it and would be of no practical use on a road tandem.

    It's not practical, it's a "theoretical fork". I'm trying to understand what happens when you push something to an extreme to help me understand the wind load on the wheel. Why is the wind load on the FRONT wheel uneven enough to affect the handling in high winds? How does a straight side wind load on a loaded bike torque the handlebars and where does that pesky rake/head tube angle/trail fit in?
    I will try to get a cheap wheel to experiment with when it warms up in six months.
    Ed

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    Quote Originally Posted by justcrankn View Post
    YESSSSSSS, steering by balance and quick maneuvering to counter the unpredictable and unseen wind forces!
    It's a double-edge sword... Yes, long trail does make the tandem more responsive to YOUR body language and countersteering inputs, but it also makes it more responsive to your stoker's body language and anything else that might push the front wheel around suh as the wind, road camber, etc.

    Quote Originally Posted by justcrankn View Post
    Why is the wind load on the FRONT wheel uneven enough to affect the handling in high winds?
    It's rather straight forward... but do your due-diligence and it will all make sense.

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    Quote Originally Posted by TandemGeek View Post
    It's rather straight forward... but do your due-diligence and it will all make sense.
    So you don't know either, eh.
    Sorry, I couldn't resist.
    Ed

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by justcrankn View Post
    So you don't know either, eh.
    The power of discovery can't be under-estimated.

    To be candid, I probably have an unfair advantage in that I've also raced sailboats for about as long as I've been cycling, but almost everything you need to know to understand what's happening can be deduced from the information and linked data in this thread.

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    Senior Member ftsoft's Avatar
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    Quote Originally Posted by justcrankn View Post
    25mph plus gusting gets tiring. I did a long ride in 40mph winds ok on the single but we only went several miles on the tandem before turning back. We have basically one day a week to ride so I hate to have to cancel.
    Do you understand how you got blown off the road? Why couldn't you just countersteer to stay in your lane? I'm still trying to understand how this works.
    Ed
    The sustained winds were only around 15mph as a crosswind. I just happened to catch a big gust. I blamed the wheels because 1) I had never been blown completely off the road ever and 2) the riders around me were not affected nearly as much. I really like the wheels, but have noticed cross wind issues on other rides as well. We have only ridden about 2000 miles on the new tandem and we never rode the old tandem for very long rides, so I only have limited experience on the tandem with big winds. It's interesting that it affects you more on the tandem. I wouldn't have expected that.

    Frank

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    Quote Originally Posted by ftsoft View Post
    ...tandem with big winds. It's interesting that it affects you more on the tandem. I wouldn't have expected that.
    Frank
    Compared to my single the tandem has 1)more side wind load 2)bigger tires 3)fat spoke blades 4)more rake. I'm speculating that with more rake, the side wind-load on the front wheel becomes more lopsided. I'm also speculating that side-wind loading on the rest of the bike does not affect front wheel stability much, but I don't have any tests to back that up.

    Thanks for the responses.
    Ed

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    Senior Member zonatandem's Avatar
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    Getting pushed sideways by a sudden high gust on tandem or single has happened only a few times to us.
    In our mountainous terrain winds can change quickly and drastically.
    To get the bike literally blown off the road, into the dirt and missing 50 dropoff wasn't any fun and looking back and analyzing it, it may not have happened if I had 60+ lbs of rocks in my jersey pockets. That's the disadvantage of being a lightweight (135 lbs).
    Were in a paceline one time with very high crosswinds and all single bikes were actually leaning . . . except for big Bill who weighed 325lbs.
    Your conditions/experiences may be different . . .

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    I know where you are coming from Crankin as "fighting" the steering on a tandem can be really tiring if you have to do it for too long ... my 2c

    We have a Trek T2000 05 which started with the standard cromalloy 55mm rake fork and some custom built 36 spoke wheels (Mavic cyclocross 700c rims, standard stainless double butted round spokes)

    Rode that for 9 months in various weather conditions. Recently upgraded to the newer model Trek T2000 Carbon Tandem fork (50mm rake) and new Bontrager Racelight Tandem wheels (24 spoke bladed, which should have come with the bike) - note got these about 2 months apart, wheels first

    1. Handling is sooooo much better (especially cornering at speed), but yes do notice my stoker a bit more when she makes "comfort adjustments" - this is due to the reduced rake. There are a number of regular rides where I have noticed the lines I take around some corners feel much "safer" than with the older fork where I might sometimes end up on or over the center line.

    2. Front wheel is much better in most wind conditions. (even though the Bontragers have a deeper rim, the lower spoke count seems to make a difference in the crosswinds).

    I don't think the tandem is much different to a Single when in comes to handling crosswind gusts - low profile/low spoke count wheels will always be better.

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