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can someone explain this type of fork?

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can someone explain this type of fork?

Old 10-25-11, 04:56 PM
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chanamagoo
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can someone explain this type of fork?

It was taking me a little bit longer than usual to lock my bike up in a crowded bike rack and got distracted by this bike next to mine...I'm fairly new to biking, so I might be missing something obvious, but can anyone explain this type of fork and what the benefits are?

(For some reason, the image shows up in landscape view instead of profile...you can see if better i THINK if you click on the image, but imagine that it is rotated 90 degrees clockwise...)

photo.jpg
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Old 10-25-11, 05:02 PM
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Cannondale. Single Side fork called a Lefty.... Single sprring. They really took off. But you don't see them often.
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Old 10-25-11, 05:03 PM
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I have never seen one in the wild, but I have seen them online, I think that it is a Cannondale "lefty". I am not sure what the reasoning behind it is. Personally, not for me.
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Old 10-25-11, 06:08 PM
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The theory is it reduces the amount of weight in the front fork area. I'd have to get an explanation from someone at Cannondale before I was convinced that it was a superior design.
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Old 10-25-11, 06:23 PM
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First time I saw one was in the movie 'The Flying Scotsman'. Would venture that it's pretty much limited to track cycling. The structural stress a given commuter bike experiences over time would make me hesitant to use it for any length of time. Looks cool, though.
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Old 10-25-11, 06:42 PM
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I don't know what the advantage of their road/hybrid version is (the bike pictured is their bad boy "urban" model), but the mtn version is way lighter than a 'normal' setup. My friend had one for a while and loved it. We have a couple of the Bad Boy bikes here at the office that Cannondale sent us to customize. It seems fine, but again, I don't see a real advantage on a street bike.

Last edited by bhop; 10-25-11 at 06:46 PM.
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Old 10-25-11, 06:50 PM
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Actually very much a part of Cannondales MTB line-up. This to me is where it makes most sense, and yet seems most suspect. Less sprung weight means a more responsive front suspension, but it seems like it would put a lot of stress on one fork stanchion.


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Old 10-25-11, 07:36 PM
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i saw this at my LBS, and i wasn't sure what to think.

my initial reaction was aversion.

can you do this with the rear forks as well?
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Old 10-25-11, 07:43 PM
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Motorcycles do this all the time with single-sided swingarms. I figure if they can figure out how to make that work they can make it work on a bicycle. I wouldn't buy one, but I wouldn't worry about the stresses involved if I were to ever ride one.
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Old 10-25-11, 08:16 PM
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Whether motorbikes or pedal bikes, there is a certain "gimmicky" aspect to it. Certainly it functions, but for the same stiffness & strength in the various axes of stress, a single arm design must be more massive when the same material technology is employed. When you throw suspension into the equation, and de-emphasize the importance of stiffness, I can see where a compromise can be reached, with less stiffness, and similar mass.
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Old 10-25-11, 09:14 PM
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It would be easier to change a front flat!
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Old 10-25-11, 09:20 PM
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British Engineer Mike Burrows makes some fast recumbents with single side support wheels.

An out of the box thinker, on some designs the wheels are in 2 parallel tracks ,
rather than following on the same track.

tadpole trikes of course have 2 front wheels single side.. as to all cars and trucks..
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Old 10-25-11, 11:58 PM
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Do they make lefty fenders?
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Old 10-26-11, 12:13 AM
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One-sided axle support. It gets around.



(or insert photo of any automobile)

They're a proven design, and various companies make Lefty hubs to go with these.
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Old 10-26-11, 03:01 AM
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The theory is that stiffness is proportional to tube diameter (squared). If you take the metal from a traditional fork and make one single fork leg, it will be fatter and much stiffer. You dont need that much stiffness so you can remove some of the material and still have a fork strong enough and stiff enough.
The advantages are less weight, better aerodynamics, easier tyre removal, less mud accumulation.
You can do the same at the rear wheel eg the folding Giant Halfway. This can make for a very slim folded package if done well.


Mono-stay axles need to be wider diameter for more stiffness but as shown above, its not a problem.
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Old 10-26-11, 06:03 AM
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Fugly
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Old 10-26-11, 08:20 AM
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I met a guy on a (road) shop ride on a MTB with one of these. They're interesting looking I think.
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Old 10-26-11, 08:31 AM
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Originally Posted by DogBoy View Post
Motorcycles do this all the time with single-sided swingarms. I figure if they can figure out how to make that work they can make it work on a bicycle. I wouldn't buy one, but I wouldn't worry about the stresses involved if I were to ever ride one.
Aircraft have been using single-sided swingarms for decades.



If you can slam a fully loaded 74,350lb F-14 Tomcat (at speed) into the deck of an aircraft carrier repeatedly, and still use it. I'm fairly certain that engineers can make a swingarm handle the roughest of terrain you will ever find on a mountain bike.

[edit] I didn't read the all of the comments before posting mine... didn't see the one of the A-10 (but then they don't land on aircraft carriers do they?) [/edit]

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Old 10-26-11, 09:12 AM
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It's for looks and to sell bikes. The main benefit is revenue to Cdale.

Oh, and I guess you could change a tube or tier w/o taking the rim off the bike.

Also, it's very unlikely that wind resistance can be minimized with this type of design. The inherent requirement that the fork provide lateral stiffness means that a single fork will need significant lateral width. As a result it they turn out to be round tubes, which are among the least efficient shapes for wind resistance. In the OP's pic where it's a road bike where you would otherwise have two aerodynamic stanchions a single cylindrical one is a poor choice.

Last edited by jbtute; 10-26-11 at 09:25 AM.
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Old 10-26-11, 10:51 AM
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The other time to be thinking about the reliability of this design is when you're standing up, hammering hard on your spindly pedals, one at a time, and then realize you've got two wheels supporting the same action. :-)
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Old 10-26-11, 11:38 AM
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I know that in motorcycling, one of the claimed advantages to single sided designs (swingarm or fork) was more consistent suspension action and, in the case of forks, supposedly less stiction. With two dampers absorbing impact in parallel, there could be an issue if one is softer or stiffer than the other. With only one, by definition, it removes that as a potential issue.

Likewise, the stiction issue was caused, if memory serves, when turning, as the forces on the two sides of the fork were different, and could cause uneven or improper suspension action. I'll be honest: I rode with a conventional fork (two dampers) and never had a problem. But I didn't race -- I commuted -- so perhaps I lacked the 'at the limit' aspect where such things matter.

I'm a fan of innovation for innovation's sake, to the extent that the alternative is often stagnation; you can choose to buy it or not, or wait until it becomes the mainstream.

I have no idea if this is a real problem for bicycles which weigh much less, go much slower, and consequently experience far less stress.
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Old 10-26-11, 01:00 PM
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Cannondale's Lefty fork has been around for a while. I've seen them for years. A friend of mine has a 29er mountain bike set up that way. It rides like any other bike.

Flevobike makes a recumbent with single swingarm rear. I'm not sure about the fork.

As mentioned before, the ability to change a tire without removing the wheel is nice.

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Old 10-26-11, 01:04 PM
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I've heard it gives slightly better clearance when doing technical things among rocks and roots. It sort of makes sense. I still won't buy one.
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Old 10-26-11, 01:10 PM
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A-10's don't land on carriers because they can't catch them...
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Old 10-26-11, 01:21 PM
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Once while passing a mountainbiker riding a c-dale, I called out," on your lefty," kinda funny, he didn't think so.
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