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Looks like they save some weight, but how do they have a better strength/weight ratio than a traditional two legged fork?

enter image description here

With the single-legged fork the fork and axle must resist huge bending all the time, producing even more of a problem than with the 2-legged fork under uneven compression.

So how is this fork constructed and what advantages and disadvantages does this bring?

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    Add "marketing" to both the pros and cons lists. So it stands out in the shop / catalog / photos, but its also attractive to the light-fingered. I'm curious why the rear triangle hasn't been offered in some single-sided format, like some sport motorbikes. – Criggie Feb 3 '16 at 22:46
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    My guess for the lack of single-sided rear triangles is that there isn't room for both cassette and disk brake on one side. Also, the chain is oily and I wouldn't have it near the disk. – ojs Apr 4 '16 at 15:59
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    @Criggie Yes, you can turn further right, but you don't usually turn past 90deg because that switches turn sides. – Jerryno Apr 26 '16 at 6:34
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    Shame Cannondale don't make a righty, for countries that ride on the left side of the road. – Criggie May 28 '16 at 21:31
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    Cannondale have done a single sided rear, which did come with a "righty" fork. It was just a one-off special though. velovision.com/ftp-admin/VVArchive/www.velovisionmag.co.uk/… Other single sided rears have been done: road.cc/content/tech-news/… The only production single sided rears I know of are various Mike Burrows designs though. – armb Nov 24 '16 at 16:06
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The single-legged fork must truly withstand heavier bending forces than conventional forks, simply due to physics and asymmetricity. But because of its different construction, the fork is actually stiffer than most 2-legged.

Pros

  • The top is attached like a dual crown downhill fork, which is much stiffer than a single-crown.

  • The wheel axle is one-piece with the bottom part, which is stiffer than a quick-release axle (which is not solid at all) and on same level as a 15 thru-axle or 20 thru-axle. This design is used also on cars where the wheel doesn't have support from the other side.

  • The biggest difference is inside. While normal forks have round tubes that slide on oil film, the Lefty uses needle bearings on a square profile (same as the front leg of Boeing airliners.):

    lefty fork, pulled out to show bearings

  • Such solution works with almost same friction under heavy side-loads, whereas sliding tubes, when side-loaded (uneven compression of legs), do get friction losses (rolling resistance wins).

  • Having conventional fork with one leg wouldn't work, such a fork would get stuck. Having bearing-fitted 2-legged fork is an overkill and unnecessary weight.

  • The heaviest Lefty is still lighter than lightest carbon 2-legged.

  • You can replace the tire without removing the wheel.

Cons

  • If you need to remove the front wheel, you need to remove the brake caliper also.

  • The axle works only with Cannondale hubs.

  • The front of bike will look unbalanced until you get used to it.

  • Pre-2013 models of Lefty are not sealed, having the bearings track just under a rubber sleeve. This required almost constant maintenance. Post-2013 models have a rubber-sealed leg with bearings further inside and with one plain bearing at the bottom which allows for service intervals as normal forks:

    image of pre- and post-2013 Lefties

  • Previous models, as some bikers on forums complained, had more linear action: they were easier to bottom than normal forks. So now the newer ones should have more progressive compression. (This is opinion based, but quite a lot of it online, there are no measurements.)

  • A Lefty is much harder to service than a normal fork. You need a couple of special tools, and the assembly is complicated.

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    Regarding punctures, with 1-legged fork you can replace the tire without removing wheel. – ojs May 23 '15 at 18:18
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    Spot-on answer. I'll just add one or two things: removing the caliper to remove the wheel is not a disadvantage because the most likely reason to do so is to fix a flat tire, which you can do with the wheel in. You need special hubs for the lefty, but a lot of brands have them, you don't have to buy them from cannondale. And I don't think maintenance on a lefty is harder than other high-end suspensions. – super May 26 '15 at 21:46
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    Another con is that you're entirely at the mercy of Cannondale when it comes to spare parts, there's no way to swap the fork for one that's still maintainable. Which is fine if you buy a new bike every couple of years, but if you ride the bike until it wears out, it's likely to be "can't maintain the fork" that means you repleace the bike. – Móż Feb 3 '16 at 21:45
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    You also forgot to mention that most of the weight savings on the fork are spent on the crown and the overbuilt hub. Lefty forks are often a wash weight wise when you consider the system as a whole. – Deleted User Apr 5 '16 at 15:09
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    The front wheel being harder to remove is a disadvantage is you need to transport the bike in a case, in a small car trunk or in a car rack that requires the front axle mount to hold the bike. I.E.you'll need to consider this if you frequently do any of this with your current bike. – Jahaziel May 24 '17 at 21:13
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My experience with Lefty goes back to 2000 when I purchased my Cannondale Super V. One thing I've liked about it how easy it is to 'turn off'. There's a small dial at the top that disengages the suspension - good when transitioning onto solid road riding.

As mentioned above by another post, the center of balance is altered. The implication of which is that it is more difficult to ride 'hands free'.Sometimes I ride hands free with it just to practice my balancing skills.

I seem to remember that the original intent was that lefty offered a longer(higher) range of motion and thus the bike was able to handle more adverse terrain. I'm not sure if that's actually true, but it sounded good at the time.

If you do get one, you'll find it to be a conversation piece. Since it hasn't been widely adopted, I'd imagine that the benefits are not overwhelming.

And one last thing, I've always considered the bike to be "much more of a bike than I am a man".

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    Gidday and welcome to SE Bicycles. Thats a good, relevant answer, and even better that its based on your actual usage. Keep up the good work. – Criggie Feb 3 '16 at 22:30
  • What is special about the 'turn off' thing you mentioned in the first point? I mean, how is that different from the remote lockout existing in others suspensions? – iled Feb 5 '16 at 17:40
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    Regarding turning off lefty - you can disable/enable while riding - also, if you put your weight forward, you can adjust where the suspension locks - all the way up - all the way down - or anywhere in between. – SRQ Coder Feb 6 '16 at 19:08
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Pro: You can run oversize and plus size tyres on a lefty.

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  • Perhaps taller, but not significantly wider tyres. There is still a fork and a maximum clearance. Good idea - welcome to the site. – Criggie May 28 '16 at 21:16
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    I am currently running a 29+ 3 inch tyre and could go to a 3.8 comfortably. – Mark Rose May 29 '16 at 19:31
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    Doesn't this make the wheel placement assymetric with respect to the frame? – Dmitri Nesteruk Nov 24 '17 at 20:58
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Like everyone, the first time I saw this fork I find it obvious that it must be weaker than conventional forks...

Until I realized that conventional forks are not symmetrical at all. One side is the spring (air or metal spring) and the other side is the damper. This means the sides always works against each other. The fork is teared a on its sides and it do not behave exactly the same whether you turn left or right. The forces are not applied to the same side of the plunger and it does not slide evenly on both sides.

Having damper and spring on the same axle is a good point for the lefty.

Unfortunately we cannot do blind test on bikes, but it would surely give lefty more points.

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Con: Because there is only one side on the fork, it limits you to using disc brakes only, since there is no place to mount any type of rim brake solution.

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  • I was going to downvote this as a dupe and too short, but noone else has mentioned this, and there's not a lot to add. – Criggie Apr 25 '16 at 20:19
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    @Criggie I agree with you. I've edited the answer to more clearly state his point, but there isn't much to add. – zenbike Apr 26 '16 at 0:19
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Pro: There is no "fork," so mud and other hub-bub will not get stuck in the front as much.

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    Welcome to Bicycles @Adam. Thanks for answering one of our questions. We recommend that new members take the tour to make best use of the site, and since you're answering see How to Answer also. Good to see you here – andy256 Feb 5 '17 at 7:37
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I'd add: Pro: probably less width overall, good for extreme mountain/trail biking Con: center of balance is shifted off center line of tire.

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    Your body, as well as the handlebars, cranks (counting pedals), and possibly rear triangle are still going to be wider than even a double sided fork. So I'm not sure what advantage is offered in "width" by not having one of the forks. – Kibbee May 27 '15 at 18:56
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    re: shifted center of gravity - If anything, it just balances out the weight of the drivetrain which is on the other side of the frame (so bikes with 2-legged forks have a shifted center of gravity in the other direction. (not that any of this is relevant to 99.9999% of riders). – Trey Jackson May 28 '15 at 20:18
  • @TreyJackson I reckon your point, for instance, I also don't feel that is relevant to my (no handed) balance when I ride with a single sided pannier. But isn't it different in the case that the shift is in the direction (opposed to in the center of mass, or close to)? – iled Feb 5 '16 at 17:43

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