How does a C'dale Lefty work?

[LegendRider]

Can someone explain in layman's terms how the Lefty works? A traditional fork creates a triangle - two fork blades and an axle - while the Lefty doesn't. I can't wrap my head around the engineering/physics principles... Someone once told me it's basically the same as certain aircraft landing gear.

[David Kirk]

The axle becomes a cantilevered beam and the fork blade needs to be designed so that it can slide up and down but not rotate.

How it works and why they do it are two different questions.

Dave

[duke]

Why do they do it? Is there an advantage besides marketing hype?
Thanks,
duke

[Louis]

Someone once told me it's basically the same as certain aircraft landing gear.

Correct for F-15 nose gear.

F-18 landings are more exciting: Pitching Deck Video (http://www.youtube.com/watch?v=4gGMI8d3vLs)

BTW, that F-15 gear is incredibly spindly compared to the F-18. The video will tell you why.

http://www.militaryfactory.com/aircraft/imgs/mcdonnelldouglas-f15-eagle_9.jpg

[eddief]

but i had to puke two minutes in.

[Ken Robb]

[QUOTE=LegendRider]Can someone explain in layman's terms how the Lefty works?

Pretty well for Democrats--not so hot for Republicans. :) :beer: :banana:

[timto]

The lefty fork axle is cone shaped - so it's wide base is what is welded to the fork - and the hub is tapered and slips over it. It has a square slider assembly with roller bearings that help prevent the whole thing from twisting around.

It rides no hands normally.

Pros
Lock out is in a really nice and handy position
It looks pretty cool
You can change/fix a flat and not remove the wheel just pry the tire off


Cons
Suspension performance (quality of travel, precision, smoothness, rebound) didn't seem as good as my FOX front fork on a Santa Cruz Blur I rode for a season.
Stems - I can't see how you could run as short as an 8cm on there due to stem/bar conflicts with the fork clamp hardware.


Mostly due to the suspension feel i'd stick with a normal setup next time. I sold the F series hardtail that had it and don't miss it. I do miss my Blur though.

[KeithS]

They don't use much of the deck on take off do they.

I have a cousin who retired from the Navy as an Lt. Cmdr. He drove an F18 off ships that weren't even sinking. He told me that the F18 is the only fighter plane that can accelerate through mach 1 vertical.

Balls the size of pickle jars.

[Jawn P]

Why do they do it? Is there an advantage besides marketing hype?
Thanks,
duke

One leg equals about half the weight. A lefty carbon dlr is about 1.4 pounds lighter than a Fox F29.

[PCR]

[QUOTE=LegendRider]Can someone explain in layman's terms how the Lefty works?

Pretty well for Democrats--not so hot for Republicans. :) :beer: :banana:

:D ;) :beer: :banana:

[Kirk Pacenti]

Fwiw, I am planning on getting one soon. All reports I've read / heard (about the newer ones), mag tests, friends who have them and web forum chatter claim that they are stiffer, lighter and perform better than nearly every other fork on the market today. Though I'll confess I'm mostly interested in it for it's 650b compatibility.

The closest thing I've heard to a complaint are the aesthetics. But since I rarely, if ever, look at my bike while riding, I am not too concerned about how it looks... ;)



Cheers,

KP

[LegendRider]

Fwiw, I am planning on getting one soon. All reports I've read / heard (about the newer ones), mag tests, friends who have them and web forum chatter claim that they are stiffer, lighter and perform better than nearly every other fork on the market today. Though I'll confess I'm mostly interested in it for it's 650b compatibility.

The closest thing I've heard to a complaint are the aesthetics. But since I rarely, if ever, look at my bike while riding, I am not too concerned about how it looks... ;)



Cheers,

KP

That's EXACTLY where I stand. I have an opportunity to pick up a complete bike with a Lefty for a good deal. Everyone raves about it, but I don't care for the way it looks... Nevertheless, I'll probably get it.

[oldpotatoe]

Can someone explain in layman's terms how the Lefty works? A traditional fork creates a triangle - two fork blades and an axle - while the Lefty doesn't. I can't wrap my head around the engineering/physics principles... Someone once told me it's basically the same as certain aircraft landing gear.

http://www.ducati.com/bikes/superbike/index.do

Rear wheel.

[stickville]

I have lefty envy. I have two c'dale hard tails both without the lefty. One hard tail is pre-lefty and the other, a Taurine 1 did not come with one. I have always wanted one, but could not justy the $$ for my type of riding. What bike are you looking at?

[Jack Brunk]

I have found them to be the best hands down suspension system around. They are everything that Kirk says. I can really tell the difference when throwing the bike into tight turns. There's no flex at all compared to the crown flexing on a standard fork. I know for a fact that the fork itself has made me a much better and confident rider.

Kirk,
I'm building up a Coconino 650b right know with a lefty and your Quasi tires. Should be done very soon. Pics to follow.

[peanutgallery]

the good: Stiff, light, goes where you point it, neat looking and the tool kit has remain unchanged since the mid-90's. Lot's of similar mechanicals to the original headshock. Always found them easy to work on. There are lots of neat little tricks that you can do to both the dampening unit and the bearings to customize the feel and performance of the form. Failure is associated with the boot that covers everything up.

You have limited places for repair, but I don't see too many folks getting excited about pulling any fork apart. Found it easier to send the whole thing back anymore. Been stung too many times by a fork that needed the smallest o-ring, bushing etc. and then waited for the part only to find another was hosed up. Send it to someone, they know what they are doing and have all the small parts you would ever need

The bad: Harsh and slow when compared to contemporary items on the market today. See "the good" as to how to fix some of that. Numb-nuts that cross thread any part of the axle contraption. Transpo of the rig can get old and people asking the same questions about it get old, too. Like all Cannondale proprietary stuff, there can and will be some quirks.

Give it a whirl, forks are the flavor of the month and this one does solve some interesting problems. 650b is an interesting option

[peanutgallery]

PS: Truing and building front wheels is a PIA

[wrestlr]

Dudes listen to Jack. He knows his MTB builds and how to push them. Rode one of his Scalpel's last night with him that had a lefty and I am sold. I don't know if I could ride a mtb, hard tail or soft without a lefty now. Take the advice and ride one if you ever have the chance.
-Mike

[Charles M]

The lefty works extremely well...

Snip from MTBR review of my Scalpel...

http://reviews.mtbr.com/files/2009/06/09scalpleft1.jpg

------------------
An easy assumption from people (including me) was that this tech simply can’t offer the stability that comes from a standard two legger… And that’s generally speaking, wrong. In fact anything in the Lefty SL weight class is less stiff… In twist flex and in front to back flex. And that’s when you loosely define the term “weight class”.

Even if it tracked worse than it’s heavier competition (and it doesn’t), the weight of the SL sits at 2.5 pounds. For weight weenie types like me, it makes for an interesting problem because we’re so used to making excuses for the lack of performance on fly weight parts that we frankly don’t know what to do when something is this light and then outperforms other things…

The FAT tube cross section and materials combine for a fork that gives exceptional stiffness.

http://reviews.mtbr.com/files/2009/06/09scalpleft2.jpg


And does so without reservation or conditions like “better than you would expect for a single leg fork”. The stiffness and tracking of the Lefty Speed Carbon is great compared to forks in the all mountain weight range.

It makes sense that compression and rebound have to be in one side on the lefty… But it’s that way on lots of two sided forks as well.

Another benefit of the massive cross section of the Lefty fork tube is that engineers have a lot of space to work inside compared to double leg forks that try and stick all of their damping into a smaller tube.

That extra room not only provides more volume for damping hardware, it also allows for the use of needle bearing actuation…

http://reviews.mtbr.com/files/2009/06/09scalpneedle1.jpg

This coupled with better volume for damping kit makes for the smoothest operation XC fork on the market (just a personal opinion). And the structure also gets credit for some of the stiffness of the Lefty…
_________________________________


Most of the criesof "Gimick" or "Marketing" simply don't credit the Cdale front end enough...

The stiffness statement is based on a lab test of fork flex and not just my opinion. The test was done by another manufactuere to boot, and they came away with "nice fork... you cant print the results"

The non SL version (the Lefty Max) is actually better performing than the SL as well and still weighs Dick.

Maintenance is simple too...

I do know folks that like a bit more "stick-tion" in fork action because it feels a bit different in the range of motion, so not saying everyone's favorite for would be a Lefty, but every person that I have seen use a version of this fork from the last couple of years has given nothing but superlatives...

It's also not overly easy to find Lefty Wheel sets.



They also have a computer controled unit that will be rolling shortly...



Anyhoo, The Lefty is a hell of a fork. Most of the negatives I have heard have all been brand based because this is a bike companies fork. It "retards" opinion... But I can tell you there is a lot of quiet industry respect for the latest lefty's when people speak honestly.

[Ken Robb]

I "get" 650b tires on rigid frames/forks but wonder if they are as valuable on a fs bike. There are so many tire/wheel options in 26" and quite a few 29ers so why would one want to use 650b wheels?

[RPS]

Though I'll confess I'm mostly interested in it for it's 650b compatibility.
I'm also curious, what makes this fork more compatible with 650b than other MTB forks?

[peanutgallery]

Clearance

[RPS]

Clearance
Assuming you are replying to my question, how does a single larger leg provide added clearance? :confused:

[peanutgallery]

Assuming you are replying to my question, how does a single larger leg provide added clearance? :confused:

No crown or bridge at the top of the lower legs for the tire to run into as they get larger in circumference, especially if it gets muddy or you live on the East Coast and a 2.3 or 2.4 does the trick. When you put 650b on traditional 26" slider forks this can be a bit of a problem. Because of the design of the Lefty, there is a great distance between the top of the tire and the bottom of the fork crown. Of that distance, let's say 100-140 is needed for the travel of the fork, if the wheel is a 650b it would fit fine.

Does this void the warranty or alter the geo of a 26" bike? Excellent questions, but the dimensions of a Lefty in the hands of a competent builder can probably result in a frame that is designed proportionately and a suspension fork that works pretty well with 650b without many trade-offs

[RPS]

No crown or bridge at the top of the lower legs for the tire to run into as they get larger in circumference, especially if it gets muddy or you live on the East Coast and a 2.3 or 2.4 does the trick. When you put 650b on traditional 26" slider forks this can be a bit of a problem. Because of the design of the Lefty, there is a great distance between the top of the tire and the bottom of the fork crown. Of that distance, let's say 100-140 is needed for the travel of the fork, if the wheel is a 650b it would fit fine.

Good points, however, I was puzzled by there being other “more traditional” suspension forks that I assume can also do the same. What about 29er forks or one of similar design to pictured below? Can they not overcome the same issues you mention without going to an asymmetrical one-legged design?

Don’t get me wrong, I have nothing whatsoever against the Lefty except I normally don’t like that much visual asymmetry. I just wondered why it was a particularly good fit for 650b. :)

[Kirk Pacenti]

Kirk,
I'm building up a Coconino 650b right know with a lefty and your Quasi tires. Should be done very soon. Pics to follow.

Jack,

I can't wait to see that one built up. It ought to be a sweet looking rig!

[Kirk Pacenti]

I'll try to address all questions in one shot:

The Lefty works great for 650b because, as others have said, there is no arch and the crown is much higher so you can run any wheel size you'd like. Furthermore you do not have to limit the travel of the Lefty when using a 650b wheel like you would with a 29" wheel. Since I ride a 140mm travel FS bike, it's important to me.

I won't go too deep into it, but fwiw, when I designed 650b MTB tires, I was specifically focusing on 5"-6" travel FS bikes. I think this is where the wheel size is going to really shine. The 650b allows you to maximize wheel trajectory, maintain "traditional" 26" frame geometries, and (imo) have a bike that handles better than either of the other wheel size options. And speaking from personal experience, I corner harder, use my brakes less and am on a whole, much faster on my 650b bikes than anything I've ridden previously.

Using a 29er fork really defeats the purpose. They are much too long for their (too little) given travel and can (for my 6' height) create more geometry / fit problems.

Hope that helps,

KP

[Jack Brunk]

I'll try to address all questions in one shot:

The Lefty works great for 650b because, as others have said, there is no arch and the crown is much higher so you can run any wheel size you'd like. Furthermore you do not have to limit the travel of the Lefty when using a 650b wheel like you would with a 29" wheel. Since I ride a 140mm travel FS bike, it's important to me.

I won't go too deep into it, but fwiw, when I designed 650b MTB tires, I was specifically focusing on 5"-6" travel FS bikes. I think this is where the wheel size is going to really shine. The 650b allows you to maximize wheel trajectory, maintain "traditional" 26" frame geometries, and (imo) have a bike that handles better than either of the other wheel size options. And speaking from personal experience, I corner harder, use my brakes less and am on a whole, much faster on my 650b bikes than anything I've ridden previously.

Using a 29er fork really defeats the purpose. They are much too long for their (too little) given travel and can (for my 6' height) create more geometry / fit problems.

Hope that helps,

KP
Kirk,

Hopefully it will be finished this weekend. I will ride the hell out of your tires with love and respect.

Jack

[terminaut]

http://www.fooriders.com/misc/lefty/lefty1.jpg

http://www.fooriders.com/misc/lefty/lefty2.jpg

http://www.fooriders.com/misc/lefty/lefty3.jpg

http://www.fooriders.com/misc/lefty/lefty4.jpg

http://www.fooriders.com/misc/lefty/lefty5.jpg

[Louis]

One leg equals about half the weight. A lefty carbon dlr is about 1.4 pounds lighter than a Fox F29.

I'm guessing that the weight difference is almost certainly due to the single shock instead of two separate shocks. I don't think it would take much analysis to prove that without the shocks an optimized two leg design is lighter than an optimized one-legger. The geometry is just more efficient structurally. That's why I don't think we're likely to see a successful Lefty for road bikes. (Although someone may build it just for kicks.)

Louis

[peanutgallery]

Depends on the design, the one in the pic would probably work well. (a few others too I am sure) The Lefty is probably the easiest to get your hands on and by far the lightest. It does look weird and that alone will put someone off. I am the same way about carbon, don't like the look

Good points, however, I was puzzled by there being other “more traditional” suspension forks that I assume can also do the same. What about 29er forks or one of similar design to pictured below? Can they not overcome the same issues you mention without going to an asymmetrical one-legged design?

Don’t get me wrong, I have nothing whatsoever against the Lefty except I normally don’t like that much visual asymmetry. I just wondered why it was a particularly good fit for 650b. :)

[RPS]

If 650b-based geometry is perfect for a 6 footer then is it safe to assume anyone less than about 5'-9" or 5'-10" should use 26-inch wheels to replicate the same ideal geometry? Likewise should riders above 6'-2" or 6'-3" use 700C rims and 29er forks?

[Kirk Pacenti]

If 650b-based geometry is perfect for a 6 footer then is it safe to assume anyone less than about 5'-9" or 5'-10" should use 26-inch wheels to replicate the same ideal geometry? Likewise should riders above 6'-2" or 6'-3" use 700C rims and 29er forks?

I don't think so. You can make an argument for wheel size relative to height based on proportions, but it's not that simple. l know lots of people as small as 5'4" who swear by their 29'ers and a lot of guys 6'2" and up who will ride nothing but 26" wheels... go figure.

Basically, it comes down to terrain, rider style and rider preference. The reason I like the 650b wheel so much is that is the biggest wheel you can fit in traditional 26" frame geometries (evolved over the last 30 years) with very minor tweaks. Usually the only adjustment needed is to lower the BB about 15mm. Which allows you to build "normal" frames as small as 13"-14".

Put another way, if you look at a 26" hard-tail, there is a lot of real estate between the rear tire and the bb shell. A 650b wheel simply uses up the available space on a well designed frame, giving you a larger contact patch, greater wheel trajectory (big wheel benefit) while maintaining the nimble handling of a 26" bike.

Everyone knows I have a clear financial interest in 650b. That being said, the wheel size works much better for MTB use than I ever imagined it would. Personally, I am not out to convince anybody... Give it an honest go, and decide for yourself. I say, ride what works best for you!

Cheers,

KP

[Kirk Pacenti]

http://www.fooriders.com/misc/lefty/lefty1.jpg

http://www.fooriders.com/misc/lefty/lefty2.jpg

http://www.fooriders.com/misc/lefty/lefty3.jpg

http://www.fooriders.com/misc/lefty/lefty4.jpg

http://www.fooriders.com/misc/lefty/lefty5.jpg


That's some sick ***** right there! :beer:

[RPS]

I'm guessing that the weight difference is almost certainly due to the single shock instead of two separate shocks. I don't think it would take much analysis to prove that without the shocks an optimized two leg design is lighter than an optimized one-legger. The geometry is just more efficient structurally. That's why I don't think we're likely to see a successful Lefty for road bikes. (Although someone may build it just for kicks.)

Louis
My initial reaction was the same as yours, but I’m not quite certain it’s that simple. The highest stresses on a fork are typically caused by loading in fore-aft direction, and/or with a combination of vertical forces, right? In that (those) direction(s) one “large” blade that is slightly off-center compared to two “smaller” symmetrical blades shouldn’t have to weigh more to be as strong or as stiff. The same should apply to side-to-side loading.

Where two blades have a considerable advantage is in controlling the front wheel in the “roll” direction, where with two blades they are placed in tension and compression (hence very strong and stiff) versus a single blade being placed in bending (much higher stresses and less stiff by comparison). However, forces in the “roll” direction are much lower than fore-aft, which means that if the single fork blade is strong enough to resist large bumps and hard braking (or combination of the two), it can probably also resist the wheel from trying to “roll” out of the bike’s plane.

If it were a bike with no fork suspension the same argument can be made for torsional rigidity. A single large blade of equal weight as two smaller blades can “in theory” be stiffer and stronger. In the case of suspension forks like the Lefty another variable is introduced which is the necessity to transmit torque for steering through a sliding strut (same as a head shock), which adds weight. However, in a rigid fork that would not be an issue.

Bottom line is that I doubt it would be about “half” the weight as suggested but it may be “possible” that an optimized single large fork blade can weigh a little less than two optimized smaller blades. I know it sounds counter-intuitive but I think it “may” be possible. We already know a single blade can work based on many examples like the Lefty, airplanes, and motorcycles/scooters, so it’s just a matter of whether the weight and performance can be equal or better. Appearance due to asymmetry is something much different.

[RPS]

Everyone knows I have a clear financial interest in 650b.
Even so it doesn’t preclude your perspective and technical points from being valid. Thanks for the follow-up. :beer:

[Louis]

RPS,

It seems to me that the biggest challenge for a 1-leg design is that you have to deal with the moment due to the unsymmetric loading and twisting at the end of the fork. Not as much of a problem with the 2-leg. That's one reason the Lefty has to be so beefy at the bottom compared to a 2-leg design. In addition, for side loads and twisting a 2-leg has the advantage of naturally putting the material away from the neutral axis since its separated by the wheel. In a 1-leg the material is closer, so to get the same GJ you need more help, whether it be from G (I don't even know what material the Lefty uses, CF or metal) more area to get the right J. About the only direction in which the 2-leg does not appear to be better (I say "appear" because I haven't actually done the shear and bending moment diagrams for the two options) would be fore-aft, because the distance between the blades does not help you there.

Until someone actually comes out with a successful road 1-legger designed to appeal to the weight weenies who are willing to use anything, no matter how hideous, as long as it's lighter, I think I'll remained convinced that 2-legs better than 1-leg (to paraphrase George Orwell).

Happy riding.

Louis

[RPS]

RPS,

It seems to me that the biggest challenge for a 1-leg design is that you have to deal with the moment due to the unsymmetric loading and twisting at the end of the fork. Not as much of a problem with the 2-leg. That's one reason the Lefty has to be so beefy at the bottom compared to a 2-leg design.
Agreed. However, with mountain bikes mostly using disc brakes, the amount of twisting at the end of the blades (one blade anyway) requires it to be beefy due to caliper mounting and associated reaction loads on fork. I agree that if we were only comparing designs for road bikes with standard rim brakes your perspective is very valid. Excellent point.

In addition, for side loads and twisting a 2-leg has the advantage of naturally putting the material away from the neutral axis since its separated by the wheel. In a 1-leg the material is closer, so to get the same GJ you need more help, whether it be from G (I don't even know what material the Lefty uses, CF or metal) more area to get the right J. About the only direction in which the 2-leg does not appear to be better (I say "appear" because I haven't actually done the shear and bending moment diagrams for the two options) would be fore-aft, because the distance between the blades does not help you there.

Until someone actually comes out with a successful road 1-legger designed to appeal to the weight weenies who are willing to use anything, no matter how hideous, as long as it's lighter, I think I'll remained convinced that 2-legs better than 1-leg (to paraphrase George Orwell).

Happy riding.

Louis
Only an educated guesstimate on my part, but if you did a bending moment diagram assuming disc brakes I think you’d find that fore-aft braking loads in combination with vertical bump loads result in stresses much higher than other stresses. I based my initial opinion on the fork leg being about 2 inches off the wheel’s centerline, while the moment arm in a more critical direction can be over 2 feet.

From a weight weenie’s perspective I think another factor that is hard to “estimate” is how heavy a cantilevered axle and hub assembly has to be compared to a road bike’s hub. I’d guess we’d be looking at over 100 grams easily. This would mitigate some of the weight savings if they were possible in the first place. Personally I’ll stick to two legs – seems to work pretty well. :beer:

[Jawn P]

I'm guessing that the weight difference is almost certainly due to the single shock instead of two separate shocks. I don't think it would take much analysis to prove that without the shocks an optimized two leg design is lighter than an optimized one-legger. The geometry is just more efficient structurally. That's why I don't think we're likely to see a successful Lefty for road bikes. (Although someone may build it just for kicks.)

Louis

The rumor mill has it that Cannondale will be doing a "Righty" one legged fork on their road bikes in the not-too-distant future.

Along with the weight, as elaborated, this thing is laterally stiff as the dickens too.

[Louis]

The rumor mill has it that Cannondale will be doing a "Righty" one legged fork on their road bikes in the not-too-distant future.

Along with the weight, as elaborated, this thing is laterally stiff as the dickens too.

Interesting. I look forward to seeing it.

Given the political opinions stated here many times I think we know who will be purchasing a fork like that and who will avoid it like the plague :p

[Kirk Pacenti]

The rumor mill has it that Cannondale will be doing a "Righty" one legged fork on their road bikes in the not-too-distant future.

Along with the weight, as elaborated, this thing is laterally stiff as the dickens too.

It's all been done before... :p This one was available in left or right configurations.

http://tinyurl.com/y9qju8u

The story goes when Lynn sold Redline, he had several hundred pair of pre-miterd fork blades left over and he just wanted to use them up. He used a custom hub and a 1" steer tube for the "axle".

Cheers,

KP

[Louis]

It's all been done before... :p This one was available in left or right configurations.

http://tinyurl.com/y9qju8u

The story goes when Lynn sold Redline, he had several hundred pair of pre-miterd fork blades left over and he just wanted to use them up. He used a custom hub and a 1" steer tube for the "axle".


Kirk, you can't fool me.

The weight savings on that one are due to using only half a handlebar...

[Jack Brunk]

You guys are totally missing how good the fork is. Just ride the thing quit trying to out think it. Leave your brains back at the house. The Lefty fork is much better than the crown fork.

[terminaut]

It's all been done before... :p This one was available in left or right configurations.

http://tinyurl.com/y9qju8u

The story goes when Lynn sold Redline, he had several hundred pair of pre-miterd fork blades left over and he just wanted to use them up. He used a custom hub and a 1" steer tube for the "axle".

Cheers,

KP

I have one of those... but unfortunately bent the leg "just riding along". LOL

Loved the Kastans and Quadangles back in the day.

[Ken Robb]

http://www.ducati.com/bikes/superbike/index.do

Rear wheel.
Much easier because it doesn't steer---at least we HOPE it doesn't. :beer: