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One for the mechanically minded/qualified to discuss
02GF74 - 15/12/10 at 03:23 PM

Single sided motorcycle swing arms and forks, in particular, Cannondale Lefty:



What is the point? Ignoring the fact that is makes wheel changing easier, I am guessing that by not having a second fork leg, the fork can be made lighter, even though some of weight saved will go into beefing up the remaining leg and wheel hub.


(If it was that a good idea, why aren't all bicycle forks like that?)

Let the discussion begin.

Howlor - 15/12/10 at 03:26 PM

Just because they can, I think it is just a case of being different to help sell bikes.

Steve

Steve Hignett - 15/12/10 at 03:31 PM

quote:
Originally posted by 02GF74
Single sided motorcycle swing arms and forks, in particular, Cannondale Lefty:



What is the point? Ignoring the fact that is makes wheel changing easier, I am guessing that by not having a second fork leg, the fork can be made lighter, even though some of weight saved will go into beefing up the remaining leg and wheel hub.


(If it was that a good idea, why aren't all bicycle forks like that?)

Let the discussion begin.


I'm not much of a cyclist, but that looks like a push bike to me!

(rather than a motorcycle)...

balidey - 15/12/10 at 03:31 PM

Cost is the number one reason for it and against it.

For: its harder to engineer it, so it costs more, so its more exclusive, so rich boys will buy it.

Against: See above, thats why its not common.

Although give it a few years and then the market will be flooded with cheapy crappy Chinese sh1t that people will buy, thinking its good because of the above, and then they will break, or not be very light.

[Edited on 15/12/10 by balidey]

02GF74 - 15/12/10 at 03:32 PM

quote:
Originally posted by Steve Hignett


I'm not much of a cyclist, but that looks like a push bike to me!

(rather than a motorcycle)...



jeeez, I'm not gonna get one past you am I?

coyoteboy - 15/12/10 at 03:51 PM

quote:
Although give it a few years and then the market will be flooded with cheapy crappy Chinese sh1t that people will buy, thinking its good because of the above, and then they will break, or not be very light.


Lefty forks have been around for about 10 years already, no-one seems to copy them. Not my personal choice of fork, I prefer the old Marzocchis on my bikes, but Cannondale like to be a bit different. IIRC they were the first to come up with headshocks - with a shorter head tube and the absorbtion within the space below the lower crown race and the fork, making a more torsionally rigid, simpler fork too.


Personal taste, there's any number of fans of each of the different designs out there.

There's even a fan of this style of fork, despite it's J shaped travel path that makes you feel like you're about to go over the bars if there's a large bump and you're turning....



[Edited on 15/12/10 by coyoteboy]

RAYLEE29 - 15/12/10 at 03:54 PM

Not exactly new is it!
canondale one must be at least 5 if not ten years old and noones bothered to copy it!
couldnt see the point then still cant.
my 748 had a single sided swingarm just made it harder to lift on the paddock stand.
bmw did the single sided swingarm first God knows how many yrs ago
honda vfr 750 had one too
Ray
im soo slow typing he got in before me
[Edited on 15/12/10 by RAYLEE29]

[Edited on 15/12/10 by RAYLEE29]

[Edited on 15/12/10 by RAYLEE29]

orton1966 - 15/12/10 at 04:00 PM

I did read an article about this some time ago, similar principle (and possibly designer) to the original lotus bike.

Memory escapes me a little but in brief: 1 large diameter tube is stiffer, stronger, lighter and more aerodynamic than two smaller tubes. The bike industry haven’t flocked to it because it’s a bit counter intuitive and they all think the hub will be weaker or flex and pull to one side, despite the fact cars have used single sided hubs since the beginning of time.

As for engineering cost/complexity: wheel hub is the same as any of the thru axle hubs, axle and axle clamp are a little beefier than some but about the same as most downhill spec. forks, crown clamps are nothing special, I think the only complexity is not allowing the fork leg to rotate on its stanchion, cannondale do this by putting the suspension above the fork leg. Again this is compensated for by only having one fork leg to make.

Really the only drawback is lack of economy of scale i.e. because everyone else uses conventional forks these are made in greater numbers and thus are cheaper to make

[Edited on 15/12/10 by orton1966]

02GF74 - 15/12/10 at 04:14 PM

^^^ thx - that was quite helpful.

quote:
Originally posted by orton1966
I think the only complexity is not allowing the fork leg to rotate on its stanchion, cannondale do this by putting the suspension above the fork leg.


The inside of the leg has a linear bearing, a bit like you get in cupboard draw sliders so that stops the leg turning plus it can be loaded up by a huge amount without the leg sticking - there is video on youtube showing some Cannondale geezer sitting on the end of the leg and it is still free to move without sticking.

I guess I need to google up the weights for Lefty and twin leg forks ...

tony-devon - 15/12/10 at 04:30 PM

WHY?

because you can, why not

why would you build your own car when you can go to the local dealer and buy one?

personal taste in style etc




ok so its got an engine instead of pedals and its a custom build, but a perfect example of... WHY NOT!

Irony - 15/12/10 at 04:53 PM

In my opinion there is no real engineering reason why these haven't caught on. People just don't like what they don't understand. It looks a bit odd therefor it's not very good. It's just too 'far' from the designs people are used to. As a race humans in general dislike things that differ from the norm.

dhutch - 15/12/10 at 05:02 PM

quote:
Originally posted by HowlorJust because they can, I think it is just a case of being different to help sell bikes.

Both cynically, as and engineer, and because its not been copied, i have to admit i side with this.

One larger tube is stiffer for the weight, and more aerodynamic than one.

However aero on a mountain bike isnt very high on the scale of it, bottom i would say, or near enough. Then you have to stop it rotating, which means some sort of indented linear bearing type affair which suddenly means you cant using standard tube, or half the machining processes that you would used to make it, and you carnt seal to it (i assume they have a round tube somewhere, either concentrically or most likely further along the same tube, for the seals) and you have to redesign and beef up the interface between the wheel and the end of the fork.

Most mtb suspention forks are asymetic anyway so i assume the canterlevering isnt a huge issue, although i did have one fork that used to cause the wheel to twist such that with a large tyre it would hit one side on down stroke and the other on rebound, due to the phase shift in load between the spring on one side an the damper on the other.

So in summary, i think its very much a case of 'not impossable to do, but you dont gain much' so most stick with what works and what people expect.

Interms of making it easy to change a tube. How long does it take to remove a QR wheel (with disk) 6seconds? if you slow? Every 10 hours of riding or so? Again: its nothing.


Daniel

kipper - 15/12/10 at 05:07 PM

I seem to remember a Morbidelli 125 grand prix bike with a single sided front fork many years ago.
I guess some-one more clued up will be able to find a pic.
Regards Denis.

andrew - 15/12/10 at 05:10 PM

its for the must have , mines better than yours ,look at me,,

bitsilly - 15/12/10 at 05:26 PM

USP.

MikeRJ - 15/12/10 at 07:15 PM

quote:
Originally posted by dhutch
quote:
Originally posted by HowlorJust because they can, I think it is just a case of being different to help sell bikes.

Both cynically, as and engineer, and because its not been copied, i have to admit i side with this.

One larger tube is stiffer for the weight, and more aerodynamic than one.

However aero on a mountain bike isnt very high on the scale of it, bottom i would say, or near enough. Then you have to stop it rotating, which means some sort of indented linear bearing type affair which suddenly means you cant using standard tube, or half the machining processes that you would used to make it, and you carnt seal to it (i assume they have a round tube somewhere, either concentrically or most likely further along the same tube, for the seals) and you have to redesign and beef up the interface between the wheel and the end of the fork.


Agreed. The wheel spindle has a considerable bending moment exerted in this configuration so would need to be larger which would driver larger bearings and more weight. Larger forks tend to suffer from stiction more than smaller ones, especially when loaded in bending as this would be.

It does little to solve the disadvantages of conventional telescopic forks, yet introduces some of it's own besides being more expensive to make. In summary, it's a fashion item.

quote:
Originally posted by coyoteboy


[Edited on 15/12/10 by coyoteboy]


This is very similar to the system now used by BMW in many of their bikes, they call it the "Duolever" suspension.


[Edited on 15/12/10 by MikeRJ]

02GF74 - 16/12/10 at 01:47 PM

quote:
Originally posted by MikeRJ
Larger forks tend to suffer from stiction more than smaller ones, especially when loaded in bending as this would be.



I think that would be true for converntional slidey type fork - this has liner roller bearing that a not affected as much - you need to find that video I mentioned (I cannot access youtube).


USE (British company) also invoneted the lefty fork, wonder who was first?



[Edited on 17/12/10 by 02GF74]