[Closed] Cannondale Lefty - advantages

We don't buy em for that, it just to wind the c'dale haters up, and get them frothing at the mouth, and to have kids tell us were missing a fork (my std reply "couldn't afford the other leg")

There are some maintenance things that are a bit more tricky than other forks, removing a wheel means unbolting the brake, and the proprietary hub design makes replacing wheels a little trickier, but there's plenty on the plus side to counter that.

Seems a perfectly legit demo - TBH I'm not all that surprised by what he's showing, though I'd have some suspicions that he picked a fork which was particularly flexy to compare with. The Lefty is actually a very good technical solution - something I've seriously considered getting to fit on a non-Cannondale bike.

In case it isn't clear I don't own one, so no bias from that perspective.

More wobblage for wonky wheels.

I've got a USE SUB fork on my bike - it completely messes with people's heads.

"How can it be strong enough only supporting the wheel on one side like that?"

"Go outside and look at your car wheels"

😀

[quote=bencooper ]"Go outside and look at your car wheels"

OMG, how do they not fall off 😯

I'm a qualified Mech Eng (CEng) and to me it makes perfect sense. It's a great design and the same basic principle is used on almost all modern cars i.e. McPherson Strut. I once designed a Rally Car suspension strut with linear roller bearings (like the latest Lefty uses) to reduce friction over standard bushings. Again it's a great idea. I can't fault it if I'm honest and I do believe it's inherently a better design than a conventional fork.

So why only Cannondale? No idea, but imagine it's the consumer marmite effect. Or do they have a patent?

[quote=moshimonster ]I'm a qualified Mech Eng (CEng)

Really? I don't think you've mentioned that before.

They've definitely got a patent on the Headshok system - a company I know was paying around £200 per frame to license it.

Really? I don't think you've mentioned that before.

**** off. It's definitely relevant. A bit like responding to a medical question if you are a doctor.

A quick google suggests it's just the needle bearing bit which is patented (well apparently also a cartridge damper, but the quote I found suggests they're not enforcing that). However that is kind of fundamental to the torsional stiffness and lack of stiction - hard to imagine how you'd make a single sided front suspension which works so well without using that.

@moshi - it's argument from authority. If you know what you're talking about (which clearly you do) then it should be possible to make your case without having to resort to that.

@moshi - it's argument from authority. If you know what you're talking about (which clearly you do) then it should be possible to make your case without having to resort to that.

Bullshit. What's wrong with just stating your profession if it's relevant to the discussion? I'm sure the OP would like to know the opinion of someone qualified as a mechanical engineer. If this is not mechanical engineering, I don't know what is?

However that is kind of fundamental to the torsional stiffness and lack of stiction - hard to imagine how you'd make a single sided front suspension which works so well without using that.

It's a good feature, but not really fundamental to the strut design. How many cars have needle roller bearing struts? Virtually none, in fact the only one I know is the Rally Car version I designed. I think it's only been used on the Lefty quite recently.

I have a degree in Astrophysics. This is happening in the universe. Therefore I'm qualified to comment 😉

hard to imagine how you'd make a single sided front suspension which works so well without using that.

USE did it with an angled linkage - has the additional benefit that it produces anti-dive geometry.

I do believe it's inherently a better design than a conventional fork.

Until you have to strip it down post a normal UK winter. That was the major disadvantage I remember, it needed TLC from a shop. That and a restricted choice of front hub. I think the USE Sub was home serviceable though, surprised that didn't catch on more - think it would take RockShox or Fox to make one for it to gain acceptance.

That was the major disadvantage I remember, it needed TLC from a shop.

Maybe true I don't know, but it's not an inherent disadvantage of the actual design concept. That would be more down to the detail design i.e. sealing etc.

I think the USE Sub was home serviceable though, surprised that didn't catch on more

Very easy to strip and service. There were two problems - it was expensive (around £750 I think), and USE didn't make the air cartridge themselves so they were in trouble when they couldn't get the cartridges any more.

"That was the major disadvantage I remember, it needed TLC from a shop. "

Unlike say ermmmm i'm trying to think of a large fork manufacturer thats had say .....24hr strip and service intervals...... what's their name....stout....badger......weasal! thats it weasal, isn't it?

I've got a O level in Art say i can say they look nice.

A lefty is a brilliant way of eliminating claggy mud clinging to your fork arch.

Other than that, I'm stumped...half the leg count of a normal fork, but for double the cost.

half the leg count of a normal fork, but for double the cost.

It's not just half a conventional fork leg though. It's very well engineered actually, especially the latest Supermax version. I would have bought a Cannondale Jekyll just for this fork except they are sold out in the UK.

I loved my Lefty when I had one but the maintenance was a bit much.

Unlike say ermmmm i'm trying to think of a large fork manufacturer thats had say .....24hr strip and service intervals...... what's their name....stout....badger......weasal! thats it weasal, isn't it?

That's the same weasel words on every manufacturers instructions - essentially you can't ride any fork more than once without a rebuild if you follow the letter of the law.. at least with say Rebas I can take them apart and have fighting chance of getting them back together in a better state, I couldn't have done that with a Lefty. I also remember riding with a guy on an event who was bitching about the ELO, when this was a new thing.. kept switching on and off without consulting him.
I'd have had one, but my nearest dealer was too far away for the servicing.

[quote=moshimonster ]It's a good feature, but not really fundamental to the strut design. How many cars have needle roller bearing struts? Virtually none, in fact the only one I know is the Rally Car version I designed.

Cars tend to have other linkages controlling wheel movement, which is usually fairly straightforward to do given location of wheels relative to the chassis, and also necessary for stuff like steering - [b]Mac[/b]Pherson struts are after all most commonly used on front suspension.

More tricky to have other controlling linkages on the front suspension of a bike - clearly USE found a way to do it, but I'm not convinced it's as good as having a single strut which inherently resists torsion.

I give you that without stating any qualifications whatsoever.

The [url= http://www.pinkbike.com/news/cannondale-jekyll-275-carbon-team-review-2014.html ]Jekyll review[/url] on PinkBike gives an interesting review, I'd love to try one but the cost to me is crazy.

One thing I'm not sure of is how Cannondale make a single sided inverted 'fork' which is reportedly as stiff as a very stiff thing but dual sided UD forks are constantly criticised for lack of stiffness. Is it the needle roller bearings that make the difference? Could Dale make a dual sided Lefty for DH?

MacPherson struts

Been googling again?

I give you that without stating any qualifications whatsoever.

You have one large chip off your shoulder.

Oh you guys

That was the major disadvantage I remember, it needed TLC from a shop

Odd, I've found over the years they require a lot less attention, I've still got a 2000 DLR in regular use and it's only had 3 damper services in that time and a bit of lube, still runs perfectly.

The only un-reliable one I've had was a Max with a manitou damper, and all the hassle was from the damper rather than the chassis.

As long as the boot is intact (older models) then they are remarkably well sealed, and dirt doesn't migrate upwards very easily so if there is any corrosion on the races its normally right at the bottom of the leg, which never actually contacts any of the rollers, even at full compression.

Tony @Thumbrrint has been running a boot-less (as an experiment) lefty on his CX bike for several years, and although the bottom of the races look awful now functionally it's still perfect.

The dampers are no more or less complex than in normal forks so there's no additional maintenance there and the days of needing a special tool to do bearing resets disappeared a decade ago.

I've not used any of the newer models where they replaced the boot with a seal and made the lower-most section round to do so, but have seen isolated reports of these suffering form a bit more wear and tear.

[quote=chillidave ]One thing I'm not sure of is how Cannondale make a single sided inverted 'fork' which is reportedly as stiff as a very stiff thing but dual sided UD forks are constantly criticised for lack of stiffness. Is it the needle roller bearings that make the difference? Could Dale make a dual sided Lefty for DH?

It's one of the things - they're what allow the Lefty to resist torsion. As stated in that video fork legs tend to be round and have no resistance to torsion, so torsional stiffness relies upon bracing between the legs and with an UD fork you only have one point of bracing. You also have fore-aft and sideways stiffness - UD forks should be relatively good at the former as the bushings are low down away from the highest torque loading, the latter has the same issue as torsion in that they have one brace less to resist independent leg motion. A Lefty also has relatively large diameter tubing which results in better stiffness than two smaller diameter tubes - the one potential point of weakness is the axle cantilevering, but clearly they've beefed this up sufficiently.

They did once make a dual sided fork using the same technology as their headshocks before Leftys existed - though I'm not sure if those had needle bearings.

I was impressed by that video when I first saw it.

It makes me wonder why making an acceptably stiff single crown upside-down fork can be so difficult if Cannondale managed to make this spectacular thing over 10 years ago.

(edit: someone managed to answer my question in the post above before I'd even asked it... amazing!)

One thing I'm not sure of is how Cannondale make a single sided inverted 'fork' which is reportedly as stiff as a very stiff thing but dual sided UD forks are constantly criticised for lack of stiffness. Is it the needle roller bearings that make the difference? Could Dale make a dual sided Lefty for DH?

Very good questions. Yes I think the bearings help, but more importantly the square section resists torsion.
They could make it dual sided, but then it would be heavy. Dale obviously decided long ago that the stiffness/weight ratio was optimal with a single leg.

[quote=smatkins1 ]It makes me wonder why making an acceptably stiff single crown upside-down fork can be so difficult if Cannondale managed to make this spectacular thing over 10 years ago.

As pointed out in the video, and I just mentioned, the issue is that an UD fork has round tubes which don't resist torsion, so you're relying on the bolted axle to do that. That and for the same weight a single tube can be made stiffer than two by increasing the diameter.

Of course you could put needle bearings in a UD fork, but you'd need two sets, increasing weight, and Cannondale's lawyers would get you.

I quite like the Lefty and would love an updated version of the USE Sub.

What always amused me was the launch blurb for the "new" Lefty a couple of years ago. Basically:- "look at our great new fork, with these solutions to the problems we always kept quiet about for the last 12 years of production (complete like lack of sealing, needle bearings migrating out of synch etc)"

http://singletrackworld.com/wp-content/uploads/2012/06/cannondale-2013-new-lefty-fork/

[quote=moshimonster ]Yes I think the bearings help, but more importantly the square section resists torsion.

It's a combination of the two - you can't really have one without the other.

I also want to click "like" on mick's post above.

the one potential point of weakness is the axle cantilevering, but clearly they've beefed this up sufficiently.

Agree with your post, but I don't think the single shear axle is an inherent weakness. It might look like one, but it isn't. No different from any car stub axle.

I've never seen a one legged rigid "fork" I wonder why?

Weakness was the wrong word - it's a point where you could potentially get flex, as it's tricky to make the diameters large given the requirement to fit bearings for a hub.

[quote=cheese@4p ]I've never seen a one legged rigid "fork" I wonder why?

[img] [/img]

It's a combination of the two - you can't really have one without the other.

Of course you can. Nothing to stop you using plain linear bearings instead of needle rollers or linear recirculating ball bearings. Not saying it would be better mind, but they are separate design features.

(complete like lack of sealing, needle bearings migrating out of synch etc)"

A big rubber belows dosent count as a seal? the bearing migration was so well hiden by cannondale it has a page in the owners manual on how to reset the bearings.

needle bearings migrating out of synch

This was one of the major problems with our Rally Car struts as it happens.

They could make it dual sided, but then it would be heavy. Dale obviously decided long ago that the stiffness/weight ratio was optimal with a single leg.

The original Cannondale Moto's were just that.

The lefty came after as a development of that because they realised they could build it single sided with sufficient strength and stiffness and save a massive chunk of weight. it also had the added benefit of allowing them to side-step the packaging constraints of building HeadShok's with any more than 80mm of travel.

cheese@4p » I've never seen a one legged rigid "fork" I wonder why?

There's also rigid lefty single crown available on some Cannondales, and a Spanish (?) company making a CF dual crown rigid lefty compatible with Cannondale hubs, Black Cat I think...

needle bearings migrating out of synch etc

Not only is it a 5 min procedure that is documented and easy to do, but the more recent Lefty's auto-reset on bottom out so it's pretty much a non-issue now.

[img] [/img]

[img] [/img]

[img] [/img]

Weakness was the wrong word - it's a point where you could potentially get flex, as it's tricky to make the diameters large given the requirement to fit bearings for a hub.

It's okay though, the bending load is very small. It's almost pure shear load so very easy to design strong enough to resist. Ever heard of one flexing or snapping off? I'll let you Google it for me 😉

Gasventinove make a lefty rigid fork called LAME, which is a thing of beauty.

Not only is it a 5 min procedure that is documented and easy to do, but the more recent Lefty's auto-reset so it's a non-issue now.

That's good to know. I was wondering about that. As I mentioned above it was a problem with linear bearings we used on car struts. Again simple procedure to re-align, but not the sort of thing you'd want to be doing in the middle of a WRC stage!

[quote=moshimonster ]

It's a combination of the two - you can't really have one without the other.

Can you have needle bearings without a square section? Maybe a bit strong to suggest you can't have a square section without needles, but that wasn't really the point, and as you say needles are clearly functionally superior.

[quote=moshimonster ]It's okay though, the bending load is very small. It's almost pure shear load

Under normal vertical loads maybe where the distance from the force is small, but how about sideways loading on the wheel as demonstrated in that video?

I have one on my 2004 jekyll.
I have used the bike through all seasons, for 10 years and taken it to Morzine for alps fun (but not gnarly rad stuff) four times.
In that ten years, it has been serviced twice, most recently just before the Alps this year. For £119 it had a new oil seal in the cartridge and new linear bearings. Robin at Evans in Kendal said it was now like new and indeed it did feel that way.
Bearing reset takes 5 mins.
Not a jot of play, very little stiction and seems to just work without any grumbling. Probably the nearest thing to a no maintenance component than I could hope for.
Ok, mine is the basic model with only adjustable damping but the spring was shimmed for my weight so I can't see needing much more adjustment.
I did go through a phase of wondering if I should get some regular forks to bring the trails alive but having seen friends' bikes blighted with fork issues, I'm not minded to. I'm sure it is enough fork for my needs.
I do fancy a new Jekyll though so if anyone at Cannondale wants to gift me one for brand loyalty, email in profile!

[quote=rockhopper70 ]I do fancy a new Jekyll though so if anyone at Cannondale wants to gift me one for brand loyalty, email in profile!

Get in the queue behind those of us who haven't got one and are still busy doing their marketing for them 😉

Surely riding one for 10 years and being only complimentary is marketing enough?
..put me at the front of the queue!

😛

It's a good feature, but not really fundamental to the strut design. How many cars have needle roller bearing struts? Virtually none, in fact the only one I know is the Rally Car version I designed. I think it's only been used on the Lefty quite recently.

The needle bearing has always been there, the updated design added a conventional bushing and seal to the lower round tube, previous leftys had octagonal stanchions and 4 bearings, a sytem they derived from the headshock fork which simialrly only has one telescopic leg (but with conventional unicrown bike forks underneath. Both the headshock and the original lefty had gaiters to keep contaminants out rather than seals.

It's not really the same as a car MacPherson strut, in the MacPherson strut the top is free to pivot, whereas a lefty is rigidly clamped. The car has a stub axle and uses the strut as the kingpin, which is why they use bushings rather than bearings as the strut isn't resiting any torsional loads, I presume your rally car must have allowed free roation at either the top or the bottom of the damper strut otherwise it would bind? The base of the strut is allso very well suppourted.

In car's it's not really the best system anyway, it's a comprimise needed to get the engine in transverse. Longtitudonaly engined cars have the option of using a double wishbone arrangement for better controll.

I've never seen a one legged rigid "fork" I wonder why?

The needle bearing has always been there, the updated design added a conventional bushing and seal to the lower round tube, previous leftys had octagonal stanchions and 4 bearings, a sytem they derived from the headshock fork which simialrly only has one telescopic leg (but with conventional unicrown bike forks underneath. Both the headshock and the original lefty had gaiters to keep contaminants out rather than seals.

Yes I see that now. I was confused by the update. Our Rally strut was octagonal too. I had a headshock on my 2003 Cannondale Scalpel, but the actual damping was horrific - pretty much non-existent.

It's not really the same as a car MacPherson strut, in the MacPherson strut the top is free to pivot, whereas a lefty is rigidly clamped. The car has a stub axle and uses the strut as the kingpin, which is why they use bushings rather than bearings as the strut isn't resiting any torsional loads, I presume your rally car must have allowed free roation at either the top or the bottom of the damper strut otherwise it would bind? The base of the strut is allso very well suppourted.

It's still a very good analogy for anyone who thinks the axle might just snap off. The Rally strut could rotate on bearings at both ends. The main gain in this application was reduced stiction, but it was stiffer in bending too.

Some interesting stuff from Mike Burrows:

http://www.cyclorama.net/viewArticle.php?id=278

In car's it's not really the best system anyway, it's a comprimise needed to get the engine in transverse. Longtitudonaly engined cars have the option of using a double wishbone arrangement for better controll.

How is this relevant to the discussion? Or do you really want an in-depth discussion of the merits of various automotive suspension designs? While double wishbone has long been considered the best suspension design, struts have still done remarkably well in racing and many very high performance road car applications too. Way off topic though.

Under normal vertical loads maybe where the distance from the force is small, but how about sideways loading on the wheel as demonstrated in that video?

Side loading at the tyre contact patch would translate largely into a tensile/compressive force on the stub axle. Not a problem at all.

No torque due to the 13/13.75/14.5" moment arm?

No torque due to the 13/13.75/14.5" moment arm?

The force [b]input[/b] might have a long moment arm, but it's only being applied to a very short stub, so the loads on the stub are going to approximate to either a tensile or compressive force depending on the direction you load up the wheel. Do you think it's a problem then or just trying to be a smart arse? Why don't you voice your concerns to Cannondale, I'm sure they can whip up a load diagram for you to ponder.

If the stub axle was very long, the bending moment would become an issue. But it's not in this case.

just to add another single sided rigid fork...

[img] [/img]

Can you have needle bearings without a square section?

but you can have a square section without.... oh never mind.

How is this relevant to the discussion? Or do you really want an in-depth discussion of the merits of various automotive suspension designs? While double wishbone has long been considered the best suspension design, struts have still done remarkably well in racing and many very high performance road car applications too. Way off topic though.

My point was that the infrance that it was the best system because it's what car's use was false. Car's use it because it's easy to design and build compared to a wishbone system, race cars use it because they have to be homologated.

Whereas the Lefty is demonstrably a much better system than the alternative on a bike (stiffer, lighter, less friction).

And the workings of the MacPherson strut as mentioned aren't particualrly similar to the lefty. If you mounted one on a bike it wouldn't work as there's nothing stopping it rotating. The only similarities are really elements of they way it looks and the stub axle (which to bring the point back round in a neat circle, is the same as the stub axle on a normal wishbone setup).

But agreed, we've gone off the point, but we went off the point when you mentioned McPherson(SIC) struts.

@aracer - now it's stopped raining it's time for a quick blast in the car. Maybe I'll see what fuel consumption I can get? I hope the axles don't snap off!

[quote=moshimonster ] No torque due to the 13/13.75/14.5" moment arm?
The torque input might have a long moment arm, but it's only being applied to a very short stub, so the loads on the stub are going to approximate to either a tensile or compressive force depending on the direction you load up the wheel. Do you think it's a problem then or just trying to be a smart arse? Why don't you voice your concerns to Cannondale, I'm sure they can whip up a load diagram for you to ponder.

What has the length of the stub got to do with the torque due to side loading? It's parallel to the load so makes no difference to the moment arm, still a torque even if it is zero length - the only difference is how much axle there is to flex, though I'm actually also interested in the interface between the axle and the leg. Not a problem because Cannondale have done a good job, but it clearly is a reason you could get flex due to side loading.

I'm quite capable of doing my own load diagrams, even in my head, which is how I worked out this would result in a torque. Looking at that video up there why do you think the conventional fork has independent leg motion due to side loading?

My point was that the infrance that it was the best system because it's what car's use was false.

I read the inference differently. Most people think the one sided axle is the dangerous/weak part of a lefty setup. All cars have a single-sided axle and wheels usually stay on just fine. Most ordinary cars happen to have struts too at least at one end, but as you're being pedantic I can see your point. Maybe you can come up with a better analogy for everyone?

aracer - I'm not saying there is no torque. I'm saying that the torque acting on the stub axle is not going to flex it very much as the resultant bending load is small due to the length of the axle. While I'm out, why don't you calculate the bending moment on the stub axle for us?

[img] [/img]

just to add another single sided rigid fork...

That fork was made by Mike Burrows. Mike loves single-sided wheels, though I'm convinced he build them first then makes up a reason for them later.

Maybe you can come up with a better analogy for everyone?

Car stub axles in general, it didn't need the MacPherson strut part, that just made is less valid as they're different solutions to different problems, just visusaly similar.

As an answer to Aracers question, it obously doesn't felx therefore is stiff enough, the axle/upright joint is pretty beefy. And bike wheel's arent going to take huge side loadings as unless they're dead on the axis of the fork they'd force the fork/bars to turn, bike forces would be much more in shearing the stub axle.

The Stub axle isn't tat much smaller than the ones on the front of my MG (they are quite small though, and competition cars use uprated parts), and the car in comprison will put much higher sideways loads on the tyre (imparting Aracers torque on the stub) and much lower shear forces (apart from maybe braking, but I'd think the shear force from that would becomparable to the sideways force from cornering on the tyres, but with a much smaller lever?).

[quote=moshimonster ]aracer - I'm not saying there is no torque. I'm saying that the torque acting on the stub axle is not going to flex it very much as the resultant bending load is small due to the length of the axle. While I'm out, why don't you calculate the bending moment on the stub axle for us?

For a side force F, the bending moment in the stub axle is clearly F.r, where r is the radius of the wheel (ie 13/13.75/14.5"). I'm ignoring here the moment due to vertical forces, though could add it in if it helps at all (it will increase the moment due to side loading from one side, decrease it for a side loading from the other side). Sorry for the delay whilst I worked that out.

Maybe you could point out where the length of the stub axle affects the bending moment in that formula?

[quote=thisisnotaspoon ]As an answer to Aracers question, it obously doesn't felx therefore is stiff enough, the axle/upright joint is pretty beefy. And bike wheel's arent going to take huge side loadings as unless they're dead on the axis of the fork they'd force the fork/bars to turn, bike forces would be much more in shearing the stub axle.

I agree - the whole point is that they've done a good job. Side loads on front wheels certainly aren't that high - though that was one of the points where the video was demonstrating an advantage for the lefty and conventional forks clearly do flex a lot due to them, so it's not something you can totally ignore, which is what makes it worth discussing.

@ben, I'm assuming you know who is in my picture above (not the first one, though he designed that), hence why I chose that, even if most here probably don't.

[quote=Rorschach ]

That diagram is wrong. Nobody does engineering to pick up chicks. Well nobody sane anyway.

@ben, I'm assuming you know who is in my picture above (not the first one, though he designed that), hence why I chose that, even if most here probably don't.

The picture of Mike? Yes, I've known Mike for years 😉

I agree - the whole point is that they've done a good job. Side loads on front wheels certainly aren't that high - though that was one of the points where the video was demonstrating an advantage for the lefty and conventional forks clearly do flex a lot due to them, so it's not something you can totally ignore, which is what makes it worth discussing.

I'd say it's more down to the dual crown stopping the leg flexing, a conventional fork flexes a lot at the crown (i had some 130mm manitou minutes that flexed so much the steerer contacted the headset cups!). they also allow differential movement in the legs allowing the wheel to twist in the same plane as lateral loading would flex the leftys singe leg and we've already covered that the lefty leg is much bigger than any conventional fork, infact I bet the stanchions on a fox 32 Vs 36 aren't that much stiffer relative to the lack of stiffness in the crown, they make it stiffer by increacing the size of the crown.

Yep, all of that makes it stiff, but most of your flex is always going to come from your weakest point, and if they hadn't beefed up the stub axle joint sufficiently you could get a lot of flex there, thus negating the stiffness of the rest of it.

For a side force F, the bending moment in the stub axle is clearly F.r, where r is the radius of the wheel (ie 13/13.75/14.5"). I'm ignoring here the moment due to vertical forces, though could add it in if it helps at all (it will increase the moment due to side loading from one side, decrease it for a side loading from the other side). Sorry for the delay whilst I worked that out.

Incorrect. The side force at the tyre contact patch is acting parallel to the stub axle axis, not perpendicular to it. What you have described above is the bending moment on the axle that would result from a 14" stick protruding out of the end of the stub axle with a vertical load acting on it i.e. acting perpendicular to the stub axle axis. That would be an issue for sure, but it's not how this axle or any axle is actually loaded.

The input torque you describe from the side load is real, but it acts clockwise/anti-clockwise directly around the centre point of the wheel on the centre axis of the stub axle. It is a pure torque as far as the stub axle is concerned, not the huge bending moment you are trying to convey.

The vertical force on the wheel does give rise to a pure bending moment on the axle, but acting at a very short distance, so it's never a problem either.

Do you get it yet? Or are you just arguing for points as usual? Draw it out and see for yourself. You said you were capable, so now's your big chance.

[quote=moshimonster ]The input torque you describe from the side load is real, but it acts clockwise/anti-clockwise directly around the centre point of the wheel on the centre axis of the stub axle. It is a pure torque as far as the stub axle is concerned, not the huge bending moment you are trying to convey.

So how does the stub axle resist that torque? What forces/torques does the load on your 14" stick result in at the centre point of the wheel? Actually come to that, what do you think the formula is for the bending moment on a stub axle length x (from leg to centre of wheel) of a sideways force F at the bottom of a wheel radius r?

I'll leave you with that, no time to draw diagrams for you now, though I've got a good one in mind for later...

Actually come to that, what do you think the formula is for the bending moment on a stub axle length x (from leg to centre of wheel) of a sideways force F at the bottom of a wheel radius r?

Practically zero. Imagine you drill a perpendicular hole through the stub axle on the wheel centre axis. Now push a 14" bar through that hole and load the end of it perpendicular to the bar i.e. parallel to the stub axle. The result is a pure torque twisting the stub axle at its centre point which is not going to create any bending moment at all - just compressive and tensile loads in the axle to resist the torque.

In order to create a bending moment, you need a force acting perpendicular to the axle (like the vertical wheel force for example), not a force parallel to it.

Is that any clearer for you?

I wonder if the OP feels his question has been answered yet?!

ha - i just finished work and checked back in to see the 3 pages of, er, engineering analysis 🙂

that Jekyl review on Pinkbike makes me quite want one