Fork vs Linkage Suspension

[InfiniteWheelie]

This thread isn’t to talk about naming (there’s other threads for that), but to discuss the differences between the two.

To kick it off I want to talk about travel. A lot of people seem to think linkage wheels are capable of higher travel, resist bottoming out on big jumps better, and are better for off-road. Even former CEO Bob from InMotion talked about how forks are great for road wheels but they’re “easy to bottom out”, so they’ll be using linkage on their off-road wheels.

I know linkage suspension has progressive travel due to the geometry of the link mechanism. However I don’t understand why a fork suspension with the same travel can’t achieve the same thing using a progressing spring. Air springs are naturally progressive, and coils can be wound tighter/looser at either end to also be progressive.

I consider fork suspension to be superior for e-wheels due to being direct mount, simpler, more hidden away etc. Therefor I’m wondering is there even a reason to use linkage on any wheel? Why can’t off-road wheels just use long travel, progressive forks?

Edited August 13, 2023 by InfiniteWheelie

[mhpr262]

I suspect the main problem is that a fork that allows long travel (lets say 4-5 inches) and hard offroad use must be pretty long and therefore beefy because of the massive lever arms involved, and if there is still to be a decent gap between fork and the upper part of the tire (to precent clogging from mud for instance) the overall width of the wheel may become an issue too, especially with upside-down type forks.

[InfiniteWheelie]

@mhpr262 I don’t think there needs to be much clearance between the tire/fork, tire/shell, tire/mudguard etc. Any extra mud build up should just be brushed away as you ride.

The Sherman S has roughly 3.5” of travel, while the longest travel linkage wheel (S22) has roughly 5” of travel. Would an extra 1.5 really make the fork (and thus the entire wheel) that much wider? I don’t think so.

There’s also other ways to make the wheel slimmer. For example the way the V13 spreads out it’s 2 layers of batteries so they aren’t stacked directly on top of each other.

While it’s true that a longer fork needs to be stronger (wider), I don’t think it’s actually a limiting factor. I also don’t think that’s what people are referring to when they say linkage is better for off-road.

Edited August 13, 2023 by InfiniteWheelie

[Hellkitten]

15 minutes ago, InfiniteWheelie said:

@mhpr262 I don’t think there needs to be much clearance between the tire/fork, tire/shell, tire/mudguard etc. Any extra mud build up should just be brushed away as you ride.

I’ve had mud jam up between wheels and mud flaps on mountain bikes and had my v11 clogged from tenacious thick dense clay/mud. I had to use a stick to get enough out just to get home, before cleaning the rest out. The more clearance the better IMO. 

[InfiniteWheelie]

@Hellkitten Maybe you’re right. I can see it being an issue for a human powered bicycle, but I figured a powered vehicle would just power through it. Maybe the self balancing function of e-wheels makes it more of an issue.

Perhaps it’s also especially important for off-road wheels to be slimmer for handling reasons. I’m not sure, I don’t ride off-road.

Slimness seems to be the one advantage linkage wheels have. I’ve just never heard that articulated as the reason for using it in off-road wheels. Instead people seem to focus on long/progressive travel, which seems to me that forks can easily match.

Edited August 13, 2023 by InfiniteWheelie

[Planemo]

17 hours ago, InfiniteWheelie said:

I’ve just never heard that articulated as the reason for using it in off-road wheels.

It isn't.

17 hours ago, InfiniteWheelie said:

Instead people seem to focus on long/progressive travel, which seems to me that forks can easily match.

They can. I covered why linkages were originally introduced in the MC market on the other thread and its nothing to do with any particular spring/damping unit being any better than the other.

The only real benefit of linkages is that it gives you the option of altering the leverage ratio at pretty much any point throughout the travel. This is quite difficult to do with springs in a fork (or on a coil over shock) as altering the windings throughout the travel (not just a plain progressive spring) can be a nightmare at best.

For euc's we really dont need that level of control, so the answer to your question is that forks can provide as fundamentally good control as linkages, the only reason to choose between them being packaging.

Fwiw, if the eon's old fork design was inferior in anyway, they wouldn't still be using it on 99.99% of MC's including cutting edge GP, MX and pretty much every other pedigree bike out there.

[InfiniteWheelie]

2 hours ago, Planemo said:

20 hours ago, InfiniteWheelie said:

I’ve just never heard that articulated as the reason for using it in off-road wheels.

It isn't.

So why is this the case? We seem to agree that the only real benefit is packaging (specifically slimness), but people seem to cite performance instead.
 

2 hours ago, Planemo said:

The only real benefit of linkages is that it gives you the option of altering the leverage ratio at pretty much any point throughout the travel. This is quite difficult to do with springs in a fork (or on a coil over shock) as altering the windings throughout the travel (not just a plain progressive spring) can be a nightmare at best.

Can you expand on this? I believe linear coils are evenly wound, while progressive coils have a tighter wind towards one end. Why would it be difficult to wind the spring increasingly tighter in the exact manner you wanted?

Edited August 13, 2023 by InfiniteWheelie

[mrelwood]

On 8/13/2023 at 3:54 AM, InfiniteWheelie said:

There’s also other ways to make the wheel slimmer.

It can only be as slim as the widest section. The ShermS is already very wide, and the shocks reach from the axle to the top of the wheel, forcing a boxy shape. And the tops of the shocks dig in to riders calves so they have to design additions to make it not hurt.

I don’t know how Inmotion plans to design theirs (or whether the plans even carry on without Bob the CEO), but they definitely won’t sacrifice their house slimness and ergonomics like that.

9 hours ago, InfiniteWheelie said:

Why would it be difficult to wind the spring increasingly tighter

I don’t think it’s at all about technical challenges. EUCs are manufactured in small batches, and getting only a few hundred custom springs or even shock designs made can be financially disruptive. Veteran was able to do linear spring suspensions with a dedicated shock manufacturer who probably uses standard springs that are readily available to them. In general, I’m not sure if EUC manufacturers’ own fork shocks would have a very good probability of making a home run at the first try. Look at the Begode EX for example. And even the V11 system is a bit cringe worthy.

I do think that currently the ShermS/Patton is the best in terms of comfort, but I do see big challenges in making an ergonomic wheel design with similarly styled shocks.

A swing arm suspension on the other hand might be the next step though, that could offer both unparalleled small bump compliance as well as a progressive mechanism for the coil/air spring. But it doesn’t have common design sources to implement like the current forks and linkages do, so it will probably require a few iterations to work well.

[Planemo]

10 hours ago, InfiniteWheelie said:

So why is this the case? We seem to agree that the only real benefit is packaging (specifically slimness), but people seem to cite performance instead.

Which people? The EUC crowd who are alll noobs in the field of suspension?

10 hours ago, InfiniteWheelie said:

Can you expand on this? I believe linear coils are evenly wound, while progressive coils have a tighter wind towards one end. Why would it be difficult to wind the spring increasingly tighter in the exact manner you wanted?

Its not difficult to alter the coil spacings. What is difficult is altering the ratio at certain points in the travel. For example a linkage can *reduce* the ratio at increased levels of travel. Why would you want this? To combat the effects of excessive progression from an air shock for example. This is one reason why fitting a coil to a linkage designed for air can be totally the wrong thing to do as you find out you are blowing through all the travel. So what do these people do..? Fit a massively high poundage spring and then find out their small bump compliance has dissappeared..

The point is that you dont always want a progressive setup, sometimes a regressive curve at a certain point in the travel is preferable. As I say I dont think its something we really need to worry about with eucs. Take a look at some leverage charts, you'll see that some follow an 'S' shape, very difficult to do with a spring..

[InfiniteWheelie]

@Planemo Thanks, those are great points. So linkage can do some fancy things with progression/regression that can't be done without it. I think you're right that this extremely high degree of control isn't needed to have great suspension on e-wheels.

I’ve been thinking in terms of coil forks so far, but now I’m thinking maybe air forks would be even better. Of course companies wouldn't need to stock multiple springs, and riders could simply adjust the pressure to suit their weight (or even to suit the terrain that day). Plus it would be significantly lighter.

Wouldn't this also allow you to adjust pedal height? Through a mix of lowering pressure and adding volume spacers, you could make the wheel sag for a lower ride height. This would be useful when riding on smooth roads that don't need as much travel. Couldn't you even remove pressure entirely to have a ridged wheel without having to disassemble like the V13?

Edited August 14, 2023 by InfiniteWheelie

[Rawnei]

I used to thing that linkage design was superior but now owning both types (S22, Patton, Sherman S) I'm leaning more towards fork style for these reasons:

• Fork style is enclosed, no dirt gets in there, this is a huge advantage on EUC as we can't use a simple link like on a mountainbike, we need a sliding mechanism
• Fork style is pretty easy to maintain if needed, they will have a long lifetime just need to change seal and oil eventually and they will keep operating with minimal wear (I already changed seals on my wheels because I wanted SKF seals, it was easy)
• At least on LeaperKim wheels the suspension with fork style is super smooth, it has a superior feel to any other suspension wheel I've ridden (I've also owned a V11 and a Master, I've ridden the EX30 so I have some experience here), I've installed a more expensive Rockshox shock with a 600lb coil on my S22 trying to emulate this smooth feeling, while it's good it's really not the same amazing small bump compliance
• Bottoming out is not a problem, I'm a 100kg+ rider with my gear on, I just set enough dampening on my Sherman S and my Patton and they don't really bottom out, I do jumps an drops, I don't need to compromise and still have amazing small bump compliance, perhaps if you are doing like 1m drops it starts to become a problem but I think that no matter what wheel you have that will be a problem if you want a smooth feeling suspension with good small bump compliance at the same time, those two things are mutually exclusive, I could install a 900lb spring on my S22 if I wanted to do that sorta thing but then small bump compliance will suck, it's such a niche and outlier example that it's not worth it.

Edited August 14, 2023 by Rawnei

[mhpr262]

8 hours ago, mrelwood said:

I don’t know how Inmotion plans to design theirs (or whether the plans even carry on without Bob the CEO), but they definitely won’t sacrifice their house slimness and ergonomics like that

One solution would be oval forks, not with a circular but an oval cross section of the fork "tubes". If Honda could make the NR750 engine with oval pistons then an oval fork is surely feasible. But I suspect that would be very, very expensive to do.

[InfiniteWheelie]

@mhpr262 That’s a cool idea. Not only would it save room, but it would actually make the forks much stronger in the direction that matters (forward/back, where all the force from acceleration/braking goes).

[Planemo]

9 hours ago, InfiniteWheelie said:

@Planemo Thanks, those are great points. So linkage can do some fancy things with progression/regression that can't be done without it.

You got it.

9 hours ago, InfiniteWheelie said:

I’ve been thinking in terms of coil forks so far, but now I’m thinking maybe air forks would be even better.

Air is easily adjustable for the end user which is why just about every MTB is specced with it. The downside is stiction from the airshaft given it needs seals to house the pressure within. There is absolutely no doubt that springs (obviously) present no stiction issues which is why they perform better in every way when it comes to stiction and therefore response. Which is why every competitive downhill MTB uses springs. Admittedly, this requires the spring rate and linkage to be set up for the individual rider concerned. Its no easy feat, but works waay better than air. If you get a chance, try a ride on a coil equipped mtb, its like a magic carpet.

[Planemo]

5 hours ago, mhpr262 said:

One solution would be oval forks, not with a circular but an oval cross section of the fork "tubes". If Honda could make the NR750 engine with oval pistons then an oval fork is surely feasible. But I suspect that would be very, very expensive to do.

The NR750 was a road version of a race bike designed to cheat and get around race regs. I dont want to state how much Honda spent to try and make it work (lots) and even then it wasnt feasible for long term reliabilty even for road bikes. I dont think any euc manufacturer will ever go the same route. The idea needed shit tons of effort, skill and monumental machining processes.

Even if it was to be available I'm not sure how it would make things better forward/back. If you had the long edge front/rear the width of the wheel would be excessive. If you had the long edge on the sides it would be 90 deg to the forces and therefore not doing a lot... unless I'm missing something.

[Planemo]

7 hours ago, Rawnei said:

Fork style is enclosed, no dirt gets in there, this is a huge advantage on EUC as we can't use a simple link like on a mountainbike, we need a sliding mechanism

True. Although not totally enclosed. The exposed dust seals and general stanchion cleanliness is paramount so as not to allow wear to the super thin stanchion coating.

7 hours ago, Rawnei said:

• Fork style is pretty easy to maintain if needed, they will have a long lifetime just need to change seal and oil eventually and they will keep operating with minimal wear (I already changed seals on my wheels because I wanted SKF seals, it was easy)

True.

7 hours ago, Rawnei said:

• At least on LeaperKim wheels the suspension with fork style is super smooth, it has a superior feel to any other suspension wheel I've ridden

True, but thats not fork vs linkages. Its only because the other offerings are so shit in their design. We still havent seen ballraces in the linkages which just about every MTB other than Walmart crap uses.

7 hours ago, Rawnei said:

• Bottoming out is not a problem, I'm a 100kg+ rider with my gear on

Bottoming out shouldnt be an issue whether its air, spring, linkage or not. Its all in the design.

Air certainly gives more flexibility in that you can add tokens to increase progression and add air to set sag without messing about with springs. But springs will, without fail, give a better ride if set up properly simply due to reduced stiction. And stiction is something that many air riders dont and can't appreciate until they switch to a decently set up and designed spring system.

I still run air front and back on my 180mm/160mm travel MTB and I have done everything possible on my setup to reduce stiction. Its still there and it still annoys me, despite it being impossible to reduce it any further. I know its there because I have experience of coils. The only option is to go springs on my bike but it will take £800 minimum to convert even using my original forks. The rear is a complete swop-out unit.

[Rawnei]

1 hour ago, Planemo said:

True, but thats not fork vs linkages. Its only because the other offerings are so shit in their design. We still havent seen ballraces in the linkages which just about every MTB other than Walmart crap uses.

The issue is we can't just gave a swing arm and call it a day, we need sliding movement for motor (or worse: pedals) to move up and down, if you don't have the sliding mechanism enclosed then it will be exposed to the elements, if sliding mechanism is enclosed it might as well also act as a shock, and then the circle is complete and were back to fork style.

Another factor is mechanical wear, even if somehow the sliding mechanism protected if it's based on anything other than a spring or air (back to fork) there will be mechanical wear over time, I don't see how any other design will solve these problems in an easy or elegant way, rollers or bushings that we see on other wheels are "serviceable" but have multiple problems like high wear and dirt interference.

So for me fork seems like the way forward, perhaps development of that can lead to more travel and maybe even progressive springs and other fancy features.

[Tawpie]

In the discussion, don't forget appearances... "looking snazzy" is certainly immaterial vs performance, but looks do matter. The look of a linkage suspension gets attention... forks are not terribly impressive looking. If the performance is similar and the cost is similar, the design and marketing folks are going to want the cooler looking option. As a suspension, the S18 left a lot to be desired... but it sure set the design side of EUC development on its ear.

The downside of linkage is that there are a lot of ways you can get it flat out wrong, and even more ways you can get it close but not truly excellent. To get fork style right you pretty much just need excellent dampers—I believe that's why LK went with FastAce... have the folks that make a living with dampers deal with it and you just figure out how to make it fit. It seems to have been a good move too, because at least for street, most feel the SS is without peer. And pavement is a very popular place for people to ride.

Edited August 15, 2023 by Tawpie

[InfiniteWheelie]

9 hours ago, Planemo said:

Even if it was to be available I'm not sure how it would make things better forward/back. If you had the long edge front/rear the width of the wheel would be excessive. If you had the long edge on the sides it would be 90 deg to the forces and therefore not doing a lot... unless I'm missing something.

Imagine you have a round fork and an oval fork with the same volume. The oval fork will be narrower (makes the wheel slimmer), while taking up more space front to back (the "pointy" ends of the oval point front/back). This makes the fork stronger when pushing in that direction (acceleration/braking).

Edited August 15, 2023 by InfiniteWheelie

[Planemo]

7 hours ago, InfiniteWheelie said:

Imagine you have a round fork and an oval fork with the same volume. The oval fork will be narrower (makes the wheel slimmer), while taking up more space front to back (the "pointy" ends of the oval point front/back). This makes the fork stronger when pushing in that direction (acceleration/braking).

Ah I see what you are getting at, yes it would increase strength in the front/back plane. But as I say oval forks wont happen anyway.

As a side note I think your idea would also increase the loading on the bushings as they are now effectively narrower. A moot point maybe.

[Vince.Fab]

On 8/14/2023 at 3:36 AM, mrelwood said:

A swing arm suspension on the other hand might be the next step though, that could offer both unparalleled small bump compliance as well as a progressive mechanism for the coil/air spring. But it doesn’t have common design sources to implement like the current forks and linkages do, so it will probably require a few iterations to work well.

I have a few CAD designs of a swingarm frame with RS internals.  You would be surprised how much the wheel arcs throughout the travel due to the short swingarm. This could have detrimental effects because your weight will effectively be shifted back to front of the axle. 

Also one of the design constraints is motor wire length if it's run along the swingarm.   I've been waiting to get a Master motor cheap to experiment more but they are still $$$. 

[InfiniteWheelie]

@Vince.Fab So I'm not the only one playing with e-wheel ideas in CAD. I've been learning from scratch specifically for this reason. I still suck at it, but now I've been able to (roughly) put together some ideas that I have.

 @Planemo I'm starting to really see the appeal of coil. I researched more, including the force vs travel charts, and I can see what you're talking about. The curve starts well above zero force, and kind of just hangs around the middle until rapidly peaking to match the coil. Not quite how I imagined it looking. Also, I actually see the appeal of having linear travel for smoothness and predictability, without certain spots lacking. You can play with negative pressure chambers, tokens etc. but it adds a lot more complexity for what seems like an effort to actually (somewhat) emulate a linear coil in the end.

Of course coil suspension is very simple, and much more supple in the beginning of the travel. In my opinion the weight increase is a non issue for powered vehicles (unlike human powered bikes). The only real downside is the need to offer a few different springs for different rider weights. Not a huge deal in my opinion, especially if the fork is a one spring design (as almost all MTB bikes are). Once you get that setup, it's basically "set it and forget it". I'm back on the coil bandwagon. 

Edited August 17, 2023 by InfiniteWheelie

[Planemo]

13 hours ago, InfiniteWheelie said:

 @Planemo I'm starting to really see the appeal of coil. I researched more, including the force vs travel charts, and I can see what you're talking about.

Don't get me wrong, air works really well providing it's being actioned properly (leverage charts again) and air obviously provides easy adjustability for a lot of different rider weights and indeed terrains. But physics prevents them from ever being as friction-free as a coil, which is most certainly noticeable.

13 hours ago, InfiniteWheelie said:

 but it adds a lot more complexity for what seems like an effort to actually (somewhat) emulate a linear coil in the end.

And thats exactly it, all the fancy trimmings, tokens, valving and effort that gets spent on tweaking air (I have even played with enlarged negative chambers on mine) is ALL to try and make air behave more like a coil. Air has only been flogged to death as much as it has because as I say, it makes sense for most applications where you have a huge range of rider weights and terrains. If you can chuck a generic air can on a whole range of bikes and get away with it, its a bonus for the manufacturers.

13 hours ago, InfiniteWheelie said:

The only real downside is the need to offer a few different springs for different rider weights. 

TBF ideally you want maybe 10 different springs. With something like an EUC (unlike a bike where you get a bit of flexibility due to the rear helping out) you could probably do with 10 springs to cover from say rider weights of 70kg up to 120Kg (5lb increments as per MTB forks).

The main difference between MTB and say the SS setup is that getting the right sag is more critical simply because of the relatively short travel compared to MTB which are going to be running at least 160mm so you have a little more leeway. So the choice of spring for the SS will be more finicky to hit the right spot of say 25% which I generally run.

As an aside, the main thing I notice with the vids I have seen on EUC suspension is that many are running hopelessly small amounts of rebound damping, bouncing down the road like trampolines. The action should be far more controlled. I've seen vids of riders pandering to the camera with them bouncing up and down like a ping pong ball to show off their amazing suspension

Compression damping isn't as critical given most EUC setups have pretty dire friction to help on compression anyway.

[okvp]

On 8/14/2023 at 5:29 PM, Rawnei said:

I used to thing that linkage design was superior but now owning both types (S22, Patton, Sherman S) I'm leaning more towards fork style for these reasons:

• Fork style is enclosed, no dirt gets in there, this is a huge advantage on EUC as we can't use a simple link like on a mountainbike, we need a sliding mechanism
• Fork style is pretty easy to maintain if needed, they will have a long lifetime just need to change seal and oil eventually and they will keep operating with minimal wear (I already changed seals on my wheels because I wanted SKF seals, it was easy)
• At least on LeaperKim wheels the suspension with fork style is super smooth, it has a superior feel to any other suspension wheel I've ridden (I've also owned a V11 and a Master, I've ridden the EX30 so I have some experience here), I've installed a more expensive Rockshox shock with a 600lb coil on my S22 trying to emulate this smooth feeling, while it's good it's really not the same amazing small bump compliance
• Bottoming out is not a problem, I'm a 100kg+ rider with my gear on, I just set enough dampening on my Sherman S and my Patton and they don't really bottom out, I do jumps an drops, I don't need to compromise and still have amazing small bump compliance, perhaps if you are doing like 1m drops it starts to become a problem but I think that no matter what wheel you have that will be a problem if you want a smooth feeling suspension with good small bump compliance at the same time, those two things are mutually exclusive, I could install a 900lb spring on my S22 if I wanted to do that sorta thing but then small bump compliance will suck, it's such a niche and outlier example that it's not worth it.

Sliding mechanism can be using enclosed and sealed forks like Inmotion Adventure with link suspension. Servicing is not that big job with KS-22 it takes less than 20mins to remove the wheel from sliders and change the rollers (1$ each) which may have been broken.

Chinese seals are bad and they leak so good brand seal are must. Changing the seals is pretty messy operation. The other thing is how long chinesium bushings and slidetubes will last, are they actually a good quality?

Linear suspension with SOFT spring is smooth both with fork and link. If it's not there is something binding or damping is too high, there is no reason why it would be not. Personally I don't wan't EUC to feel like an old Cadillac. I like to feel the road. People are complaing that Patton bottoms out higher jumps.

There is reasons why motorcycles rear suspension went from stereo fork style suspension to mono linkage style. One is cost (only one suspension system), progression of travel...

Biggest thing currently is that you cant get good fork shock (with decent damping system) for EUC, they all are made by Chinese very low end companies. With linkage suspension there is a possibility to change the suspension with quality air or spring shock (with lots of spring rates).

[Rawnei]

7 minutes ago, okvp said:

Sliding mechanism can be using enclosed and sealed forks like Inmotion Adventure with link suspension. Servicing is not that big job with KS-22 it takes less than 20mins to remove the wheel from sliders and change the rollers (1$ each) which may have been broken.

Chinese seals are bad and they leak so good brand seal are must. Changing the seals is pretty messy operation. The other thing is how long chinesium bushings and slidetubes will last, are they actually a good quality?

Linear suspension with SOFT spring is smooth both with fork and link. If it's not there is something binding or damping is too high, there is no reason why it would be not. Personally I don't wan't EUC to feel like an old Cadillac. I like to feel the road. People are complaing that Patton bottoms out higher jumps.

There is reasons why motorcycles rear suspension went from stereo fork style suspension to mono linkage style. One is cost (only one suspension system), progression of travel...

Biggest thing currently is that you cant get good fork shock (with decent damping system) for EUC, they all are made by Chinese very low end companies. With linkage suspension there is a possibility to change the suspension with quality air or spring shock (with lots of spring rates).

If sliding mechanism is already enclosed might as well act as suspension also, but you're replying to something that was also written before Adventure was announced.

I have an S22, I was one of the first people to advocate how easy it is to service the wheel, just changing rollers is not enough, on my S22 the paint inside the channels has come off in places where rollers have moved the most creating uneven surface and stiction not to mention sliders themselves rubbing against opening of channels, an open design is problematic in multiple ways, it works for a while but will eventually wear in different ways.

Chinese seals do not leak by default, that's a QC problem in FastAce factory not installing seals properly, one don't "have to" change seals if QC worked as it should which it doesn't for any of these wheel manufacturers, changing oil seal is not a particularly painful or messy procedure, I have done it twice, it was easy but it's not relevant you are mixing apples and oranges here.

Your whole argumentation how suspension should "feel" comes down to tuning, tune the rebound and dampening to make it feel like you want.

Motorcycles don't need the wheel to slide up and down, as they have two wheels the rear wheel can be on a swivel so it's not a valid comparison as there's completely different challenges to overcome.

EUC suspension is still very new, it will take time before it's perfect, as we can see all the manufacturers have different approaches, time will tell what works best.