Let's Talk Axle Path

I mean I rode only one HP Bike which is more of a mid pivot bike (Kavenz VHP16). I mainly bought it because I sold my Downhill Bike and only had a Privateer 141 which I loved Geometry wise.

Looking at the rear-end only it performed great. Good in chunky stuff and decent on more mellow terrain. But my main Problem was that I always had the feeling I only had grip on the front tire like it is a knives edge. If I moved my body a bit to far to the back I lost grip and if I moved it too far above the bars I had the feeling of going OTB. A lot of that is mostly due to the short chainstays of the bike. But the more I reflect on it I think both axles moving to the back and therefore shifting your body mass forward in relation to the axles was also a big issue for me. I started riding as a 6 six old in the early 90s and never really got rid of my rear focused riding style.

One reason I switched to the Privateer 161 after a long pause in Winter due to Covid and several colds. I was testing a Down Country bike with a linkage driven single pivot in a bike park. I was quicker with that bike down the mountain than with the Kavenz which felt kinda odd. But that told me exactly that my riding style matches better with a traditional suspension layout.

Next summer/spring I want to test a Dreadnought from a buddy against my 161 to see if the axle path thesis beeing a part of my problem is true or if it was only the short chain stays. Reflecting on the rides and feel of the HP bike I think overall it is not a suspension layout which really caters to my riding style.

90% rearward and do what you want with the last 10% 

I'd like to poke the "Magnified Axle Path" charts in the eye. Companies/media, please show charts that are more visually accurate, as a lot of charts have double to triple the rearward axle path in a line measured on a screen (chart is full width of page) - while actual rearward path might be a tiny 20mm. 

I ve had a Deviate Claymore for a little less than a year, and now the Highlander 2. I test rode the Cannondale HP, and didn't like how "soft" and vague it felt like described above. However both Deviates are riding a lot closer to a 'normal" Enduro bike. For reference, i ve had an SB160, a Scor4060 and a Stumpy Evo to compare to.

Between the 2 bikes, the Claymore is much more of a big bike, in a good way. tons of traction, confidence, and move forward despite any chunk. i do not feel any vagueness, and it s still very playful.

The H2 is more of a trail bike, and with a float X shock on, it is not feeling as plush or soft as the typical HP bikes. I think Deviate is, and has been ahead on the hp Hype, and their linkage helps a lot with the wheel path coming back.

I do have to admit i had to mess with shock tunes and set up on claymore to find a good support and not stay deep in the travel. The extra traction on those HP bike is very noticeable. Also staying active under breaking in braking bumps style hits. 

I do big pedal days on various terrain in the desert mainly, on both this bikes, and honestly with the minimal weight difference, i would just pick the Claymore anyways because it s really close in pedal efficiency and weight, but then beneficiate to all of the plush.

I would be curious to try few others, but so far i like the feel, even for everyday bike.

I think some smaller manufacturer or riders like Neko like to stay on a 4 bar, because it is a lot easier to control what the wheel path and overall kinematics is. Also easier to work on shock tunes, and have a better control of the rear wheel via your shock.

What you describe sounds just like super-short chainstay bikes, not necessarily a high pivot. I'm super curious to hear your feedback on that Dreadnaught to verify your theory. 

LONG RANT INBOUND

From my limited experience, it sounds like one of the main benefits of high or mid-high pivot bikes is that the idler pulley on most designs acts like a chainless rear suspension- it is typically tuned to reduce any chain pull and subsequent drag on suspension performance. Its hard to sus out this difference along with the change in axle path. 

A more rearward axle path will obviously help the suspension react to mid sized hits better, but I suspect the effect is less dramatic than having a more raked out head tube angle in the front. Think about where on the tire your wheel hits a 6 inch sized square edge- its not the bottom. its around the 4 or 5 oclock position on the wheel. Draw a line from here to your main pivot- no matter the design, even a dirt jumper-style bottom bracket pivot location, you're getting plenty of rearward movement. A well tuned high-speed compression can get pretty close to parity with high pivots in this regard, and this is seen in racing as high-pivots don't automatically win every world cup/enduro race. 

Where I think the greatest benefit of high pivots, esp. mid-high pivots, is in geometry preservation. Short chainstays are great for tight or strongly bermed trails, but we've all probably felt that instability or fore-aft sensitivity that short chainstays give (think most of mid 2010s Specialized bikes). Designs without an idler tend to allow for rearward axle movement in the first third of travel to give higher antisquat for pedalling and smaller square-edge hits. However, every manufacturer is scared of too much antisquat deeper into the travel because nearly all of antisquat comes from chaingrowth. For instance, the entire point of the DW patent is to optimize chaingrowth around the sag point for excellent pedaling efficiency, but then switch directions after that to make sure total chain growth isn't too much, and it actually has regressive chain growth towards the end of the travel. This is probably critical back when we had dual and triple chainrings, no clutches, and canted derailleur trapezoids. I personally don't think this is relevant now. The downsides of high chain growth is drag on the suspension, reduced small-bump compliance, and ultimately grip. These things actually don't matter in the bottom half or third of travel. Tying this back to short chainstay instability, low chain growth or regressive chain growth (without an idler) necessitates shortening of chainstay length deeper in travel when stability is needed most. If your low speed compression tune is good, you should only be using the last third of your travel on big landings or very large hits, when small bump compliance & grip matters the least. It is stability that matters the most here, and the less forward-moving your axle path is during the last third the less your chainstays will shorten the more stability there is. 

This brings us to the current Specialized Enduro- big S put their main pivot as far forward of the bottom bracket of nearly any design, giving a much more vertical and straight rear axle path. The last 1/3 of the travel is going to move forward far less than nearly any other non-idler design out there. For those that haven't ridden the bike, go try it. While not perfect, the rear suspension performance is incredible, even with poor suspension setup. I suspect this pivot placement was accidental, as Specialized wanted the main pivot to co-locate with the forward linkage pivot so they had to put it there. It really made me sad when the new Demo prototype seems to have regressed with the main pivot behind the bottom bracket. 

Finally, bringing these two things together, we get Neko's design. It has a really high pivot (like the previous gen Scott Gambler that he loved and the rest of us loved so much too) without the complications, weight, and drag of an idler. This, like the Enduro design (another one of Neko's favorite bikes) minimizes chainstay shrinkage. The Enduro approach keeps chain growth under control in the beginning of travel since the main pivot location isn't that high, but Neko's doesn't so he employs the strange chainring thing that I forget the name of to maintain good traction with high chaingrowth. Neko's design therefore attempts to balance the best of both worlds- traction around the sag point, but geometry preservation throughout the suspension travel. I happen to think the Specialized Enduro approach is better, but it has its own strength and manufacturing issues (as anyone whos owned the latest Enduro knows full well). I personally think the ultimate design is still a mid-high pivot, but combine it with a gearbox and dual chain approach like the Dave Weagle patent on BK's race prototype. Or even better, a reliable version of Effigear's offset output shaft gearbox (this single-stage approach lacking a concentric output/input has the highest potential for efficiency of any gearbox design, but thats another forum) that includes a mid-high pivot location without any pulleys extra chains, etc. With this or the dual chain approach a design can have literally 0 chaingrowth and practically identical performance to a chainless bike. 

Anyways, my two cents.
 

your experiences are on the money.

I rode high single pivots in the early 2000's when I was racing DH seriously, they were shit lol

20 years later, I'm at Thredbo and a guy I knew from Sydney just got a Supreme, we swapped bikes (I was on a Meta AM29) and within 100m the rearward axle path took my heart.

There is a section on the top of the Thredbo DH track that is a small kicker but lands into some big rocks, every other bike you need to brace for impact pretty much, the rear end shortens and the stability is decreased. On the supreme it literally propelled you forward when landing on the same section, it was incredible. I did another lap and in the same section I pumped the lander! If you saw this section you would think it's ridiculous, but the supreme made it possible.

Where that bike lacked was the lower section of the track, which is basically a big pump track.

Terrain and pivot placement dependent, results may vary. But I love them.

I'm all in on the reward axle path half way through travel, then back to 0 at full travel. I think this is the best of both worlds if you get your dynamic sag and average position correct, you use the best of the axle path.

Trek Session

Commencal V5

Frameworks

Crestline RS205

Atherton AM200

*I'm going to assume the new Intense M1 will be close to this.

Here is an average axle position from a run at Killington during the US Open on Supreme V5.  The average ride was between 40%-90%, This window has 4-5mm of reward axle path. 

Average position- 26%

Dynamic Sag- 26%

Max Travel- 198mm of 225mm (2 hits at 198mm and 3 hits @ 175mm)

Yeah, great question. It really surprised me, but the axle path of the Deviate and Trek were basically a non-issue for me during testing. There was never a time when I was testing either when I thought the rear axle path was magical or terrible. I had some theories about what I was expecting to feel on both bikes, and didn't feel it. The Deviate is a much more rearward axle path than the Trek by the way, the Trek is more of a "mid pivot" have-your-cake-and-eat-it-too design.

What I expected to feel on the Trek and especially the Deviate was an unpredictable and inconsistent rear center, where the back of the bike would surprise me in unwelcome ways by either being further back or further forward than I was expecting in a given situation. I talked about this a lot in the hour-long test session video, but the Ohlins fork and rear shock on the Deviate were both phenomenal and did a great job of controlling low speed shock movement. I think that's why I never noticed the rear axle doing something unpredictable- because it wasn't. The rear shock was stingy with big movements, but happy to let the shock move around for little impacts and small bumps. Really impressed. I think if you put an entry level Fox, Marzocchi, or Rockshox shock on there with no low speed compression knob, you'll start noticing a lot more suspension movement and maybe some of those negative, unwanted rear axle moving around problems I expected.

On the flipside, there was never a time on either bike when I thought the rear axle path saved my bacon, either. I think Big Bear is a great test area for 90% of riding scenarios, but it doesn't have the same super violent impacts or g-out turns you would get in a place like Whistler. I suspect an extreme rear axle path becomes more apparent in those 10% riding situations.

So what you are saying is that you need to ride the Deviate with an entry level shock. Sorry the bias in your conclusion is glaring. Basically you are saying that the undesirable kinematics that you expected from the Deviate didn't occur so it must be because of the shock, not because your expectations were incorrect........

This is quite an interesting topic, I've had a couple of high pivot bikes and probably wouldn't buy another... Kinda.

I had a norco aurum, which was great I thought. It was always terrible in corners and front end grip was kinda vague. I thought it was a sizing thing perhaps. 

I then got a norco range and thought this is way better. Could still feel the rearward axle path, but it turned better etc etc.

Which led me down a real rabbit hole, I put a wrp link in it which gave fully rearward axle path and dual crown.

Anyway, I thought the bike was awesome, held speed well through rough stuff. Nice and stable. Until I rode it back to back with my ebike, a vpp Crestline. I was noticeably more confident on it and it handled way better. Far less fussy on front wheel weighting. 

And that's the crux of high pivot stuff with extreme rearward axle path. The chassis is inherently more stable under compression events and front wheel weighting dynamically changes more than normal pivot bikes. During cornering events that stability requires different technique to make them turn as does front wheel weighting. It's kinda like 29er vs 27.5 riding, subtle but you know it's there. It's not to say it's better or worse, just a personal preference thing. They absolutely do what they say on the box when it comes to straightline rough sections though. 

I say I wouldn't buy another high pivot bike 'kinda' because I picked up a Crestline rs205, it is night and day easier to ride faster with a more consistent rear center. I used the same parts as my norco so it was a pretty good comparison I thought. So I guess that answers the question... I want a axle path that yields a predictable and easy to ride chassis because for my level of riding will best suit. 

I hope the bias in my conclusion was glaring, because I tried to spell it out as clearly as possible. I had an expectation for the Deviate and, to my surprise, that expectation wasn't met when I rode it. I'd love to ride it with an entry level shock to see how the axle path feels with less damping and more suspension bob.

So while we wait for you to do an entry level shock comparo is it safe to assume that High Pivots (because they have inconsistent rear centers) require factory level shocks with lots of LSC in order to ride good? 
 

First and foremost, there have already been a ton of great contribution, I love getting to hear other riders experiences and insights, especially on a topic that despite being around forever, seems to be having a refined resurgence.

Okay, now we can strap in for a bunch of word vomit. TLDR: High pivots are great for the right rider/terrain, static geometry can be confusing, suspension has trade offs, blah blah blah.

Axle path is an interesting discussion. As a few others have stated, there’s no denying that a rearward axle path offers some noticeable benefits. But I also think it requires balance when being implemented. I’d argue the Dreadnought  is at the extreme end of things - ie. long static chainstays, and rear centre grows through the entire travel range, and it has fairly high anti-rise.

As an interjection before my monologue below, I really like the comments above about how LSC is a bigger factor because there’s less chain influence. Also, after reading @hamncheez2003’s comment, I came to the conclusion he LOVES high pivots, but had to use the cop out that they’d only be good with a gear box and 2 chains, which I have to admit sounds like something I’d love to try. 

This past season I’ve been lucky enough to be riding both a Kavenz VHP18 and a Hope HB916 (both bikes having ext rear shocks). Previously owned a MY20 SJ Evo for 3 seasons (again, with an ext Storia). I’d classify the Hope a mid-pivot bikes, as it has less than 10mm of total rearward growth. The VHP18 is maybe a mid-high pivot and with about 20mm’s of rearward. But on both bikes, at ~60% of its travel the axle path arcs forward, and I think this is really important. This means that the rear centre length change from sag to bottom out is fairly minimal. I think this is one of many aspects of where the predictability or vagueness can come in. If your axle path has an inflection point, it means that the max length is reached at some point before bottom out. Full disclosure, I haven’t ridden a bike that grows all the way through its travel, but there is a difference in feel between the VHP18 and Hope. I can be lazier on the Hope in corners and it doesn’t really feel all that different. But on the VHP18 if I don’t push hard into the corners, I can feel the rear end growing and feeling a little lazy/vague for sure. This is solved by really pushing with my legs through the rear end as I enter the corner, or riding the front tire and just having the rear follow the arc. 

With that said, the inverse is true in a straight line. The Kavenz is notably more bump-eating and smooth (yes it’s 20mm more travel but I’m also running less sag, so it’s comparable). The Hope still feels improved over the non-high pivot bikes I’ve ridden on square edge impacts. The VHP18 also feels slightly more glued to the ground and less eager to “pop” off jumps and such, and I’d say the Hope feels pretty normal on jumps, nothing weird and has enough pop when I need it.  Additionally, I rode a lap at whistler bike park on the VHP18 this summer without a chain or rear mech (it was for testing, not because I crashed and snapped a hanger…) and I honestly didn’t notice much difference in how the suspension performs, which shows that the idler is doing it’s job of separating out chain forces.

Another aspect is how a lengthening rear centre applies more weight on the front tire as both ends go through their travel. This is can give that balanced/centred feeling, but when it’s too extreme, it can force you to ride aggressively. And if you don’t, you’re fighting the bike to try and get over the back end and apply less weight over the front and having your weight forced forward can be fatiguing. Personally, the Kavenz feels like the first bike I could corner in moderate terrain with almost no weight on the handle bars, and just being centred and driving through my legs. Plus, those short stays mean you can “swang off the back” like Mr. MoiMoi himself, right???? I’m all for proportional chainstays, but I think that these numbers start to get messy when you’re mixing in axle paths. Around 50% travel, the Specialized Enduro and Kavenz VHP18 have almost identical rear centre lengths, despite an 17mm difference in the static numbers. I’ll be the first to say I thought the Kavenz chainstays were laughably short, yet after the first few rides I was eating my words.

Although not necessarily related to axle path, both the bikes I’ve ridden have anti-rise values equal to or a little less than 100%. Personally, I think this performs better in a wide range of trails and terrain than a value >100%, and better than values <60% in sustained steep terrain with crux moves and chassis stability are important. This is based on my terrain, and my experience, and I can understand how and why others might like values outside of my specified range, so don’t come for me with your pitchforks!!

It looks like most bikes coming out with high pivots this days have shifted away from an extremely rearward axle path. The new Commencal Supreme v5 is less rearward than the previous iteration, as is the Druid v2. It’s like anything in suspension kinematics, there’s a trade off, and I think that trade off is “how much rearward axle path can you get before cornering is effected”.

So for me, based on my fairly limited experience on a couple high pivot bikes, I think that 10-20mm of rearward arc, followed some amount of forward arc, seems like a good compromise. I’d love to try one of the Frameworks DH bikes, because I really feel as though Neko has balanced on a fine line of rearward axle path without adding an idler. But even Neko talks about how the trade offs he’s made for the DH frame won’t work on the enduro bike and it will likely end up being a more traditional 4bar arrangement. It probably goes without saying, but I don’t think high pivots will become the norm, there are plenty of suspension designs out there that do a fantastic job and require less complexity (although complexity is somewhat subjective in this case). However, I love that there are more and more high pivot options becoming available, because I really do think they offer an advantage for the right rider on the right terrain. And I personally plan to continue riding high pivots as they really suite the steep natural terrain and bike parks of the PNW, at least on bikes with 150mm+ of rear travel.

Having owned two of the more "extreme" HP bikes over the last few years (Deviate Highlander mkI, 150mm and Forbidden Dreadnought), I have a few thoughts on this. These are the main things I believe that HP bikes do differently, independent of geometry:

1. The effective increase in rear centre length as a function of travel has a unique effect on dynamic weight distribution. I find this most noticable in those extreme g-out situations i.e. the last 10% that Team-Robot mentioned. I believe this is why HP bikes with extreme rearward axle paths can feel weird off of jumps and drops - however with correct suspension setup and small technique adjustments it can feel different but crucially without being unpredictable.

2. The rear wheel seems to hang up less on square edged hits through straights and I find they "want" to accelerate through rough stuff as opposed to pack down. The highlander in particular really wanted to John Deere the shit out of everything in front of it.

3. The addition of the idler gives frame designers more flexibility to fine tune kinematic characteristics like AS/AR and pedal kickback, BUT there's still an infinite number of ways to execute pivot/idler placement (regardless of it being a HP design) that contribute to how the bike rides.

What I'm getting at here is that we can't lump all HP bikes into the same basket in terms of ride-feel. I've also found small geometry differences can have profound effects on how the bike rides. Comparing the dreadnought to the highlander (geo comparison here), the dreadnought corners like a housefly and is night and day in terms of agility and ability to change line/direction quickly. The compromise made here is that it feels slightly more involved in rough stuff. In my experience the only common denominators between them are points 1 and 2 but they felt much more noticable on the highlander. Perhaps the HP facets are magnified by the longer static rear centre length? 

One final thing I think is relevant is that both me and my HP frame-owning friends have found they ride much, much better with shock rebound set to the faster end of the spectrum. Still not 100% sure why.

TL;DR - unsurprisingly, there are a large number of static and dynamic variables that affect how bikes feel to ride regardless of suspension layout and axle path but HP seem to me to share some common characteristics to varying degrees.

I have been trying to think why a growing rear-centre makes bikes feel awkward on more flowy/bermed corners and I have a vague idea that might be completely wrong. 

When you're going straight over chunky terrain, having the back wheel go backward and up makes it easier to roll over obstacles since the axle path wants to move the wheel in the same way it is already getting pushed. That makes the rear feel 'smoother' compared to a low pivot/shortening-rear-centre setup as the latter's axle path wants it to go back towards the thing you just hit which increases the force required to move the wheel. These are high(er) speed impacts where you need to keep your centre of gravity a bit back so you don't get hung up/chucked forward, and with a growing rear centre there is plenty of room to do that. 

When you're on a flow trail in a bermed corner, I find myself usually standing a bit taller for a continuous arc or trying to really push into the rear of the bike to get it to snap in a tighter line. Either way I'm attempting to get myself (and my centre of gravity) behind the bike or almost over the rear wheel. If I have a lengthing rear-centre it is going to be hard to get to this point unless I move way back (which may be difficult depending on the bike's reach), and if the axle path grows but then shortens at the end of travel that could through you off if you push hard enough into the pedals to get near the end of the shock's stroke. 

However like Team Robot mentioned (with respect to the Deviate/Trek) you could get around these points with some tuning to low vs high speed on the shock. You can't make a low-pivot bike's rear axle move out of the way as easily but you could let it open up more freely in that scenario. Similarly the rear end on a high pivot (with growing rear centre) wants to get away from you in a berm but you could firm up the low speed to support you better in that scenario. 

So I have owned and ridden quite a number of full suspensions throughout the past 6-7 years. I've had a few rockys, a few specialized bikes, GTs, had a Canfield as of recent, and I've ridden countless others (forbiddens, slashes and sessions, megatowers) as demos, rentals, small test rides, whatever you may call them. Of them all, I really enjoyed the Canfield the most, although the megatower and dreadnought bikes were extremely good- forbidden being the best in the chunk. 

To my point; I'm rather insatiable, so I made my own. My pivot point is about a foot above the bottom bracket. Nothing too complicated about the design, it's a single pivot with a rathee unique leverage ratio 2.8-2.5-2.8 (start-mid-end). The rear suspension feels bottomless. And while the bike is big and heavy, I cannot emphasize my next point enough. If you're going to make a bike with a rearward axle path, the wheelbase and headtube angle need to be equally absurd. You cant have a trophy truck with a rally car front end. My initial WB is 1335mm and hta is 59. Doing these things will make the bike easier to ride faster, as I have found.

With these slacker (more rearward) axle paths, we can start having lower sag numbers, and still get better compliance than a regular bike in chunky sections, because of the way the wheel moves. Now we have all the more support (less sag) in the end of the travel because of the higher spring rate (or air pressure), which means less harsh bottom outs. This also allows you to run less compression, which means better small bump.

In terms of cornering performance, at least on my bike (kinda blowing smoke up my own ass, I'm sorry), I like how the front end naturally weights up more under high-compression turns. The rear wheels moves away from me more, and the front wheel gets way closer to me. This means that the bike is really easy to ride on the edge of grip, there is a huge margin for error on this bike, like none other I've ever experienced.

Jumping the thing feels just like any other bike, really, with the exception being that there is more forgiveness when you land a nasty case.

Climbing performance is pretty much entirely determined by the positioning of the idler pulley, which makes things easy from an engineering standpoint, less compromises.

The big fat issue with high pivot bikes as a whole is chain retention. It took me more time to figure out how to make the chain stay on than how long it took to engineer and build the thing for God's sake. These things eat up chain with their suspension like crazy, and I think I'm going to add a secondary tensioner to my design this winter. I highly recommend the use of a SRAM derailleur with any bike of this nature, the clutch is strong, but it doesn't impede on suspension performance anything like what the shimano units do (touchy subject, I know, just my opinion)

Lots of interesting points here. There are some comments stating that the fork/front axle moves back a lot, but I don't think that's really that big of a deal since it is moving up too. I don't think the front center changes too terribly much with a fork when it moves.

10 minutes later...

Just for shits and giggles, I measured my Sentinel. I think a fairly average trail bike at 150mm rear travel, 160mm front, and maybe slightly slacker than average 64 degree head angle. At 0mm sag, the front center is about 31 3/8" (sorry internet, I don't have a long metric tape measure). At bottom out, the front center is about 29 5/8". It was a fairly linear shortening of the front center through the travel. I was surprised too, that was more backward movement than I thought it would be. It was right around 1.75 inches backwards, 44mm back from full extension to full bottom out. I believe this amount of rearward movement will change with a steeper or slacker head angle. 

If you have a really rearward axle path on maybe slightly larger travel bike, there could be a lot of center of gravity movement in relation to the axles. I was talking with one of the more well known suspension design guys years ago, and he was saying that the big rear axle paths just shouldn't work as well as the race results indicate. He said there was just too much difference in front to rear weight distribution as the suspension cycled. This was when Pierron was just annihilating people riding like his hair was on fire. I called bullshit. But you know what, Commencal went away from a winning design, and I believe now has less of a rearward overall axle path. I believe Specialized did that as well. Their new new main pivot looks more rearward, and I would guess that would make a shorter lever arm and more arc in the wheel path, assuming the FSR link is in the same ballpark. Lots of things can change with four links, but I don't think the Specialized DH bike is getting a more rearward axle path either. Maybe that suspension guy wasn't full of it. A lot of the highest pivot bikes have toned it down, and more bikes have come to be more up and down in their axle paths, with less rearward motion. 

How does this relate to my first thought on the front center getting shorter through the travel? I dunno, maybe some companies are trying to limit the variables, and if more weight is in your feet anyway, the rear end being a consistent length (or center of gravity staying in the same spot between the axles) might be the most important thing.

Maybe traction and balance are paramount for some of these designs instead of just bump absorption and feel. 

Sorry to break it to you, but the amount of horizontal and vertical travel when it comes to the fork can easily be calculated with some trigonometric functions:

Hor_mov = Travel*sin(HA)
Ver_mov = Travel*cos(HA)

So yes, it will of course change with changes of the headtube angle. Plus it can change on the same bike depending on how you measure it - do you measure it compared to the 'static' wheelbase? Parallel to the dynamic wheelbase from the BB, which changes where in the travel you are front AND back? Straight from the BB to the front axle? Etc. The most valid one would probably be the parallel to the dynamic wheelbase one as it will give you the actual front centre (and rear centre) measurement in regards to weight distribution compared to the BB. But then again, maybe the actual front .vs rear centre measurement could be where the centre is the actual CoG of the whole system and how the two lengths change through the travel in regards to that. But then you also add rider position into the mix

I'm not an engineer so forgive my primitive take. I just saw this PB article on this new prototype Aper bike: https://www.pinkbike.com/news/first-look-the-aper-kompace-has-rising-pi…

If you think about, a curved rear axle path doesn't make any sense at all. Shouldn't it be a linear, rearward and upward diagonal line to match the fork? If you landed flat, the wheelbase could theoretically stay exactly the same.

Has this been tried before?

A big question in this thread is if it makes sense to keep the wheelbase the same anyway. If you do that then your CoG will move forwards when going through the travel, which might be a big negative.

There's also the problem of one side of the bike's suspension moving more than the other side, so you're not in sync anyway. The biggest benefit is probably something that's predictable and current layout might be more predictable than parallel paths.

Plus using rotating links it's nigh on impossible to make a linear axle path (google Chebyshev linkage, Lawwil might be adapted to come close, etc.). And it makes little sense in doing it as it will not give a big advantage, it might even make sense to have a curved path and make the path itself an advantage. After all cars don't have linear movement of the wheels even in the highest echelons of motorsport where millions are spent on this topic and they don't seem to have an issue with it. Plus linkage forks can be made to work and they don't have a linear path as well...

It was kind of fun reading this for a while and seeing what everyone thinks. I haven't ridden all high pivot bikes, but I've ridden a good number. Here's my take...

The change in weight distribution thing is very real. I find it most obvious whenever I'm transferring weight around on the bike actively, such as lifting the front. It actually drives me crazy having the amount you have to lift change so dramatically throughout travel. Also noticeable cornering in being easier to oversteer. A lot of people tend to unintentionally unweight the front going into corners so that could be good for some people.

Going off weight distribution, there is something to be said for an axle path where the rear center doesn't change much through travel and an axle path that is forward proportional to front and rear centers. When the rear center doesn't change, the force to lift the front is consistent through all of travel. When the axle path is shortens the rear center such that front center and rear center are proportionally the same through travel, there is no for/aft weight shift as the bike compresses. 

Magnified axle paths lead us astray often. It makes it seem like various axle paths are more different than they actually are. If you scroll back up to the axle path plot above and consider the axle path at around sag point, the Aurum and Session look wildly different. In reality, if you draw a line tangent to each path at that point, there's a 2 degree difference in slope between the two. This is an approximation of course, but we aren't going to be an order of magnitude off. The slope of that line is really what's going to give a certain axle path its feel at any given point. I guess what I'm trying to get at here is the general trend of the axle path is more noticeable than a very specific shape. If you were to come up with a frame that had a perfectly linear rearward axle path that kind of averaged out that the Aurum and plotted both non-magnified, there deference is negligible. But the fact that the Aurum remains reward until the end is noticeable compared to the fact that the Session becomes forward near 50% travel.

If you look at the Stumpjumper Evo and the Ripmo, which are similar style bikes, axle path is actually extremely similar. This plot is true scale. Ripmo is the one with slightly less travel. My take is axle path is not what gives these bikes their character. Other aspects of their kinematics and geometry make a bigger difference.

Well surely a very reaward axle path will have a influence compared to a Stumpy or a Ripmo? Maybe saying axle path doesn't have as big of an influence people think it has would be a better way of saying it?

We were talking about comparing a conventional Horst and DW bike. 

Good point, missed that one, I was aiming more overall (I think that part is clear). And your comment also makes more sense then, the axle path will be similar, but the AS can be quite different. Let alone the leverage ratio, which is wholly unrelated to other kinematic properties.

Yeah as long as the axle paths are in the same ballpark. Magnified axle path just makes it look like things are less similar than they are quite often. The thing I like about more rearward axle paths, mainly in the first half of travel, is the vertical displacement of the wheel doesn’t also pull the wheel over the bump at a faster rate. On medium sized and larger bumps immediately after the wheel has gone into a hole I do notice less of that getting hung up sensation compared to a more conventional axle path. But Dreadnought vs Range, for example, I couldn’t blindly tell them apart due to axle path alone. The difference in anti rise is quite apparent however. 
 

On another note related to plotting axle paths, for my own use at least I always plot them relative to the BB instead of top of travel. Easier for me to visualize how it will impact things with travel increases or geo changes.