[jstuhlman]

So watching the commencal vid today got me thinking about rearward axle paths. Have heard peeps touting their benefits. Three questions:
1.) what bikes feature this (Commencal, Canfield Bros., Zerode come to mind...others?)
2.) if this is actually a benefit for dh riding why don't other companies develop it/design this path
3.) would it also benefit more AM type bikes designed for pedaling and descending?

Go ahead. Drop some knowledge on me. I ride an unrideable bike, I obviously need the help.

 

[HAB]

Most bikes have a somewhat rearward axle path in the first part of their travel. The degree to which this is true varies a bit, and bikes like the Jedi, Zerode etc just have a bit more rearward travel than most. Like anything, it's a compromise. The big reason you don't see it more on AM type bikes is that having a very rearward axle path means having a bunch of chain growth, which leads to more feedback at the pedals. This is generally more tolerable on a DH bike, but kinda sucks on something you pedal a lot. A well designed idler can mitigate a lot of this, but comes with its own drawbacks (added complexety/weight/drag/difficulty in using a front derailleur).

 

[johnbryanpeters]

http://www.santacruzbicycles.com/en/es/news/344

 

[ianjenn]

Multi Chain RIngs? Nobody uses 2 up front anymore. Doesn't The Jedi have over 2" of rearward travel? This article is saying 20mm is the most you should have? This is what happens when you live in SC and are constantly inhaling other people's weed....

There is almost no pedal feedback on The Zerode. It has been awhile since I had The Jedi but think it was the same. The idler works well in that regard.

 

[Westy]

I performed an exhaustive dynamic suspension optimization analysis and determined that the most important axle displacement vector component is actually in the vertical direction.

Also, rearwardness in travel is less important if you drink the bigger wheel purple drank.

 

[johnbryanpeters]

I performed an exhaustive dynamic suspension optimization analysis and determined that the most important axle displacement vector component is in the vertical direction.

You're just another marketing shill.

 

[Westy]

You're just another marketing shill.

Please, that is ///Marketing™ Shill® to you.

 

[FlipSide]

I came here expecting a gif of Michael Jackson moonwalkin'...

Don't forget Cannondale. They nailed that rearward axle path sh!t more than 20yrs ago.

 

[jonKranked]

in real world practice what rearward travel "accomplishes" is that on big/square edge hits at speed there is slightly less of a reduction in forward momentum to the sprung mass of the bike.

 

[ianjenn]

Since we are talking about rears.... NSFW

 

[Udi]

2.) if this is actually a benefit for dh riding why don't other companies develop it/design this path

It has benefits and drawbacks.
Bump absorption improves, but geometrical stability suffers, and the rider CoM moves forwards under suspension compression - this isn't ideal for DH, and may be part of the reason these designs aren't mainstream. They also add weight and complexity, a Zerode for example is so far behind current standards for weight that most people (me included) would rule it out purely on that basis, and even bikes without the gearbox like the Commencal V4 come at a significant weight penalty. Personally I think the V4 is a cool implementation since the pivot is lower (thus it'd suffer less from geometrical variations) and the weight penalty is also smaller. I'll answer the question about AM bikes later.

 

[OGRipper]

How come nobody ever talks about forward rebound path when this comes up? Seems like it would be a drawback, particularly in chatter/successive hits.

 

[jackalope]

I vehemently disagree with both Westy and Udi (who is also probably an undercover marketing shill). Vertical wheel travel of any amount just upsets your CoM and is therefore inefficient, bottom line. In collaboration with @mtg, I developed my patent pending, 100% horizontal wheel path system -

The suspension design, currently dubbed as the Wheelbase Tensioning Force system, allows for 100% anti-skwatz and 100% skwatz, a highly variable wheelbase, and explosive if somewhat uncontrollable acceleration out of berms. While I don't have any production models ready to ship quite yet, I am currently taking orders provided you're willing to pay in full up front (Price is whatever a new Crabon Demo is plus $1) . Please send $$$ to my Paypal email account:

WTFlahar @ aol.com

 

[Udi]

Please send $$$ to my Paypal email account:
WTFlahar @ aol.com

I know this is a scam because your email address has "lahar" in it. Nice try asshole.

 

[ianjenn]

I am not sure I would say so far behind. The YT Carbon Pro I am testing now in size LG was 37LBS my Zerode G2 in size LG was 38.5LBS. Kiran Mackinnon XL V-10 is 37LBS he uses real DH parts. The gearbox is for sure added weight, not sure what effect removing 1lbs off the back wheel has on suspension.

But why would a standard drive-train bike that is rearward in design be heavier than a VPP or FSR design?

 

[canadmos]

I vehemently disagree with both Westy and Udi (who is also probably an undercover marketing shill). Vertical wheel travel of any amount just upsets your CoM and is therefore inefficient, bottom line. In collaboration with @mtg, I developed my patent pending, 100% horizontal wheel path system -

The suspension design, currently dubbed as the Wheelbase Tensioning Force system, allows for 100% anti-skwatz and 100% skwatz, a highly variable wheelbase, and explosive if somewhat uncontrollable acceleration out of berms. While I don't have any production models ready to ship quite yet, I am currently taking orders provided you're willing to pay in full up front (Price is whatever a new Crabon Demo is plus $1) . Please send $$$ to my Paypal email account:

WTFlahar @ aol.com

Looks like a Morpheus

 

[mtg]

The suspension design, currently dubbed as the Wheelbase Tensioning Force system

Bottom line: inefficient.

 

[hmcleay]

The attached diagram (courtesy of linkagedesign.blogspot.es) illustrates the story pretty well.
I have put a coloured dot against each of the designs that use an idler pulley to facilitate a more rearward axle path.
The remainder use what I call a 'conventional' drivetrain.


Over the last 10 years or so, suspension designs have matured quite a bit in relation to pedalling performance. It's pretty hard these days to find a bike that is genuinely unrideable (as opposed to 'RideMonkey Unrideable', which is a very long list).
For any design with a conventional drivetrain, the only means of tuning the pedalling performance is to alter the axle path.
Small changes in axle path make fairly large changes in pedalling performance, so the window of 'rideable' axle paths is fairly narrow.

At the front of the bike, we've seen head angles get slacker every year. And each time we get used to a slacker version, we feel that the old 'steep' HA is now unrideable.
To me, it makes a lot of sense to unshackle the constraints from the rear axle path, and let it evolve in the same way that head angles (and other geometry) has evolved.
The only way to do this is to incorporate an idler pulley, to de-couple the existing relationship between axle path and pedalling performance.

What is the 'ideal' axle path? nobody can answer that. It will very much come down to personal preference.
The obvious benefit of the rearward axle path is that the suspension behaves like it has a lower wheel rate when presented with a large obstacle, whilst still retaining the same 'vertical' wheel rate which is relevant for things like pumping and cornering.
As Udi points out, the downside is that the lengthening of the chainstay makes the bike less playful, as it is harder to pop your weight off the rear of the bike.
Perhaps if(when) idler bikes become more mainstream, there will be enough consensus to settle on a preferred axle path region 'window' where there is a good trade-off between these traits.

To specifically respond to OPs questions:
1. a few more: i-track, Ghost, Bulls, one other not yet released, and quite a few older brands trying different stuff back in the 2000s.
2. other companies don't develop it because idler pulleys are seen to be 'whacky' by the market. Most larger brands would see a drop in sales if they released a bike with an idler pulley. I'm sure that more companies will start to jump on board once the design starts to mature, and the market perception becomes more favourable.
3. this is definitely relevant to AM/Enduro bikes, and shouldn't be confined to DH bikes. the concept of having large amounts of travel that can eat large obstacles, whilst still being a great pedaller up the hill are key ingredients to a good AM/Enduro bike. Stay tuned for one being released in the next few weeks.

How come nobody ever talks about forward rebound path when this comes up? Seems like it would be a drawback, particularly in chatter/successive hits.

We already have this situation with the forks being at an angle.
If a front wheel traverses a sinusoidal terrain, the rebound speed will be much higher than the compression speed (as it 'pops' off the top of each bump).
The same will happen at the back of the bike if there is a rearward axle path.
assuming the rebound damping on the shock can be tuned to suit the riders preference, then this shouldn't be an issue.

 

[Sandwich]

in my opinion and experience, a high pivot (more than an inch and a half above the chainring) is a bike that handles the rough stuff really well but doesn't corner as well. They are superb going through chunder, but in tight turns with high Gs they pack up, the chainstays get long, and they don't sprint out as well as other bikes. The way the geometry changes makes it a mor difficult bike to stay on top of. I feel like there's a happy medium where you can get some of the axle path effects without the geometry concerns, and that's where the majority of bikes currently rest.

 

[jstuhlman]

very curious to see what's coming (zerode) and to hear feedback/reviews/marketing hype/specs. thanks all - good info and interesting food for thought.

 

[xy9ine]

^yup. stoked to see the rest of this:

 

[Udi]

I feel like there's a happy medium where you can get some of the axle path effects without the geometry concerns, and that's where the majority of bikes currently rest.

Definitely agree with the happy medium comment, however I don't think all that many bikes nail that just yet.

On bikes without an idler, AS curves (and to a lesser extent pedal feedback effects) strongly limit how rearward the axle path can be - common knowledge to you / others here. I feel ideally the rearward travel values would be slightly higher than this. However on bikes with an idler, there seems to be an attitude of "well, we've invested the time/effort/weight in implementing the idler, let's make the most of it by putting the pivot really high / making the axle path heavily rearward". In my opinion this is a mistake. Particularly with the advent of 650b and improved bump absorption / rollover characteristics, there isn't a need to run the axle path so rearward at the cost of geometrical stability.

3.) would it also benefit more AM type bikes designed for pedaling and descending?

It would actually benefit AM bikes more. As I said above, axle path on non-idler bikes is restricted by the AS curve - which in turn (with all else equal) is heavily dependent on chainring size. Most AM bikes these days are running 1x 32T chainrings (unlike the 36-38T on a DH bike), which leaves almost no opportunity for rearward travel. On top of this, on a DH bike you can further compromise acceleration performance slightly for the sake of axle path since it's not particularly important (not many DH bikes actually do this, but I like the ones that do) - however you can't make this compromise on an AM bike since acceleration performance is so important.

Combined with the reduced travel, AM bikes end up being substantially inferior to DH bikes in bump absorption (if both are optimised with all things considered).

However this leads me to the other big mistake many "idler-happy" manufacturers make. They're almost always stupidly heavy, and just like acceleration performance, weight is a huge consideration on AM bikes. Lightweight modern AM frames are usually 2.5-2.8kg for frame including a modern air shock. If you can't keep it at ~3.1kg or less with air shock, then you're wasting your time and/or designing for a minority.

I'll add though that this isn't completely unreasonable either, if that minority is the intended audience - people who for example shuttle their AM bikes because their tracks are faster / more enjoyable on a shorter travel bike, and don't actually need to climb on them. In that case the weight compromise would be acceptable - however, ideally you'd implement your idler and axle path within a competitive weight.