[Pegboy]

Rather than explain the physics behind this, which I'm not sure I can do, I'll give you a real life test. Take a fast corner, hit it Sam hill style, standing proud with high COG. You'll find the bike turns in quickly. Now hit it again, but tucked Steve peat style. Not only will the bike not turn in as easily, but you'll need to give the bike more lean angle. No particular style is quicker, that's governed by other factors. But you don't see too many motocross riders trying to lower their COG in corners do you?

PS - this has been known, although not necessarily well understood, in motorcycle dynamics for a while now. Although most of the study centers around road racing, where things are a bit different and low COG does help.

Ok, I'll agree to an extent. I, however, have been watching a bunch of moto lately and guess what...the only time those guys sit down is in corners. Intentional or not, this lowers cog along with suspension compression. Same with road racing, those guys drop their knees, inside shoulder and head into turns.

Initiating turns has nothing to do with it...it's the fact that you have to go from one turn to another. That is one reason why ski racers angulate (upper body relatively vertical with feet and legs leaned way out). You can arc turns by leaning in, but when you have to quickly switch directions and turn the other way, it slows down timing and takes more effort.

Take a four foot long bar and hinge it to the floor to represent point of tire contact. Flop it from side to side like a windshield wiper. Now take a 5 lb weight and slide it from the base to the end of the bar...obviously it makes a difference.

Yes, the body has a more significant affect but when we are trying to refine things as much as possible it does make a difference.

And back to your moto comment; take a YZ 250 from the late 80's and stand it next to a 2012 YZF 450...you think those engineers had no concern with cog?

 

[hmcleay]

It reminds me of this concept... http://www.i-tracksuspension.com/index.html

Idlers, when designed well (Not this case) can be very good, and with the new X-11 group we can see them on AM Bikes too, not just DH Bikes.

Thanks for the link Vrock.
Thought i'd try and bring this thread back on [i-]track a bit. Pun intended.
Obviously I'm a big fan of these 'floating idler' suspension designs. Unfortunately, as noted above, this is a poor example of how to implement it.

When looking at this design, it's difficult to 'see' how chain tension will affect the suspension movement. On one hand, the chainline is well below the main pivot, so it appears that chain tension would extend the suspension (loads of anti-squat). On the other hand, the chain applying force to the idler would seem to cause the suspension to compress.
In order to quantify the overall affect of these, it is necessary to do a graphical analysis (method currently not public knowledge).
Fortunately, i-track suspension has collaborated with Linkage software to provide graphical analysis of these suspension systems.

With this particular design, anti-squat is around 100% at sag. No problems there. Also beneficial is that 'Frame AS' and 'Total AS' are pretty much equal at sag, meaning minimal pedal feedback at sag (see i-track suspension website for discussion on 'Frame AS' and 'Total AS', and how they relate to pedal feedback).
The problem with this design is that anti-squat increases all the way throughout suspension travel, and ends up being around 500% at bottom out. Among other things, this causes significant pedal feedback in rough terrain.

Full credit to the Redalp guys for trying something different. But to me it looks like they don't fully understand the theory behind their design.

The first i-track prototype is currently being developed, and will showcase (albeit only scratching the surface) what is possible with these types of suspension systems!
And yes, the advent of 11sp drivetrains means that we can work on a 6-7" AM bike that pedals bike a XC bike!

Cheers,
Hugh