There are many factors at play here: (* Note, some generalities made for the sake of simplicity)
1. Tire choice / Set up - Obviously beefier tires will give you more traction, but as you noted the Ibis and the Scalpel had the same tires, so it's not the entire story. Wider rims will cause the tire to be more "square" ie. the offset between center tread and sideknobs will be less. This will decrease the vagueness of the transition from upright to leaned over. It will also increase the rolling resistance as the beefier sideknobs are touching the ground more often. Will this help traction, sure, but again it's not the entire story (don't expect a revolution with slightly wider rims). Go fully extreme and you get to the plus sized tires. A plus sized tire at low pressure (under 20) will change your rough climbing and help you transition into a mountain goat. But, they roll slower and can fold under extremely aggressive riding (e.g. no one on a triathlon forum).
2. Bike Geometry - Mountain bike geometry is all over the map. So many seat-tube angles and head tube angles. As a rule of thumb the steeper the better the bike will behave going up, the slacker the more confident on the down. Seeing as though you like the up and down better, this probably isn't the key.
3. Suspension Travel - This is potentially it. With short travel bikes the volume of the air canister is low, which means the shock rates ramp up quickly. This means the bike has to be set up stiff to not blow through travel AND the rate ramps up quickly as you work into that travel. It's Stiff x Stiff = 3xStiff. When the Cannondale guys talked about taking bands out, I assume they meant taking out volume reducers which makes the rate more linear. This makes the bike feel "plusher" at the expense of increased bottoming out. (Note, this is why most DH and long travel bikes run coil instead of air-shocks they're much more linear).
The increased travel and changes in spring rate cause a few things to happen.
a. With the increased sag, the travel can extend into a recess keeping better contact and control. (Just as car suspensions extend into pot-holes, they don't just skip over them.
b. Small bump sensitivity improves. This helps you stay isolated from the ground and keep the pedals churning. Your center of mass moves in one direction instead of bouncing up and down.
c. Longer travel (and wider bars) instantly add smiles, so even though you may be going slower, you're having more fun.
4. Suspension design - The Ibis uses a DW-Link which is a highly engineered system. It is designed to allow plush suspension under pedaling and braking with minimal pedal-bob. The Specialized uses a Horst-Link which is a moderately engineered system for plush suspension under pedaling and braking but with more bob during pedaling (hence the "Brain" to help eliminate that).
- There are other designs out there. The simplest is called a Single-Pivot, which means the rear triangle is solid and the chain stay is connected via a single pivot to the downtube / seat tube.This is the system that Cannondale uses. (Benefits: Light, Simple to maintain) This means that the rear-axle will follow a simple arcing path. If the pivot is place high (a la Orange Dh Bike) The arc of the axle will be moving up and backward as the suspension compresses. This makes for a great feeling on the downhill as the rearward movement of the axle allows the wheel to track over rocks well, but a lot of pedal feedback because the axle is moving away from the bottom bracket as the suspensions compresses. The increased length causes the chain to pull backward on the cranks and suddenly your pedaling is affected by the ground. Low single pivots are still affected, though to a lesser degree, but they also give up the plush downhill. This is because the axle travels more or less vertical.
The engineered systems tend to have the rear axle follow a complex path, to try to maximize plushness which reducing pedal feedback etc.
Pivot location also affects the anti-squat of the design. This is the tendency for a suspension to extend /stiffen under pedal load. High anti-squat creates a strong pedaling bike that has less active suspension. On a single pivot this is easier to see as the height of the pivot is a big determinant. On a complex suspension, it's more complicated.
The other issue with single-pivots is that suspension tends to stiffen up when braking. Horst-link and Dw-link are less prone to that (they remain "Active under braking").
The advance course covers how "Leverage Ratio" changes with each design...
I'm willing to bet that this is a large part of the difference you are feeling.
Short Travel Bikes:
Many XC bikes have simple suspensions: Yeti ASRc is single pivot, as is Cannondale and the Scott Spark.
Giant Anthem does not, they use "Maestro" I've never ridden it. It's designed to get around some of the single pivot issues.
Trek Top Fuel has pivots on both sides of the shock which causes the rate to be a bit linear, but like Specialized doesn't pedal as well.
Specialized Epic uses the Horst-link which is active as well.
Yeti SB4.5 is their shortest travel bike with "Switch Infinity"
You start getting into the more plush designs when you go 1 travel length further to the 120ish range
Yeti sb5c
Ibis Ripley
Pivot Mach 429
5. Misc -Suspension set-up.
a. Rebound and compression damping
b. Shock Pressures
- Bars
a. Width
Further Reading and watching
http://blistergearreview.com/recommended/suspension-101-designs https://www.youtube.com/watch?v=yBJPLY4xukU (Instant Center) https://www.youtube.com/watch?v=D0bAVTiFyy4 (Anti-squat)
I talk a lot - Give it a listen:
http://www.fasttalklabs.com/category/fast-talk I also give Training Advice via
http://www.ForeverEndurance.com The above poster has eschewed traditional employment and is currently undertaking the ill-conceived task of launching his own hardgoods company. Statements are not made on behalf of nor reflective of anything in any manner... unless they're good, then they count.
http://www.AGNCYINNOVATION.com