As with pedalling acceleration, obviously when you brake your weight shifts forwards. In other words, whenever you touch the brakes, the normal force on the front tyre increases, and on the rear tyre decreases (no surprises here). In a steady-state geometric sense (ie constant braking on a smooth surface without wheel lockup), having 100% anti-rise on the rear end of the bike would completely negate the effect of the rear brake (though there would still be some extension of the rear suspension from the effect of the front brake shifting more weight forwards). While this sounds good in a sense, it's only basically a static analysis.So after reading this and a few other threads, reading a moto suspension book or two, and a couple of actual prototypes under my belt I think I am starting to get a good understanding of the the pedal/brake induced forces and the design to enhance/counter those forces.
I would like to hear peoples thoughts on the brake induced forces. I understand that "brake jack" (where the suspension extends or firms up under braking) is bad. I personally like to have a bit of "brake squat" to balance out the compression of the front fork under braking. I would imagine that to much of this would be bad for traction and in the event of larger hits under braking, would probably allow the suspension to bottom easier. I personally don't use a ton of rear brake, so I don't think I would notice the disadvantages of this as much, but everyones riding styles are different.
What are your thoughts? Others talking about it helps me (and others I would imagine) to understand the true advantages/disadvantages in "real-world" bike riding, as opposed to all of the marketing hype in the bike industry.
Thanks a ton,
-Hollis
Considering the suspension system dynamically - when you first hit the brakes or when, for whatever reason, the braking force rapidly increases (such as the wheel regaining contact with the ground after skipping off a bump), the initial reaction of a bike with any degree of anti-rise is that the rear suspension tries to compress itself (in other words, prevent itself from extending due to weight transfer). This means that, due to the inertia of the bike/rider mass (which can only accelerate towards the ground due to gravity, since the tyre can't actually "pull" the bike/rider towards the ground since it just rests on top of whatever surface it's on), the rear wheel will try to move itself upwards. If that upwards, compressive force on the suspension is applied too quickly and too hard (too much anti-rise), the wheel could actually hop off the ground. This is a pretty extreme case on flat smooth ground when the rider just grabs the brakes, because the rider can't actually apply the braking force all that suddenly. However, with stutter bumps, the fact that the wheel is constantly breaking and regaining contact with the ground (and as a result, also breaking/regaining traction) very rapidly means that you can get the sharp compressive forces required to cause wheel hop, decrease traction, and cause excessive harshness to be felt by the rider.
There's more detail in this post http://www.ridemonkey.com/forums/showpost.php?p=3127717&postcount=20 if you're interested.