Higher Tire Pressure = More Suspension Compliance?

[AzBob_imp]

^^^^^. True, however I can't agree with

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

Pre-load has no effect on compression damping (and therefore brake dive). If we had fully-adjustable forks up front, you'd want to up the compression damping to combat brake dive, but we don't, so all you're really doing is reducing your ride height and reducing your fork's range of travel. I'm not sure if we have progressive springs, but if we do, you may also be unnecessarily increasing the harshness of your ride by pushing the spring into the stiffer progressive rate sooner.

I run recommended tire pressures (36psi front), with front pre-load set for my weight (220+lbs w/gear, right at 2nd line) and experience very little brake dive.

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player. Therefore Honda (and others) recommend higher preload settings for heavier loads. I found that the bike tended to "wallow", particularly leaned over and going over small road irregularities. A bit over active. Upping the rear preload one notch has made an improvement. There are so many variables to suspension set up. Most are not available on the CB. Not needed really as it's damn good as is. Thanks for that Honda.

Cheers

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player.
That's incorrect. A linear (i.e. non-progressive spring) requires the exact same force to compress the spring the first inch, second inch, or last inch. This value is expressed as k in Hooke's law and known as the "spring rate," expressed as a weight over a distance, e.g. 100lbs/inch.

The pre-load adjustment adds load to the spring, which increases/decreases the force the spring exerts on the bike (since it can't move the ground). Increasing it won't add more ability to the spring to absorb weight/force, so the original post about it reducing brake dive is wrong. All he did was absorb the brake dive with the pre-load (in other words, dialing it into the spring before it happens, pre-compressing it). Of course this manifests itself as appearing to have reduce brake dive, but that's not really what happened. However, it can certainly make a bike easier to ride, but at the cost of reducing spring life and having it operate outside of its design envelope.

In other words, the amount the bike dives is the same, regardless of pre-load -- he made it dive (in his garage) by an inch or two (by upping the pre-load), and then when he's out on the street, it will dive another inch or two. Let's say one inch in both places, for ease, for a total of two inches of dive. If he didn't do anything to the pre-load, the bike would still dive two inches upon application of the brakes (at a given constant speed and application) -- the same. Do you see what I'm getting at? You can't increase the damping effect of the suspension via pre-load. The proper adjustment is the compression damper adjustment, which would actually _reduce_ the brake dive without changing the bike ride height, which we don't have. He (you, me, anyone) can effectively reduce the brake dive to zero by adjusting the pre-load to max so that it hits the bump-stops. That doesn't mean the compression damping has changed one iota.

I'll say it one last time for effect: pre-load has no effect whatsoever on compressing damping. It is merely for setting the appropriate ride height so that the spring is as close as possible to its load rate, which is where it was designed to operate, regardless of the weight carried. This is why the first thing you generally do with a bike suspension that you want to work optimally is set the sag correctly. Attempting to modify compression damping characteristics by using the pre-load for other than its designed purpose is a fool's errand.

If one feels the bike exhibits too much brake dive, the only real cure is to do something to the damping of the front suspension: increase the oil weight, get new valves, or get whole new cartridges/forks.