This is perhaps the most important skill set a character can have. Unlike other skills which are fairly specific to certain classes and concepts, everyone needs to be able to climb some what to traverse the module. However, I've noticed numerous inconsistencies in the modifiers of several of my characters. My wizard had a 10 in climbing yet had a <10 modifier during his life span. I played a similar wizard later with less climbing skill and but an even higher modifier.
At the time of the first wizard I may have reported what I now know to have been bug, if only I knew it was a bug. Without knowing how climbing skill is determined, players can't be certain whether or not their climbing skill is as it should be. I'm not suggesting that you release any hidden modifiers, but it'd be helpful to know what the most significant contributors are or what the general range should be for our characters.
Different climbing, different modifiers. It's why there are ladders, ropes, tools and free climbing.
Str and such are higher factor in rope climbing. Climbing / tumble higher in free climbing. Ladder is just easy all around.
Weight and negative attributes below 10 affect highly in climbing as well.
If I remember correctly from my sorcerer who had 12 strength and 100 lbs of carry capacity, having a load over 70 gave a -1 to my climbing mod on ropes/climbing claws, along with an additional -1 for every 10 lbs over that. So, if I had like 9X lbs of weight, I'd be at a 7 climbing mod.
I don't know how it factors in with characters with higher strength and more carry cap. but hopefully this helped.
Climbing a rope with 90ish pounds, 12 str and 1 tumble is a total climb score between -2 to -5. It fluctuates even with no difference to the character itself or the method used to climb.
Armor Check penalty is also a factor. In general if you're wearing armor with an armor check modifier (anything heavier than Leather) don't forget to strip down to your skivvies if you want to be spiderman. I want to say that ACP is doubled for climbing (-2 ACP = -4 climbing mod), but I haven't done extensive research on it, so don't quote me.
I wouldn't focus too much into it. If you have trouble climbing with basic skills and stat boosts, get a ladder.
I wish I could carry a ladder. :p Or a climbing claw, even. Climbing stuff is HEAVY tho.
Anyways, armor check doesn't seem to factor in at all. I've got maxed climb, and have spent a LOT of time at the bottom of cliffs bruising my elbows/knees, seeing if there's any way I can tweak the modifiers. Removing/equipping my full plate and weapon/shield seemed to have no noticeable impact. Makes sense too, at least for the armor. How would you rather climb a cliff? Wearing the 50lbs of steel crafted to be balanced around your body, or stuffing the entire thing into a backpack and having it hanging off your back?