I agree with Woodburner and I think I understand trying to get the times down to a pattern and "formula" (you didn't read my Soap Box post last week DID you?) LOL
I've found that no rib will really be done in under 3 hours. But you have to define "done" also. I don't like the ribs to get to the point where they fall apart, because then they're hard to cut and all I hear all night long is how good the ribs are
I go for "tuggable" the point that when you pull with your teeth, the meat comes off clean and perfect to eat.
Yes WB, if you take spares, cut off at the chine bone, you'll get St. Louis. (next time I do some, I'll add a photo) I don't cut mine that way very often, I look at the spares and the meat and see what the meat looks like then cut if it's stringy looking.
Here's a low res photo of St. Louis and where to cut, I'll find a better one:
You DO cook the rib tips don't you?
As for the 4lb spares. Was there only 1 in a pack? The Sam's around here sell them in double and triple packs. I've found the best to be around 3lb each. As Stuart point out, bigger ribs come from older animals. Don't buy the big ones unless that's all they got.
I've found for 1/2 pound variances in weight can take an additional hour.
SuggestionNext time you try ribs, weigh each rack. Take notes, and see how much longer the heavier racks take. First time I did this, I noticed a lot that helps later. Now, when I do ribs, I weigh every rack. Helps out with my consistency when I'm doing a bunch.
Just Smokin' Okie