Originally posted by bachsta
what is a good diameter to length ratio for a minimum diameter rocket
If it's less than about 10:1, it'd be real difficult to get 1 caliber stability without using a heavy nose and fins so light (or of an excessively swept design) that making them strong would be impossible without ruining stability.
Many minimum diameter high performance designs are longer than the appear to need to be because the weight of the components themselves is so low. These tend to be built for speed more than for altitude. Speed depends on behavoir during thrust. Altitude comes from trading speed for coast time and involves weight (too little being as bad as too much) and speed.
There are too many other variables related to your question as well as things not being considered in order for there to be an easy answer.
I'll bet that 95% of high performance rockets built are built around what the builder thinks looks good, or on the length of the parts that are available. And that includes high performance kits. I doubt more than a few will ever say to take their stock size tube and cut it at such and such a length for the optimal design.
My cluster airframe birds are built for performance. The main tubes are 34" long because that's how they came. They could be half as long, but that'd save only 1 ounce on a 10 ounce rocket, which is already so light it probably doesn't coast as high as it could. Unfortunately one of the major components can't be simulated in any software available to me, so I'm stuck with trial and error. With all the other variables I have to work with, length is way down the list of priorities.