Over the years the USDA,in conjunction with the FDA, has done lots of what is called HACCP testing (Hazard Analysis and Critical Control Point Evaluation) to determine what they refer to as the CCP's (critical control points) for both safety (CCP1) and shelf life (CCP2). Most of that research was directed at the food business/commercial food industry but the same guidelines apply to home food canning.

That testing shows that given the alkaline pH of water, the minimum effective amount of vinegar to be used in pickling is 1:1 of 5% to insure a CCP1 - safety pH of 4.6. Increasing the amount of vinegar so you get 4.5 pH gets you to CCP2 - limited shelf life. Increasing the vinegar even more so the brine is even more acidic gets you longer shelf life (since pH rises over time).

If you look through the many approved recipes you'll only find a couple that use less than 1:1 while the majority of them call for a much higher ratio of vinegar to water.

Back in Grandma's day when they used much stronger vinegar they could get by with using less of it and more water but it was much more hit n' miss pickling and safety too.

If you want to read more about it you can dig into all the research publications published/linked at NCHFP and USDA.

Hope this answers your questions.

Dave

PS: it really only comes into play when using untested personal recipes.