Where do you get this caustic mixture? I have heard of others on this forum doing a similar thing. I assume that you are doing this because you want the product to work better? Couldn't you take a really cheap product and add enough caustic to make it work, like foamy brush
soap?
Caustic plays a big role in most alkaline presoaks, but there are other ingredients in a quality product- solvency, surfactants, etc. Having said that, I had a owner of a pretty large tunnel chain told me that the best tire cleaner they used was back in "the old days" when they managed the locations themselves, and was a mixture of Dawn dishwashing detergent and sodium hydroxide.
As RPH mentioned, caustic has its' risks. I wouldn't use the caustic if I could get away with it. If you are cleaning to your satisfaction with an off the shelf one drum product I would stick with it.