For a foam cannon?
I think I was using some leftover TW zipwax as a presoak when I took these pics.
I have also had really good luck with stuff like meg's NXT, and GC soaps. Megs Shampoo + is really thick and actually hard to get rinsed out of all of the cracks if mixed wrong.
Most soaps can be mixed strong enough to make shaving-cream foam. It really does't seem to clean better when its that thick. I try for a 4-5 dwell in the shade (if I have it) then PW rinse. This will help loosen the grit(even in gaps) and soften the bug jerky.
If you want an even stronger soap try CG CW+G.
Don't use onr with a foam cannon as it will just be a waste. I
do use onr as a 1 bucket wash to follow up PW/foam washes. You will usually get some light traces of grime left by the PW. The onr will clean that up fast and allow you to dry the vehicle fast. It adds maybe 15 min to the total wash.
This is the safest way *I* have found to wash really dirty/muddy cars. I had a 1 mile drive down a muddy gravel road until just this spring. I could take a truck that looked like a mud-runner and wash it perfectly clean (with no marring) in about an hour.
Now if I totally missed the mark with the PW assumption, and you are using a garden-styled pump sprayer; I would use onr to pre-soak the panels then wash with 2BM with 1 being more onr and the other being a rinse bucket. That is my onr method for only somewhat dirty cars.