How can I remove the "series" text from the tooltip on pie charts?

Specifically how do I remove the “series” in the attached screenshot. I’ve been digging and I do see that you can edit tooltip.setFormatter() and I got quite close but I’m not sure how to get the default formatter as a starting point to modify. I was able to re-create most of it but I’m not sure how the chart color is setup in the formatter or how the first line is smaller. It would be great to have a consistent look. And even if there is another way where is the default format stored? I tried to do a get but it’s alwasy null. I’ve been trying to find it in the source but it’s not obvious either.
chart.jpg

As an extra bonus it would be great to be able to change “Series 1” to say something like "Cars: ", "Units: " or whatever the quantity is for.

If anyone is interested I just figured it out. Instead of editing the tooltip you can just name the DataSeries to what you want. So for example in this case it could be new DataSeries(“Car”).