@MrRowl - nice trick! The btHeightfieldTerrainShape is a concave shape though.
I'm not sure what you're getting at...
It is a concave shape, but still btConvexTriangleCallback ends up getting called. Making this change can improve the frame rate of my app from around 15 to 25 FPS on lower-end mobile devices.
Hehe - I guess I need to go back and take a second look. I didn't expect concave shapes to end up in convex callbacks, but like I said I didn't look very deep. I still think its a good mod that you made (it was a compliment - not sarcasm). I had the same frame rate drop and I ended up just reducing the size of the heightmap to just the few height points around the player rather than the whole map.