My Race Camera iPhone app displays speed in large numbers (MPH, Knots, and MPH) as well as altitude, heading, elapsed time, elapsed distance, top speed, and g-forces in 3 axis. In normal mode it can be read easily inside a car, but if in the sunshine you can reverse the display to read the numbers better.
In addition, it records the video display for later playback and logs all the displayed data for graphing with Excel.
The only issue is that you have to have and iPhone 4, 5, or 6. Android coming soon!
I developed this specifically for Bonneville LSR because I just could not find anything that displays and records for less than $1000. It works well but more features are coming. When not being used for racing, people use it like a Dash Cam because it has endless loop recording.
Only $4.99! I am not making money on this believe me!
You can download it from iTunes at
https://itunes.apple.com/us/app/race-camera/id724048633?mt=8