Google is finally rolling out support for speedometer readings and speed limits in Maps on iOS, and these also work through CarPlay.
The move comes a whopping five years after the same functionality was added to Android, bafflingly. Still, it's finally here on iOS too. This being a Google app, it might however take a few weeks for the rollout to be completed, so don't fret if you don't see this just yet.
Google Maps now includes a speedometer that adjusts between km/h or mph based on your region. You can enable it in Settings > Navigation > Driving options. Additionally, the speed limit feature changes the speedometer color to encourage driving within the posted limits. It's important to note that the speedometer in Maps is for informational use, and you should always verify your actual speed with your vehicle's speedometer.