I think you are confusing the bitrate of the camera thats in Mb/s ( megabits / second ) and the MB/s ( Megabytes / second ) thats the mesurments for SD cards and how much data they can read / write every second.
At 13 Mbits bitrate of a dashcam you dont get anyway near to 3 Megabytes of date needing to be saved every second, so a regular SDXC class 10 / U1 should do just fine, at least it have been so in all of my dashcams.
You can go faster if you wish, its allways nice to have good transfer speeds from the card in the card reader and to the PC.
This is not least most true if you drive for long time and want to save it all for a journey / trip video, but for normal day to day where you only pick a 3 minute file here and there containing some traffic dumbass, overall speed of the SD card is of lesser importance.
Just took a look of one of my 3 minute files.
The average bitrate of the recording is 15 megabits, and the file is 340 Megabytes in size, so thats 340 MB divided with 180 seconds ( 3 minutes ) so thats only 1.8 Megabytes written to my SD card every second, far less than my Kingston SDXC class 10 / U1 can handle ( think it have a write speed of 10 Megabytes / second )
I know many dashcam makers recomend SD cards with writespeeds of 30 - 40 MB/s but thats just insane even for a 4 K dashcam thats not even made yet.
I have seen file sizes just over 500 MB from the same camera as above mentioned 3 minute file, but that was with 25 Megabit firmware, and even that is well below 5 Megabytes of data needing to be written to the SD card every second.
Extrapolating on those values a 50 mbit recording will generate a little over 1000 megabytes / 1 Gigabyte for a 3 minute recording, and thats still only 5.5 Megabytes of data needing to be written to the SD card every second.
So a kingston SDXC class 10 / U1 like the ones i have a fjew off should be able to handle around 90 Mbit bitrate, and thats allmost up where Sony and Gopro action cameras are when they record 4K footage at the highest bitrate.
I have just gotten a 64 Gb kingston clas 10 / U3 card, that one can handle 90 MB/s read speeds and 80 MB/s write speeds, well over what current 4 K action cameras can crank out of data.
And it was only like 100 DKkr more expensive than the normal U1 cards i use.