Which sensor should I use?

I’m trying to measure the speed of my car using Arduino Microcontroller , but the problem is that I don’t know which Sensor should I use in order to measure the real speed. I have found many Sensors but they only use for small motors which aren’t possible for cars.
Any suggestions? Need your help

A GPS module works well.

Check for "can bus" or "OBDII"

http://arduinodev.com/hardware/obd-kit/

Or you can get cheap OBDII bluetooth from ebay and try to read data from bluetooth

jremington:
A GPS module works well.

Can you give more information or some links to help me measuring the speed of vehicle from the GPS module? It looks difficult since Im new on Arduonio

To get the ground speed from a GPS module, set it for NMEA output and read the $GPRMC sentence, which gives the ground speed in knots (among other information).

http://aprs.gids.nl/nmea/#rmc

geologic:
Check for "can bus" or "OBDII"

Freematics OBD-II Adapter for Arduino | ArduinoDev.com

Or you can get cheap OBDII bluetooth from ebay and try to read data from bluetooth

Thank you geoglogic for this help, my goal is to find the speed and get the output through my Phone using GSM module. So does the "OBDII" work well on that?

albusaidi:
Thank you geoglogic for this help, my goal is to find the speed and get the output through my Phone using GSM module. So does the "OBDII" work well on that?

i have one OBDII bluetooth that i use to read data from my car with my android phone, it works ok. In your case you should use arduino + bluetooth module + GSM module to read data from OBDII module and send it by GSM. I never used OBDII with arduino, but i think it could be done.

Or you can spend 40$ and buy obd-kit and wire it directly to arduino + GSM module.

jremington:
To get the ground speed from a GPS module, set it for NMEA output and read the $GPRMC sentence, which gives the ground speed in knots (among other information).

GPS - NMEA sentence information

Thank YOU jremington, i have found $GPVTG is more suitable than $GPRMC.
Ok but also my gps module will be used to track my car, so does it support multiple functions to use it again for measuring speed or should I use another one?

so does it support multiple functions to use it again for measuring speed or should I use another one?

I don’t understand. What do you want to do?

jremington:
I don't understand. What do you want to do?

I think he mean if the GPS module can be used for multiple purpose.

Ok but also my gps module will be used to track my car, so does it support multiple functions to use it again for measuring speed or should I use another one?

You can do both, the GPS module give you a sentence wich contains geolocation, altitude, speed, ..

Check the link below for more information.

NMEA