Problem with reed switch.

I have made a speedometer for my bike using a reed switch. Now the problem is it is working fine till about 30 kmph but after that I am not getting correct values. Though I am not sure but I this might have something to do with the debounce time or maybe something related to the magnet I am using. I am from India, I can't get a reed switch of another make easily here so can't tell what is the bottleneck. If anyone has experience with reed switches, please help me out.

Hi, your reed switch is a mechanical switch, what is happening is that the magnet is going past the switch so fast that the reed does not switch over and make contact.
A Hall-Effect device would be more suitable as it is not mechanical and will react faster and give you an output.

Tom… 8)

Thanks Tom.

try using a stronger or longer magnet or you could make a shaped pole piece to "extend" the time the switch is in the magnetic field

Or move both the switch and magnet nearer to the wheel hub for less angular velocity.

Henry_Best:
Or move both the switch and magnet nearer to the wheel hub for less angular velocity.

Same angular velocity, less linear velocity (more time for switching)

Reed switches are fast for mechanical devices, debounce times are a few ms IIRC.