Trail Tech speedometer acurate?

[David]

A friend of mine has a Trail Tech Speedometer and it said he was topping out at 143km. All he has is a 400ex with a DMC Alien, K&N, jet kit. I know its wrong for sure. Is their was way to fix it?

[2000400EX]

You have to make sure that it is calibrated correctly for the size of the front tire that it is installed on, otherwise you WILL have an incorrect reading. Mine is accurate within a couple of mph's.

[firedawg805]

As long as you set it up for the right size tire it's very accurate. Been clocked by police radar and they both coincide.

[speedy400]

my buddy's pred said he got going 189mph on a motocross track:eek: , and we got going like 30 or something pushing it,yeah its tough to calibrate it with all those equasions(sp?)-darren

[wilkin250r]

The speedometer is based on a sensor that fits inside the tire, and it counts how many times it sees that sensor go around, and then calculates the speed based on tire size.

If you have a 20 inch tire, the circumference is 5.236 feet. That means the quad moves 5.236 feet for every rotation of the tire (we'll pretend it has perfect traction)

So if the speedometer "sees" the sensor 17 times per second, then it means you are traveling 89.012 feet every second (17*5.236) This relates to 60.69 miles per hour.

However, if the speedometer "thinks" that you have 22 inch tires, it will think that you are traveling at 97.91 feet per second, which is 66.76 miles per hour. All it ever sees is how many times the sensor goes by in a given time. You have to calibrate it for your tire size.