Fun times: getting a new cycling computer to work! Wanna help?

Hey, everyone!!!

I have an interesting problem: maybe someone here can help me out a bit.

I bought a new cycling computer. This unit, a BRIO Bikemate, is a nine function, wired unit that works as a speedometer, odometer, tripmeter, and other cool stuff.

Thing is: I really have no idea how to program it. Here's the fun part.

With the structure of my tires and the front forks, I can't have my sensor and magnet where the instructions would suggest. Instead of having them about two inches from the centre of the tire...they're now two inches from the top of the frame.

My tire frames, by the way, are 24 inches in diameter.

The instructions suggest taking the wheel diameter (in millimeters) and multiply it by 3.1416 to figure out the "wheel factor) which is then inputted into the computer as a four digit numeral. Thing is: how do I account for the added distance between where the sensor is and where it should be?

(Barracuda made a bike comp that's almost exactly liek this one, down to the two buttons on it, so that may help).

If anyone can help me out...I'll treat them to a coffee, energy drink, anything when they're out my way.

Thanks! If anyone has any questions, I'll try to answer them.

-Oliver

 

The distance of the magnet from the axle makes no difference in the setting. The system doesn't work by detecting the speed of the magnet across the sensor, it works by counting the number of times the magnet passes the sensor.

The magnet will pass the sensor once per revolution no matter where you place the magnet.

The suggestion for putting the sensor close to the axle is so that the magnet and sensor pass as closely as possible without touching.

 

you don't, the distance the magnet is from the hub has no effect on the calculation... the inside of the hub makes the same number of rotations as the outside.

 

I don't think I agree. Wouldn't the time for the magnet to make a full rotation to the sensor be shorter if they were both closer to the center of the wheel, as opposed to being closer to the rim?

 

If the magnet/sensor is placed closer to the axle, the magnet has a shorter distance to travel, but it also moves more slowly for a given rotational velocity.

You have to mount the magnet to a spoke and the sensor to the fork, right? Pick a spoke to watch, then slowly rotate your wheel and note how the entire spoke passes the fork at once.

 

One revolution of the wheel is one revolution of the wheel..whether it's close to the rim or close to the hub.The hub and the rim make the same number of revolutions unless you have some sort of time warp phased spoking...just kidding on that last bit.

 

Yeah, I'm man enough to admit when everyone's right...thing is, I didn't realize that the wheel rotation would be the same from the centre of the wheel and the rim. For some reason, I had the solar system in my mind, and the fact that Mercury goes around the sun faster than Venus, Earth, everything like that.

Thank you guys for your help!

-Steven

 

huh?

 

yeah, and it's called angular distance. Circles are always 2 x 3.1415926545 radians (or 360°), be it small or large

 

your rim diameter is not needed. what you need is the distance your tire covers in one wheel revolution.

it's called circumference

using this method gives a good enough result, but it doesn't account for the changes in the wheel during motion (deformation during riding).

here's an alternative method:
1. make a line on the ground and align it with a spot on your wheel
2. roll the bike along until the wheel makes 1 complete revolution
3. mark that spot on the ground
4. measure the distance (in meters) between the two
5. multiply the result by 1000.

the figure that you get is your "wheel factor"

 

Try here for calibration numbers.


http://sheldonbrown.com/cyclecomputer-calibration.html

 

Let us know how it goes. I think they recommend installing the magnet as close to the hub as possible because in this location the magnet goes past the pickup as slow as possible. I'm wondering if it's installed too far out from the hub if the magnet will go by so fast the pickup won't register the individual 'ticks'.

 

i've installed magnets close to the hub, and close to the rims - didn't really see any difference if installed it correctly...