Q I’ve recently fitted a new front tyre, and now I find that my speedometer doesn’t work.
I haven’t touched the cycle computer, so what’s gone wrong ? Are the two connected?
A I’m sure that when you took the wheel off to fit the new tyre you made sure to fit it correctly and when you came to put the wheel back on your bike you noticed that there was an arrow on the side wall of the tyre indicating ‘forward’ or ‘direction of travel’. Maybe there weren’t any words, but you realise that the tread pattern is designed to shift water off the road and give better grip, so the tread pattern is a sort of arrow to cut into surface water and spread it out the sides. If it’s on the other way it would tend to gather water and channel it into the middle of the tyre and weaken the grip.
So, if you have done it all right, well done, but the front wheel itself can be fitted either way round unless you have disc brakes.
I think that what has probably happened is that when you replaced the wheel the little magnet which is fitted to one of the spokes on one side and because the wheel is the other way round it is now on the opposite side. This means that it no longer passes closely to the little sensor fixed to the front fork and from which a wire runs up to your cycle computer.
This is easily cured. The magnet is locked onto the spoke with a simple screw fitting. It may have a slot at the back for a coin to use as a screwdriver, and it may have a knurled pattern on the edge so that you may be able to turn it without tools.
Anyway, just unscrew the magnet and move it across to a spoke on the other side of the wheel.
My photo shows a magnet close to the little black sensor and you need to make sure when you re fit the magnet that it passes somewhere near the middle of the sensor.
Of course, not all tyres are directional, like racing tyres, or knobbly mountain bike tyres in which case it is easy to take the wheel off, turn it round so the magnet is on the proper side, and refit the wheel, but I feel it is easier to swap the magnet across as I’ve just described