At my SVA my digital speedo was low throughout the range, usually only by 0.1 - 0.5mph, but anything too low is a fail.

My speedo has a single magnet mounted on the front offside wheel and you enter your wheel / tyre circumference in 10ths of inches. I put in 713inch/10. This was fractionally too low. If I want it to read higher I have to make it think it is travelling further for every revolution of the magnet? So increasing the wheel / tyre size should put the apparent speed up? Is that right or am I barking?

Help

Mike

Could you not reset the speedo? Then adjust the diameter to a tenth or so higher?

Andy

I had a similar dilemma and worked it out like this.

If your speedo is correct you travel 60 miles per one hour.

You are indicating that you are travelling 59 when in reality you are travelling 60.

Therefore you need to increase pulses on your speedo for that distance hence you reduce your circumference/diameter by 2-3%. This will give you a slightly over-reading.

That's how I did it - seemed to work

That's how my pushbike speedo works. It multiplies the times the magnet passes the sensor by the tyre circumference so if you put in a bigger circumference you get a higher speed reading.

quote:

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Originally posted by Peteff
That's how my pushbike speedo works. It multiplies the times the magnet passes the sensor by the tyre circumference so if you put in a bigger circumference you get a higher speed reading.

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I had a similar problem with my mechanical speedo when I went for my SVA. My solution was to take the needle of the dial and reset so it didn’t quite read zero.

For the purpose of the SVA test your speedo can read slightly fast, providing it falls within the tolerances. You will need to look these up in the SVA manual.

Speed = distance / time


the more distance in the same time results an bigger speed!

sow if you increase the wheel diameter or the circumstance (wheel diameter * pi)
then automaticly your speed reading is going upwards....

Tks