speedo pulse calibration help needed

[RemaL]

I've had a broken Speed sensor I used on my tiger kit car. I've replaced my Induction Sensor for 15 hole speed disc with a LED INDUCTIVE SPEED SENSOR
http://www.merlinmotorsport.co.uk/p1354/LED-INDUCT...

Now I am using the speed disc as it's easily mounted and I can get to it. I've put 2 bolts 180 degrees apart which the LED Sensor pics up.

But unsure how to set my ETB digital speedo to work correctly?

before with the 15 holes per rotation it was set at about 48000 pulses and seem to read the speed right when on the road

my rear tyres are 215/40/16

Anyone help me work out how many pulses I need to input per mile?

[xRIEx]

I make the rolling circumference to be about 1.817m, so taking a mile as 1609m that is 885.47 revolutions per mile, 1771ish pulses per mile.

Edited by xRIEx on Tuesday 19th June 18:58

[RemaL]

xRIEx said:

I make the rolling radius to be about 1.817m, so taking a mile as 1609m that is 885.47 revolutions per mile, 1771ish pulses per mile.

ahh right. much different from what I had worked out today

---

a google shows this all approx

215/40/16's are 913 revs per mile
Magnetic Sensor - using a reed switch using prop shaft revolutions, Number of magnets x differential ratio x tyre revs per mile or per kilometre = calibration number


So 2 magnets/bolts x 3.91 diff ratio we have x 913 revs per mile = 7139.

which may show why the cars wheels are turning we get a very low speed readout as the 15 hole speed disc -48000 pulses. = low speed read out

will give your readout a go and mine.

Huge difference between them

[xRIEx]

Sorry, I meant rolling circumference in my previous post, not radius.

My calculations were only based on wheel circumference, not diff ratio - where is the sensor attached? If it's on the prop shaft then yes, you will need to take that into account.

My workings:

16" wheel diameter = 406.4mm
Tyre section 215mm x 40% = 86mm
Rolling diameter = 406.4 + (82 x 2) = 578.4mm
Rolling circumference = 578.4 x 3.142 = 1817mm

[rog3k]

I had cause to recalibrate my ETB speedo & I phoned them - they told me what I needed to do (I had changed the diff - although I also calculated it by the different diff ratios)

[FlatPack]

Surely given it was working accurately with the 15 pulses per rotation it's dead simple (assuming you haven't moved where you're measuring from or anything else).

Before, 15 pulses per rotation was ~48000 pulses per mile.

So that's 48000 / 15 rotations per mile = 3200 rotations per mile.

Now you've got 2 pulses per rotation, so 3200 * 2 = 6400 pulses per mile. Done with the same calibration you had before.

[RemaL]

well cheers all. i'll give them a go. i inputted my 7140 pulses last night and worked much better. shall be hoping to take the car out tonight and give it a run. and see which amount works best with the sat nav