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Digi speedo setting - way off

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Blue_SV650S
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Joined: 27 Nov 2008
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PostPosted: 20:49 - 19 Mar 2010    Post subject: Digi speedo setting - way off Reply with quote
I got a digi speedo on my KTM 250

i.e. one like this ...

https://www.motorcyclenews.com/upload/174744/images/300x200/939942748633.jpg

Ok, so I set it up (21" wheel) and it just seemed stupidly OTT speed reading ... long story short, I decided to calibrate it using 2 sat navs (side by side).

To get the speed to be the same as the sat-navs (presume they are there or there abouts) I had to dial in 1345 ... now that is a long way off ....

How can it be that far out?!!? Thinking
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carvell
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PostPosted: 20:55 - 19 Mar 2010    Post subject: Reply with quote
It may not be picking up the wheel rotation on every rotation properly.

What you want to do is line your tyre valve with a crack in the pavement, wheel your bike forward so that the tyre valve is back at the bottom where it was before, then measure from the crack in the pavement to where it is now. That's the easiest way of measuring your wheel circumference (which is what the speedo wants).
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Blue_SV650S
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PostPosted: 21:12 - 19 Mar 2010    Post subject: Reply with quote
carvell wrote:
It may not be picking up the wheel rotation on every rotation properly.

What you want to do is line your tyre valve with a crack in the pavement, wheel your bike forward so that the tyre valve is back at the bottom where it was before, then measure from the crack in the pavement to where it is now. That's the easiest way of measuring your wheel circumference (which is what the speedo wants).


But it was reading way FASTER (which would require more RPM/picups).

2205 relates to a diameter of ~27.6" (probably about right for a tyre on a 21" rim). I did measure the circumference with a tape BTW and it wasn't far off the 2205 (can't remember exact value)

1345 circumference relates to a wheel of ~17" dia (~13" rim??) that is a BIG difference Shocked Confused
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Last edited by Blue_SV650S on 21:20 - 19 Mar 2010; edited 1 time in total
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Kickstart
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Joined: 04 Feb 2002
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PostPosted: 21:17 - 19 Mar 2010    Post subject: Re: Digi speedo setting - way off Reply with quote
Blue_SV650S wrote:

To get the speed to be the same as the sat-navs (presume they are there or there abouts) I had to dial in 1345 ... now that is a long way off ....


I presume 1345 is the circumference in mm. Strangely that appears to be pretty close to the circumference of a 17" wheel (without tyre).

Presume it works off a magnetic pickup? Where is that mounted?

All the best

Keith
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Blue_SV650S
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PostPosted: 21:23 - 19 Mar 2010    Post subject: Re: Digi speedo setting - way off Reply with quote
Kickstart wrote:

Presume it works off a magnetic pickup? Where is that mounted?

All the best

Keith


Yes, circumference in mm

As for positioning I can't see that would make any difference - we are counting revolutions and multiplying it up to get a speed ... it is only going to pass the sensor once a revolution regardless of distance from hub hub!!! Wink


Anyway, the magnet is in the disc and the pickup is screwed into the caliper mount .. (stock KTM position BTW, not my idea)
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Kickstart
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PostPosted: 21:27 - 19 Mar 2010    Post subject: Reply with quote
Hi

Would be if one of the disk mounting bolts is magnetic. Also some chance of interference from the ignition system.

All the best

Keith
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Blue_SV650S
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PostPosted: 21:39 - 19 Mar 2010    Post subject: Reply with quote
Kickstart wrote:
Hi

Would be if one of the disk mounting bolts is magnetic. Also some chance of interference from the ignition system.

All the best

Keith


I see the thinking of the magnetic bolt, but if you double 1345, you get 2690 ... NOT 2205 ...

Can't find a pic of my exact disc, but here is one that demonstrates the point ....

The eyelet down the bottom takes a magnet ...

https://www.ktmcyclehutt.com/ktm-parts/productimages/54809060300_lg.jpg

As for the ignition system ... that is an interesting thought ... I could always 'cut' the motor when in motion and see if the speed suddenly changes ... Thinking
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Kickstart
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PostPosted: 21:44 - 19 Mar 2010    Post subject: Reply with quote
Hi

Would think it might register if you just revved the engine, but you never know.

Magnetic disk bolts or bobbins are not unknown. Think some Bimotas used them as standard.

All the best

Keith
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KevTM
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Joined: 15 Apr 2004
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PostPosted: 08:26 - 20 Mar 2010    Post subject: Reply with quote
No idea but my Vapor one uses a small magnet on the front disc and you calibrate it by entering the circumference of the wheel (preferably with your weight on the bike).. there's a few ways of doing it but either way mine seems perfect (well as close to as poss.). I did hear some people say that with the vapors they get crazy readings above 20-30mph... could possibly be a damaged sensor/pickup doo-dah ?! Confused
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