Speedo conversion

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Speedo conversion

by EH Axiomatic » Thu Jan 15, 2015 8:54 pm

Speed conversions made easy.

No need to buy speedo conversion stickers.
You can convert KPH to MPH in your head!

I’m not a fan of this type of sticker,


MPH……………KmH
13………………..20
25………………..40
31………………..50
37………………..60
43………………..70
49………………..80
55………………..90
62………………..100
68………………..110

If I was to use one, I'd rather read it left to right, or should I say the opposite way , like in this format below,

KPH……………MPH
20………=……….13
40………=……….25
50………=……....31
60………=………..37
70………=………..43
80………=………..49
90………=………..55
100…….=….…….62
110…….=………..68

But that’s just me…..

No need to buy the sticker that goes on the speedo fascia either. (shown in the photo )
Also the 200 Kph fascia or the repo versions are rare and expensive.

When I go past a Road speed limit (kph) sign and I ask my passengers to convert that sign into MPH they look at me with bewilderment.

You know you can convert KPH to MPH in your head!
All you need to know is the Six times table!

When you go past a Speed Limit sign (in Kms of course) - Just drop the zero off and multiply it by 6.
For example an 80 kph sign… ignore the 0 and multiply the 8 by 6 = 48 MPH… simple
Try another one
100 kph, drop a zero leaves you 10…
10x6= 60MPH

This quick calculation will also keep you below the police radar.

But for the advanced mathematicians who crave more accuracy- for all the calculations above add a 1

So 80kph becomes 8 x 6 = 48 plus 1= 49
Now you are more on par with the sticker type above.
But with a wobbly EH speedo do you really need this accuracy as it will keep you below the radar anyway.

There is also another reason for speedo inaccuracy to be considered and that is modern tyre sizes – especially when compared to the EHs factory issued 6.40 x13 tyres.

So, on the net you may find the 6.40 x 13 tyre modern equivalents are either a
P175/75/R13
Or
P185/70/R13
These tyres may also introduce slight inaccuracies so for further investigation you may also like use a tyre comparison program to further check your speedo accuracy and to see if you are in the ball park with the tyres you are using.
The link below is one I like to use regularly so it is saved in my favorites.

http://www.rimsntires.com/specspro.jsp

It gives differences in speedo readings, offsets, potential clearance issues and more etc
As it says
“Play" with specs, try different settings compare results, see differences…….

I hope this helps someone
At least I know you don’t need a speedo sticker
Unless you want to...
or you don’t know the six times table ;) :geek:

(do your own maths E&OE)
Ps This method also prevents Alzheimer's :lol:
Attachments
speedo sticker copy 001.JPG
speedo sticker copy 001.JPG (208.39 KiB) Viewed 10066 times
80 Kph sign drop the 0 and x by 6.jpg
80 Kph sign drop the 0 and x by 6.jpg (6.93 KiB) Viewed 10066 times
Dogmatic Axiomatic
 
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Re: Speedo conversion

by BrennoEH » Thu Jan 15, 2015 9:29 pm

Someone is off their medication again
 
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Re: Speedo conversion

by hcap » Thu Jan 15, 2015 11:00 pm

Ted I get it for those folk that are younger than me and only know kph you just have to remember the approximates
All off the 6x tables so 40 km is 4x6 or 24 on an eh dash 50 is 5x6 or 30 ... 60 is 6x6 36mph ........ Add one after multiply to be more accurate
 
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Re: Speedo conversion

by utility8 » Fri Jan 16, 2015 9:07 am

Shit, too busy thinking, i just got photographed.
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Re: Speedo conversion

by hcap » Fri Jan 16, 2015 10:25 pm

Must be those new tyres ute8.........years ago however my business partner lost his licence in morrabin in one day because of those silly photograph machines
 
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Re: Speedo conversion

by EH Axiomatic » Fri Jan 16, 2015 10:47 pm

utility8 wrote:Shit, too busy thinking, i just got photographed
hcap wrote:Must be those new tyres ute8.........

Yes , Based on the tyres you were using P265/50/R15, ,I believe ; and other things being equal , the factory speedo will be out by about 10% on the faster side.
: When speedometer reads 60mph (96.6km/h) actual speed will be 65.8mph (105.9km/h): 9.7% faster. (see screen shot photo)
So this will get you into photograph and fine territory!
Unless you have made compensation with a speedo reduction box or some other method of compensation?
I don't know what transmission you are running or your diff ratio- perhaps some manipulation of the transmission speedo drive gears may give you an adjustment you need if not already done.

or you could customise a table type sticker to suit your speedo reading requirements.
Attachments
tyre comparison.PNG
tyre comparison.PNG (88.57 KiB) Viewed 10026 times
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Re: Speedo conversion

by utility8 » Sat Jan 17, 2015 2:10 pm

Um, not so.
I did my trade as an instrument maker.
The driveline is 327/T700/9" so calcs are really a waste of time.
Simple answer, a ratio box inline with the speedo cable.
End result, an EH speedo as accurate as you can get.
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Re: Speedo conversion

by EH Axiomatic » Sun Jan 18, 2015 12:22 am

utility8 wrote:The driveline is 327/T700/9" so calcs are really a waste of time.Simple answer, a ratio box inline with the speedo cable.End result, an EH speedo as accurate as you can get.

Yes when you get to the later transmissions and diff ratios and/or combos that differ from the Holden Catalogues you would need one of those.
I was going to do a chart from the Holden Parts catalogues for the more traditional or should I say "old school" combos of diff, trans and tyres but no need to while this link is available.

http://codes.oldholden.com/Speedo/
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Re: Speedo conversion

by Harv » Wed Jan 28, 2015 1:22 pm

G'day Utility8,

I've got a similar line-up in my EK wagon (327/TH350/VP LSD). I did the calcs (including rim size etc) and think I have the right drive/driven gears in the box to get the original speedo running right. Having said that, I wouldn't mind betting that I need to change the pair a few times to fine tune it. Is your ratio box a fixed ratio, or adjustable? Any details very much appreciated.

Cheers,
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Re: Speedo conversion

by utility8 » Wed Jan 28, 2015 6:31 pm

The ratio box has almost infinite variations. The one I have has a gear train of 4 gears. Mine was calculated over an exact measured mile. The revolutions of my speedo cable were counted. An EH speedo requires 1000 revs per mile. So, the instrument guy at a local outlet then did the calcs to make the ratio box output equal 1000 revs from whatever input I had. Saves the fiddle.
You can get pretty close by changing the driven gear to suit, but you'll probably only be able to make 5 kph increments of change.
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