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Speedo Calibration
https://www.ausmini.com/forums/viewtopic.php?f=2&t=74322		 Page 1 of 2
Author:  tracytracey [ Fri Nov 25, 2011 3:44 pm ]
Post subject:  Speedo Calibration
I am in the process of changing from offset to centre speedo and am having real trouble finding one with the correct TPM(1320) as I have 12" wheels. Is it easier to buy an incorrect gauge and then either
A:get it recalibrated or
B:change the speedo drive to suit
Cheers James
Author:  TheMiniMan [ Fri Nov 25, 2011 4:24 pm ]
Post subject: 
speedo drive gears are all the same in Aust (originally)

except for the very very late Phomy ones with their stoopid "Economy" f/d gears
Author:  Timbo [ Fri Nov 25, 2011 4:41 pm ]
Post subject: 
You'll probably find that the wrong turns per mile don't matter that much. The old magnetic Smiths speedos are pretty poorly calibrated from the factory. I bought a new one a couple of years ago for the Moke, its turns per mile are wrong so that the speedo under reads, but despite that, the odometer over reads.

Tim
Author:  GT mowog [ Fri Nov 25, 2011 5:45 pm ]
Post subject: 
There are (were?) 5 factory speedo drive ratios, but nearly all Ozzy cars were fitted with the same drive as Matt has said ^. This was 6:17. The other drives available (if you can find them!) were 7:15, 5:18, 7:16 and 6:16. They are damn expensive too!
Author:  74snail [ Fri Nov 25, 2011 6:19 pm ]
Post subject: 
GT mowog wrote:
There are (were?) 5 factory speedo drive ratios, but nearly all Ozzy cars were fitted with the same drive as Matt has said ^. This was 6:17. The other drives available (if you can find them!) were 7:15, 5:18, 7:16 and 6:16. They are damn expensive too!


Just for interests sake , where do you find the ratio, I,ve had a look at my Austin Vanden Plas speedo and my Austin America speedo and cant see a ratio printed or stamped

.
Author:  GT mowog [ Fri Nov 25, 2011 6:39 pm ]
Post subject: 
74snail wrote:
GT mowog wrote:
There are (were?) 5 factory speedo drive ratios, but nearly all Ozzy cars were fitted with the same drive as Matt has said ^. This was 6:17. The other drives available (if you can find them!) were 7:15, 5:18, 7:16 and 6:16. They are damn expensive too!


Just for interests sake , where do you find the ratio, I,ve had a look at my Austin Vanden Plas speedo and my Austin America speedo and cant see a ratio printed or stamped

.


The only place I've been able to find these gear ratios is in some of the parts books and even then not always straight forward.
Author:  Timbo [ Fri Nov 25, 2011 8:36 pm ]
Post subject: 
74snail wrote:
Just for interests sake , where do you find the ratio, I,ve had a look at my Austin Vanden Plas speedo and my Austin America speedo and cant see a ratio printed or stamped

.


On big central Mini speedos the turns per mile is usually printed on the face of the speedo, just near the odometer or tucked in behind the round aluminium hub of the needle. Its a number somewhere around 1280 on speedos marked in miles (often with RPML after it). On later Mokes marked in km its something like 800, often without any units.

Tim
Author:  Timbo [ Fri Nov 25, 2011 8:44 pm ]
Post subject: 
James, just reading back to your original post. If you can find a common old 1280 RPML speedo, its going to be pretty close to the 1320 you're after. Its only 3% difference, well within the accuracy of a standard Mini speedo.

Tim
Author:  bnicho [ Fri Nov 25, 2011 9:27 pm ]
Post subject: 
There is a UK site somewhere which has what gears to use with x speedo, y diff ratio and z tyres. I'll see if I can find it again.
Author:  MiniVLT [ Sat Nov 26, 2011 5:53 am ]
Post subject: 
I've been playing with Guess-works site. I like it!

http://www.guess-works.com/Tech/ratio.htm

Cheers Shane
Author:  74snail [ Sat Nov 26, 2011 7:27 am ]
Post subject: 
MiniVLT wrote:
I've been playing with Guess-works site. I like it!

http://www.guess-works.com/Tech/ratio.htm

Cheers Shane


That site lists a number which is on the face of my Austin Vanden Plas speedo 1120 , I did,nt really think that the number meant anything but it looks like it is the TPM for the speedo , I put in the standard tyre size 145x10 , 1:1 drop gears , pre 84 4 speed syncro , 3:44.1 diff , TPM 1120 , not knowing the worm and pinion ratio I used 5/16 which came up as the suggested combination , and it came up as 1kph out :shock: with 165/70x10 is came up with 2kph out :shock: so thats the last piece of the puzzle the worm and pinion ratio , as far as I know I,ll have to take it to the gauge place in Geelong or Heidelburg to find that out unless I can use the serial number and find a factory Smiths catalogue / parts manual

.
Author:  winabbey [ Sat Nov 26, 2011 10:39 am ]
Post subject: 
This is the Smiths UK catalogue. May be of some use.

Image

Image
Author:  Morris 1100 [ Sat Nov 26, 2011 10:55 am ]
Post subject: 
Even if you have the wrong TPM speedo you can still calibrate it to be correct at one particular speed.
You could calibrate it to be correct at 50kph and it will only be slightly out at 40 or 60 and a bit more out at 30 and 70.

If you can get a speedo with a fairly close TPM firstly check is the odometer is reading correct or fairly close then calibrate the speedo.

If you have a GPS calibrating a speedo is easy. A bit fiddly but easy.
Author:  southy00 [ Sat Nov 26, 2011 5:43 pm ]
Post subject: 
i have a similar issue to this, im trying to figure out if my speedo is accurate enough. I need some help with the final drive ratios. Any ideas?
Author:  drmini in aust [ Sat Nov 26, 2011 5:45 pm ]
Post subject: 
southy00 wrote:
i have a similar issue to this, im trying to figure out if my speedo is accurate enough. I need some help with the final drive ratios. Any ideas?

If it is a `71 Clubman 1100, the diff ratio is probably 3.647:1.
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