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Thread: Speedo reading

  1. 21st February 2019, 07:16 AM #11
    pgsaapl
    pgsaapl is offline Member
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    D2 speedo reading

    Hi,


    I made the same tire transition on my 2000 D2 TD5 3 months ago (to Pirelli Scorpion AT255 70R16's, and it has resulted in a ~ 3% increase in actual speed, relative to the speedo readout (checked using GPS speedometer apps). Being a nerd, I created a spreadsheet to estimate the like change in rolling radius, and came up with a similar number (diameter increase of about 1"). I do a lot of country kms, and reckon it has made cruising at 100-110km a bit easier for all concerned.


    Paul
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  2. 21st February 2019, 10:34 AM #12
    grizzz
    grizzz is offline Fossicker
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    Been there Doing That

    I made the same tyre change and it appears the speedo now reads correct.
    This is done by comparing with a GPS and the speed indictator signs that display your speed. Actually more than 1 of these
    With all 3 being with in 1 or 2 km/hr they cant all be equally wrong can they?
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  3. 21st February 2019, 01:13 PM #13
    AK83
    AK83 is offline TopicToaster Supporter
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    Quote Originally Posted by grizzz View Post
    I made the same tyre change and it appears the speedo now reads correct.
    ....
    That's normal.
    The std tyres will give a higher speedo reading that actual(say 5% or whatever) .. and the increase in tyre diameter(eg. 235/70 to 245/75) will correct that.
    So the end result is usually correcting the speedo to read more accurately.

    The thign to watch for tho is the expected difference to actual difference .. which is accounted for by the actual tyres fitted.
    I think Rick said, these variations could be from the same manufacturer on different batches of tyres of the same model too.

    My brothers D2 has 245/75 BFG KO2s and it reads 5km/h slower on the speedo than actual now.
    Whereas my D1 on it's new Chinese Hifly 245/75s' now shows 0-1km/h faster than actual .. both at 100k/h.
    Arthur.

    All these discos are giving me a heart attack!

    '99 D1 300Tdi Auto ( now sold :( )
    '03 D2 Td5 Auto
    '03 D2a Td5 Auto
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  4. 21st February 2019, 04:39 PM #14
    discodude94
    discodude94 is offline Fossicker Silver Subscriber
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    have alook at these calculations for different tyre sizes

    Quote Originally Posted by Barkz71 View Post
    Hi all, I have just gone to s 245 75 16 from 235 70 16 on my 02 Td5 Disco. Has anyone got an idea how much the speedo will be out if any? I thought there was a chart but couldn't find one when searching. Cheers Brett
    disco data .xls
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