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Thread: Change of wheels - calibrate speedo?

  1. #1
    Regular Member cossie's Avatar
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    Default Change of wheels - calibrate speedo?

    I am really undecided as to which wheels to keep at the minute. I had both sets up for sale in the For Sale section but both have pro's and con's!

    I am currently on my 18" multispokes with a tyre size of 225/35/18 (wheel and tyre diameter is 59cm). The originals are 215/50/17 (Wheel and tyre diameter is 65cm) The 18's give me a good clearance for lowering if I want to later on but the ride is very firm. The 17's are stock, a bit boring but a more comfortable ride.

    Because of the difference now in total diameter, it looks to me like the speedo is now really over estimating the true road speed (I would say a true road speed of 25mph is displayed around 30mph on the clocks). This gives me some problems in speed determination in traffic etc, but more importantly it will clock up the mileage more than it should. (Although my fuel consumption will be better indicated on the BC - ha! )

    I have read somewhere that there may be an option in tech 2 to change the wheel/tyre diameter to calibrate the speedo to a more accurate reading? Is this true and if so anybody near Manchester/Cheshire with Tech 2 to do that for me for a few beers??

    Thanks in advance

    Paul

  2. #2
    Regular Member ScotsDragon's Avatar
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    Vehicle : Vectra

    Trim : SRI

    Engine : 1.9 CDTI 150

    Year : 2007

    Mileage : 50000

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    Should you not be running 235/40/18 to keep speedo right.

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    Regular Member coldo's Avatar
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    Quote Originally Posted by ScotsDragon View Post
    Should you not be running 235/40/18 to keep speedo right.

    I changed mine for a set of Astra wheels... Pentas with 225/40/18

    I have checeked the speedo against my sat nav speed and it is the same before and after at all checked speeds (20, 30, 45, 60, 70 and above). I check it becuase I was a bit parraniod to be honest.

    I also used my op com to change the wheel size setting on the ECU (cant remember where the option was)....

    hope that helps.

  4. #4
    Regular Member cossie's Avatar
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    I agree they prob should be 40 series profile, but the wheels came with 35's in good condition - seemed a shame to ditch 4 good tyres.
    So it can be doen with Opcom then - anyone have Opcom/Tech 2 that may assist then please?

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    Regular Member Chris B's Avatar
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    Quote Originally Posted by cossie View Post

    I am currently on my 18" multispokes with a tyre size of 225/35/18 (wheel and tyre diameter is 59cm). The originals are 215/50/17 (Wheel and tyre diameter is 65cm)

    Paul
    Paul two questions:

    Are you sure the diameter on the 18's is 59cm, I make it 61.5cm
    Are you sure the stock / factory set up is with a 215/50 profile? I thought they were 225/45's?

    If so that brings the two much closer together and if stock is 215/45 then the difference is neglible!!

    Oops looked at a few other posts - I'm wrong - ignore me..............
    Last edited by Chris B; 5th April 2012 at 14:04.

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    Regular Member cossie's Avatar
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    Quote Originally Posted by Chris B View Post
    Paul two questions:

    Are you sure the diameter on the 18's is 59cm, I make it 61.5cm
    Are you sure the stock / factory set up is with a 215/50 profile? I thought they were 225/45's?

    If so that brings the two much closer together and if stock is 215/45 then the difference is neglible!!
    Chris

    The stock wheels I have just taken off are definitely 215/50/17 Chris. And as best as I measured the wheels on the car this morning 59 was within a good tolerance Chris.

  7. #7
    Regular Member Chris B's Avatar
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    Quote Originally Posted by cossie View Post
    Chris

    The stock wheels I have just taken off are definitely 215/50/17
    Yep sorry, my mistake

  8. #8
    Full Member merikiito's Avatar
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    Vehicle : Insignia CDTi SRi NAV 160

    Trim : SRi

    Engine : A20DTH

    Year : 2009

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    Quote Originally Posted by ScotsDragon View Post
    Should you not be running 235/40/18 to keep speedo right.
    Should be 225(235)/45/18 as per the handbook

    The 235/35/18 is much too small and you may not even be able to match this size up with Tech2/Opcom/Vauxcom

    Sell the tyres you have and get some correct size ones
    Lois Griffin: Peter! You're bribing your daughter with a car?
    Peter Griffin: Ah, c'mon, Lois, isn't 'bribe' just another word for 'love'?

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    Full Member merikiito's Avatar
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    Vehicle : Insignia CDTi SRi NAV 160

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    Check here: http://www.etyres.co.uk/tyre-size-calculator.htm

    You will find your current tyres are 25mm out comparred to your old ones and as such are not recommended to be used
    Lois Griffin: Peter! You're bribing your daughter with a car?
    Peter Griffin: Ah, c'mon, Lois, isn't 'bribe' just another word for 'love'?

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    Regular Member kdadidog's Avatar
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    on my old vectra I used op-com to go from 16's to 19's and it was fine. see if you can get someone with op-com/ tech2 to change it.

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