Actual Speed when Speedo says 100km/h
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  1. #1
    Fellow Frogger!
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    Actual Speed when Speedo says 100km/h

    Was wondering if anyone knew the actual speed in a GTi6 when the speedo says 100?

    The reason why I'm asking is that purchasing 195/50/15s may not be so bad or may well make things worse than originally thought.

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    Eg: Putting 195/50/15s would theoretically put the speedo out by 3.3% or actual speed 96.7 when speedo says 100.

    Therefore, if from factory actual speed was 103 when speedo is 100 this would in fact correct itself running 195/50/15s???

    However, if factory actual was 97 then running 195/50/15s would make the matter even worse.

    If I'm being loopy please let me know

    I know for a fact my Camry was 3km/h out but which way can't remember. Wheels/Motor do these test all the time.

  2. #2
    1000+ Posts brenno's Avatar
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    Most speedos read higher than actual speed. I'd be surprised, and concerned if it was reading lower.

    Edit - I had it the wrong way around....I'm quite clearly an idiot.

    I wouldn't put 195/50's on a GTi6. It's the wrong size and will affect the handling.

    Get a good set of 195/55's and then enjoy the car as it was meant to be. Anything less and you may as well buy a Pulsar.

    <small>[ 26 September 2003, 05:25 PM: Message edited by: macquered ]</small>

  3. #3
    Gem
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    I think my speedo may be out a little, or everyone else is speeding!
    Anyone know if it is easy to get it checked?
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  4. #4
    1000+ Posts tekkie's Avatar
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    macquered:
    I wouldn't put 195/50's on a GTi6. It's the wrong size and will affect the handling.

    Get a good set of 195/55's and then enjoy the car as it was meant to be. Anything less and you may as well buy a Pulsar.
    Tad extreme, isnt it? I mean we are talking 5%.

    The profile of the tyre will almost change by that much during the normal wear. Not like he is putting 225/40 or so.
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  5. #5
    who? when? huh? GTI124's Avatar
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    Brenno making exaggerations, well I never! :p

    If you're tight on cash and can pick up some 2nd hand 195/50s, then go ahead. But if you have the choice at new, you should stick to 195/55. I think Pulsars pretty good, actually. :p
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  6. #6
    1000+ Posts brenno's Avatar
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    OK I might be exaggerating, but I've had 2 sets of 195/50's on my previous 306 and would reccomend against it. It just didn't feel right.

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    Budding Architect ???? pugrambo's Avatar
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    macquered:
    Most speedos read lower than actual speed. I'd be surprised, and concerned if it was reading higher.

    I wouldn't put 195/50's on a GTi6. It's the wrong size and will affect the handling.

    Get a good set of 195/55's and then enjoy the car as it was meant to be. Anything less and you may as well buy a Pulsar.
    i would have thought that speedos would read higher than actual speed otherwise everyone would be getting caught speeding
    i do know that holdens in the late 70's early 80's read 12% higher than what the actual road speed was
    no wonder we had all those wonderful fiqures of what people could get out of a holden
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  8. #8
    Fellow Frogger!
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    It's funny how all threads lately lead to being soley tyre threads. roll_lau roll_lau

    I was only thinking perhaps 195/50/15 may actually affect the speedo positively.

    There are many cars that are actually travelling between abt 96 and 104 when speedo says 100. Sad but I've always been interested in this fact especially when we emphasise so much on speed cameras etc

    Another thing is perhaps an upgrade to 16" wheel could be used in conjunction with a 205/50/16 instead of 205/45/16

  9. #9
    1000+ Posts brenno's Avatar
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    Argh Pugrambo you made me realise that what I meant and what I wrote are completely different. I'll have to be more careful. Double Argh.

    Will fix it now.

  10. #10
    Fellow Frogger! WRX2PUG's Avatar
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    And what's wrong with 17 inch 225 40s?
    Got to get traction somehow
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  11. #11
    1000+ Posts cruiserman's Avatar
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    I think my speedo may be out a little, or everyone else is speeding!
    Anyone know if it is easy to get it checked?
    Get a GPS unit. I often use mine in the Landcruiser, big difference in actual speed depending on whether I have the 31" tyres or the 35" ones on. The GPS gives an up to the 2second readout of speed. The longer you have it turned on in a trip the more acurate it gets.
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  12. #12
    Budding Architect ???? pugrambo's Avatar
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    macquered:
    Argh Pugrambo you made me realise that what I meant and what I wrote are completely different. I'll have to be more careful. Double Argh.

    Will fix it now.
    lol
    i wasn't picking on you
    it did have me wondering though and i thought you may have had it back to front
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  13. #13
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    According to my mate Adrian's GPS (he's been on a few AF Sydney drives with me) my 306XSi is doing 106km/hr when it reads 110.

    Derek.

  14. #14
    Fellow Frogger! bennymarsh's Avatar
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    Kristian:
    I know for a fact my Camry was 3km/h out but which way can't remember. Wheels/Motor do these test all the time.
    My vienta is about 97 when it says 100 if that helps!

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  15. #15
    Gone Fishin' Ray Bell's Avatar
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    Originally posted by Gem
    <strong>.....Anyone know if it is easy to get it checked?
    Extremely easy...

    Just go to the freeway where there is a 'speedo check' section and set your speed to 100kmh. Then, using a stopwatch if you can, and being as accurate as you can with both the watch and the speed, time each km.

    Divide the time taken in seconds to cover the km into 3600 (trust me, this is dead right!) and you have your average speed over that km.

    Obviously 36secs is 100kmh, 30secs is 120kmh.

    Naturally, this kind of dead accurate evidence isn't acceptable in a court of law.

  16. #16
    Gone Fishin' Ray Bell's Avatar
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    Originally posted by pugrambo
    <strong>I do know that holdens in the late '70s early '80s read 12% higher than what the actual road speed was
    Garbage!

    I drove many of these cars and tested their speedos. They were very accurate, maybe 2% fast at the most.

    Unlike so many other things... 180B was 10% fast for instance.

  17. #17
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    My friend had a 20 year old Merc. He was concerned about speedo accuracy as everybody seems to be overtaking him when he's already speeding.

    We got a GPS and on freeway it's quite accurate. Acutal speed was 93km/h when indicated 100km/h. We thought it was out by too much, but a Wheels road test back in the early 80's confirmed that figure. So looks like it was the way the speedo was designed I guess...

  18. #18
    Gone Fishin' Ray Bell's Avatar
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    'twas law in Germany... they were required to read fast.

  19. #19
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    I too had wondered why I was being passed by everything on the road. I checked my odometer over one of those 5km checks on the freeway, and it was definitely out. So I then took it to the RACQ test centre at Zillmere, where they ran it up on a dyno and took readings. They then gave me a list of the actual road speeds, and what my car's speedo was showing. The only one I can remember off the top of my head was that when my speedo reads 112km/hr, I'm actually only doing 100k. Apparently the maximum leeway between actual speed and the speedo reading (by law) is only 10%, so my speedo is technically 'illegal'. Of course, this also means my odometer says I've travelled further than I really have, so when it comes to selling the car it'll look like more kms on the clock.

    Can't remember how much the test costs, but it wasn't much - probably cheaper if you have RACQ membership. The dyno is checked for accuracy on a regular basis, so the results should be accurate. I was also told that it's the only certified reading you can get (I asked Peugeot service and was told they couldn't do it). By the way, my car is absolutely standard (306 XR automatic sedan), with the standard recommended tyres which are no where near worn.

    penelope_s

  20. #20
    Budding Architect ???? pugrambo's Avatar
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    there are places where you can get speedos calibrated
    the thing is any change of tyre will effect it a little
    3 x '78 604 SL

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    1 x secret project

    1 x '98 406 STDT troop carrier and i don't care if it stinks, i don't sniff it's arse Death by wank tank

    1 x '99 406SV 5spd wagon, time to burn more fuel

    1 x 1994 605 SV3.0


    WTD long range fuel tank for 605

  21. #21
    1000+ Posts Damien Gardner's Avatar
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    Actually there is little corelation between Speedo and odometer. In the older units the speedo is activated by friction (magnetic i think)and the odometer, is gear driven off the speedo cable.
    The later electronic speedo's "circa ford '82 are just that electronic, however the odometer is still gear driven. I haven't a clue on more modern applications though, '82 being the youngest vehicle i've owned.

    I have found that odometer accuracy varies greatly, especially when being paid per km
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  22. #22
    Gone Fishin' Ray Bell's Avatar
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    Originally posted by penelope_s
    <strong>I too had wondered why I was being passed by everything on the road. I checked my odometer over one of those 5km checks on the freeway, and it was definitely out. So I then took it to the RACQ test centre at Zillmere, where they ran it up on a dyno and took readings. They then gave me a list of the actual road speeds, and what my car's speedo was showing. The only one I can remember off the top of my head was that when my speedo reads 112km/hr, I'm actually only doing 100k. Apparently the maximum leeway between actual speed and the speedo reading (by law) is only 10%, so my speedo is technically 'illegal'. Of course, this also means my odometer says I've travelled further than I really have, so when it comes to selling the car it'll look like more kms on the clock.

    Can't remember how much the test costs, but it wasn't much - probably cheaper if you have RACQ membership. The dyno is checked for accuracy on a regular basis, so the results should be accurate. I was also told that it's the only certified reading you can get (I asked Peugeot service and was told they couldn't do it). By the way, my car is absolutely standard (306 XR automatic sedan), with the standard recommended tyres which are no where near worn.
    You're right there, Penelope... only the RACQ dyno is accepted in court. But it still relies on you reading the instrument and telling the truth... highly questionable things when things come to court.

    Now you know how to use the speedo check things, you won't even have to spend that small amount...

  23. #23
    1000+ Posts Pugnut403's Avatar
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    Electronic Falcon speedos are totally electronic. There is no cable coming out of the gearbox, just an electronic sender. I am talking about an '83 model here, but AFAIK they were the same from the first elecrtronic speedo in '79.
    (BTW, I can remove and replace ford gearbnoxes in my sleep cry spanner spanner spanner
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  24. #24
    Sense Pug307's Avatar
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    I believe the 307 & muxed 206 just use data from the ABS sensors to calculate speed for the speedo.

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  25. #25
    Fellow Frogger!
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    According to my GPS, my Clio is doing 94km/h or so when it reads 100. 113(114)km/h when it reads 120.
    (so from now on I can safely cruise at "speeding" pace of 115-120 on the speedo?)

    Also Odometer matches with those 5km odo checks.

    Ps. running on factory 175/65R14.

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