[sstman]

Heres an interesting one!, I fitted an integrated ICE/Sat-Nav unit into the 968 recently, and found that the reported speed on the display of the Nav unit was always about 8-10 % slower than the speedo on the car. It wasnt a big deal, so I had ignored it.

However!, just downloaded into my Iphone 3G, a nifty little app, that tells you where all the speed camera's are in your area, via a gps database, works very well, in my area, and has a real clever option to give you a 'HUD' onto the windscreen at night to warn of upcomming speed-traps, whilst giving you a large digital readout of your current speed and GPS position!. It does what it says on the tin! brilliant!.

Now here's the thing, the speed readout displayed on the sat-nav in the car, and the speed displayed on the I-phone app, are in sync perfectly! the car is saying i am travelling at 70 MPH, and both bits of tech, are displaying 62 MPH, and they stay in step throughout the speed range from 19 to 120 MPH.

The clock on the car cant be that far out surely?? However its on the right side of the law, so "sorry officer, I was only doing 68 MPH!" LOL

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[flash]

yup - i have a copy of an article that shows it off quite a bit, and just as you indicate

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[Fox944]

My tomtom navi & speedo are almost 100% in sync. It actually surprised me...iexpected the speedo to be optimistic....havnt tested the two above 90MPH...but up to about 90, hey both have nearly identical read outs.

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[ds968]

i had an exact readout at 100 mph with my previous tires- 265 40 rear, 235 40 front. i have not tested it yet with the new ones - 255 40 rear, 235 45 fronts, though I suspect there might be a delta at 100 now.. we 'll see - waiting for them to put back the digital board on the frontage road where i can go 100 without too much concern, but it has not been there for a while..

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[Darryl]

My mechanic friend/Porsche guru has made mention of Porsche speedometers being exhagerated on purpose...I though he was kidding, but perhaps not. I can't think of a legitimate reason they would do this, though.

- Darryl

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[flash]

per an article in Autocar published May 27, 1992:

actual speed versus indicated speed:

30 read 32
40 read 42
50 read 53
60 read 64
70 read 75
80 read 86
90 read 97
100 read 107
110 read 118
120 read 129
130 read 139

keep in mind that tire diameter affects speedometer reading - at 80 mph, reading 86 is 7% error - this can vary by manufacturer, but as an example, a Conti SC2 stock tire diameter of 225-45-17 is 25" - drop the profile and run a 235-40-17 and you lose .7" - that is 3% - wear that tire down to the wear bars, and you lose another .5" or another 2%

it's not hard to see the possibility of error

in measuring fun run routes in the past, i have seen error - i have not worked out exactly how much - now that i have a GPS in my car, i will see how far mine is off

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[Kim]

My coupe, at an indicated 100 kph on my GPS, shows 110 kph in the car (205/55/16 inch fronts), Interestingly, the odometer is out only by 5 km in (shows 105 km) an hour at 100 kph on the GPS.
My cab shows 105 (same front tires as coupe)(shows 100 km in one hour at 100 kmh on the GPS)
My Cayenne shows 105 (odometer is OK)
My wifes Murano shows 100

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[timbits]

<!--quoteo(post=69574:date=Mar 29 2009, 10:05 AM:name=Darryl)-->QUOTE (Darryl @ Mar 29 2009, 10:05 AM) <{POST_SNAPBACK}><!--quotec-->My mechanic friend/Porsche guru has made mention of Porsche speedometers being exhagerated on purpose...I though he was kidding, but perhaps not. I can't think of a legitimate reason they would do this, though.

- Darryl<!--QuoteEnd--><!--QuoteEEnd-->

I'm no expert on German law, but what I've heard is that in Germany car speedometers aren't allowed to read slow only faster. Since there is going to be some impreciseness (tire wear, mechanical issues, etc) in the speedometer reading they are intentionally set a touch high.

Of course this might just all be hearsay... I don't have any confirmation of this.


~ Tim

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[flash]

i'm sure there is more going on in that speedo than there used to be with cable driven stuff - there is probably as much variance between cars as there is on any given gauge

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[ds968]

so where are the sensors on the 968 ? front or rear tires ?

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[Kim]

I think front driver's side

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[sstman]

Seems I started something here! lol, well all I can say, is that the application I bought for the I-phone cost me 59 pence, it works very well, if you consider the sort of costs some of these gizmo's can be priced at, and the displayed speed in exactly in step with a £800 ICE/SatNav as regards the MPH readout. I will just cruise along at 80 MPH as displayed by the car, as then I'm doing a really economic 68 MPH in reality.

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[flash]

which app is it?

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[Dirk]

All cars sold in Europe will be optimistic about speed, the manufacturers and importers can't afford multiple claims from drivers that get done by the many speed traps we have.
I have been using (Tomtom) Navigators for a few years now and typically find 5-10% difference, regardless of make of car.

The Tomtom I presently have is set to give a warning when 6 km/h over the limit and that's the main reason I always have the navigator switched on, it allows me to drive very close to the legal maximum with hardly a chance of a big speeding ticket.

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[sstman]

<!--quoteo(post=69618:date=Mar 30 2009, 02:29 PM:name=flash)-->QUOTE (flash @ Mar 30 2009, 02:29 PM) <{POST_SNAPBACK}><!--quotec-->which app is it?<!--QuoteEnd--><!--QuoteEEnd-->

Its called I-HUD, got it on the UK App-store

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[968cruzin]

lot of posts here, but my speedo, checked the same way is 5mph slow. so going 70 really going 75. Does anyone know how to fix it??? I switch between my Murano and gets confusing so would really like to fix it.

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[Fox944]

<!--quoteo(post=72402:date=May 22 2009, 05:59 PM:name=968cruzin)-->QUOTE (968cruzin @ May 22 2009, 05:59 PM) <{POST_SNAPBACK}><!--quotec-->lot of posts here, but my speedo, checked the same way is 5mph slow. so going 70 really going 75. Does anyone know how to fix it??? I switch between my Murano and gets confusing so would really like to fix it.<!--QuoteEnd--><!--QuoteEEnd-->


what size wheels/tires are you using?

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[Johannvb]

I downloaded the app, very cool! Since the 968 is still undergoing clutch surgery, I tested it in our family car a Nissan Qashqai and the speedo in there is also over by approximately 5 kph.

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[968cruzin]

<!--quoteo(post=72426:date=May 23 2009, 06:28 AM:name=Fox944)-->QUOTE (Fox944 @ May 23 2009, 06:28 AM) <{POST_SNAPBACK}><!--quotec-->what size wheels/tires are you using?<!--QuoteEnd--><!--QuoteEEnd-->

they are oem porsche rims with 225/45Z R17 94W on front and 225/45Z R17 99W on rear.
Thanks much

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