ivangene

Hey all,
I have noticed the speedo is off on my 99 C2 by quite a bit (and not in the way that will help the re-sale)
I am running 285 - 30 -18's on the rear (asume thats the one with the speed control) if not 225 - 40 -18's in the front

Is there a way to fix this, and is it something I can do (some mechanical skills) or only dealer/indy
Also getting near time for tires so if I HAVE to i could change diameter tires.. but like the low profiles.

Love to get this fixed, though it keeps me below speed for the radar traps.
Ed

kabel_Boxster

more than +4 mph?

ivangene

@ 29 on the dial (digital) its 25 so about 4 off

himself

Many 911's are off. It's a common "problem." I don't think it affects resale in any way nor do I think it needs to be fixed. Mine has been off since I owned it.

-td

kabel_Boxster

very common, SOP from the factory in general. I've seen hundreds of posts from users (911, 996, 997, 896, 897) reporting the same +4 mph.

Thundertub

ALL speedos from factory are "optomistic." Yes, I understand your concern about the actual miles driven (Odo meter will register an equal percentage higher). But as strange at this may seem, the error is fairly consistent all the way up. I have run many many miles comparing the digital speedo to a high quality GPS's readings. Yes, you can fiddle with the tire diameter, but do you really want to screw up the handling in order to worry about 4 mph? Porsche may have done it intentially to help keep you from running afoul of the local polizei, or to run you out of warrenty a few miles early, but basically it is no big deal.

Beside, if you are driving your car for YOUR pleasure, rather than saving it for the next guy to enjoy, what real difference does a few percent really make?

Steven C.

+1 for mine

LVDell

If you are concerned about it matching perfectly then change the RD of the tire you use. Increase it if you want to bring the speedo back DOWN and increase it if you want to bring it UP. In your case it sounds like you might be going, say 57, when the speedo shows 60? If that's the case move up to the next size in RD. Just understand that you will affect your gearing by doing that.....make it taller (longer).

Patrick

If it were about ending the warranty early, it would be a big deal because that is fraud. I used to think that was Porsche's reason. But the error is actually just programmed into the speed display, and the odometer is reasonably accurate. (I don't think the speed display error is "reasonable", though.) This can be demonstrated two ways: One is to use the diagnostic mode on the EATC to display the actual speed in kph and observe the difference in the displayed speed. The other is the display on my datalogger shows the error clearly in MPH. The datalogger reads the correct speed, so the speedometer is working correctly, and the speedometer display reads high, simply because it is programmed to.

spiderv6

I believe this 'error' is intentional on the part of Porsche.

Something to do with laws in Germany that require manufacturers not to understate speed (but my speedo said 55mph officer!) or face large fines. Therefore they play their hand cautiously and overstate the speed.

rb101

I've gotten use to having the speedo off, my car is 5 miles over and my wifes BMW 525 is 3 mph over. The odd thing is my 944 is spot on.

Rick
99 996C4
87 944S

Toreador

My 996 is the same, and surprisingly, so is the Lambo

Patrick

Now that I believe can be fixed.

ElTorrente

Yeah - mine is off by +5mph at 90mph, and when I did 160 on gps, it was off by +8.

ivangene

I have check the odometer too and it reads the same (long) ni other words if I have 29 on the speedo and am going 25, then in 1 hour I have traveled only 25 miles but the odometer moved 29...

some simple math says then that my car with 104k only actually has about 90k this is a "little" error that can really add up. (hense my concern about resale on high milage cars.

Personally I dont think any 996 is worth less than mine with this many miles unless it is not drivable, rebuild or has some major mechanical/body/interior issues (as mine does not)

In this case I plan to drive the wheels off the thing and get as much out of her as I can.

Ed