jimkuhr

It seems like my speedometer is reading between 3 and 5 MPH on the high side (i.e. showing faster than I'm actually going). This is based on readings from a couple of those radar signs that show your speed. Does anyone know if the dealers can do a good job of calibrating the speedometer? Any other thoughts on calibration?

Drive on!
Jim

wwest

At what speed?

Above 80MPH that's probably acceptable, within reasonable tolerance.

Indicating 40 when doing 35, no.

Did you change out your wheels/tires from original?

Tires worn thin or not fully inflated?

MKW

From 20 mph and above all 996 speedos run 4-5 mph higher than actual speed all model years , even TTs . There is a TSB for some early '99 cars for speedo recalibration, but that was a software glitch where the digital speedo didn't match the analog pointer. There is no fix for the former problem. Article in Car and Driver 2 moths ago said Porsche and BMW both purposely do this to compensate in case owner puts on bigger tires with larger diameter , since BMW and Porsche owners are more likely to do aftermarket wheel packages.

Carrera Rod

as the previous poster indicated, they allow margin for different size wheels. Funny thing is they can't adjust for 19 inch wheels. My '99 has always been off by 4MPH with my 19's.

Just gotta live with it

jimkuhr

I have the 18" factory wheels on the car and I had assumed that they would calibrate for the wheel size but your posts make sense. I guess I'll just have fun thinking I'm at 75 and watching the spoiler pop up! Thanks again for the input.

Drive on!
Jim

MKW

On the C5 Corvette, a microprocessor compares rpm / gear with speedo readout and recalibrates speedo after a hundred miles when you change to aftermarket tires of different diameter so that speed is always spot on. Porsche should do something similar since it's owners change out tire packages a lot also. Speedo calbration running fast from factory on purpose seems so low tech in 2002.

Palting

MKW,
As soon as you said Corvette, I had my doubts. I don't believe a car can calibrate it's own speedo based on the rpm/gear if you change the diameter of the wheel/tire. Or, another way to put it, the self calibration is based on the fact that for a set rpm/gear, the car will travel a set distance based on the circumference of the stock wheel/tire combo. Therefore, since the self-calibration assumes that there is a correct speed for a set rpm/gear, the calibration would definitely be off if there is a different wheel tire combination that results in a different distance traveled for every tire rotation. The only way to accurately calibrate a speedo is with a measuring instrument independent of the car.

MKW

Palting , I know what you are saying - but somehow the C5 does it. Just ask any C5 modder. C5 owners were skeptical initially , too. Even Kevin Brown, the C5's initial roll-out chassis chief confirmed its existance. He did say if you put on a giant truck tire, it would be out of recalibration range.

Gramps

If Vette recalibrates itself, how come the Hypertech Power programmer advertises that it can be used to calibrate for wheel/tire size changes?

MKW

The Hypertech Power Programmer is basically hype, like their name ,as any time spent on a C5 board will tell you. Some of their claims have not been borne out in testing. Only thing it's good for is changing shift kickdown sensitivity on an automatic.
If you change tires +/- 1/2 to 1" diameter bigger or smaller it will recalibrate.

Frank Brown

I have a 1999 C2 with factory 18" wheels. The digital and analog speedometers match, however they both read 10% high. When it reads 88mph, I'm really doing 80. At 44mph, I'm doing 40. I have verified this by both highway mile markers, GPS and police radar (no, not by receiving a ticket). I have taken it to the dealer (Brumos) and asked if it could be calibrated. It was returned to me in the same condition as I took it in.

I don't buy the "done on purpose because Porsche owners have a tendency to put larger tires onthe car". This just doesn't make sense to me. Of course what does make sense is that Porsche would do it on purpose to save on warranty work. If the speedometer reads 10% high, then your odometer will also show 10% more miles on it than actual (also verified with highway mile markers and GPS). Porsche is cheating its customers out of 4,800 miles of warranty by having their speedometer / odometer read 10% high. Since the more expensive warranty usually occurs towards the end of the warranty period, how much money do you think Porsche saves. Now, don't get me wrong, I love my Porsche and think it's a great company, but I also don't like being cheated. BTW, Jaguar does the same thing.

STRSHP

Welcome to the club, so to speak. I took delivery of a 97 Boxster, first in the DC area and immediately noticed the problem. Did a whole thread on Pete's Boxster Board. Checked via marked distances, time and with the radar information carts the locals set out. 10% over is just what it read. Complained for 2 years. Then there supposedly was a software mod. Got that done, NaDa.

I hoped that when I got my 996 that this problem had been solved. Seems like Porsche doesn't give a ??? about this issue. My 87 Bronco II is spot on speedo display. Seems like if Ford can do it to a vehicle that is just as likely to have wheel mods, Porsche could on a car this expensive.

So now when I am going down the road it is all that new math I have to do, let's see actual times 10% equals... <img src="graemlins/soapbox.gif" border="0" alt="[soapbox]" />

j2nh

10% above 40 MPH is about what I am experiencing on my 01. Not acceptable. Confirmed with GPS. Plan on talking to my dealer and Porsche. I don't get it. Why not fix a known problem? This type of error is not excusable. At some point somebody is going to get involved (government agency) and make Porsche look very bad and potentially cost them some $$.
Regards
Jim

Brent B. Adams

Posted my results of a AAA dyno job on my car a couple of times at funcarsonline. Short answer is I have an 8% error factor on the high side across the board. Interestingly enough the test showed the odometer exactly correct, even if just a one mile test. Don't know if odometer is really off 8% also. It it were true you'd think some enterprising lawyer would have already have a class action going against Porsche. I was told by Porsche service that anything up to 10% was acceptable. Maybe to them, but not to their owners.

996FLT6

My car seems to be a difference of +2 mph on the digital readout and it's a '99. Seems like 10 percent is a bit too high. I have 18 inch rims. Regards. Mike