missmy993

I just compared the displayed digital speed against a gps and from 30-85 mph the gps indicated a speed about 3.7 mph less. I used an old gps that did not measure distance traveled. Anyone compare milage and gps milage to see if odometer is effected by speedo error?

Thanks.

leedav

Never have. My GPS showed 119 when the digi speedo showed 121

Res Ips

Was that you on the Beaverton Hillsdale Hiway?

washington951

i have one of these 'black boxes' in my 951 to adjust for my larger-than-stock wheels, but it could also be used to fine-tune your speedo if wanted. as measured by GPS, mine is dead-on now.

http://www.atrol.com/era.htm

from their site:
Any change in a vehicle's tire size or rear axle ratio will cause the speedometer (and odometer) reading to be inaccurate. The Electronic Ratio Adapter (ERA) is designed to correct this problem. It receives the current speedometer signal from the vehicle speed sensor and
sends the correct speed signal to the speedometer. The ERA installation is
a snap with only four wires (input, output, hot, ground). Set the dip switches following the Abbott Calibration Table and your ready to go. The ERA has one of the widest pulse ranges available.

STRSHP

reading 4+ mph faster than the radar warning set ups along the highway.

krisd

I have compared mine (99 with 18 inch wheels) to the GPS and the speedo was 4 mph fast at all speeds above 15 mph. I have compared the odometer to the speedo check signs on the highway and it was dead on. It doesn't bother me at all.

Kris

Fro

If you are trying to get the digital speedometer to match the analog (needle) speedometer, it can be adjusted by pulling the needle and re-adjusting it.
I had to do this when I changed the gauge faces from black to white.
A little trial and error ended up with about perfect sychronicity!

HiWind

Hey guys,

Is this manual approach the only way to get dil to match 'real' gps speeed?
Thanks

Matt

Hurdigurdiman

for what its worth. I have a radar detector which shows speed. A Garman which shows speed and when i am driving, nothing matches up with my car speed reading. They are all 5mph out at 50mph. I have 18 inch wheels on mine. I havent even noticed if the digital speed matches the the other speedo on the car. I don't give a Sh** what they say as long as they are working. If a cop asks me what speed I was doing after he pulls me over. I will say no, I was hoping you could tell me haha.

nick49

This topic was big in the late '90s with new owners.

The dealer change the speedo to read closer to the actual miles per hour. Had it done in my wife's Boxster in about '01 or '02. The dealer did it at no charge on my last service before the warranty expired. Wow, time flies. The Boxster has not been to the dealer or any shop since. It's been a very trouble free car and still looks like new.

Sneaky Pete

No kidding time flies Nick.....this tread is 8 years old.

EDoyle

My speedo is seemingly about 4 mph off as well. I'm glad to read that the odometer is not affected by this.

HiWind

Yeah old ... but its good plus I believe in keeping thread together - ask himself.

I should explain why I ask cos it's not a cop concern. I ask not because of odo either (not affected as you'll understand in a sec) but because I can pull the kph off the car's ecu via the odb2 cable and that kph is .... wait for it ... almost exactly the same as the gps! So the car's ecu knows the 'real' speed but for various road-use reasons discussed above and on a couple other threads the kph or mph displayed is different.

So why care? Well when tracking the car, one way to know if you've improved how you take a corner is to see your exit speed, or likewise your top speed on the straight. It gives you something beside just how it feels to work with. Now using data from my gps/data logger I see one number - the ecu's - during analysis and another number when driving - the dial's. And as you know the difference of a second on the track can be determined by only a 2 kph difference in 3 or 4 corners. So while I'm driving I have to mentally be adjusting the speeds to match the analysis - not ideal. My OPC says it can't be done using PIWIS etc... But I always ask RL first.

We are not the Borg but definitely THE collective (c). What say ye motley crowd?

Edgy01

Just to update things on the thread, the DOT mandates that we get an optimistic speed display. However, the ODOMETER will read precisely the measurement of a mile. There is another speed that is never displayed but resident within the cars' logic circuits--its actual speed. That one is necessary to do things like control raising the spoiler at 75 mph. It's supposed to come up--but if you notice when you're doing an indicated 76 mph the spoiler remains down. Because of the built in fudge factor, it will take a little more indicated to finally deploy your spoiler.

HiWind

Thanks Dan - that's a reall neat way of confirming what I said re odb2 ecu data. But my question is CAN it be modded back to accurate (not MAY it)?