...... our speedometers (2k2-2k3 for sure) were off by 3-4mph? Or is it just my car?
Get on the highway and get your speedometer right at 80mph. Set cruise control right then (it'll hold that speed instantly because of the drive by wire), then reset your average mph reading on your trip computer. Do this in an area where the distance you'll cover is flat, so that your car doesn't speed up or slow down. Your average speed will be 77mph.
Our speedometer increases in increments of 2. For example, between 0 and 20mph, u have 10 lines, same for 20mph and 40mph. The manual says that when u have cruise control set, if u press the Accelerate button once, the car speeds up 1 mph. When u press the button, the speedometer moves up one increment. Does that mean u actually accelerated 2mphs instead or 1 and the speedo is accurate, or does that mean u accelerated 1mph and the speedo is completely off? If that's the case, then the margin for error gets higher as speeds increase.
Any inputs on this? I know it sounds crazy, but i get annoyed by this when i travel long distances and using cruise control.
Help me understand...

 

Get rid of Uncle Bens Used OVER Sized Tires And the problem will go away

You running 235/45 on factory 17x7 Thats gotta do somthing Gay Like that

 

It was like that from the first day i had the car. The different tires didn't change a thing. How do u explain the inconsistency in the cruise control?

 

Don't you have some Opsys Installs to complete you ricer

 

You do realize we are talking about mass produced vehicles that are made of parts that are manufactured within tolerances? Not every speedo, etc. is going to be perfectly calibrated.

At least your car is actually travelling a tad less than indicated...would suck if the other way around and you got a ticket for 3-4 miles over when you didn't even know what happened.

 

nothing on my car is ricey.

 

'Car and Driver' did an article/study on this issue about a year or so ago. It found that inacurate speedometer information is a common issue/problem with many car makers.

In the article, I believe Nissan vehicles tended to be off by about 2.3% or something like that. GM cars seemed to be the most accurate.

Check out these links:

http://www.caranddriver.com/article....&page_number=1

http://www.caranddriver.com/article....rticle_id=1907

Peace.

 

I thought every car's speedo was a little high "just in case."

And about the cruise. Try locking it on 70, then press it 5 times. Are you now going 75 or 80? My guess is it'll be somewhere in between.

 

If i'm at 70 on the speedometer and i press the accelerate button 5 times, the needle goes up to 80mph for sure.

 

there's your answer, the book is wrong.

 

not necessarily if our speedos are moving up in increments of 2mphs and are off by a serious margin to begin with. But oh well.

 

I think the cruise control works off the driveshaft rpm, not the speedo. Correct me if I'm wrong.

 

some food for thought.....typically.......

215/55 17 = 26.3" diameter
225/50 17 = 25.9" diameter
235/45 17 = 25.3" diameter

The smaller the diameter, the faster your speedo will register in relation to your car's true speed. Notice there is not much diffenence between the GLE/SE tire diameters, but your tires are an inch shorter than the GLE tires, that's a good bit. My GLE has what I consider the most accurate speedo of any car I have ever owned.

Probably not as noticable on our cars, but my 4Runner with it's tall suv tires is sensitive to tire pressure. The difference between 30 and 35 psi is very noticable when you time it between mile markers on the freeway.

 

When i still had my Potenza's, the speedo was pretty accurate (GPS) up to 60mph. Didn't get a chance to test it beyond that.

Now with lower profile tires, i'm sure it's off by a good percent (approx 3mph according to the tire size guide)

 

Go get a stopwatch, set your car at 60mph cruising. Then when you reach one mile marker, hit it. when you reach the next, hit it again. (use the a- pillar as a visual guide, so you can eliminate some of the inaccuracy of hand measuring). Also, this should be done on a straight and level road. The watch should read 1 min exaclty. If less, then your speedo is low. If more than your speedo reads high. Most cars have a tiny bit of error built in, but it really isnt all that significant at legal speeds. I put my car to that test ( I use 235/50/17) and it turned out my speedo reads a little low.