speedo accuracy

Just curious what other members have noticed when driving by those radar screens as far as the accuracy of their speedometers. I went by one in my sti and my reading was 45 on my speedo and the radar screen read 43.

 

I'm consistently a couple mph higher on the speedo than on the sign - back when it worked.

 

Stock rims and tires?

 

Probaby a good thing.

 

speedos are generally allowed a pretty wide tolerance - i think it's 5% in MA. Even the radar guns only have a tolerance of 2-3%

 

my speedo is faster compared with radar signs.

 

Every speedometer I've ever had a chance to compare with a more objective source like that has been a couple mph faster. Speedometers are optimistic, and I'm pretty comfortable saying that as a blanket statement.

EDIT: Even my Scanguage, when plugged into my OBDII port, reads slower than my speedometer (yes, on the same exact car at the same time).

 

I'm glad they are optimistic. Gives you just a little bit of safety margin when driving. (maybe fewer tixs) And, yes it has stock rims

 

mine is 4 mph less exactly on my speedo then my gps on teh Forester and the same in my old WRX.. also even when I use the 19s on my Foz in summer it is right at 4-5 mph difference

 

I always find it's like 2mph off, which mine is too. Only cars I've noticed from factory with VERY accurate readings are the S2000 and the Nissan Titan.

 

I am about 5% high across the range of 30-80mph on both cars (stock size tires, but not stock).

 

At 55mph indicated my GPS unit says 50mph. That's on stock size rims/tires with about 50% wear.

 

My speedometer was 2mph fast @ 60 on my stock 215/45/17 tires. I put the 225/45/17 dunlops on and it was spot on.

Now i'm reading around 4 fast @ 60 because of the snows. lol

 

stock sized tires, my cars both read about 5% higher than actual speed (GPS). now the XT6 reads pretty much right on, and the wagon reads about 8% slow (stock tires are about 22.7" tall, my snow tires are almost 26"). I have to be very careful in it, because 70mph on the dash is almost 80....and I'm used to going 80 on 35, so if I shoot for 80, I'm going more like 90 :eek3:

 

Holy crap... why so big?

 

because 205/65 was the only size Revo1 that was on clearance for a 15" wheel. they fit the wheel wells just fine (I'm even lowered almost 2"), but screws up my speedo. my 215/45r17 summer setup is only about 24.5" tall, so they're much closer.

will be interesting to see how the calibration is effected when I put an EJ trans in it this spring.

 

I thought putting tires on that are that much different from the stock diameter was bad for the car for other reasons as well. So the only problem is the speedo calibration? Hmmm... :hsugh:

 

yea, doesn't hurt anything.


I had 29s on both my lifted '88s. stock suspension/brakes/axles/etc. just a body lift.

 

yeah my gps says that I am going slower than the car reads by about 3-4 mph