bgirls

Hi new here with a problem.

My wife went past one of those speed check radar sign on a trailer, she was in a 35 going 35 by the speedometer and it said she was going 31. no other cars near her, i took the gps for a ride and it is off by 4 mph @ 55 on the speedo. so 59 on the speedo is 55 on the gps. this gps is assumed correct as it was consistant with 2 gps units. any hints or suggestions?

Thank you, Scott

Wingless Wonder

iTrader: (7)

If your car has had the original equipment tires replaced, are they the same size as the originals? Even replacements of the same size can vary a bit in diameter compared with the originals, but not as much as choosing a tire that is way off from what's specified.

If the tires are the correct size, I'd bring it to the dealer to see if they have an explanation or a fix. Your GPS device is probably accurate enough so I don't doubt that your vehicle speedometer is displaying an error. I've used a cheap GPS handheld and also one of those in-car 'computers' with built-in accelerometers and both pretty much matched my speedometer readings within +/- 1 mph at any legal speed.

EDIT: All modern cars use speed sensors at the wheel(s) to measure vehicle speed by counting wheel rotations. This is pretty much subject to the same variables as the old speedometer gear and cable in the transmission when it comes to tire diameter or wheelspin in slippery conditions.

bgirls

they are the same p metric number but the diamater could vary from the origonal, i just checked the bridestone site. the origonal tire was a potenze RE 92 and the replacement i put on was the HP 50. both list a overall diamater of 26.6. i will investigate this after the seventh of august as we are leaving on vacation in the a.m., thanks for the reply and i will post when i return.

ldivinag

iTrader: (3)

on my 2002 wrx, the speedo was off by 1-2 mph at around 65.

this wasnt a big deal.

but when i traded it in for an 04 STi, the speedo on that is like yours. i posted this around aug 2003 on another board.

what was weird is that the odometer was dead on. it was like the STi speedo was getting a diff signal.

anyways, i confirmed this with a gps back then, and recently, i just got a new handheld nav (a tomtom) and that also confirmed the diff in the speedo reading, 4 years later.

i'm still running oem tires (second set) so it's not that issue.

i learned to live with it.

do a careful mapping of the speedo. on mine, at around 30mph, the reading is off by like 2-3.

as i go faster, the reading goes to up 4-5 mph diff... odd...

walt

my sti reads 4mph fast-this is common