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Discussion Starter #1
installed my handheld gps today.

went on freeway, set cruise on 60. gps read 56.1

set cruise on 65. gps read 61.1'ish

set cruise on 70. gps read 66.1'ish.

on slower speed, the diff in speed is less, like 3 MPH. like going 35, the gps would read 33.5.

hence, i believe that the tire size is 1 size smaller. will test if odometer is also affected. in previous experiences, it does. will be driving abour 70 miles tonite and will confirm...

while it's not the otherway around, ie, speedo is reading SLOWER than actual speed and hence getting a ticket, other drivers might honk or beep or flash highbeam at you for the wrong reason...

my previous experience is in my truck. where when i went to a bigger size tire, the speedo would read SLOWER. and when i went to a smaller size tire than originally, it would read FASTER. only way to fix this was when i went from 29" tires to almost 32" ones, was to re-gear the front and rear diffs (change the ring and pinion) with a diff ratio. from a 4.10 to 4.88 gears.

FYI, on my wrx, the speedo was almost dead on with the 16" OEM tires. when i went to 17" rims and 225/40 kumhos, it was slightly SMALLER so the speedo read about 1.5 MPH off...

will send something to SOA about this. i believe a recall is in order for new tires that are slightly bigger... ;)
 

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Yeah for some reason I was pretty sure the speedo was reading too fast. It just felt like it. Of course my truck's speedo reads a little slow for the same tire reason. Thank's for the confirmation. So if the speedo reads too fast the odometer is going to register more miles than there actually are on the car. I guess the fact my trucks speedo is too slow makes it all even out. :p
 

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radar detectors, which is best bang for buck!

i checked this with my gps also and my speedo was a little high as well. i got more like 2mph off, 4 is a bit much to tolerate imho.
 

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Heh, I just check mine by speeding through construction zones. The ones around here always have that large "YOUR SPEED IS XXX" "SLOW DOWN"
sign. Heh. I guess I need to see how close mine is again. I thought it was dead on.
 

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Discussion Starter #6
Introduction

sakura-iro said:
i checked this with my gps also and my speedo was a little high as well. i got more like 2mph off, 4 is a bit much to tolerate imho.
what speeds were you checking.

like i said... the lower the speed, the lower the difference...

just wanna add, that i wasnt using my antenna that i normally have plugged into my older garmin 12XL unit.

so i was getting and EPE of 16-17. whereas with the external antenna, EPE would be 10-11...
 

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That sounds about right though. It would be like a percentage differential rather than a static difference.

Hmm....anyone know if you can adjust those little bastards?
 

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MRT (in Australia) sells a box that will adjust the speed signal to the ECU. Otherwise, I think it's illegal since it would tamper with the odo as well -- even if you're making it more accurate. Not sure, but I think that's right.
 

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I can also confirm that the speedo reads "high" I went through the "Your speed is xx" and it was off by about 3 mph. Speedo read 45 sign said 42. I guess Subaru is looking out for us... :wink:

CoreySTi04
 
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Pretty much every odo in any vehicle is off by a small percentage, I would have expected the same from the STi. I once read an article that said pretty much all speedos are 0ff 2-5 kph, so maybe 5 miles is a bit too much off. But always expect speedos to be off a tad.
 

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My neighborhood had one of those speedo things and it read slower than i was going but I didnt give it much thought...nice to know.
 

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Discussion Starter #12
turbs said:
Pretty much every odo in any vehicle is off by a small percentage, I would have expected the same from the STi. I once read an article that said pretty much all speedos are 0ff 2-5 kph, so maybe 5 miles is a bit too much off. But always expect speedos to be off a tad.
yeah, but when it comes time for warranty work...

"sorry MR D... but your odomete reads 36002... you're ouot of warranty..."
 

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So...worst case scenario:
For every 56 miles driven, odometer logs 60 miles.
For every 560 miles, 600.
For every 5600 miles, 6000.
For every 56000 miles, 60000.

Thats 4000 miles....thats one additional oil change, earlier servies throughout the life of the vehicle, and a lower (granted it is incremental) resale value. Yeah...this isn't a HUGE issue, mostly bothersome. My biggest irk about it is that I've noticed I tend to be a tad slower than others on the freeway when using cruise. Increasing the speed put me into cruise numbers where I start seriously looking for traps and waiting for my V1 to chirp.

Huh...and all this time I thought everyone was just trying to get around the car with the crazy wing to see what it was.

Please let us know what SOA says to your inquiry about this.

Thanks,
Scott.
 

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Discussion Starter #15
okay... fired off a note to SOA via their website.

i'll let everyone know what happens.
 

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good idea scuba steve, that's what I'm going to do.
 

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Mine's definately high. I noticed it right away...when it said I was doing 80 mph, when I was staying right with the rest of the freeway traffic. To me, i'd guess it's like 5-6 mph high.

BTW, what or who is "SOA"?
 
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