Speedo error
 

I spent at least a hundred miles and repeated testing of my speedo on my 04 Sti last month because I couldn't figure out why everyone drove so fast when I was in my Sti. Basically speedo error is terrible. The stock tires are only ~1/3rd worn. Taking the averagwee of numerous mile timings I come up with these numbers. At a speedo reading of 75 , the car is only traveling at 72.36mph, meaning our speedos read high, 3.6% high to be exact! If I were to go to a larger OD tire, relative to wheel revolutions, the speedo would read lower or more accurately. I haven't calculated how much closer but I suspect that instead of being 2.6 mph off at 75, it would probably only be off 1-1.5 mph now. Any feedback on this topic would be appreciated. I was thinking of going with 235's once stock tires (which I love) wear out because I was hoping this would hel[p a little with the incessant understeer at the track. I know I ideally need a smaller rear sway bar or larger front one, but I'm not looking at keeping this as a track car forever and don't feel like entering mod hell.

PLease don't take this the wrong way but, you need to read more on vehicle dynamics .... to reduce understeer you need more rear sway bar or less front .... and all speedos are incorrect to some degree unless they are based on GPS ..... if your testing was not done using a GPS unit it was basically a waste of time

You can't imagine the thoughts that went through my head when I saw "speedo error". If I was you I'd go for the thickest sway bars you can in front and rear to make the chassis more rigid. Then get used to driving it with this as steering will become much more predictable. If want a pseudo-track car get a set of good coilovers and find you favorite track and street settings. Coilovers make a huge difference (Pinks are nice too).

accuracy
 

Hello Luke, my bad on the sway bars. Reread it today and realized I had it backwards. As far as testing a speedo, those mile markers on highways are quite accurate when travelling in a straight line. Besides, I didn't base my numbers on 1 -2 miles. It was more like 20-25 miles of repeated timings. I have no problem with a 1 mph speedo error, but a 2.6mph (3.5%) error is pretty bad in 2005. At the track at a 125 reading, I'm only doing 120. Embarrassing when asked your speds and you're giving bad numbers!
Is there a tire out there as good as the RE070 for an Sti and would 235's help with cornering as well as provided the fringe benefit of reducing the speedo error by reducing the rpm the wheels are turning? RE050's. SO3's, already heard thet PS2's don't compare by a few guys.

eh i have a 04 sti cluster in my wrx and its way off! for sure like you said i thought it was cause i put it in my wrx but now i know its just not calab'd right

anyways i just use my blitz power id meter to read the speed now
edgar, :)

go to the dealer and have it reclab'd

I haven't had an exact stock diameter tire on my RS in years- I just check to see what the speedo error is, and do the math in my head when I am on the freeway. It's second nature now. The performance of your car is far more important than the number on the needle behind your dash anyway.

Cutting from Car And Driver:

"So we sought out the rule book to find out just how much accuracy is mandated. In the U.S., manufacturers voluntarily follow the standard set by the Society of Automotive Engineers, J1226, which is pretty lax. To begin with, manufacturers are afforded the latitude to aim for within plus-or-minus two percent of absolute accuracy or to introduce bias to read high on a sliding scale of from minus-one to plus-three percent at low speeds to zero to plus-four percent above 55 mph. And those percentages are not of actual speed but rather a percentage of the total speed range indicated on the dial. So the four-percent allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph. "

[url]http://www.caranddriver.com/article.asp?section_id=4&article_id=1906&page_number=1[/url]


From another www I found this interesting comparison:

Subaru Impreza WRX 3.2%
Ford Focus 2.1%
Chrysler PT Cruiser 1.07%
Toyota Condor 2400 1.54%
Volvo V70 T5 0.14%

Basically, Subie speedos are the least accurate out there based on this test! sORRY bAN, ACCURACY COUNTS TOO! Hope it doesn't say anything about other "accuracies" such as tach,etc.