eXstasy

Hi all,

Can anyone tell me their speedometer reading while you are cruising on the highway in 8th gear, at 2000rpm? I'm reading about 76mph, just wanted to confirm if this is correct.

Thanks!

melbitoast

iTrader: (1)

that sounds about right. i'll check later on my way home (about an hour from now, if my car's ready).

mugenh22a4

iTrader: (9)

Do the speedos on the ISF report higher than the car's actually going? My E46 M3 reported 10% higher by design, which was annoying

syzygy

No. The Lexus speedometers are actually remarkably accurate, often within 2.5% if you compare them to GPS readings. So at 60 MPH the reading is accurate to within 1.5 MPH.

There's a reason why many German cars have speedometers that often read much higher than the actual speed. It has to do with stricter rules on speedometer readings in europe. The rules are such that it's better to have too high of a reading than too low. Car and driver explains this in an article -

"The European regulation, ECE-R 39, is more concise, stating essentially that the speed indicated must never be lower than the true speed or higher by more than one-tenth of true speed plus four kilometers per hour (79.5 mph at a true 70). Never low. Not even if somebody swaps a big set of 285/35R-18s for stock 255/45R-16s.

There's your explanation of high-reading European speedometers, with the highest readings on Porsches and BMWs that are most likely to lure owners inclined to fool with tire sizes."

As far as the old IS300 goes, I believe somebody had the following results - traveling at 100 MPH (according to the IS300 speedometer), the GPS read a traveling speed of 97.5 MPH.

I have no reason to believe that the ISF would have an error worse than that of a 10 year old IS300. If anything, the ISF is likely even more accurate than +/- 2.5%.


I'd be interested to hear of any ISF owners have done informal tests like this to see how much of a discrepancy there is between ISF speedometer reading and GPS speed readings (which are widely accepted to be accurate +/- .1 MPH (one tenth of a mile per hour)).

Joe Z

iTrader: (10)

I locked in my F at 2,000 rpms on the cruise control.
Even with my non oem tire sizes, I was rolling at a steady 76-77 mph on the needle .. (flat fwy road)

For shiits & giggles, my "Vehicle Speed Sensors" were only reading 73-74 mph, on the Tech Data screen.

Joe Z

eXstasy

Thanks for the info Joe Z. I forgot to mention, I'm not on OEM sized tires. 275/30/19 in the rear. Just wondering how different it is from the stock reading since I forgot to check it myself.

itsmike177

iTrader: (3)

2008 ISF OEM wheels and OEM sized tires. 8th gear, 2000rpms, speedometer reads at 79 mph. GPS reads at 78-79mph.

eXstasy

Hey, thanks. I'm actually surprised that JoeZ and I have lower readings than you and you are on stock sized rims and tires. I'm on OEM rims and my tire size should be shorter than stock.

melbitoast

iTrader: (1)

Same here. Checked mine today at lunch.

Joe Z

iTrader: (10)

That's right.. are needle is showing slightly slower than actual speed.. by approx 2.5%

Joe Z

eXstasy

Ah okay, I think I originally got it backwards.

Since our tires are shorter, the speedo displays a bit higher than our actual speed. Got it. 76-77 -> 78-79 sounds like a 2% difference, as expected.

Joe Z

iTrader: (10)

^^ Well our tires are turning "faster" compared to stock... and so is the needle..

So if you put too F's side by side and the OEM is doing 79 mph on the needle and I set mine to 79 on my needle, I would basically be really only going 76 mph.. (slower)

I would have to Go Faster up to 82mph to match the 79 mph oem tire speed..

Now if that's not confusing, I don't know what is.. LoL

Joe Z

PHXF

OK I'll be the forum idiot. "Vehicle Speed Sensors"...is this a hidden screen or have I just not wandered across it yet?

Joe Z

iTrader: (10)

Yes, it's a hidden menu via the touch nav screen..
Can be used by Techs to check for small issues.

Joe Z

Axtellz

60mph = 2150rpm in 8th
(my F has the 4.08 gear swap)