Re-calibrate guages w/ 20's?
 

Is it possible to have your MPH and NAV computers adjusted to reflect 20" wheel size?

I notice now that my speedo is wrong and my MPG calculation on my NAVI seems out of whack. Can the dealer adjust this for me or am I SOL?

Yes, it should be possible to recalibrate your speedo (dunno anything bout NAV though). If the dealer doesnt want to do it, call up a few monster truck stores...they do it all the time. its probably a good idea to get this done, especially on an automatic transmission car...how off is your speedometer now?

The wheel diameter setting in most trucks [I won't claim all] is configurable via the ECU or by mechanical means. Synergy, I think you may be SOL with regards to your GS.

Interesting stuff, keep the info comming.

Yeah definetly let us know... I need to do the same...

What wrong with your speedo? Me and a lot of memebrs have 20's on GS and do not have any problem with the sppedo :confused:

I don't have NAV so I do not know if there's any consequences with the NAV system. But I think my speedo is still 99% right on the spot.

well with 20s the overall diameter is off by an inch, so the speed would be off coz' it's determined by axel revolution i believe?

i know on acura nav you can adjust the speedo (somewhat) but i am not sure about lexus

Jacob, there isn't really nothing wrong with the speedo it's just alittle off.. Nothing major that needs immediate attention.. I just know it's off abit and if I could change it I would...

I think that it is off more than a little - like 5 - 7 MPH. I can tell that I am going faster than it says...

I also note that I am getting much worse MPG (around 13-14MPG) since I put on the wheels compared to 18-20MPG.

It must be a wheel calibration issue, right? Never had these problems w/ 17's....

no it's not the calibration, it's the heavy wheels buddy :) ever since i put on 19 my mpg dropped too. those wheels are heavy to turn specially from stop. welcome to the luxury club :)

I don't think my speedo is that off.. I definetly see what Romy is saying though.. And as for the MPG I wouldn't have a clue if I was getting more or less before the 20's since I pretty much put them on when I bought the car...

NAV speed is running off your speedo based on the nav schematic that I have.

The speed sensor emit pulse wave to the car ECU and the speedo to display speed. i don't know if you can do any calibrate, maybe your dealer will know. The circumference of your tire is what effect the speed, since the speed sensor measure the rotation rate of the wheel to calculate speed per roration/ie distance.

There are several "speed limit remove devides" you can buy, to remove your top speed (149m) and recal for your large wheel.
I have not seen these devices install on a Lexus before, but they do work on honda or supra.
look for these on yahoo you will find them


want to know how much your speed is off compare to stock, the right way?

click here, enter your stock tire size and the new one, it will tell you how much off are you, you should have look at this before getting the tire anyway. Now it's too late :mad: (ie if you are off too much, then change your tires)
http://www.miata.net/garage/tirecalc.html


Anh

According to the calculation, with 20's, it's only 2.4 mph or 4% off at 60 mph. That's why I do not see a big difference on the speedo.

Is that +or - ???

your car is going faster than what it says