It seems to me that my speedometer is too optimistic.

The fantastic mpg first tipped me then I ran tests with the road side speed signs, then my hand held GPS.

Everytime the Lexus seems to be going slower than the speedo says. Something like at a real 70mph the GPS says more like 67.

ANyone else seen or experience this? I have not checked the mileage (via odometer).

keek

 

keek, I agree....@ 70mph I felt everyone was pulling away and it just seemed slow. I took a trip and set my GPS on the dash and found:

At 70 mph indicated I was actually going 68mph
at 80 mph indicated I was actually going 79 mph

I guess if I car run 90mph all the time everything will be correct.

I knows that throws off the mpg as well. I wonder if that is adjustable on my next service.

RT

 

Yeah, I've noticed that my speedo reads a bit on the slow side as well.

 

lol this seems to be a problem with all lexus cars.

on the bright side, your speeding ticket will be underestimated

 

the other way for me, it says 50mph but radar says 47mph

it's deviation on speedo, happens in every car model

 

Haha! But as rominl reports the speedo deviation happens on multiple models.

 

I've never had one this bad. My ls430 is pretty dead on.

Just bothersome knowing the speedo is faster than the car.

keek

 

wouldnt tire pressure have effect on it, lower pressures would affect the rotations per mph reading. That is how TPMS detect the pressure something to do with the rotations of the wheel during motion I believe

 

This is not unusual. Many cars experience the same thing. My last Benz (2004) was about 2-3 off.

 

i doubt that. so when the car is stop the tps won't detect the pressure? not really

 

http://en.wikipedia.org/wiki/Tire_Pr...itoring_System

according to wiki, indirect type TPMS are measuring wheel speed (which is already on the car for the ABS system anyways) and other measurements . While it isnt measuring a "pressure number" its comparing it to the other tires That checking of the differences b/t the tires is enough to alert the driver that something is wrong with a tire. Direct would be the direct measuring of pressure. Since at a stop the wheel speed of all tires is 0, therefore no differences b/t the 4 tires so nothings wrong. But lets say its detecting 4 wheel speeds (lets say 60 is the speed for correct tire pressure): 60, 60, 60, 55 then the system is going to flag that theres something wrong and youll eventually find the 55 tire is low on pressure. I think this is one of the reasons why cars dont tell you specifically which tire has the problem, because what if you had 55 55 55 60 how would the system know which tire has a problem since its just checking differences b/t tires

not sure what lexus uses.

 

that would be silly as well. so if all 4 tires gradually loses pressure to 25lb (which will happen) together with maybe 1-2psi difference, it will never say anything?

i am pretty sure that's not the case. on our sc430, when we put back the stock wheels after 3 yrs, the light turned on. i read and all tires were at 25lb. the light was on when the car was stopped or rolling. when we were at gas station, i pumped everytihng back up to 35psi, and the light turned off

i can't say for sure neither, but at least that's my experience on the sc430