landar Posted November 3, 2009 Share Posted November 3, 2009 On a recent trip, I noticed that my speedometer was reading a bit higher than my Garmin GPS was indicating. Since I have 17" aftermarket rims, I am thinking its normal to be off a few percent. On a level stretch of highway, I turned the cruise control on and set the speed so that the speedometer needle was pointing precisely at the 70 mph mark. The Garmin reads 67 mph. Ok, I am not all that happy with that but blame it on the wheels. Then I get to thinking about how my odometer must be racking up more miles than I really have. So, I decide to set the trip and check it with the Garmin miles. When the Garmin showed exactly 100.0 miles travelled, the Lexus odometer showed 100.5 miles. Pretty darn close. In fact, within 0.5%. Not bad at all. Then, I decide to check the average speed indicator on my Lexus. I reset that with the cruise still on and it reads 67 mph! Same as the Garmin. That convinced me that the car speed sensing system knows how fast it is going (and is almost dead on) but the analog needle reading is off. I don't think there is anyway to correct the needle reading but thought it was interesting. I can live with it. Quote Link to comment Share on other sites More sharing options...
blake918 Posted November 3, 2009 Share Posted November 3, 2009 My '99 is off too (with stock sized rims and tires), and it drives me batty. The trip computer, GPS, and radar speed signs all show the same 3mph error in my car, so 3 against 1, and LS's speedometer is the loser. It's kind of ironic that Lexus tries to slow you down by 3mph when they make a car that goes 150mph. Some claim that 5%-10% error is "acceptable." Right. I've driven many GMs with perfectly accurate speedometers, so this obviously isn't rocket science. I've grown to live with it by using the on-board trip computer, Garmin, or judge the speed based on the RPMs. I know for sure that before my next car purchase, the Garmin is going to go on the test drive with me. I took a video of mine a while back... Quote Link to comment Share on other sites More sharing options...
amcdonal86 Posted November 3, 2009 Share Posted November 3, 2009 I think the "mis-calibration" is intentional on the part of Lexus. They want you to drive slower! The car knows exactly how fast it's going! Quote Link to comment Share on other sites More sharing options...
pauljcl Posted November 3, 2009 Share Posted November 3, 2009 I think the "mis-calibration" is intentional on the part of Lexus. They want you to drive slower!The car knows exactly how fast it's going! My 2009RX350 is also "off" by 3 mph (at most speeds 60-80mph). I too believe it is intentional to show a little faster speed than actual -- helps prevent tickets. Most cars do the same. Quote Link to comment Share on other sites More sharing options...
landar Posted November 3, 2009 Author Share Posted November 3, 2009 Oh this is "eye opening" More than a strange coincidence that all of us have the +3 mph needle increase BUT the car knows the real speed! So yes, I would agree that it sure looks intentional. We bad boys need some restraint. Wonder if it is gov't mandated? I also agree Blake, it is not rocket science. (good video BTW...same thing I did). My Chrysler speedo needle is dead nuts on. (of course they were probably trying to make it +3 and missed ). Quote Link to comment Share on other sites More sharing options...
GEN Posted November 3, 2009 Share Posted November 3, 2009 My Ls400 does this, my VW Passat did and my Porsche 928 also indicates a higher speed than the TomTom. Possibly they do it for fifferent reasons.. all the best Quote Link to comment Share on other sites More sharing options...
fblonk Posted November 4, 2009 Share Posted November 4, 2009 Both of my 98 LS's are off by around 3 mph. Thought it was just me. I love this site. fblonk Quote Link to comment Share on other sites More sharing options...
VBdenny Posted November 4, 2009 Share Posted November 4, 2009 Mine is dead on. I have 225/60/VR15 tires insead of factory 215/65/15. I didn't have a GPS when I had the original size tires on so I could only guess on that. Quote Link to comment Share on other sites More sharing options...
Just hanging on Posted November 4, 2009 Share Posted November 4, 2009 Also consider that the road speed indicated by the Garmin GPS is not exact but an approximation. I've had three different Garmin GPS devices and none have been advertised to be perfect. Quote Link to comment Share on other sites More sharing options...
VBdenny Posted November 5, 2009 Share Posted November 5, 2009 still closer than any speedometer. My Garmin register x7.8mph max on my last trip and I call that to the 1/10th of a mph. Quote Link to comment Share on other sites More sharing options...
amcdonal86 Posted November 5, 2009 Share Posted November 5, 2009 My '97 LS400's speedometer is dead-on-balls accurate. It seems to me that they started inflating the speedometer readings in 1998. Quote Link to comment Share on other sites More sharing options...
dasha1 Posted November 5, 2009 Share Posted November 5, 2009 My 1998 has stock tires and rims and the Garmin GPS indicates about 2-3 mph less than the speedometer at speeds b/w 60 and 80. I just noticed it two days ago and was wondering about it and then happened to read about it here. Interesting. My 99 LS has the stock Nav system which does not display speed. I might check it at some point against the Garmin. Quote Link to comment Share on other sites More sharing options...
blake918 Posted November 5, 2009 Share Posted November 5, 2009 Also consider that the road speed indicated by the Garmin GPS is not exact but an approximation. I've had three different Garmin GPS devices and none have been advertised to be perfect.My Garmin shows exactly the same speed that K and Ka band radar speed signs show, and it shows the same speed as my car's onboard trip computer, so I have 3 different devices that are in agreement that the speedometer shows the wrong speed -- which is enough to convince me. As it was said before, the car knows how fast it is going; the speedometer is where the problem lies. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.