PVD Wheels
11-08-17, 04:08 PM
#31
I hate to tell you, but unless the sensor it at the outer edge of the wheel, there is no possible way for the car to know if you have 17, 18 or 24 in wheels.
So unless you are saying the speed is provided by the TPMS (and we know it isn't because you will still show speed if you remove the TPMS) your statement is completely incorrect.
It is based on revolutions per mile, probably captured at the axle half shaft. That speed is determined by the tire size, not the wheel size.
If you have the exact same height tire, a 17 and 18 inch wheel will rotate at the exact same speed at the 8.5" mark. Since you can swap wheels straight across, the sensor can't be measuring at the outer edge of the wheel. If you are getting variances in speed between 2 different sets of wheels, it is because your tires are not the exact same height.
If you have stock wheels and old tires, your reading will be off as the tread is lower.
If you have stock wheels and new stock tires and your reading is off, it was set incorrectly from the factory.
https://tiresize.com/tyre-size-calculator/
If you really want to test this, get two 17" wheels and two 18" wheels and mount tires on them that are exactly the same height. Even 3/32 can throw this off.
Now mount those tires on the car in any configuration you want. (17s on front, 18s on rear; 18s on front, 17s on rear; 17s on left, 18s on right; 18s on left, 17s on right; 17s on front left/rear right, 18s on front right/rear left) and you will get the same exact speed reading every time. It's physics, not programming.
So unless you are saying the speed is provided by the TPMS (and we know it isn't because you will still show speed if you remove the TPMS) your statement is completely incorrect.
It is based on revolutions per mile, probably captured at the axle half shaft. That speed is determined by the tire size, not the wheel size.
If you have the exact same height tire, a 17 and 18 inch wheel will rotate at the exact same speed at the 8.5" mark. Since you can swap wheels straight across, the sensor can't be measuring at the outer edge of the wheel. If you are getting variances in speed between 2 different sets of wheels, it is because your tires are not the exact same height.
If you have stock wheels and old tires, your reading will be off as the tread is lower.
If you have stock wheels and new stock tires and your reading is off, it was set incorrectly from the factory.
https://tiresize.com/tyre-size-calculator/
If you really want to test this, get two 17" wheels and two 18" wheels and mount tires on them that are exactly the same height. Even 3/32 can throw this off.
Now mount those tires on the car in any configuration you want. (17s on front, 18s on rear; 18s on front, 17s on rear; 17s on left, 18s on right; 18s on left, 17s on right; 17s on front left/rear right, 18s on front right/rear left) and you will get the same exact speed reading every time. It's physics, not programming.
So with that what I am saying is that MY - 2013 ES 350 U/L Package with Factory '18 has a speedometer that reads 3-5 MPH faster at 50ish and above. The facts are the car has what it has. And does what it does. Period.
Also if someone thinks that every different brand of tire of the same size (ex. 225/45/18) is exactly the same measure, I think its wrong. I think, I remember talking to Michelin, Tire Rack and few other some years back and they substantiated that its true.
Now with that all said you bring a point I did not think of, about tires and tread depth wear. But.... all tires wear. So I will be checking the New Tires for the speed difference soon as I can. The old tired were worn all the way down. Thanks.
11-08-17, 04:12 PM
#32
Intermediate
Lets be clear. Hope you don't see any where I claimed that the 18" wheels are throwing it off. Or that I am debating that the wheels (not tires) have something to do with "mine" being off. Im kinda getting the feeling when you started with "I hate to tell you". Ill leave it at that I'm not saying that and never did.
11-09-17, 05:32 AM
#34
Fact: All speedometers have a tolerance in the US of between ~3 and 5%. As tires wear
Fact: Your registered speed on said speedometer, with OEM sized tires, will not be on the high side (for litigious reasons).
http://www.oecbi.com/blog/vehicle-sp...-really-going/
Fact: Your registered speed on said speedometer, with OEM sized tires, will not be on the high side (for litigious reasons).
http://www.oecbi.com/blog/vehicle-sp...-really-going/
11-09-17, 08:51 AM
#35
I have other cars, and I have never had the speedo off more than 1mph, some have double din aftermarket Navi's that give you the speed readout.
Ill say it again until I am proven wrong. I don't think every tire of different Brands of the same size is the same measure. There are some differences of size measurements from tire to tire of the same size.
I can be going 80 according to my ES 350 speedo, but really only going 75-76 mph.
Ill say it again until I am proven wrong. I don't think every tire of different Brands of the same size is the same measure. There are some differences of size measurements from tire to tire of the same size.
I can be going 80 according to my ES 350 speedo, but really only going 75-76 mph.
11-09-17, 06:56 PM
#36
Intermediate
But I can't see the variances in passenger tires to be that far off as to make your speedometer off be more than 3 mph. I have 15K on the stock tires and there is less than 1 mph variance between the speedo and GPS.
11-10-17, 05:55 AM
#38
The 3-5mph float at 50+mph on the speedo from registered read and actual read is pretty disappointing, to be sure....especially if reading higher than actual. While the 55mph read when only traveling 50mph may minimize the likelihood of a speeding ticket, it also represents 10% more miles on your odometer than actually traveled. This results in unnecessary devaluation over time. It also would reflect a higher mpg than actual, if calculated using the odometer.
This issue brings up a question...with such a larger percentage of vehicles (lexus and other) including nav in their builds, I wonder why speed is not calculated by gps? I suppose connectivity may be an issue at times.
This issue brings up a question...with such a larger percentage of vehicles (lexus and other) including nav in their builds, I wonder why speed is not calculated by gps? I suppose connectivity may be an issue at times.
11-10-17, 09:41 AM
#39
Speedometer and odometer are not tied together. Odometer is much more accurate. I've verified this on the highway.
11-10-17, 12:45 PM
#40
Interesting. While the speedo and odo may not be directly linked, I assume they receive input data from the same source (wheel rotation)? Unless calibrated using GPS, how would the car know distance traveled other than rotation of wheels.
11-10-17, 05:44 PM
#41
Pole Position
I tend to trust the portable radar units the police park alongside the road more than GPS. I have noticed our previous Toyota/Lexus speedometers are always about two MPH optimistic at city street speeds, ~40mph. So speedo may read 40 but radar unit reads 38. I don’t know if that is linear - dependent on speed, as I have only seen these in town. I have seen similar reports in auto mags. I don’t know how this speed measurement compares with the precision of other brands
i guess my point is simply that I don’t think it is entirely dependent on the tires, wear or tire/wheel combos. Numerous factors impact the readout on the dash including the manufacturer’s calibration and perhaps even temperature/weather.
i guess my point is simply that I don’t think it is entirely dependent on the tires, wear or tire/wheel combos. Numerous factors impact the readout on the dash including the manufacturer’s calibration and perhaps even temperature/weather.
Last edited by TechNut; 11-11-17 at 07:01 AM.
11-10-17, 06:01 PM
#42
I tend to trust the portable radar units the police park alongside the road more than GPS. I have noticed our Toyota/Lexus speedometers are about two MPH optimistic at city street speeds, ~40mph. So speedo may read 40 but radar unit reads 38. I don’t know if that is linear - dependent on speed, as I have only seen these in town. I have seen similar reports in auto mags. I don’t know how this speed measurement compares with the precision of other brands
i guess my point is simply that I don’t think it is entirely dependent on the tires, wear or tire/wheel combos. Numerous factors impact the readout on the dash including the manufacturer’s calibration and perhaps even temperature/weather.
i guess my point is simply that I don’t think it is entirely dependent on the tires, wear or tire/wheel combos. Numerous factors impact the readout on the dash including the manufacturer’s calibration and perhaps even temperature/weather.
In my case I'm fairly certain its the calibration of the Factory being off.
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