Speedometer vs GPS indication

[Rinat]

Hello,

Would like to ask your experience about difference of Speedometer and actual GPS speed.
Before on my FJ cruiser with using 285x75 r16 i had the same speed Speedometer = GPS. But now on 285x70r17 at my 200 i have 10% difference, speedometer shows less than GPS. I think this is OK for stock wheels, but not 33".
I drive my 200 in Kazakhstan and made adaptation of instrumental panel to Celsius and KM instead of miles and Fahrenheit. And have some doubts if speedometer arrow has some connection with panel "firmware".

Regards,
Rinat.

 

[chilibit]

The speedometer assumes the stock tire circumference to calculate speed which, by the way, ignores vertical displacement. The satellite merely tracks a point in space. The stock speedometer under-estimates speed as the tire circumference increases.

 

[Rinat]

I will be grateful if someone compare speedometer vs GPS on their LC200. Doesn't matter which tires.

 

[alta]

I like this site to play with tire sizes: Tire Size Calculator

Your tire size (circumference) is about 4% larger than stock, so 10% doesn't sound correct.

And you should see virtually no difference between the 2 sizes you mentioned, as they are nearly identical in diameter.

My radar detector has my speed displayed using its gps. I have found that my radar detector displays about 6% higher than the speedometer with my 305/65r18s. This is very close to what is expected (6.7%). I will say that all my cars over the years seem to register (speedometer) 1-2 miles per hour faster than actual speed (unscientifically comparing to various gps devices and traffic radar displays). Perhaps to add a factor of safety? My German cars seem to be closer to accurate than the Toyotas.

I am not sure what could be happening, but 10% doesn't sound right.

 

[Cruisin911]

If its a concern, you can always install an adapter that will fix the speedo for the larger tires. Tons of companies make them. I ran one on my tundra when I went to bigger tires.

 

[Sandroad]

You should have only about 4% difference between actual speed and speedometer speed with that tire size, compared to stock. Do you have an accurate gps unit?

 

[tominboise]

You can always check your speedo accuracy using a stop watch and a known distance. Set the cruise on 80mph and time a mile. Should be 45 seconds.

 

[TonyP]

Download a speedometer app for your phone.

 

[Fisher23]

Measure the actual height of the current tire. is it 833 mm?
You may want to check using a stop watch time at a steady speed over a km and see actual time/speed.

 

[Rinat]

I like this site to play with tire sizes: Tire Size Calculator

Your tire size (circumference) is about 4% larger than stock, so 10% doesn't sound correct.

View attachment 1950468

And you should see virtually no difference between the 2 sizes you mentioned, as they are nearly identical in diameter.

View attachment 1950466

My radar detector has my speed displayed using its gps. I have found that my radar detector displays about 6% higher than the speedometer with my 305/65r18s. This is very close to what is expected (6.7%). I will say that all my cars over the years seem to register (speedometer) 1-2 miles per hour faster than actual speed (unscientifically comparing to various gps devices and traffic radar displays). Perhaps to add a factor of safety? My German cars seem to be closer to accurate than the Toyotas.

I am not sure what could be happening, but 10% doesn't sound right.

Yes, i have 3.8% difference of tires height, compared to stock on LC200. And have 10% difference between Speedometr and GPS in radar detector. Something went wrong after my panel "update".
Thank you for information. I will try to check once again, compared to my phone or Garmin Montana.

 

[Rinat]

You should have only about 4% difference between actual speed and speedometer speed with that tire size, compared to stock. Do you have an accurate gps unit?

Yes i have Garmin Montana and probably will try to use mobile phone instead of radar detector

 

[Rinat]

If its a concern, you can always install an adapter that will fix the speedo for the larger tires. Tons of companies make them. I ran one on my tundra when I went to bigger tires.

Thanks for tip, if i relay find that there some problem with panel i will check this option too.

 

[Fisher23]

I use a Montana, and the 680 is way more accurate in the stans than the 650, plus it works went out of cell range.

 

[Markuson]

Maybe try this:

Go to tiresize.com ...look up your specific brand...exact model of your tires.

Click details/specs for each tire.

**You will then be able to view each tire’s **rotations per mile driven.**

Divide the two numbers against each other to get percentage difference between them.

You should get numbers close to reality...UNLESS...treads on older tires were significantly worn, which would also shrink its circumference and

 

[99Cruiser]

My speedometer reads faster than gps stock tire size. If speedometer shows 80mph, gps shows 75-76. I also hate the speedometer. The increments are horrible. No 5mph increments in between only 2mph lines.

 

[Markuson]

My speedometer reads faster than gps stock tire size. If speedometer shows 80mph, gps shows 75-76. I also hate the speedometer. The increments are horrible. No 5mph increments in between only 2mph lines.

Someone recently reported that their 285/70/17 KO2’s actually were more correct than their stock tires/wheels.

 

[gaijin]

Someone recently reported that their 285/70/17 KO2’s actually were more correct than their stock tires/wheels.

I've been "reporting" that for years!

Long story short:

By law, in Japan Toyota are not allowed to manufacture a vehicle that will display a speedometer speed that is under actual speed for any circumstance under which the vehicle is approved for use.

As a result, in U.S. spec LC200's, the speedometer displays about 3-4% faster than actual with stock P285/60R18 tires. The odometer, however, displays the total miles driven accurately. Cruise control also indicates about 3-4% faster than actual.

When the Toyota approved LT285/70R17 tires are fitted, the speedometer is dead nuts on - displayed speed is essentially the same as actual speed. The odometer, however, displays about 3-4% fewer miles than actually driven. Cruise control also displays speed accurately.

All confirmed by years of monitoring use on my 2013 LC200 using both stock P285/60R18 tires and LT285/70R17 tires with speed verified by outboard GPS units.

I'm too lazy to search all my old posts, but they're there.

HTH

 

[Markuson]

I've been "reporting" that for years!

Long story short:

By law, in Japan Toyota are not allowed to manufacture a vehicle that will display a speedometer speed that is under actual speed for any circumstance under which the vehicle is approved for use.

As a result, in U.S. spec LC200's, the speedometer displays about 3-4% faster than actual with stock P285/60R18 tires. The odometer, however, displays the total miles driven accurately. Cruise control also indicates about 3-4% faster than actual.

When the Toyota approved LT285/70R17 tires are fitted, the speedometer is dead nuts on - displayed speed is essentially the same as actual speed. The odometer, however, displays about 3-4% fewer miles than actually driven. Cruise control also displays speed accurately.

All confirmed by years of monitoring use on my 2013 LC200 using both stock P285/60R18 tires and LT285/70R17 tires with speed verified by outboard GPS units.

I'm too lazy to search all my old posts, but they're there.

HTH

Shoulda known that was you. Heh

Nice thing is...if it’s you, I know it’s correct.

 

[MikeVpdx503]

I've been "reporting" that for years!

Long story short:

By law, in Japan Toyota are not allowed to manufacture a vehicle that will display a speedometer speed that is under actual speed for any circumstance under which the vehicle is approved for use.

As a result, in U.S. spec LC200's, the speedometer displays about 3-4% faster than actual with stock P285/60R18 tires. The odometer, however, displays the total miles driven accurately. Cruise control also indicates about 3-4% faster than actual.

When the Toyota approved LT285/70R17 tires are fitted, the speedometer is dead nuts on - displayed speed is essentially the same as actual speed. The odometer, however, displays about 3-4% fewer miles than actually driven. Cruise control also displays speed accurately.

All confirmed by years of monitoring use on my 2013 LC200 using both stock P285/60R18 tires and LT285/70R17 tires with speed verified by outboard GPS units.

I'm too lazy to search all my old posts, but they're there.

HTH

Same here, when I switched to LT285/70R17 tires, my onboard speedometer now reads dead on with onboard GPS. Odometer is still off though...my ODC brain wishes there was an easy fix for this, but the rest of me is dealing with it.