Speedometer questions

I bought a used 24 Platinum running 295/60R20 tires.

I have noticed that when I first turn it on and drive it will be off as suspected. While running Waze, I’ll notice my dash Speed and Waze speed are off by 2-10 (depending on speed). However, while I’m doing highway speeds (70+ mph) the dash will initially be off by 7-10 mph vs Waze, I’ll set the cruise and then gradually Waze will start to drop closer to my dash speed.

I know Waze isn’t the gold standard of accuracy, but this seems odd.

Anyone else deal with this?

alternative solutions?

 

Try this app on your phone to give you a comparison. I have found it is very accurate.

https://play.google.com/store/apps/...gpsspeedometer.odometer&pcampaignid=web_share

 

You may know this, but your speedometer will always be off by the same percentage at any speed, based on the larger circumference of your tires relative to stock tires.

For example, if the circumference difference is 10%, when your speedometer reads 30, your actual speed will be 33. If the speedometer reads 60, your actual will be 66...and so on.

I've found that Google Maps GPS speed often varies from this basic rule. Sometimes it's on the money, other times not so much.

 

This I knew.

What I am dealing with is not exactly the same, but maybe a better example.

I get on the highway and set my cruise to 75. Waze will say I’m going 84. One mile later - 83, another mile 82, and so on until I am matching or the dash is only 1-2 mph slower. However, I never change the cruise set speed from 75.

 

My Waze does the same. I never paid much attention until I went up on tire size and was trying to gauge how far off the speedo is.

 

Same exact thing happens with Waze and google nav with me. Its not the truck its the phone GPS.

 

There’s a tire size calculator where you can put the oem size in and then your current setup, along with the “speed” at which you want to calculate for. For me 75mph on the dash, I’m doing 80. If the dash is showing me 35 in closer to 38/39. I just keep aware what I’m doing in certain speed ranges

 

Agree the phone GPS. The more satellites it can connect to, the better the accuracy. Try the speedometer app on your phone to compare.

 

My truck does this also on Google Maps in my 2024 Tundra. I never had this happen in other vehicles I drive. I assume it’s the phone/Carplay given I’m not flying past other cars…

 

use a garmin gps unit, those are more accurate since they use the sats instead of your phone for gps. apps using your phone gps are never updated in real time or not as accurate vs a dedicated unit like garmin

 

2024 Platinum here too with the exact same Waze vs speedo huge gap readings. I have noticed that the two readings vary more so during the first 20 - 30 minutes of a drive. I am running stock tire size and I am getting it too. I almost feel like the truck "learns" the farther into a drive I get because the speedo vs Waze gap decreases within a mile per hour or so about an hour into a drive. I don't Waze around town, so I don't have any insight on those trips, but I do notice it when I am "going somewhere" and am using Waze. It honestly freaked me out on my drive home from buying the truck because I noticed that it was off 7-9mph. I have always run bigger tires on all of my trucks, so I am used to speedo vs gps readings to be off, but this is out of the norms of running 33's or 35's for sure.

 

Glad I am not the only one with this. I also knew it would be off, but the difference changing the the longer I drive while not changing the truck speed really threw me off.

 

Your speedometer on your truck is off due to the increased diameter of your aftermarket tires (and maybe the lift). 2" diameter difference multiplied by Pi will give you a good start at the affected numbers.

The Waze calculator is based on data, GPS and all of the variables that lead to a phone not working properly all of the time, dropping calls, crashing, resetting your position on your route etc.

As for the changes to those numbers in real time, your Speedometer is incorrect and your Waze is taking time to orient itself. Like this:

Truck ---> ? <--- Waze

 

Allegedly the Toyota Speedo is off by a few MPH as in 75 is actually 73 before you change tire size....but that tire size isn't that different from stock

 

Yeah, I think after using the difference calculation I'm going to operate off the below assumption and this should keep me pretty close:

• 0-34 (+1)
• 35-55 (+2)
• 55-80 (+3)
• 81+ (+4) and slow the f down

 

Based on the tire circumferences posted above, your speedometer will always be 4.4% slower than your actual speed. So, your rough calculations are pretty close.

The actual calculation is (speedometer reading) x 1.044 = actual speed.

 

Waze very often puts my speed 3-7 mph above my speedo in my 22 Limited. It is bone stock with original tires. I use my dash cam to verify my truck speedo is accurate and it is. Waze does not do thin in my 2016 Accord, never. There is something about the Tundra, maybe because I am using Apple CarPlay in it that causes it to act this way.

 

I have 35x12.5R20 tires so I got a HUD off of Amazon and used the Acecar version. Plugs into the OBDII port under the dash below steering wheel, & the wire hides very easily. It uses the Toyota ECU speed sensor and then you apply factors to correct for your tire size. Auto on/off, self dimming. Small tint/laminate you stick on lower windshield and image shows speed as a heads up display. It will also show tach, water temp, etc, but I just do the digital speed reading.