Speedometer APPS

Do you use one to check your speed against the vehicle? I want to get one to check how far off my speedo is since I have much bigger tires than originally. If you have a favorite, which one is it. I have an android phone. Thanks.

 

I have GPS Race Timer. It shows 0-60 and quarter mile times (def not needed for the 4R LOL) but also current speed. It's on an iPhone. I want to do this test too, to see how accurate my speedo is on the stock wheels and tires, espec as some folks on the forum say their speedo got more accurate after upsizing.

In my limited testing so far: With my 4R showing 28 mph, the app showed 26/27. And with my 4R showing 48 mph, the app read 45/46. Those were short stints though and at low speeds, so I plan to try it again next time I'm on a good highway run. Will report back.

I'm no genius, but if the actual speed is lower than the reported speed on stock tires, I'd think that could in fact be corrected by upsizing. Larger diameter = longer distance covered per rotation = higher speed than the car thinks it's going.

 

Google maps has one built in, but for checking the speedo I used the one below. It's good at night with low light when needed, accurate and does the job. I tested after going to 285s and found with them the speedo is accurate at all speeds

 

I am not sure how accurate this calculation is but I was playing with this to see if my old Pathfinder Snow tires that I have on rims would fit my new 4Runner. Just plug in the OEM tires and whatever size you want to change to and it does a nice calculation for you: https://www.tacomaworld.com/tirecalc?tires=265-70r17-285-70r17 below is if you switch to 285s https://www.tacomaworld.com/tirecalc

 

Same here.

Keep in mind that the 5th gen at least reads a bit high (maybe 2 MPH at highway speeds). With 285's (32.9") I am perfectly accurate.

 

UPDATE: On long highway stretches yesterday in the 60s, the speedometer consistently read from 0-2 MPH higher than the reading on my GPS Race Timer app. Most of time time it was 1 mph higher. So I peg my Limited as off by 1 mpg. Per the chart posted by jrsuss above, that would mean that upsizing the Limited wouldn't correct the speedometer but instead result in it reading about 1 mph too low instead of 1 mph too high.

Note that my truck only has about 4500 miles on it, so the tires are at almost full new diameter.

 

UPDATE #2: I tested it again while driving in the 70s. Indicated speed consistently read 1-2 MPH faster than the reported speed on GPS Race Timer. The difference was 2 MPH more often than it was 1 MPH. So I'd peg the speedometer as being ~1 MPH high when driving in the 60s and roughly 1.7 MPH high when driving in the 70s. Presumably, these numbers would increase a wee bit as the tires wear down.

 

Your speedometer probably off by about 3% or so. The faster you drive, the further off it will be. That's why you probably don't notice it at lower speeds. At 30 MPH, it would be less than 1 MPH off, while it would be about 2 MPH off at 80.

 

Did you try a radar and or a different phone? Ex had an iphone that would read different than her older iphone. We ended up with 2 android and 2 iphones side by side and 3 of 4 phones matched the highway radar speed signs

 

I can't swear that the Race Timer app or the iphone itself are accurate -- though I don't know why they wouldn't be.

I've also compared my reported speed against highway radar signs, and they seemed to match more or less. But you pass them so fast I don't think it's a very reliable measurement -- even if the radar system and the display are generally accurate.

I do think that it's important to take multiple readings with the GPS app over a good distance and average them out, since the GPS sometimes lags or you can lose the signal. The results I posted above were taken over a few miles of driving, not just one quick look.