Milelage redux

[Big Ray]

so I downloaded a GPS speedo app on my phone recently.
Turns out I'm going @5 mph faster than indicated
Thought about, then realized I have bigger tires than stock.
Went on tacomaworld to verify sure enough...that was it.

So basically, I have no idea what my mileage was on the epic road trip
Doesn't matter, it was a blast, I met some cool CK5ers and picked up 2 cool pups on the way.

Good times!

 

[Big Ray]

Here's the difference chart...I did 75 80 indicated on the trip home...no wonder the mileage sucked, whatever it was! Lol those 400s rock!

The site addy

225/75-R15 vs 33/10.5-R15 Tire Comparison - Tire Size Calculator | Tacoma World

33/10.5-R15 tires are 4.79 inches (121.74 mm) larger in diameter than 225/75-R15 tires and the speedometer difference is 14.5%

www.tacomaworld.com

Speedometer Difference​

Speedo Reading	Actual Speed
20 mph (32.19 km/h)	23.39 mph (37.64 km/h)
25 mph (40.23 km/h)	29.24 mph (47.05 km/h)
30 mph (48.28 km/h)	35.08 mph (56.46 km/h)
35 mph (56.33 km/h)	40.93 mph (65.87 km/h)
40 mph (64.37 km/h)	46.78 mph (75.28 km/h)
45 mph (72.42 km/h)	52.62 mph (84.69 km/h)
50 mph (80.47 km/h)	58.47 mph (94.1 km/h)
55 mph (88.51 km/h)	64.32 mph (103.51 km/h)
60 mph (96.56 km/h)	70.17 mph (112.92 km/h)
65 mph (104.61 km/h)	76.01 mph (122.33 km/h)
70 mph (112.65 km/h)	81.86 mph (131.74 km/h)
75 mph (120.7 km/h)	87.71 mph (141.15 km/h)
80 mph (128.75 km/h)	93.55 mph (150.56 km/h)
85 mph (136.79 km/h)	99.4 mph (159.97 km/h)
90 mph (144.84 km/h)	105.25 mph (169.38 km/h)
95 mph (152.89 km/h)	111.1 mph (178.79 km/h)
100 mph (160.93 km/h)	116.94 mph (188.2 km/h)

 

[shady]

I was watching my speedometer in the nearly new, stock minivan. Comparing it to the gps one Google maps has built in during trips.
And I noticed that it was within 1-2 mph pretty regularly.
BUT.... Every now and then, different days, it was as far as 6-7 off.
So myself, I don't particularly trust the gps ones as exactly "accurate".

If you want to correct your speedo, make sure to check it against the GPS on a few different days, to make sure it's consistently the same amount off. Before you decide on a correction %.

 

[cheavyk10]

My Speedo is off a bit but when I go to calculate milage I use the A to B milage from Google maps if on a highway road trip.

 

[Big Ray]

The new tires are 17% larger, so it makes sense. The chart matches my results driving around town today.

 

[rampage]

5 mph off at what speed? Too high or too low? If at 10 then that’s 50% off if at 50 then that’s 10% off. It’s always off by a percentage. You can calculate the mileage you’re off if we know what speed you took your ‘5 mph off’ reading at.

 

[Big Ray]

At 40 here in town. Speedo said 40, gps said 45.
If you look at the chart you'll see the error is cumulative.
The faster you go the larger the error.
Fwiw, the first column is the stock tire size, which equates to 225-75 -15. Formerly h78-15.
The tires on there now are 33-10.50 15.

 

[rampage]

Like I said, it’s always off by a percentage. You get a tire that’s 17% larger in diameter then your speedo will read 17% slow. Once you know what your percent diff is the while your driving, say at 30 mph, just take 10% (which is 3mph) and add half of that number (1.5mph). Add those together 4.5 mph to 30 to get 34.5mph, which is close enough for me. I’m sure I made it sound harder than it actually is. I use to do it all the time and it was easy once you get the hang of it.
And since your speed is reading 17% slow, so is your odometer. Just multiply what ever mileage you recorded on your trip by 1.17 to get your actual mileage. So say 500 miles x 1.17 = 585 miles.