Calculating odometer, MPG & MPH after larger tire size

[dawudih]

Went from a 265/70r17 stock Bridgestone tire to a BFG KO2 275/70r17 & I'm trying to calculate my new odometer, speed & mpg. Is this an acurate method?

Original tire is (((265*0.7)/25.4)*2)+17)=31.606"
New tire is (((275*0.7)/25.4)*2)+17)=32.158"
32.158-31.606=0.552
0.552/32.158=0.01717 or 1.717% increase in odometer, mph & mpg

So, calculated mph is 18.5; corrected would be 1.717% more, or 18.82
Indicated trip states 100 miles; corrected will be 1.717% more, or 101.7
And indicated speed is 60mph; corrected would be 61.03

Does this seem correct???

 

[Fl_tigers]

Went from a 265/70r17 stock Bridgestone tire to a BFG KO2 275/70r17 & I'm trying to calculate my new odometer, speed & mpg. Is this an acurate method?



Original tire is (((265*0.7)/25.4)*2)+17)=31.606"

New tire is (((275*0.7)/25.4)*2)+17)=32.158"

32.158-31.606=0.552

0.552/32.158=0.01717 or 1.717% increase in odometer, mph & mpg



So, calculated mph is 18.5; corrected would be 1.717% more, or 18.82

Indicated trip states 100 miles; corrected will be 1.717% more, or 101.7

And indicated speed is 60mph; corrected would be 61.03



Does this seem correct???

Almost dead on!

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[wanderMT]

1.7% probably within margin of error for speedo/odo - fuel measurement - new tire vs worn tread.

 

[BlackWorksInc]

This is why I just installed a Speedohealer in my 4th gen and set it to correct for my 35's.

 

[04rnr]

theres also apps, that you can download something like Speedometer that uses GPS to track your speed. This way you can at what speed your speedo say vs actual speed. Im not sure how accurate those apps are, but they are free lol

 

[Fl_tigers]

theres also apps, that you can download something like Speedometer that uses GPS to track your speed. This way you can at what speed your speedo say vs actual speed. Im not sure how accurate those apps are, but they are free lol

I know waze has one built in and it's relatively close to accurate.


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[dawudih]

Thanks for the graph and quick responses. More curious & board at work; doesn't make much difference I guess.
After my recent bilstein lift and heavy tires, I've lost only 1.2 mpg after 1 tank of gas. About a 6% decrease in economy. I would have guessed a lot more.

 

[jwkilgore]

Keep in mind that different brands have different diameters for the same published size and as mentioned the diameter will vary as they wear. And finally, most people report that you are actually traveling slower than the speedo is reporting on OEM tires. I believe 275's should actually zero out the discrepancy such that you'll be going exactly as fast as the speedo says. They definitely will after wearing a bit.

If you really want to know, find a straight level section of highway with little traffic or wind and set the cruise at a precise round number. Then use a nav app on your phone to get your GPS speed which is generally spot-on.

 

[4rcybr]

This is why I just installed a Speedohealer in my 4th gen and set it to correct for my 35's.

Found your writeup (http://www.toyota-4runner.org/4th-gen-t4rs/178078-speedohealer-v4-4th-gen.html), but I didn't see mention of which 'model'. Online retailers seem to list a different model for each type of bike. Speedohealer

Is there any difference?

 

[BlackWorksInc]

Found your writeup (http://www.toyota-4runner.org/4th-gen-t4rs/178078-speedohealer-v4-4th-gen.html), but I didn't see mention of which 'model'. Online retailers seem to list a different model for each type of bike. Speedohealer

Is there any difference?

The bike specific units come with pre-wired pig-tail connectors for the specific model.

You want a "Universal" kit like I mentioned toward the end of the first page.

 

[4rcybr]

The bike specific units come with pre-wired pig-tail connectors for the specific model.

You want a "Universal" kit like I mentioned toward the end of the first page.

All that looking for a model number and I missed that.

Thanks.

 

[BlackWorksInc]

All that looking for a model number and I missed that.

Thanks.

Eh, I should have mentioned it in the first post. Time to go update that...

 

[Storm Runner]

Went from a 265/70r17 stock Bridgestone tire to a BFG KO2 275/70r17 & I'm trying to calculate my new odometer, speed & mpg. Is this an acurate method?

Original tire is (((265*0.7)/25.4)*2)+17)=31.606"
New tire is (((275*0.7)/25.4)*2)+17)=32.158"
32.158-31.606=0.552
0.552/32.158=0.01717 or 1.717% increase in odometer, mph & mpg

So, calculated mph is 18.5; corrected would be 1.717% more, or 18.82
Indicated trip states 100 miles; corrected will be 1.717% more, or 101.7
And indicated speed is 60mph; corrected would be 61.03

Does this seem correct???

This assumes that your settings from the factory were correct to begin with. On my truck with stock tires, my speedo was off by about 2mph, which I tested by using multiple speed limit radar guns around town. Going to bigger tires actually fixed my speedo. Once I switched from stock 265/70 to my current 255/80, my speed was dead on at all the radar signs.

 

[dawudih]

This assumes that your settings from the factory were correct to begin with. On my truck with stock tires, my speedo was off by about 2mph, which I tested by using multiple speed limit radar guns around town. Going to bigger tires actually fixed my speedo. Once I switched from stock 265/70 to my current 255/80, my speed was dead on at all the radar signs.

Sounds true, just comparing it to stock though. I'm not measuring the accuracy, only the difference between the two sized tires.

 

[PWD4R]

This assumes that your settings from the factory were correct to begin with. On my truck with stock tires, my speedo was off by about 2mph, which I tested by using multiple speed limit radar guns around town. Going to bigger tires actually fixed my speedo. Once I switched from stock 265/70 to my current 255/80, my speed was dead on at all the radar signs.

Don't judge by the radar shit around town. They're always a little on the slow side. Even on my 4runner with 33s it's a MPH slow. On my corolla it's like 2-3 depending on speed. Every time I've been pulled over they say I was going a few MPH slower than what I showed

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[BlackWorksInc]

This assumes that your settings from the factory were correct to begin with. On my truck with stock tires, my speedo was off by about 2mph, which I tested by using multiple speed limit radar guns around town. Going to bigger tires actually fixed my speedo. Once I switched from stock 265/70 to my current 255/80, my speed was dead on at all the radar signs.

Those speed signs are inaccurate by 1~2mph I've noticed.