Quick question re: revolutions per mile

[anonymous user]

If my OEM tire (goodyear eagle ls) was rated at 880 revs per mile, and my new tire (hankook rs-2's) are rated at 915 revs per mile, then does that mean that i've been calculating my MPG's incorrectly?

So hypothetically lets say a round number like 400 miles on a fillup, of 10 gallons of fuel. This would net me 40mpg's.

So the ratio of the new tire (915/880= approx 1.03977% change) would change it to 400 milesx1.03977= 415.9 miles? So then that would change my MPG from 40 to 41.59?

What i'm trying to aSK is does the speedo recalibraTE for my new tires, or do i need to multiply it (1.03977) every tank in this case?

thank you!

[Tamago]

speedo does not recalibrate.

you do have to factor in your new wheel circumference.

[anonymous user]

Thanks Tamago, then that means i have been "underestimating" my mpgs for all my cars (not that it matters much when i get 13 MPG in the wrx coming out of a straight at 130 entering a chicane..haha) :w00t:

[Tamago]

actually, overestimating.. if you went with a smaller overall diameter, your actual GROUND mileage is less than your odo tells you. odo says you've traveled 400 miles when you've actually only gone 384.7 miles.

[EasyDriver]

If my OEM tire (goodyear eagle ls) was rated at 880 revs per mile, and my new tire (hankook rs-2's) are rated at 915 revs per mile, then does that mean that i've been calculating my MPG's incorrectly?

So hypothetically lets say a round number like 400 miles on a fillup, of 10 gallons of fuel. This would net me 40mpg's.

So the ratio of the new tire (915/880= approx 1.03977% change) would change it to 400 milesx1.03977= 415.9 miles? So then that would change my MPG from 40 to 41.59?

What i'm trying to aSK is does the speedo recalibraTE for my new tires, or do i need to multiply it (1.03977) every tank in this case?

thank you!

http://www.miata.net/garage/tirecalc.html try this site for the info you want....

[Yaris Hilton]

If your tires are turning more times per mile, your speedometer is now reading faster than you're actually going, and your odometer is showing more distance than you've actually gone.

[roadrunner]

I agree with Yaris Hilton, that you have been showing more distance than you've actually gone. What I do suggest is this......next time you go a long distance on a highway that has mileage markers, keep track of your odometer and what the highway markers shows. Very likely they will show different distances. The highway will show less miles than your odometer.
GL, Roadrunner

[The little red pill]

Another option, If you have a portable GPS, most will show your realtime MPH and you can use that instead of your speedometer. I have a Garmin Nuvi 255w and it shows my MPH on the main screen.

[Zaphod]

Can't you just change your speedo gear?

[MadMax]

Can't you just change your speedo gear?

It's electronic, not mechanical. I am not sure if the ECU is reprogrammable and it has always made me wonder as I have larger wheels on my Yaris and my speedo is spot on according to my GPS.

That means either the dealer reprogrammed the ECU/speedo when they put the wheels on, or the stock settings on the speedo are off.

[Tamago]

It's electronic, not mechanical. I am not sure if the ECU is reprogrammable and it has always made me wonder as I have larger wheels on my Yaris and my speedo is spot on according to my GPS.

That means either the dealer reprogrammed the ECU/speedo when they put the wheels on, or the stock settings on the speedo are off.

there IS an actual speedo gear in the transmission though... just not sure how you'd shim it since it's fed from the end of the speedo sensor and top loaded on the differential.

[daf62757]

You are actually decreasing the value of your car with every mile your odometer shows. If you car is going a mile but shows 1.2 miles (for example) you are racking up more miles that are going to make the value of your car less in a few years.

Also your car insurance might be over charging you for insurance if they are rating your coverage by the miles your odometer is showing for annual mileage.

Of course if you keep the car until the wheels fall off, it doesn't matter what size the wheel is.

[Tamago]

LOL you are actually decreasing the value of the car by driving it no matter what the odo reads..

[Zaphod]

It's electronic, not mechanical. I am not sure if the ECU is reprogrammable and it has always made me wonder as I have larger wheels on my Yaris and my speedo is spot on according to my GPS.

That means either the dealer reprogrammed the ECU/speedo when they put the wheels on, or the stock settings on the speedo are off.
It may be even easier then, just give the ECU the new diameter and you're good to go.

There has to be a way to make it work though, as popular as it is to change wheel and tire sizes these days. I'm thinking that a dealer might have legal issues with changing the diameter without recalibrating the speedo.

[nemelek]

I agree with Yaris Hilton, that you have been showing more distance than you've actually gone. What I do suggest is this......next time you go a long distance on a highway that has mileage markers, keep track of your odometer and what the highway markers shows. Very likely they will show difference distances. The highway will show less miles than your odometer.
GL, Roadrunner

I do this check myself. I drive 10 highway miles ane compair that to the odometer. If the odometer showes 11 miles for every 10 miles driven than it is now 9% fast. If your speedometer showes 110 mph you are actually doing 100 mph.

[daf62757]

LOL you are actually decreasing the value of the car by driving it no matter what the odo reads..

True, but the value decreases at a greater rate the more mileage the car has.

[Tamago]

True, but the value decreases at a greater rate the more mileage the car has.

i wasn't arguing that point.

but it's a car.

and econocar

it's not an exotic.

use it for what it was meant to be. basic transportation.

[EasyDriver]

Try this for better understanding: http://www.miata.net/garage/tirecalc.html

[Tamago]

http://www.miata.net/garage/tirecalc.html try this site for the info you want....

Try this for better understanding: http://www.miata.net/garage/tirecalc.html

you're 2 days late. to your own post...

[The little red pill]

I don't know about the above posts. But check this site out!

http://www.miata.net/garage/tirecalc.html

[Tamago]

www. use a calculator and quit reposting the same crap .com ?

[daf62757]

i wasn't arguing that point.

but it's a car.

and econocar

it's not an exotic.

use it for what it was meant to be. basic transportation.

I would disagree with you. As gas prices go higher, this car becomes more valuable.It isn't just basic transportation....that is what a Dodge is for. This car is a statement!

[EasyDriver]

you're 2 days late. to your own post...
Muuussssttt quit drinking! Or maybe it's premature senility!!!!!