Quick question re: revolutions per mile - Toyota Yaris Forums

anonymous user · 07-18-2009, 07:55 PM

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 · 07-18-2009, 07:58 PM

speedo does not recalibrate.

you do have to factor in your new wheel circumference.

anonymous user · 07-18-2009, 08:03 PM

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)

Tamago · 07-18-2009, 08:48 PM

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 · 07-18-2009, 09:51 PM

Quote:

Originally Posted by 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!

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

Yaris Hilton · 07-19-2009, 01:24 PM

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 · 07-19-2009, 05:51 PM

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 · 07-19-2009, 09:36 PM

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 · 07-20-2009, 01:00 PM

Can't you just change your speedo gear?

MadMax · 07-20-2009, 01:25 PM

Quote:

Originally Posted by Zaphod

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 · 07-20-2009, 01:41 PM

Quote:

Originally Posted by MadMax

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 · 07-20-2009, 01:45 PM

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 · 07-20-2009, 01:48 PM

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

Zaphod · 07-20-2009, 04:26 PM

Quote:

Originally Posted by MadMax

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 · 07-20-2009, 04:27 PM

Quote:

Originally Posted by 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 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 · 07-20-2009, 09:44 PM

Quote:

Originally Posted by Tamago

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 · 07-20-2009, 09:54 PM

Quote:

Originally Posted by daf62757

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 · 07-20-2009, 10:06 PM

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

07-18-2009, 07:55 PM	#1
anonymous user rarer than JDM -1 of 1! View User's Garage Drives: 07yaris Join Date: Oct 2008 Location: windward oahu Posts: 402	Quick question re: revolutions per mile 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! __________________ It's not what you drive, or how much $$ you throw at the car. Mod the ballast on the front left first!

07-18-2009, 08:03 PM	#3
anonymous user rarer than JDM -1 of 1! View User's Garage Drives: 07yaris Join Date: Oct 2008 Location: windward oahu Posts: 402	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) __________________ It's not what you drive, or how much $$ you throw at the car. Mod the ballast on the front left first!

07-19-2009, 05:51 PM	#7
roadrunner Yaris Hypermiler View User's Garage Drives: 2007 Silver Liftback Join Date: Aug 2006 Location: Perkasie PA USA Posts: 102	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 Last edited by roadrunner; 07-20-2009 at 06:24 PM.

07-19-2009, 09:36 PM	#8
The little red pill Taking care of Bubbles Drives: 2009 Yaris LB "Bubbles" Join Date: Apr 2009 Location: on my computer chair Posts: 100	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. __________________ 2009 Absolutely Red LB. "Bubbles"

07-20-2009, 01:45 PM	#12
daf62757 Nothing beats a Toyota! View User's Garage Drives: 2013 Yaris 5 dr liftback Join Date: Jan 2009 Location: Indianapolis, Indiana Posts: 564	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. __________________ Big Dave Indianapolis, IN Synthetic Oil....its in my car.....for at least 10,000 miles!

07-18-2009, 07:58 PM	#2
Tamago Start another Oil Thread! View User's Garage Drives: ZZW30 Join Date: Dec 2006 Location: South FL Posts: 4,890	speedo does not recalibrate. you do have to factor in your new wheel circumference.

07-18-2009, 08:48 PM	#4
Tamago Start another Oil Thread! View User's Garage Drives: ZZW30 Join Date: Dec 2006 Location: South FL Posts: 4,890	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.

07-19-2009, 01:24 PM	#6
Yaris Hilton Half a Bubble Off Plumb Drives: 2009 Yaris Sedan Join Date: Mar 2009 Location: Bristol, Tennessee, USA Posts: 1,593	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.

07-20-2009, 01:00 PM	#9
Zaphod Drives: Big Yellow Join Date: May 2009 Location: Somewhere in the vacinity of Betelgeuse Posts: 179	Can't you just change your speedo gear?

07-20-2009, 01:48 PM	#13
Tamago Start another Oil Thread! View User's Garage Drives: ZZW30 Join Date: Dec 2006 Location: South FL Posts: 4,890	LOL you are actually decreasing the value of the car by driving it no matter what the odo reads..

07-20-2009, 10:06 PM	#18
EasyDriver Drives: 2008 Yaris Meteorite LB Join Date: Feb 2009 Location: Southern Michigan Posts: 61	Try this for better understanding: http://www.miata.net/garage/tirecalc.html

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