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-   -   larger tire effect on odometer and mpg computer? (http://www.jeepgarage.org/f109/larger-tire-effect-on-odometer-and-mpg-computer-70582.html)

Goonbash 01-19-2014 12:51 PM

larger tire effect on odometer and mpg computer?
 
I know my speedo is now slightly inaccurate with the larger tires (reads slightly lower than actual road speed). Do any of you high tech guys know if this also effects the odometer? Seems like it might not clock miles quite as quickly as it should if it is based on the speedo, or is the odo based on gps or something where it is still accurate?

also is the onboard gas mileage and "range" calculation based on actual fuel consumption in which case it would still be accurate or is it based on tire revolutions or something that would now make it inaccurate?


Thanks

Jim_in_PA 01-19-2014 01:01 PM

Re: larger tire effect on odometer and mpg computer?
 
Revolutions per mile is affected, so logically, yes, the odometer will be affected.

Goonbash 01-19-2014 01:29 PM

Re: larger tire effect on odometer and mpg computer?
 
What does your logic tell you about the onboard mpg and range calculation?

chucksc 01-19-2014 01:40 PM

Re: larger tire effect on odometer and mpg computer?
 
Logically they would both be screwed too!
:)

Goonbash 01-19-2014 01:49 PM

Re: larger tire effect on odometer and mpg computer?
 
Unless the are claculated by fuel consumption and not tire revolutions.

chucksc 01-19-2014 01:50 PM

Re: larger tire effect on odometer and mpg computer?
 
but the actual miles would be screwed due to the effect the wheel size has. hence my reply..

Goonbash 01-19-2014 01:52 PM

Re: larger tire effect on odometer and mpg computer?
 
I agree with you if the system is linked to speedo/odo and not nav/gps. Which is what i am trying to find out.

is everything in the EVIC based on speedo/odo.?

theoretically the speedo is supposed to be innaccurate too but i have a guy with the same larger tires telling me his speedo is accurate to within 1km/hr everywhere compared to his gps and several phone apps, on the other forum. So his odo and mpg calcs would still be quite accurate.

fnkychkn 01-19-2014 03:40 PM

Re: larger tire effect on odometer and mpg computer?
 
what is original tire size?
what is replacement tire size?

Goonbash 01-19-2014 04:49 PM

Re: larger tire effect on odometer and mpg computer?
 
265/60r18
275/65r18

i have done the tire clculator thing. Trying to find out if mpg and range numbers in evic are solely based on speedo/odo.
a guy on the other forum says his onboard 430n nav system and phone apps show his speedo to still be within 1km/hr of accurate even with the new larger tire size.

i am just trying to find out if my mpg and range numbers are still close to accurate or if i should just completely ignore them.

fnkychkn 01-19-2014 05:33 PM

Re: larger tire effect on odometer and mpg computer?
 
that's almost 5% speed variance. the only speed where there would be a 1 km/h difference is 20 km/h. the speed difference will grow exponentially as actual vehicle speed increases. at 5%, 100 km/h cluster speed = 105 km/h actual speed.

trip computer calculations are based on cluster speed/distance. if EVIC says 100 km to empty, the tank will be empty in 100 km (cluster distance) which equates to 105 km (actual distance).

depending on which transmission you have, shift points may be affected.

pretty sure your dealer can adjust tire size configuration in TIPM/BCM/etc. to compensate for the inaccuracy.

Goonbash 01-19-2014 06:19 PM

Re: larger tire effect on odometer and mpg computer?
 
Thanks. Ya i looked at the variance on a tire size calculator and decided i could live with it so i went ahead with the tire swap.
The guy on the other forum says his nav unit shows his speedo as still accurate.

good to know my range reading will allow me to go slightly further than it reads.

i have the new 8speed transmission. Wouldnt trans shift points be by engine rpm?

i was under the impression from all the other tire swap posts that there was NO way to reprogram forbigger tires. Are you sure the dealer can do it on a 2014?

fnkychkn 01-19-2014 10:36 PM

Ill look into it tomorrow and get back to you.


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