Spedometer inaccuracy?

[otterhere]

Wow, y'all have given me a headache; did I mention that I'm math-challenged??? It doesn't bother me; I just move with the flow of traffic anyway, keeping a safe distance behind whoever's in front of me.

Certainly not going to take it back to the dealer and complain; too happy.

[IllusionX]

Originally Posted by otterhere

Wow, y'all have given me a headache; did I mention that I'm math-challenged??? It doesn't bother me; I just move with the flow of traffic anyway, keeping a safe distance behind whoever's in front of me.

Certainly not going to take it back to the dealer and complain; too happy.

but you don't want your ODO to show 20% error if you are on a lease.

[floydisrock]

Math is easy--> http://www.discounttire.com/dtcs/infoTireMath.dos

[b_hickman11]

Originally Posted by PK198105

yes but if downgraded after to 17's without resetting the ecu the speedo would be wrong

Arent the tires on the 17's smaller than the ones on the 15's? I always thought the bigger the rim, the smaller the tire.... Usually you can stand them up side by side and they will be the same height. One has more tire while the other has more rim.

[tetzyamis]

To get diameter in mili meter:

Width/Height/Rim
Rim * 25.4 + Width * Height / 100 * 2

So,

175/65/14
14 * 25.4 + 175 * 65 / 100 * 2
= 355.6 + 227.5
= 583.1 mm

185/60/15
15 * 25.4 + 185 * 60 / 100 * 2
= 381 + 222
= 603 mm

And,

1 - 583.1 mm / 603 mm = -3.3%
which makes 185/60/15 to show 3.3% slower in speedo than 175/65/14.


I always thought Toyota adjusts this as PK198105 says.
But IllusionX's dealer's test shows that Toyota doesn't.
I guess I gotta find that out myself by testing mine since it came with 185/60/15.

[IllusionX]

Originally Posted by PK198105

they dont but the dealer will readjust the ecu, at least my dealer does. as a rule as soon as the diameter changes the indicated speed will be different from the actual speed. therefore if your wheel diameter changes but your overall diameter (wheel+tire) stays the same or close to the original then your speedo will be ok , but if the overall diameter changes from stock then the speedo will be wrong

which dealer do you go to ?

And i just don't think the ECU is THAT flexible in reprogramming ??? Because if the dealer has the resources to do it, then other people out there can do it. At least, the mechanics has to learn how to do it, and sooner or later, the information will leak.. People will use this to ALTER their ODOMETER readings, hence illegal... ???


haha btw, PK, i posted in the Quebec forum with the question.. let's hear the answers...

[IllusionX]

Originally Posted by XZR

non ta vitesse est calculer avec les speed sensor dans le centre des bearing de roues pour un vehicule avec ABS et dans la trans. si pas ABS

translation: the speed is calculated with the speed sensors at the middle of the wheel bearings for cars with ABS, and it is in the transmission for those without ABS.



sooooo........... if you are 20% off, you might want to take it back to the dealer to have them checked. Because if your speedo is showing 60mph and you are really going 80mph!~ Hmm... it could be very bad! that's 250$USD speeding ticket in Champlain, NY

[Chrsto4]

Interesting thread. I just thought I was crazy because my GPS usually says I'm going faster than my speedo shows. Hmmm....I AM sane - who knew.