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Discussion Starter · #1 ·
I had my dealer install 265/70 R17s instead of the delivered 265/65 R17s on my 2004 SR5 V6 4WD 4Runner at tire replacement. I did this to gain about 1/2 inch in ground clearance but primarily to give additional sidewall height to ballon out at low tire pressures providing better footprint for operating off road in deep soft sand. I already had a 2 1/2 inch lift.

I quized the dealer if it might be worth a reprogram for performance, etc. and was told not to worry about it. Of course I know the speedometer/odometer is off about 3 % and there is affect on the mileage remaining vs gas in the tank calculation.

I see no real change in performance, or with ABS, VSC, etc. but would be interested in any comments.
 

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Toyota computers can not be reprogrammed. If you want to change the speedo and make it closer to actual, you need to get a TRUSPEED speedo recalibrator (or equivilant). You can use a handhelp GPS to fine tune the MPH by the turn of a screw while driving and comparing to a GPS. It is very accurate and affordable. Many TS members have them and they have been installed in every Toyota that I have tried so far. (Lots of them :tu: ), inculding 4 runners/Tacomas/Tundras and sequoias. All of these thru 07 can be done if you know how and what wires to connect to.
 

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Discussion Starter · #3 ·
Mustang,

Thanks for the input.

I'm not really concerned with the speedometer/odometer. I know how much that is off and can easily compensate.

Was more interested in any possible affects, if any, on things like transmission shift points, fuel mixture, VSC, ABS, etc. Basically overall performance because of the vehicle "thinking" it has gone less distance than it really has.
 

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Mustang,

Thanks for the input.

I'm not really concerned with the speedometer/odometer. I know how much that is off and can easily compensate.

Was more interested in any possible affects, if any, on things like transmission shift points, fuel mixture, VSC, ABS, etc. Basically overall performance because of the vehicle "thinking" it has gone less distance than it really has.
Your VSC/ABS is feeding the speedometer first (incorrect info) and then sends the signal to ALL the other sources after that, that need the speed signal input. By not changing the speedometer readout ALL other output signals to The ECU/Tires pressure ECU/4WD ECU/Nav ECU/Trans Ecu/Suspension ECU/Radio/Sun roof ECU/AC ecu AND Body ECU(and maybe a few others) will all receive incorrect readings and MAY have adverse effect on the outcome of such signals. Thats why having the a correct speedo makes such a big difference and why tires size and gear ratio DOES matter.
Not all toyotas are like this, but your 4 runner just happens to be.
 

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Discussion Starter · #5 ·
Mustang,

Thanks for the input. I went to Superlift web site and got a copy of the install instructions and dealer list for my area.
 

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I did the same tire change, 265/65 R17 to 265/70 R17. With the stock tires my actual speed (as measured by local digital highway signs) was about 2miles/hr less than the indicated speedometer display. After the change the actual and and the displayed are exactly the same. So it appears that Toyota may have intentionally set the speedometer display to be slightly more than the actual speed. Maybe they anticipated the tire size change by customers. My dealer also indicated that the slight difference between the two tires would not affect any computer information,ABS ECU etc,and would not void any warranty's.
With the tire change 1 actual mile driven works out to .94 miles on the odometer display.
As a side note I was told that doing a lift would void certain warranty issues,especially with the drive train.
 

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That little of a tire change and 2mph is slight, but does bug alot of people. Thats why i recommend the TRUSPEED, it is up to them if it bothers them enough to spend the money to fix it.
While it may only be 2mph, That speed calculation does affect everything such as trans shift point/abs ect... it has to. It is part of the entire system, your just changin one of the inputs, so everything across tthe board has to change accordingly. It may or may not be noticable. It was very noticable in my Tundra.
Your right it will not void any warranties.

A lift MIGHT void certain parts of a warranty, only due to improper installation or broken lift components or abuse and then the DEALER has to prove that whatever broke or was broken, WAS CAUSED BY THE LIFT. That kind of proof is almost impossible to prove, unless its blatantly obvious, like a missing bolt or improperly install component, OR VISUAL DAMAGE OF THE TRUCK BEING JUMPED.

It usually depends on the dealership and the PERSONS running it. How well they are willing to work with you.

I know a dealership that installs PRO COMP/Fabtech/Donahoe and RCD lifts, and the vehicle maintains the TOYOTA warranty at that dealership. Other dealers may vary, but then again they have to prove fault in the lift kit.
The MAGNUSSON/MOSS act protects consumers from that blatent statement. "If you lift it, it voids ALL WARRANTY". They have to put it in witing and then PROVE IT!
 

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Discussion Starter · #8 ·
Agree with Mustang on the lift vs warranty and my dealer says no warranty problem with my lift or tire switch.

I have a GPS and plan to check the speedometer with it.
 

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Changing tire sizes makes no difference to the ABS, VSC or any other alphabet acronym. What everyone calls a speed sensor does not actually measure speed, it only counts the rotations of the transmission output shaft. The sensor then sends this signal to the vehicle computer, which uses a stored value to calculate the vehicle speed. Putting bigger, or smaller tires, on doesn't change the transmission output shaft speed so the computer is happy.
The only thing that happens is the vehicle is actually going faster, or slower, than the indicated speed.
 

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Changing tire sizes makes no difference to the ABS, VSC or any other alphabet acronym. What everyone calls a speed sensor does not actually measure speed, it only counts the rotations of the transmission output shaft. The sensor then sends this signal to the vehicle computer, which uses a stored value to calculate the vehicle speed. Putting bigger, or smaller tires, on doesn't change the transmission output shaft speed so the computer is happy.
The only thing that happens is the vehicle is actually going faster, or slower, than the indicated speed.
You are partial correct, it does not measure the transmission output shaft only it also measures the rotation of all 4 tires and then calculates from there. The transmission sensor is only really a back up if the other should fail. The ECU computes this to come up with a vehicle speed. The ECU has been programmed for a specific tire size for that vehicle. If you change the tire size then your changing the Speed of the rotation at a given RPM ,which is how the ECU then calculates its various outputs. The shift points will be moved and ABS operarion will function differently. THEORY may not prove this, but REAL WORLD findings do.
I have installed way to many of these devices and had inputs for each owner on how much better the truck performed afterwards. I wont argue with anyone, I know what I have found and thats what works for me and all the people I know who have this product. If anyone doesnt agree, thats cool :tu: To each or his/her own.
The little tire size change in this particular forum may not be noticible enought to worry about, but everyone deserves to have as much info as possible. It can cause things to change.
I agree with THEYOTAGUY
The ECM looks at the pulse width from the speed sensors at each wheel AND the actual speed of the vehicle,as well as other inputs to determine operation of the ABS.So if the wheel sensors are reading the equivalent of 70 mph,and the speedometer reads 70 mph,yet the truck's actual speed is 77.7 mph,it WILL alter the function of the ABS.
:D
Oh, one more thing... HAVE A GREAT WEEK EVERYONE!:D
p.s. even the NTSB says changing tire size will affect ABS.;) and just about every other automitive forum if you "GOGGLE" it.
We all can't be wrong?:confused: :D
 

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Discussion Starter · #11 ·
OK here is the result of my GPS check.

40 mph speedo = 41.1 mph GPS
50 mph speedo = 51.4 mph GPS
60 mph speedo = 61.7 mph GPS

or just a little under 3% low for the speedo which is about the expected variation for my tire size differential.

BTW I did the check over 10-15 miles on level pavement in cruise for each speed.

I don't think I will bother with a TruSpeed for this small correction, especially since they cost about $200.

Thanks for all the feedback.
 
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