275/70/16's...could this cause possible air-fuel mixture issue??

[paulphilly]

I recently replaced oem 265/70 BFG RT's with 275/70 BFG KO's. Since replacing my oem tires with KO's, I have not been able to reset my factory installed tire pressure monitoring system after several tries. I have 36psi in all 4 tires and in my spare BFG RT 265 tire which is the preset psi from my dealer during the PDI. SO, I called a very reputable local tire company today and found out some pretty interesting things. First, the reason my TPMS is not resetting is simply because the system regulates itself based on tire revolutions. Therefore, due to my 275's "telling" the computer that I have less revolutions, my TPMS light is staying on and not resetting because it thinks I have "low tire pressure". Moreover, this is the reason the tech explained to me today that based on this reason, I should be very careful with the 275/70's because the revolutions are different which directly affects the air-fuel mixture, ABS, gearing, etc....BECAUSE, he says, the computer is preset for 265/70 revolutions! So, is this the reason for me experiencing minor vibrations at 60mph or higher (even after having my KO's road forced balanced) due to air-fuel mixtures causing my engine to misfire a bit and not perform smoothly? Or, am I just feeling every nook and cranny in the road due the KO's stiff sidewall (BTW, I am running 36psi all around, including oem spare)? He further states that due to the variation in tire sizes, it could affect my overall performance and ride. He thinks I should seriously consider going back to 265/70's due to possible MPG loss, incorrect fuel mixtures, and ABS and brake performance differences. I know its a lot to swallow, but can any of this be true and does any of it make any sense? Please help, I am worried about my baby.
Thanks, Paul
PS: any help on this tire pressure monitering system would sure help as well. Should I just pull the fuse, or take out the bulb? I dont like it anyway!

[nhparrot]

Originally Posted by paulphilly

Should I just pull the fuse, or take out the bulb? I dont like it anyway!

No fuse to pull without affecting other circuits.

[jim65wagon]

Personally I do not believe the 275/70's are big enough to affect your ABS, and I don't believe the computer would go off tire revolutions to maintain proper air/fuel ratio or ignition firing, otherwise you would have to drive at a set speed to maintain your tire revolutions. Faster or slower and you would misfire. Your engine idles fine when you are stopped at a redlight, correct? No tire revs there. The tire height will affect your gear ratio, but since your only about a half an inch or so taller its not much to be concerned about. Your speedo is only off about 1 to 1 1/2 mph at 60 right? Keep your tires, you're just a little paranoid playing with your new baby. The KO's are a lot stiffer than the Trails were. Relax. Chill. I still get 18.5 mpg on the freeway with my 265/75's and they're a bit taller yet. Try various tire pressures until you get a comfortable level. I usually run 38 all round. Enjoy your truck.

[ed brewer]

Maybe the problem is having a spare tire a different size than the four on the ground??? I don't know, just a WAG.

Ed

[mustang67408]

Originally Posted by paulphilly

I recently replaced oem 265/70 BFG RT's with 275/70 BFG KO's. Since replacing my oem tires with KO's, I have not been able to reset my factory installed tire pressure monitoring system after several tries. I have 36psi in all 4 tires and in my spare BFG RT 265 tire which is the preset psi from my dealer during the PDI. SO, I called a very reputable local tire company today and found out some pretty interesting things. First, the reason my TPMS is not resetting is simply because the system regulates itself based on tire revolutions. Therefore, due to my 275's "telling" the computer that I have less revolutions, my TPMS light is staying on and not resetting because it thinks I have "low tire pressure". Moreover, this is the reason the tech explained to me today that based on this reason, I should be very careful with the 275/70's because the revolutions are different which directly affects the air-fuel mixture, ABS, gearing, etc....BECAUSE, he says, the computer is preset for 265/70 revolutions! So, is this the reason for me experiencing minor vibrations at 60mph or higher (even after having my KO's road forced balanced) due to air-fuel mixtures causing my engine to misfire a bit and not perform smoothly? OTHIS IS A BUNCH OF WHOOOIIIEE Or, am I just feeling every nook and cranny in the road due the KO's stiff sidewall YES (BTW, I am running 36psi all around, including oem spare)? He further states that due to the variation in tire sizes, it could affect my overall performance and ride. The change in tire size isnt big enough to make a major impact He thinks I should seriously consider going back to 265/70's due to possible MPG loss, incorrect fuel mixtures, and ABS and brake performance differences. NOT IN MY OPINION I know its a lot to swallow, but can any of this be true and does any of it make any sense? Please help, I am worried about my baby.
Thanks, Paul
PS: any help on this tire pressure monitering system would sure help as well. Should I just pull the fuse, or take out the bulb? I dont like it anyway!

The tire pressure warning system has NOTHING to do wth tire size. Please read the attatched document. The computer has no idea what size tires your running , nor does it care. It adjusts itself fo whatever inputs it sees.I would stay with whatever tires you want and work on turning out the light.
Have you tried resetting it? I know this is a dumb question, but 90% of the people i ask this, didnt do it properly.(pg 202 of attachment)(pg 204 of owners manual)
#1 set tires ressure to specs-all 5 tires
#2 Using the owners manual reset procedure or page 2 of the attatchment, reset the light.
#3 If the light doesnt go out, you will have to go to the dealer and they can clear the memory of the tire ystem and reset the light.

Now if any of the sensors are not properly mounted in the rims, or they have been damaged, this might activate the light and set a code that cannot be reset. If when changing tires someone damages a sensor and it has to be replaced, only the dealer can replace it. Each sensor hs a ID# whichhas to be input into the computer thru the TOYOTA SCAN TOOL. Then the ecu will recognize the sensor. I have seen places swap out the metal sensors for rubber ones, or install new ones and not tell the customer.
Per your owners manual:

The use of non–genuine wheels will
cause the air pressure sensors to
transmit the electronic code in different
manner, resulting in the system
failure.

The use of different type of tires
with genuine wheels may also
cause the malfunction of the system.
To initialize the system, perform the following:1. Park the vehicle at a safe place and
apply the parking brake. Stop the engine.
2. Adjust the pressure of all the installed
tires to the specified level. (See “Tires”
in Section 8.)
3. Turn the ignition key to “ON”.
4. Push and hold the reset switch until
the low tire pressure warning light
blinks three times.
Initialization is completed over for more
than 20 minute.
When initializing the system, make sure
the low tire pressure warning light blinks
three times. If the warning light does not
blink three times, initialization failed and
the tire pressure warning system will not
function properly. In this case, initialize
the system again.
Do not push the reset switch without adjusting
the tire inflation pressure to the
specified level. Otherwise, the low tire
pressure warning light may not come on
even if the tire pressure is low, or it may
come on when the tire inflation pressure
is actually normal.
If you push the reset switch while the
vehicle is moving, initialization is not performed.
If the low tire pressure warning light does
not blink when you push and hold the
reset switch, have the low pressure warning
system checked at your Toyota dealer.
 The tire pressure sensor is integrated in the air valve of a disc wheel. It measures the pressure and the
temperature of the air in the tire and transmits the measured values and a recognition ID to the tire
pressure monitor receiver.
 If the battery voltage drops, the tire pressure sensor assembly must be replaced. Furthermore, if the
battery voltage drops, the sensor will be unable to transmit signals, which causes a DTC to be output.
 Sensor with five different ID code range are used on one vehicle.
 Each sensor has a built-in semi-conductor to directly measure the inflation pressure of the tire.
 Frequency of the sensor is 314.98 MHz.

[JeffD]

It may take you a couple tries to get the system to reinitialize. I took me about four before it worked and the light went out.