Tires: tire inflation, toyota highlander, tire inflation

Question
QUESTION: I purchased a 2004 highlander A/D with G/Y TT's on it at P235 70R16. They are new. What would my psi be on inflation?

ANSWER: Dear Patrick,
Thank you for using AllExperts.
My records show that your Toyota Highlander originally came equipped with size P225/70R16, and that your tire information placard required 30 psi front and rear for that size.  Would you please confirm that for me?  I need to be sure.
The new tire size of P235/70R16 is somewhat over-sized.
Here is the load/psi comparison:
P225/70R16 @ 30 psi = 1,701 lbs per tire load capacity
P235/70R16 @ 26 psi = 1,709 lbs per tire load capacity
So your new inflation would be 26 psi front & rear IF your original tire size was P225/70R16...and your original tire placard recommended 30/30 psi.

The larger tire (P235) does not need as much air pressure to carry the equivalent load of the smaller P225.  Please ignore the tire pressure shown on the tire sidewall...I am using tire industry load & inflation charts.

If you should have any further questions, or if this is not clear, please don't hesitate to contact me again.

DT

---------- FOLLOW-UP ----------

QUESTION: As a follow up to my last question. The tires psi is 44 and and hen i recieved the vehicle thge psi was at 30. The previous owner said the tires were expensive but are crap because the car slid and braking per ft. was bad as well as gas mileage. So I pumped them up to 40 psi and had them for 2 weeks now and I see dramatic improvement in all areas. Is this bad and should i go down to 26.

Answer
Dear Patrick,
At 40 psi your tires are significantly over-inflated.  The original owner has erred in applying the larger P235/70 tires for the following reasons:
1.  The Toyota Highlander owner's manual does not recommend the application of optional tires sizes.
2.  The P235/70 tires are significantly outside of (tire)industry guidelines for replacement tire overall diameter difference vs. original tires.  
3. Your odometer and speedometer accuracy is now adversely affected as well as your braking efficiency. The odometer inaccuracy alone would make it very difficult to accurately assess fuel economy.  
4. The center of gravity of your SUV has now been increased, thus increasing its rollover risk (a major reason that Toyota doesn't want larger tires on it).
5. Your higher tire pressures are increasing what we tire experts call the "lateral stiffness" of your tires, thus adding to rollover risk.
I would reduce the pressures per my original rec. and return to the original tire size as soon as this is possible.
DT