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Discussion Starter · #1 ·
I have had my CT for a week and half now and seeing as I have petrol station not far from home and I was passing I thought in would just check the tire pressures to make sure they are ok.

In the drivers handbook it says They should be Front 33psi Rear 32psi so I checked them and all 4 were 42psi ! ( this would be from the dealer ) I have left them like that for the moment.

Any ideas ?
 

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Recommended tyre pressures are a compromise between road holding (higher P is better), ride comfort (lower P is better) and economy (higher is better). Just take your pick and don't overdo it.
 

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I have had my CT for a week and half now and seeing as I have petrol station not far from home and I was passing I thought in would just check the tire pressures to make sure they are ok.

In the drivers handbook it says They should be Front 33psi Rear 32psi so I checked them and all 4 were 42psi ! ( this would be from the dealer ) I have left them like that for the moment.

Any ideas ?
At 42 it is probably riding pretty hard. I added about 4psi to each of the factory numbers 38 frt and 36 rears. Use similar numbers on the wifs Prius with good results.
 

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I'm no expert, but on my older vehicles, I've experienced drops in pressure during the cold seasons up to 7 psi, and vice versa in hot weather, so when 33 psi was recommended, I'd keep it around 36.5 or so. Good or bad idea? I don't know, but I ultimately never had any issues of uneven wear or bad fuel economy.
 

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The best advise is to follow the manufacturer's recommendation and have the pressures as indicated on the driver's door jam. For the ones with 17" tires, that's 33psi front and 32psi back. This also gives the best wear for the tires and the optimal handling characteristics of the car as designed.
As always, tire pressure should be checked once a month when the tires are 'cold'.
Eventually, when my dealer gets a Nitrogen machine, I will switch over to Nitrogen. The pressure does not deviate then due to heat/cold variances.
 

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I use 42 all around. Did you check your tire pressures while they were cold?
 

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Eventually, when my dealer gets a Nitrogen machine, I will switch over to Nitrogen. The pressure does not deviate then due to heat/cold variances.
I haven't heard that one before. I can't find any other sources for this bold statement, either.

It's true that nitrogen will maintain your tyre's pressure longer than just air, due to the molecules being larger than oxygen. But 80% of air is nitrogen anyway, so if you leave the air in long enough and regularly check your tyre pressures and refill, you end up with almost pure nitrogen in your tyres anyway.
 

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i think 42 psi is too high if the temps were taken cold. i wouldn't deviate too much from the factory recommended cold pressures unless you're willfully trying to alter handling and/or ride characteristics. for the ct200h, i keep mine at around 35 or 36 psi or so cold in all tires.
 

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Discussion Starter · #11 ·
They were checked after I had been driving a while so I will check them again cold but 42 would still seem quite high even for a warm tire.
I wonder why the dealer set them at 42 ? I think I will drop them a little bit and email the dealer today to ask their theory.
 

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Just to add to this thread so people can compare. I'm currently running 45psi on all four. Some might say its too high but I've always used the 10% rule on all my cars. Which I put the pressure at -10% of the indicated max psi on the tire. I havent had any problems so far on 6 different cars with a broad spectrum of tires from performance and all seasons.

Also I'm using nitrogen on all four from the dealer. Its free from my dealer and I just take it to them when ever I want to fill them up and what ever pressure I want so why not.
 

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I'm using 45psi on all 4 tires. I don't necessarily agree with the rule of thumb that you should follow the owner's manual specification. That was the problem with the Firestone tires on Ford Explorers about 10 years ago. The Ford recommendation was much lower than the Firestone recommendation, which led to lots of tire failure.

I think that you're better off being closer to the tire manufacturer's specification. The Michelin tires that come with the CT have a max rating of 51 psi. So, I'm closer to that than the 32psi that Lexus recommends.
 

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I haven't heard that one before. I can't find any other sources for this bold statement, either.

It's true that nitrogen will maintain your tyre's pressure longer than just air, due to the molecules being larger than oxygen. But 80% of air is nitrogen anyway, so if you leave the air in long enough and regularly check your tyre pressures and refill, you end up with almost pure nitrogen in your tyres anyway.
I have nitrogen in my RX. Every time I take the car up in the mountains my check pressure light comes on. I'm a summer mountain visitor so it's not just the temp, altitude affects it as well.
 

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Even if you fill your tires with nitrogen the pressure will change with temperature. The Ideal Gas Law dictates how a gas's volume behaves under temperature and pressure. Nitrogen is not exempt from that law and will expand when hot and contract when cool.

Consumer report did a test of nitrogen in tires and I have seen similar tests written up on the net. I was all ready to put nitrogen in my tires until I did a bit of reading on the subject and have since changed my mind.

Tires - Nitrogen air loss study
 

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Nitrogen

I haven't heard that one before. I can't find any other sources for this bold statement, either.

It's true that nitrogen will maintain your tyre's pressure longer than just air, due to the molecules being larger than oxygen. But 80% of air is nitrogen anyway, so if you leave the air in long enough and regularly check your tyre pressures and refill, you end up with almost pure nitrogen in your tyres anyway.
Yes air is 78% Nitrogen, but the Nitrogen amount will not increase when you check you tire pressures and refill; it will continue to remain close to the make-up of air: ~21% Oxygen, ~78% Nitrogen. The Nitrogen will not build up because it will attempt equalize with the mixture being pumped in.
Nitrogen -- N2 -- 78.084%

Oxygen -- O2 -- 20.9476%
Argon -- Ar -- 0.934%
Carbon Dioxide -- CO2 -- 0.0314%Neon -- Ne -- 0.001818%

However, Nitrogen will somewhat reduce the pressure loss, but it will still lose pressure. Nitrogen or Air you need to check pressure and measure the pressure when cold.

Here is a pretty good article on Nitrogen:
The Straight Dope: Is it better to fill your tires with nitrogen instead of air?

and about improving mileage:
Do Nitrogen-Filled Tires Enhance Fuel-Efficiency?: Scientific American
 

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Ford Roll-Over

I'm using 45psi on all 4 tires. I don't necessarily agree with the rule of thumb that you should follow the owner's manual specification. That was the problem with the Firestone tires on Ford Explorers about 10 years ago. The Ford recommendation was much lower than the Firestone recommendation, which led to lots of tire failure.

I think that you're better off being closer to the tire manufacturer's specification. The Michelin tires that come with the CT have a max rating of 51 psi. So, I'm closer to that than the 32psi that Lexus recommends.
Ford tried to correct thier rollover problem by recommnding a low inlfation pressure of 26 PSI at the same time Firestone was experiencing a tire tread separation problem which the lower pressure exacerbated.
Ford Explorer Rollover Firestone Tire Tread Separation Recall

It is normally best to go with the tire OEM recommneded pressure; sometimes you can gain a little mpg by over-inflating.
 

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Ford Roll-Over

I'm using 45psi on all 4 tires. I don't necessarily agree with the rule of thumb that you should follow the owner's manual specification. That was the problem with the Firestone tires on Ford Explorers about 10 years ago. The Ford recommendation was much lower than the Firestone recommendation, which led to lots of tire failure.

I think that you're better off being closer to the tire manufacturer's specification. The Michelin tires that come with the CT have a max rating of 51 psi. So, I'm closer to that than the 32psi that Lexus recommends.
Ford had a problem with roll-over and tried to correct it by underinflating the tires to 26 PSI. At the same time Firestone had a tread separation problem which was exacerbated by the lower tire pressure. Normally it is best to go with what the tire OEM recommends in this case 32 PSI. Sometimes you can overinflate an get a little better mileage because you slightly increase the tire circumference, but then you have the possiblity of decreasing handling and increasing tire wear.

here is an article about the Ford Firestone tire problem:
Ford Explorer Rollover Firestone Tire Tread Separation Recall
 

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Manufacturer's recommended pressures are a compromise to give all-round reasonable comfort and handling. Few people argue with the idea of a 10% increase in pressures, which can sharpen up handling, braking and economy.
 
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