[RX135]

I recently came across a strange experience. My car is normally parked on open road when I am in the office. On this day, as usual I started back home at around 8:30 pm. I started driving and heard some "gad-gad-gad" sound as I was driving. I stopped immediately. Got out of car and did inspection all around. Nothing, everything is normal! Checked if doors are shut properly. Yes, they were. I decided to drive on, got back at home. I have Michelin pressure guage, it showed something like 31 psi against recommended 28. That is fine, I said. I normally maintain 28-30 psi.

Next day, I had to visit in-laws with family. Again, same noise making me absolutely uncomfortable. Funny thing, no one else noticed it. But when I asked my wife, she started noticing it as well. I was worried, drove down to Fiat dealer. Got friendly salesperson and service manager with me in car and drove around. They didn't find it much different (why?), but service manager thought it to be high pressure in tyres. I had checked it last night, but we anyway drove to nearby petrol pump with electronic pressure guage. To my utmost surprise, it was 34/35 psi. I was shocked.

Service manager told me that it is common in summer that pressure in tyres rises and I should maintain 27psi instead of 28psi. The noise reduced considerably, but it was still there. I came back home, opened boot and tightened the screw for spare wheel. The noise was completely gone next day.

Side effect of this story is that, now ride quality has improved even further. Gone are any big/small potholes, broken roads. No vibrations inside.

Now questions for everyone:

1. Have you noticed your tyre pressure increasing in summer? One of my friends was shocked when he found 40 psi in his Santro tyres.
2. Is it recommended to lower the pressure than company suggested pressure? 27psi instead of 28 psi?

[5u3zEr0]

I have never heard of this before and sounds strange. I guess I will check the tyre pressure in a day or two and find out. Though off late I have been feeling road irregularities a bit more.

[k36]

Last sunday, on way to Mahabaleshwar, I topped my fuel tank at the Reliance petrol pump, and first time (2 weeks after delivery) checked the tyre pressure of my Swift. I know that checking tyre pressure just after driving 30KM on highway at noon in summer is not a good idea, but still I did.
And guess what ... it was 44 psi instead of the recommended 33 .
I've no idea how much was the pressure when I took delivery. The dealer might even have over filled so that I get good FE

Anyway, I got it reduced to 40 and continued on. Didn't observe any effect on handling. Probably I don't know how does it feel to drive with 33 psi.

[SLK]

The car's specifications mostly say... the pressure is to be measured when cold.

i.e. Say Delhi...
in winters... the temp when car is parked is 10..... and you put the recomended air. So when you drive it would be up by 1-3psi.... but thats normal (b'coz your cold temp is fine)

in summers... the temp when the car is parked is 35..... and you put the recomended air. So when you drive temp of the tyre would rise by a few degrees.... and the pressure by 2-3psi, again its normal.

So I guess its not much of a problem unless you fill up your tyres in the winter and drive in summer.... .

Originally Posted by RX135

it showed something like 31 psi against recommended 28.

thats 3psi higher.... obviously it would make a difference in ride. Specially now you have 27psi!

Also there is difference in gauges..... I have an electronic one... and when it says 33psi ... another manual one (attached to the pump) says 42psi.

[shuvc]

Originally Posted by k36

And guess what ... it was 44 psi instead of the recommended 33 .

Same case with my Baleno .. dealer had put in 40+ in all tyres. I reduced it to 27 when I discovered this after 2 weeks. Not sure why they do this.

@RX135, is your friends Santro new ?

[SLK]

Originally Posted by shuvc

Same case with my Baleno .. dealer had put in 40+ in all tyres. I reduced it to 27 when I discovered this after 2 weeks. Not sure why they do this.

My Alto had 44-45psi... the power steering felt funny. It was corrected the next day. Also the alignment was OUT like anything (Car used to make seperate front and rear wheel tracks). The dealers are supposed to do a PDI... but they seem to forget that most of the times.

[speedsatya]

Originally Posted by k36

Anyway, I got it reduced to 40 and continued on. Didn't observe any effect on handling. Probably I don't know how does it feel to drive with 33 psi.

NEVER DO THAT !!!!!!always check cold air pressure ..doa search and you will find topics on this and many arguments on this

[RX135]

SLK, I tend to fill in 1-2 psi more than recommended pressure since tyres are bound to lose the air over period of time. In fact, for highway drive it is recommended that you add 2-4 psi. But, I guess it was bad this time since it went up to 34psi. I thought it may be because the car heats up in sun, but then it should cool down in evening. On second thought, if one fills up in evening and drive in afternoon, pressure might shoot up.

Shuvc, my friends' santro is 3 year old. So, it's not dealer overfilling it. But, I suspect what you say might be true, i.e. dealers filling up more to increase FE.

My question still remains. Is it recommended to have lower than company suggested pressure? Do tyres tend to increase pressure in summer? If yes, how?

[Rehaan]

Originally Posted by RX135

My question still remains. Is it recommended to have lower than company suggested pressure? Do tyres tend to increase pressure in summer? If yes, how?

RX135,

My understanding is that heat causes gas to expand.
Therefore for the same volume of gas, temperature is proportional to pressure. (~Charles law)
(Temp goes up, pressure goes up; temp goes down, pressure goes down)

So given the fact that you filled air at a colder time, and since the volume didnt decrease and the temp went up, the pressure went up too.

My take on it is that when you fill your tires in the summer, you should fill to the reccomended pressure as the pressure reading you will take then will be of the hotter air anyway due to ambient temperatures (remember tire pressure measurements should always be taken when the tire is cold (ie hasnt run more than a few slow km, or been given enough time to cool down)

Hope that answers most of your queries.
cya
R

[5u3zEr0]

My question still remains. Is it recommended to have lower than company suggested pressure? Do tyres tend to increase pressure in summer? If yes, how?

I think if you check tyre pressure before 9/10 in the morning or in the evening after sunset, when air temperature is lower than during the day, the tyre pressure will not be so high and the difference in tyre pressures will not be so high.