Tyre Pressure

[Vicz]

Guys, after travelling for about 20km, can an originally pressure of around 230 goes up to about 265?

[Nhrisuzu]

i think quite possible..

 

pumped once at 10am (5mins after starting engine) at 235KPA.. reached beach road via AYE/ECP at 10.35am.. wanted to pump again at 235.. the machine released air for me..

 

hmmm.. think can be possible.. anyway, using caltex's air pump..

[Beei]

Some possibilities:

 

1) Tyre pressure gauge not accurate

 

2) After 20km, tyre is hot, air inside expand, pressure go up

[Mnphosis]

of course!

 

1km already can go up 5-10 kpa.

 

at 5-10 km, 30-40 kpa increase is very very normal.

[Dragos]

can, but not a good way to check......best is to check tire pressure when the tire are cold..or rather drive to your nearest petrol station to check..

[Sonicmood]

Highly possible...

[Kklee]

Should be normal.

 

Also, tyre pressure differ based on the time of the day due to temperature and tyres on either side of the car may differ depending on the location of the sun.

 

Some readings taken. Analog gauge by visual approximation.

 

0615 hrs - At rest.

Front 238/238

Back 230/230

 

0800 hrs - After being driven.

Front 259/259

Back 262/262

 

1200 hrs - At rest. Hot afternoon.

Front 248/248

Back 255/255

 

1230 hrs - Driven about 16km. Mixed expressway / city.

Front 265/265

Back 269/269

[Mnphosis]

yours fwd ah?

 

how come rear heat up so fast leh?

 

my fwd front 255 rear 235

 

after 15 km, rear is only 250 but front is 285-290

[Kklee]

Summary ...

 

Mine - Pressure difference for 16km

Front 17/17

Rear 14/14

 

Yours - Pressure difference for 15km

Front 35/35

Rear 15/15

 

Yup, mine FWD. As above, if based on difference, our rears are more or less the same.

 

I'm working with constrains because the analog gauge I have is not accurate. The accuracy different should be about minus 10-15. It's difficult to find out actual because my digital gauge, the readings goes in steps of 5 e.g. 240/245/250/255.

 

Based on your front readings, is yours a >1600cc car and using normal air ?

[Mnphosis]

yup i guess you r right. its an suv and i am using a digital meter so prob more accurate :)

[Mnphosis]

however, i would be of the opipnion that fwd vehicles heat up the front tires much more as often, the fronts are warm to touch but the rears are just ever so slightly "warmed"

[Kklee]

Agree. Next, is to find out whether nitrogen really runs cooler.

[Siyexcalibur]

You can calculate exactly how much the pressue will increase with temperature using laws of Physics.

 

A fresher course in secondary school physics.

 

P = R.d.T

 

where p is pressure, R is a constant which is 0.286 kJ/kg/K for air, d is density of air and T is TEMPERATURE in Kelvins.

That would mean that the pressure will increase by 20% if the temperature in Kelvins (not Celsius) increase by 20%

 

examples of conversion of Celsius to Kelvin. Kelvin = Celsius + 273.15

20 C = 293 K

40 C = 313 K

60 C = 333 K

 

Note the air in tyre is hotter than the rubber but not as hot as the rim but you can approximate it by measuring the temperature at the joint between the rubber and the rim using a thermocouple.

 

I hope the above will provide some enlightenment on how much the difference is between cold tyre pressure and hot tyre pressure.

Edited May 28, 2008 by Siyexcalibur

[Alfpoon]

hi guys,

 

need some advise here...if i am going on a long road trip like 300km taking about 4hrs drive, should i lower my tyre pressure?

 

what is the pressure to lower to?

 

I'm on 17"s.

[Eyke]

why would you want to lower your pressure?

 

just make sure it's not under-inflated, so that they don't overheat.

[Kingcopa]

Just to hijack this thread. I am currently on T1R, what sort of tyre pressure shld i have? Follow the spec of my ride or higher?

[Robo]

depends on your ride itself. follow the manual liao den see if its comfortable. if not u can try +/- 10% i guess...

 

or wad's the recommendation of the tyre shop??

[Kingcopa]

follow ur car spec lor