Enquiry on air pressure

[Meng]

Greetings from a newbie here.

 

Can I check with all the experts here on how to find out the amount of air pressure needed for the tyres? I saw that there are some printings on my tyres but not too sure if that's the correct thing to look for. Eg. for 195/50/R15, does it mean that the air pressure shd be 195 and is the one in mind when pumping air into the tyres.

 

Thanks in advance for your advice.

[Laweis09]

i think you got it wrong.... the 195 is the width of your tyres in mm.....the 50 is a code associated with the max speed allowed for your wheels and the R15 is the radius of your wheels in inches.... look at your car manual for the suitable tyre pressure ......normally for your case should be between 210-230 kPa

 

pretty sure about this but correct me if i am wrong.... hope it helps though

[Johnchong]

Huh... Sure or not...

 

195 width of tyre, correct.

50 is the height of the sidewall as a percentage of the width. (50% of 195 in this case)

15 is the size of the wheels/rims in inches

R means Radial construction. It's the most common type of tire construction nowadays. Another example would be ZR.

 

The speed rating you're referring to is shown elsewhere on the tire. It's shown in letters. Common one is "H"

[Mario]

Look at the side of your door. The pressure should be written there.

For R15 should be ard 220 and 210. But you will have to confirm it urself by looking at the pressure as per recommended.

[Yeobh]

Here is the interpretation:

a) 195 = width of tyre in mm

b) 50 = 50 series - it means the tyre wall height is 50 % of the the width

c) R15 = diameter of rim in inches.

 

Open your car door , at the side of the body frame you should be able to see sticker indicating the tyre pressure either in PSI, Kg/cm2 or Kpa. The information should be also available from the user's handbook.

[Laweis09]

knowledge enhanced!....sorry for the wrong info there though

[Meng]

really enriched my knowledge. thanks guys.

[Hoppe]

220-225 kPa should be okay.

[Silklee]

Hi

I really dont know where to post this query of mine, so just tompang on this thread.

 

I recently changed from a 205/55/16 GR90 to a 215/45/17 CSC5.

 

On the GR90, I will pump anything behing 32 to 34 PSI. Upon the change, the workshop guy told me to pump more than 240 KPA (=35 PSI). He even went on to say that he would actually recommend more than 240 KPA. He says can go up to 250 KPA (=36 PSI). The reason for the higher pressure, according to him, was due to the softer sidewall on the CSC5.

 

Is there anyway for me to calculate or find out the correct air pressure to pump. Comments please.

 

I am driving a 2008 civic (aka FD1).

[Roberttan]

Hi

I really dont know where to post this query of mine, so just tompang on this thread.

 

I recently changed from a 205/55/16 GR90 to a 215/45/17 CSC5.

 

On the GR90, I will pump anything behing 32 to 34 PSI. Upon the change, the workshop guy told me to pump more than 240 KPA (=35 PSI). He even went on to say that he would actually recommend more than 240 KPA. He says can go up to 250 KPA (=36 PSI). The reason for the higher pressure, according to him, was due to the softer sidewall on the CSC5.

 

Is there anyway for me to calculate or find out the correct air pressure to pump. Comments please.

 

I am driving a 2008 civic (aka FD1).

that is NO calculation of tyre pressure for tyre only conversion of tyre pressure (US psi to Metric KPA)

generally tyre pressure determine by the Car : Load / driving condition.

now aday most car manufacturer playcard/manual/ petrol cap / driver door / door pillar provide full information about tyre size , pressure .

most passenger car tyre pressure falls btw 200kpa to 260kpa.

and car maker usually recommend for comfort / fuel economy

and My POV lower the tyre profile higher the pressure (exp from 60% down to 40% aspec ration) upair by 15-20%

[Ungtiong]

depends on the timing u pump the air.

 

i once pump 35PSI during a cold raining day (car parked for more than 10 hours, travel short distance about 5 mins, never speed) and checked the pressure the next day in the hot afternoon, the pressure is all the way to 38PSI!!!!. could be the petrol station gauge got different calibration (tried checking 3 petrol station near my house at one go..different by 10 kpa!!!. last time got one station even jialat one pump my tyre to 300 kpa although setting is 240kpa!!!!!, i drove off, the ride feel very funny, straight away go next one, confirm 300 kpa!!!!)

 

for R15, I find the comfortable (can tell, the ride is very smooth and quiet) range is pump 34psi after driving 15mins on a normal morning.

 

best way is to buy a digital pressure gauge (about $15 at petrol station). measure ur tyre pressure in the morning before u move off, then measure again when u reach the petrol station before you pump ur air. Then u know how to 'adjust' for the pressure. The recommended pressure is always for cold...thats y can be as low as 210 kpa...after driving around to ur petrol station, the pressure will rise 10 even 20 kpa!! liao.

Edited October 11, 2012 by Ungtiong

[Kklee]

Hi

I really dont know where to post this query of mine, so just tompang on this thread.

 

I recently changed from a 205/55/16 GR90 to a 215/45/17 CSC5.

 

On the GR90, I will pump anything behing 32 to 34 PSI. Upon the change, the workshop guy told me to pump more than 240 KPA (=35 PSI). He even went on to say that he would actually recommend more than 240 KPA. He says can go up to 250 KPA (=36 PSI). The reason for the higher pressure, according to him, was due to the softer sidewall on the CSC5.

 

Is there anyway for me to calculate or find out the correct air pressure to pump. Comments please.

 

I am driving a 2008 civic (aka FD1).

 

Here is what I've gathered over the internet. Note, the interpretation could be wrong.

 

GR90 205/55R16 Load Index 91V = 615kg per tyre @ 36 psi thus 4 tyres can support 2460kg

CSC5 215/45R17 Load Index 87W = 545kg per tyre @ 36 psi thus 4 tyres can support 2180kg

 

For load at different pressure, I was not able to find 91 but found 89 instead which is a good approximation for the GR90's 91V.

 

PSI - 26/29/32/35

Load (lb) - 1091/1157/1213/1279

Load (kg) - 495/525/551/581

 

Therefore if at 32psi, 4 tyres support weight of 551x4=2204kg ( assume that for load index 91, the weight supported is higher )

 

For load index 87 for P215/45R17 (for CSC5)

 

PSI - 26/29/32/35

Load (lb) - 996/1067/1135/1201

Load (kg) - 452/485/515/545

 

Therefore if at 32psi, 4 tyres support weight of 515x4=2060kg

 

I found that Honda Civic 2008 - Curb Weight - 1336kg. If 5 passenger + luggage is about 400kg, total weight is 1736kg.

Assume that the front is heavier and the weight distribution is 60% front and 40% back, the weight at the front wheels would be 1128kg.

 

Thus at 1128kg, for the CSC5 with load index 87, the front 2 tyres @ 32psi support up to 515kg x 2 = 1030 kg which is less that 1128kg.

Therefore, the front pressure should be increase to maybe 35psi. But even that will not meet the 1128kg thus maybe the passenger load should be lighter.

 

If the 35psi is cold tyre pressure, actual tyre pressure during usage can be higher, just make sure that it doesn't exceed the maximun.

Of course, having a higher load index of 91 is much safer.

 

If pump nitrogen, to be safer, it is good to pump slightly higher because the rate of expansion during usage is much less.

Edited October 11, 2012 by Kklee

[Gee]

Oh Wow..

So cheem.. And so far i just follow roughly what's stated on label at door frame.

 

[Kklee]

Oh Wow..

So cheem.. And so far i just follow roughly what's stated on label at door frame.

 

The label at the door frame is your insurance - factory specs.

I would think it takes into consideration the tyre profile and load index.

If upsize or downsize, it will be a concern.

 

If label say 32psi, after the tyre heats up, maybe it goes to 34psi. I will take that as the "correct" pressure to support the weight of the car.

If using nitrogen at 32psi, you probably won't get up to 34psi, maybe 33psi ?

 

Of course that is my take.

[Beregond]

dun need to be so chim go count untill like that..

 

normal tyres 17' on a civic pump 36 psi is ok.

 

how much we pump is really up to indv.

 

eg: i pump tyres once for a lady. normal 32 psi. then she told me your car feel very bumply afterward. i go drive with her i feel perfectly normal.

reason. she never pump tyres in her whole life b4. alway driving around under pressure 20+ psi.

 

but i got some friends they pump 32 . they say too soft. same car same size rim.

 

its up to indv driver to find the tyre pressure best suit for their comfort and driving / handling/

 

nomal jap car 1.3-2.0 u cannot go wrong range 32-26.

 

bigger size mpv suv low profile tyres car 40+-

[Gee]

yes true lah.

different person different car etc..

if follow the factory guidelines thereabout imho best (consider no mod).

some said,

pump too hard, suspension suffer, wheels as well(?), loss of grip, botak centerline faster.

pump too soft, FC increase, car handles like sponge, botak sidelines faster.

got to be just nice..

[Beregond]

yes true lah.

different person different car etc..

if follow the factory guidelines thereabout imho best (consider no mod).

some said,

pump too hard, suspension suffer, wheels as well(?), loss of grip, botak centerline faster.

pump too soft, FC increase, car handles like sponge, botak sidelines faster.

got to be just nice..

 

basically the pros and con is not too chim.

 

if your tyres is under pressure. u will find your car ride very soft feeling like your suspension very good.

and your breaking distance is very short

 

but the cons is your steering will be harder depend on car, esp when not moving.

u will encounter higher fc and your car pick off slower.

and lastly u will encounter uneven wear of tyre ( outside wear.)

 

if u over pump. u will find you steering lighter ,your fc will mostly be lower, and u pick off faster.

 

but the feedback from road bumpness is very direct and more sensertive

and u lose out in braking distance. and if really over pump too much, u will have tyres wearing in the middle.

[Kklee]

but i got some friends they pump 32 . they say too soft. same car same size rim.

 

Tyres the same ?

 

Can be same size but load index different due to different make.

Possibly soft sidewalls.

 

E.g. GR80 and ZE912, same size, same pressure, different feel. GR80 is a comfort tyre.

To make the ride feel like the ZE912, it is possible to over pump.

The point is, at what expense? Safety or ride comfort ?

 

What one choose is individual, nothing happen of course is good. The choice is always yours.