Recommended Tyre Pressure (in Sri Lanka)

[Sifaan]

Hi!

(My first question on AL )

There are websites that give recommended tyre pressures for various vehicles.

Can these numbers be used as-is in Sri Lanka, or should they be adjusted for the climate here?

e.g. the Agent says they usually advise 24 (front) / 26 (rear) but the website suggested 34!

even for the previous car the recommended pressure we found on some websites were higher than what was recommended here (but I don't recall the numbers now)

Thanks

/Sifaan

[Watchman]

I guess it varies on the vehicle and the suspension on it.

But basicaly you gotta balance between 2 things, better grip/comfort Vs. better fuel economy

When you got higer inflated tyres, the wheels wont stick to the ground as much so you'll get better fuel figures and your tyres will last longer... But that will also mean you ride would be stiffer/bumpier and less grip on the road.. So i guess you gotta try it out personally to see what the sweet spot is on your car... I tend to stick at around 28psi...

And welcome to AL

Edited August 6, 2010 by Dilesh

[dilku]

Hi!

(My first question on AL )

There are websites that give recommended tyre pressures for various vehicles.

Can these numbers be used as-is in Sri Lanka, or should they be adjusted for the climate here?

e.g. the Agent says they usually advise 24 (front) / 26 (rear) but the website suggested 34!

even for the previous car the recommended pressure we found on some websites were higher than what was recommended here (but I don't recall the numbers now)

Thanks

/Sifaan

I use 30 psi.

[Sifaan]

I use 30 psi.

Doesn't the recommended pressure vary with tyre sizes (mine are 195/65 R15)?

[jerryda]

Doesn't the recommended pressure vary with tyre sizes (mine are 195/65 R15)?

http://www.tyrepower.com.au/tyre_pressures.aspx

[heavyD]

Doesn't the recommended pressure vary with tyre sizes (mine are 195/65 R15)?

Yes it does. And your vehicle manufacturer also states the amount of tyre pressure needed.

[SeanD]

The ratings on the door are really the minimum safe pressure the manufacturer is allowed to spec in cohesion with your car's weight, etc. Look it up, there's plenty about it online. Run underinflated tires at your own risk - ride comfort will be the last thing on your mind when your tires explode when you're driving at speed (one of the main results of underinflated tires). By the way, the recommended pressure is when your tires are "cold" ie. not been run for three hours and have been sitting in the shade.

[Sifaan]

The ratings on the door are really the minimum safe pressure the manufacturer is allowed to spec in cohesion with your car's weight, etc. Look it up, there's plenty about it online. Run underinflated tires at your own risk - ride comfort will be the last thing on your mind when your tires explode when you're driving at speed (one of the main results of underinflated tires).

Well, that's the confusing bit... because the pressure the agent recommends is LOWER than what the manufacturer / websites recommends (but those are probably calibrated to colder climates, if that makes a difference).

By the way, the recommended pressure is when your tires are "cold" ie. not been run for three hours and have been sitting in the shade.

So, let's say recommended pressure is 30. If I go to the shed first thing in the morning then maybe I can pump air for 30... but if the car has been running around all day and is hot, then 30 would be under-pressure, isn't it? So we should go for 31? 32? more?

Cheers

[SeanD]

Well, that's the confusing bit... because the pressure the agent recommends is LOWER than what the manufacturer / websites recommends (but those are probably calibrated to colder climates, if that makes a difference).

Correction: They are properly calibrated to the car, for all climates. While the climate will have an effect on the tire pressure, this as I said is the minimum recommended pressure for the CURRENT climate the car is operating in, but taking in a lot of factors such as weight distribution of the car, etc. When I lived in the States, people would always make sure that this pressure was maintained (people there tend to overinflate when they do decide to fill their tires) during the summer and winter seasons. So if the pressure was one level in the winter, you would have to make sure that it was the same level in the summer, as the extra heat would tend to expand the air in the tire in the summer. A lot of people there use a portable digital pressure gauge which can be bought for around 3 dollars, but I'm not sure you can get them here yet. You can really see the effect of heat on pressure when you check the pressure on one side that the sun is shining on early morning, and find it is a lot higher than the side that is in the shadow.

Here is some good reading material on the subject if you're interested, along with reasons for maintaining manufacturer recommended pressure: http://www.cartalk.com/content/features/Su...Tips/tires.html

So, let's say recommended pressure is 30. If I go to the shed first thing in the morning then maybe I can pump air for 30... but if the car has been running around all day and is hot, then 30 would be under-pressure, isn't it? So we should go for 31? 32? more?

Cheers

Depends on how far away the shed is. If the car has run more than about 1km, the pressure in the tire will have increased a few PSI. How much really depends on the environment and distance you've been driving.

What I used to do in the States is measure the pressure after the tires were cold, then measure it again with the same gauge at the shed, and put in enough air to make up the difference (it would have gone up by about 2 PSI though the station was less than 2 miles away). In Sri Lanka I do the same thing, and though the shed is about 1.5 km away, the PSI has almost always gone up by about 2. Though I need 33PSI in the front, I tell them to then put in 35. Usually when I've come home and let the car sit for 3 hours or so, the pressure has come back down to 33PSI.

The reason for me being so picky is due to years of high speed driving on highways where I saw loads of blowouts happen with often fatal accidents. A lot of these could have been avoided with proper tire maintenance and care, including proper pressure (not underinflating so the air will expand more due to more rubber being in contact with the surface, leading to premature failure, or overinflating so much that the damn thing can't handle it). You may not think this is important in SL, but anyone doing a lot of driving outside of Colombo is almost always reaching highway speeds on our roads as well, and underinflated tires can be dangerous. Read that link I gave you carefully. If I sound overly paranoid, it's cos it's better to be safe than sorry

By the way, who do you think knows what's best and safest for the car, the local agent or the person who manufactured it?? Got to take everything agents say with a grain of salt.

Edited August 7, 2010 by SeanD

[Sifaan]

A lot of people there use a portable digital pressure gauge which can be bought for around 3 dollars, but I'm not sure you can get them here yet. You can really see the effect of heat on pressure when you check the pressure on one side that the sun is shining on early morning, and find it is a lot higher than the side that is in the shadow.

Didn't know such things existed. Thanks for the tip - I'll get myself one

The reason for me being so picky is due to years of high speed driving on highways where I saw loads of blowouts happen with often fatal accidents. A lot of these could have been avoided with proper tire maintenance and care, including proper pressure (not underinflating so the air will expand more due to more rubber being in contact with the surface, leading to premature failure, or overinflating so much that the damn thing can't handle it).

Well, I was only thinking of the tyre wear and fuel economy perspectives, which are already good enough reasons to have correct tyre pressure

By the way, who do you think knows what's best and safest for the car, the local agent or the person who manufactured it?? Got to take everything agents say with a grain of salt.

Well, all other things being equal, I would trust the manufacturer over the agent

But "local conditions" are one of the unequal thingies - e.g. certain service intervals tend to be more frequent than manufacturer spec because of temperature/UV, dust, quality of fuel, etc.

That's why I was wondering if our climate had an effect on tyre pressure... from what you say, if there is a change, it should be to a higher pressure (because manufacturer spec is cold reading, and most of us would measure at a shed, which means a hot reading)

Anyway, thanks for the insights!

[miniace]

30 Psi for normal Profile

MINIACE

[MkX]

mine is 195/65 R15 - EK3 any suggestions. I currently keep 28-29psi.

[SeanD]

mine is 195/65 R15 - EK3 any suggestions. I currently keep 28-29psi.

Are these the stock rating of tires for that car? Look inside the door beam on the drivers side (or sometime on the panel between the door and the steering wheel). If your car has had some work done on the paint these may have got erased, but the proper ratings should be there. It will also be in your manual (two different ratings for heavy loads and normal loads).

If it's not the stock size and rating then I'm not sure how it works. But about 30 PSI per side would be what I think. 28 psi (at shed tire temperature) just sounds too low imho.

[MkX]

Are these the stock rating of tires for that car? Look inside the door beam on the drivers side (or sometime on the panel between the door and the steering wheel). If your car has had some work done on the paint these may have got erased, but the proper ratings should be there. It will also be in your manual (two different ratings for heavy loads and normal loads).

If it's not the stock size and rating then I'm not sure how it works. But about 30 PSI per side would be what I think. 28 psi (at shed tire temperature) just sounds too low imho.

Yep sticker is there with below details.

185/70 R13 - 1.9/1.9 Kg/CM²

185/65 R14 - 2.0/2.1 Kg/CM² = 29.8psi ???

But my original wheel size is 14 and changed to 15 now.

And another thing the sticker says LSD. Does 1996 EK3 came with LSD?

[SeanD]

Yep sticker is there with below details.

185/70 R13 - 1.9/1.9 Kg/CM²

185/65 R14 - 2.0/2.1 Kg/CM² = 29.8psi ???

But my original wheel size is 14 and changed to 15 now.

And another thing the sticker says LSD. Does 1996 EK3 came with LSD?

Sorry machan I don't know the criteria for when rim sizes are increased. But 30 psi would probably be right - as you can see there is an increase in the pressure as the size has increased according to the sticker. You may want to do some searches on Google. Not sure about the LSD but there are plenty of Honda experts here who would be able to answer that question.

[MkX]

Sorry machan I don't know the criteria for when rim sizes are increased. But 30 psi would probably be right - as you can see there is an increase in the pressure as the size has increased according to the sticker. You may want to do some searches on Google. Not sure about the LSD but there are plenty of Honda experts here who would be able to answer that question.

The issue i faced it when i bought the car it was around 31psi. So I kept it as it is around 30psi. But when i travel in roads with lot of patch work i got lot of vibration in suspension. Then I tried with 28psi and it's reduced with noticeable change.

[Sifaan]

The issue i faced it when i bought the car it was around 31psi. So I kept it as it is around 30psi. But when i travel in roads with lot of patch work i got lot of vibration in suspension. Then I tried with 28psi and it's reduced with noticeable change.

I'm a newbie at this, so I may be totally off the mark here... is it possible that there is some fault in the suspension that is being masked by lower tyre pressure?

[SeanD]

The issue i faced it when i bought the car it was around 31psi. So I kept it as it is around 30psi. But when i travel in roads with lot of patch work i got lot of vibration in suspension. Then I tried with 28psi and it's reduced with noticeable change.

Well this is just the physics of tires, higher inflated tires will normally result in a bumpier ride. Remember that the tires are also a part of the overall suspension system in your car, and are the first thing to absorb the bumps you're encountering. When you reduce the pressure, there is more surface area in contact with the road, but that's also putting more work on the tires and the treads are no longer hitting the ground the way the tire was designed to handle the road.

That's why you often get bulging centers when you remove the tires and have them unable to stand up by themselves - the heat distribution across the treads is not equal with underinflated tires as opposed to correctly inflated ones, and areas that were not designed to be in friction with the road are now rubbing on the road, and with thousands of kilometers causes changes in the rubber that can often be dangerous because the strength of the tire is now compromised. This is possibly why some cars recommend higher pressure in front (my N16 recommends 33 in front and 30 at the back) so that the additional weight of the engine bay doesn't lead to the front tires being differently aligned to the road than the back ones.

In your particular case, if there's nothing wrong with your suspension system, then underinflating tires is not worth the safety risk as well as the increased wear on the tire, IMO. But then again, I have no idea what the correct pressure for your current tires should be for your car, as I'm assuming it was not designed to run with R15s, so perhaps 28/29 is the magic number after all.

[Sifaan]

In your particular case, if there's nothing wrong with your suspension system, then underinflating tires is not worth the safety risk as well as the increased wear on the tire, IMO. But then again, I have no idea what the correct pressure for your current tires should be for your car, as I'm assuming it was not designed to run with R15s, so perhaps 28/29 is the magic number after all.

I was once in a Tuk Tuk when he was pumping air and he asked for 34. I was a bit surprised and asked him about it and he said smaller tyres need more pressure, and that lorry/tractor tyres need very little pressure (anyone have any experience? and what's a typical pressure for a motorbike?). This seemed a bit counter-intuitive (bigger tyres means bigger, heavier vehicles, so shouldn't they need more pressure?) but I didn't press the case.

Of course, even if the Tuk Tuk guy was right, a lorry tyre is bigger than a tuk tuk tyre in terms of rim size, width, and overall diameter, so it's not clear which parameter should increase to reduce the required pressure. (e.g. even if you changed from R13/R14 to R15, presumably the overall diameter is the same, or at least similar).

Edit: The plot thickens; these sites (1, 2) suggest that tyre pressure increase if you increase rim size, and this one suggests you decrease :S

Edited August 8, 2010 by Sifaan

[SeanD]

I was once in a Tuk Tuk when he was pumping air and he asked for 34. I was a bit surprised and asked him about it and he said smaller tyres need more pressure, and that lorry/tractor tyres need very little pressure (anyone have any experience? and what's a typical pressure for a motorbike?). This seemed a bit counter-intuitive (bigger tyres means bigger, heavier vehicles, so shouldn't they need more pressure?) but I didn't press the case.

Of course, even if the Tuk Tuk guy was right, a lorry tyre is bigger than a tuk tuk tyre in terms of rim size, width, and overall diameter, so it's not clear which parameter should increase to reduce the required pressure. (e.g. even if you changed from R13/R14 to R15, presumably the overall diameter is the same, or at least similar).

Edit: The plot thickens; these sites (1, 2) suggest that tyre pressure increase if you increase rim size, and this one suggests you decrease :S

I know tires have a maximum pressure rated on them (at least most do). Wonder if the three wheel guy is using that as his guide It would probably be a lot lower cold pressure though, as I'm sure he has run quite a bit before he puts air in and the air in his tires has already expanded a lot. In any case, it's a complicated issue and I don't know that it has to do with the tire size as much as the rim size and the weight of the load it has to bear... But the first site you've given has a good explanation of the point I was making earlier about the differences between cold tire pressure and pressure at the shed.

[Sifaan]

I know tires have a maximum pressure rated on them (at least most do). Wonder if the three wheel guy is using that as his guide It would probably be a lot lower cold pressure though, as I'm sure he has run quite a bit before he puts air in and the air in his tires has already expanded a lot. In any case, it's a complicated issue and I don't know that it has to do with the tire size as much as the rim size and the weight of the load it has to bear... But the first site you've given has a good explanation of the point I was making earlier about the differences between cold tire pressure and pressure at the shed.

Well, I wasn't planning on taking the tuk tuk guy's statement at face value

Once I get the tyre pressure gadget I ordered (on ebay) I'll be better equipped to play this game!

This site has an interesting practical test to check if the pressure is OK.

[MkX]

SeanD thanks for the effort taken to share the experience. I'll try with 30psi again and see.

[SeanD]

Hey look, we will no longer have to figure out when we're low on air ourselves: http://autos.yahoo.com/articles/autos_cont...is-symbol-means

[Sifaan]

Hey look, we will no longer have to figure out when we're low on air ourselves: http://autos.yahoo.com/articles/autos_cont...is-symbol-means

aftermarket systems like this (http://cgi.ebay.co.uk/TyreSure-Digital-Tyre-Pressure-Monitoring-System-TPMS-/270542283937?pt=UK_CarsParts_Vehicles_CarParts_SM) are already available, but 27000 to monitor tyre pressure?? I think I'll just make sure to measure once a week with the gauge I ordered

[shanX]

I was once in a Tuk Tuk when he was pumping air and he asked for 34. I was a bit surprised and asked him about it and he said smaller tyres need more pressure, and that lorry/tractor tyres need very little pressure (anyone have any experience? and what's a typical pressure for a motorbike?). This seemed a bit counter-intuitive (bigger tyres means bigger, heavier vehicles, so shouldn't they need more pressure?) but I didn't press the case.

Average lorry/bus tyre need to be pumped 50-55psi afaik

[harshansenadhir]

Though I need 33PSI in the front, I tell them to then put in 35. Usually when I've come home and let the car sit for 3 hours or so, the pressure has come back down to 33PSI.

I understand tire pressure differences due to temperature change. However, if you need 33 psi while you're running the vehicle, shouldn't they be pumping 33psi? Simply because tire pressure is what we're particular at, not the volume of air inside. or else you want it to be at 33psi when you keep the vehicle parked for some reason ?