Tire Pressure - Why 40 Lbs?

[PMK]

Any thoughts on why the tire shops routinely fill tires to 40 lbs pressure, and the effects of doing so?

[apetley]

Only dubious reason I have heard is that it improves fuel economy.

When I bought my new Triton the tyre pressures were 60!!! psi from the Mitsu main dealer.

The ride was jarring to say the least and vastly improved dropping the pressure to that recommended.

[Dave the Dude]

I had the same with the Izusu dealers. Mine were 50psi when the book/stickers specify 30 ish !!!!!!

We are talking about Thai logic here ....Hard tyres=tyres roll easier= save money (You just go to paradise in a crash as well)

Dave

Edited January 27, 2009 by Dave the Dude

[noahvail]

I had the same with the Izusu dealers. Mine were 50psi when the book/stickers specify 30 ish !!!!!!

We are talking about Thai logic here ....Hard tyres=tyres roll easier= save money (You just go to paradise in a crash as well)

Dave

Hmmmm... I must be getting cynical in my old age. 50 psi in a 30 psi tyre will wear the centres of the tyres out very fast, meaning you have to buy new tyres...maybe from the dealer?

[luckyboy]

Hmmmm... I must be getting cynical in my old age. 50 psi in a 30 psi tyre will wear the centres of the tyres out very fast, meaning you have to buy new tyres...maybe from the dealer?

Really cannot understand too, not a single staff TOYOTA agree with sticker 30psi, since everyone's laughing at my pressure makes me doubt. Moreover the Vigo ride quality is poor I see a lot of new isuzus lately, Toyota's going down.

[dave_boo]

understand too, not a single staff TOYOTA agree with sticker 30psi, since everyone's laughing at my pressure makes me doubt. Moreover the Vigo ride quality is poor I see a lot of new isuzus lately, Toyota's going down.

Ahh, the famous "We're (insert company's name) Service Techs...plus we're Thai and you have to respect our tradition of that even when being wrong you can't make us lose face". Don't want to sound cynical, but the majority of Thai 'mechanics' wouldn't even pass a high school mechanics class in a Western country. If you think that something is obviously wrong, it most likely is! Obviously a 3rd world grease monkey that may have received 2 weeks of training knows more than the engineers and technicians at a first class tyre manufacturer!

And I don't buy the 'you'll save on petrol' if you keep your tyres over-inflated. The contact patch does NOT decrease enough to significantly lower the rolling resistance. Furthermore the extra shock transmitted in an over-inflated tyre will shorten you shock absorber's lives, negating any money saved on petrol. Another thing to consider is that by over-inflating there's a chance you will raise the vehicle. Ever get under a vehicle and look at it? Very few are streamlined. By raising the vehicle you increase the amount of air that can travel under it which would result in greater turbulance. Meaning that any gain you were going to get is mostly lost by increased resistance from the air.

As far as the Isuzus and Toyotas going down; I think it's a combination of stupidity on the 'mechanics' part and the drivers. These trucks (and that's all the SUVs are in LOS) are not designed to handle as cars! No matter what type of skid, roll, anti-locking control you put on them, they're still trucks and need to be treated as such. I've put no less than 200k miles in trucks and have never come close to rolling one over; and this is in driving conditions ranging from perfect to sand covered to black ice covered roads. Of course when teaching me to drive gramps ONLY let me drive during winter; his reasoning being if I could handle the vehicle than I could handle it at any time. And this was with a '79 Ford pickup with a 429 and 4 (if I remember correctly-could have been a 3) speed manual transmission.

[luckyboy]

Yes, but almost every Thai don't agree with the 30psi setting I've been to many service centres at various location very funny indeed including tire shops I even make calls to hotline technical dept of these and still you get the usual 40/45psi suggestion, can explain these???

[goldfish]

Explain these? Yeah, they're idiots. If you want to confirm the tyre pressures then phone either Toyota (not Toyota Thailand) or the tyre manufacturer. Dave is correct, although he left out the lazy comments and the fact they would need to think to operate a pressure guage.

Mmm, think I need another coffee

[luckyboy]

Explain these? Yeah, they're idiots. If you want to confirm the tyre pressures then phone either Toyota (not Toyota Thailand) or the tyre manufacturer. Dave is correct, although he left out the lazy comments and the fact they would need to think to operate a pressure guage.

Mmm, think I need another coffee

How could it be possibly to employ idiots to work for all these automobile industries?, whereby their knowledge is seriously taken into account just imagine this is not ice-cream, you're driving on them.....your life.

[Plus]

I think there are some valid reasons for overinflating.

Perhaps they count that 30 psi is a recommended pressure at a room temperature (whatever that is), a car at a gas station needs to get a few extra psi so that it comes down to 30 when the car cools down.

Also, for pickup trucks, 30 psi is recommended for empty load, right? The fully loaded truck weighs nearly twice that, so pressure needs to be set higher.

Also, the pressure drops as time goes by, if you don't check it regularly you might find that it's close to recommended value after a couple of weeks as it is.

[dave_boo]

I think there are some valid reasons for overinflating.

Perhaps they count that 30 psi is a recommended pressure at a room temperature (whatever that is), a car at a gas station needs to get a few extra psi so that it comes down to 30 when the car cools down.

Also, for pickup trucks, 30 psi is recommended for empty load, right? The fully loaded truck weighs nearly twice that, so pressure needs to be set higher.

Also, the pressure drops as time goes by, if you don't check it regularly you might find that it's close to recommended value after a couple of weeks as it is.

Wow, I'm going to have a field day with this post!

ALL pressure measurements are done on a 'warm' tyre. If you doubt me, read the sidewall of your tyre. There's a good chance two values are listed, the lower one is the cold one.

Most pickups have, either in their manuals or on the driver's side door jam a sticker, information that tells you exactly how much you need to increase your pressure due to load. Don't try and out think the engineers!

If you have a tyre that leaks 10+ psi in a couple of weeks you shouldn't be riding on it first of all. Second of all just because it's going to drop down to a safe level after some indeterminate span of time should not allow you to put the little bitty points of contact your extremely heavy vehicle has with the road in jeporady.

[skippybangkok]

at 32 PSI, i have always had the outsides of the tire bald way before the middle part. Believe early 30's is too low. Not science, just my experience.

[neverdie]

OP, I have previously posted about tyre pressures before on TV. If you do a thai visa search, the last post was only a few weeks ago, it was titled whats ur tyre pressure, OR SOMETHING LIKE THAT. There was some good discussion there.

I wont go over all that again, but I will simply say this, the thai practice of blowing tyres up like baloons is fundamentally flawed, most places dont even use guages because their thumb or foot does the trick.

Don't be fooled by these incompetent antics of fools that have no decent formal education on the issue. Dave-boo is spot on by stating that the Tyre Manufacturer gives you a range of pressures printed right on the side of the tyre - they do this for a reason.

The best advice you could be given is to adjust your tyre pressures to within the Manufacturers range, perhaps starting at the lower end of the scale & working upwards, depending on the type of use your vehicle is getting, its normal load and your driving style.

Without any doubt, the tyres & brakes fitted to your vehicle are the most important component in the vehicle, they should be monitored and maintained closely.

By the way, the difference between cold & hot tyre pressures is said to be approximately 10% based on normal usage. Therefore, if you were inflating your tyres to 34psi when cold, it would be possible that they increase by approximately 3psi when heated. Naturally if you start with 50psi & in extreem conditions that is heading upwards towards 60psi, a pressure which I would DEFINATELY NOT chose to drive on in a standard type tyre. If you have a sports tyre with low profile tyres, its highly likely that you will find the pressure rating will be higher than a standard type profile tyre found on other vehicles.

In my experience, tyre pressures indicated on tyre placards or tyres relate to cold pressures.

Edited January 28, 2009 by neverdie

[Plus]

From what I see people do at self-service air pumps, hardly anyone puts over 40 in your generic car/pickup truck.

If you put 36 psi in a hot tire of a loaded truck, it would probalby drop to 30 next morning without load. Even if it drops to 33 it's not a big deal. It might further drop another 3 psi in a course of two weeks or a month until you get a next chance at a pump.

[neverdie]

Tyre pressure should be checked at least weekly....with an accurate guage, not those ones that are constantly dropped at the service stations.

Having said that, I have found those new digital ones (at some servos) to be accurate....most likely because the guage is NOT in the handpiece.

[thaicbr]

Yer they always had good auto air pumps at Jet stations but now they have been taken over by PTT they are taking them out and replacing with the little canisters......why i ask you say........well to put it briefly, Thai drivers are lazy bastards and get the petrol attendant to put air in the tyres.......bloody idiots

[neverdie]

The guys there always use to laugh at me when I would go there and insist on doing it myself then whipping out my own guage to check the pressures were right.....NOW I've bypassed them and bought my own compressor, easy just a few hundred baht and u can do it at home....when the tyres are cold.

[asiaworld]

actually from my experience i must agree with those 'pumping up' the tyre pressure . Even thou Toyota shops i know do follow the manual . ones in Phetburi & Srinakarin roads.. So i usually go & ask them to pump it up a bit .. @ 30 PSI it feels FlaT > 32-33 is rideable ok.. but 35-38 is nicer. Depending on the load going upto 40 is reasonable, while anything above that is silly.. Btw. besides the recommended pressure your tyre will also have Max. pressure written on the side.. Usually it says 50psi.. so in that case anything below 40psi shouldn't hurt .

[dotcom]

Explain these? Yeah, they're idiots. If you want to confirm the tyre pressures then phone either Toyota (not Toyota Thailand) or the tyre manufacturer. Dave is correct, although he left out the lazy comments and the fact they would need to think to operate a pressure guage.

Mmm, think I need another coffee

Goldfish has it right.

Forget Toyota, locate a dealer of your brand of tires & ask them. I would use the upper level - so if it's 32 to 34 I would use 34. COLD.

[Plus]

They are taking out air pumps at old Jet stations? Bastards.

There are some others that have self-service pumps but it depends on the owner of a gas station.

On my Sportrider they never use those little canisters, they say not enough air or something and self-service pumps usually have a que.

Now I have a real problem here - no air pumps at LPG stations and I pracitcally never go to a regular gas station. Pumping air is a special occasion for me.

Tyre pressure should be checked at least weekly....with an accurate guage, not those ones that are constantly dropped at the service stations....NOW I've bypassed them and bought my own compressor..

That's an overkill for general population, they (we) are left at the mercy of gas stations and their attendants. I bet vast majority of drivers don't own pressure guages and 90% of females wouldn't even know what they are and how to use them.

[neverdie]

They are taking out air pumps at old Jet stations? Bastards.

There are some others that have self-service pumps but it depends on the owner of a gas station.

On my Sportrider they never use those little canisters, they say not enough air or something and self-service pumps usually have a que.

Now I have a real problem here - no air pumps at LPG stations and I pracitcally never go to a regular gas station. Pumping air is a special occasion for me.

Tyre pressure should be checked at least weekly....with an accurate guage, not those ones that are constantly dropped at the service stations....NOW I've bypassed them and bought my own compressor..

That's an overkill for general population, they (we) are left at the mercy of gas stations and their attendants. I bet vast majority of drivers don't own pressure guages and 90% of females wouldn't even know what they are and how to use them.

What the overkill is, is when your driving or riding your vehicle and you have a sudden and unexpected tyre deflation & you end up upside down on ur scon. I guess its all about how you view road safety really. I'm only regurgitation what the tyre manufactures state. When I was driving long distances on very bad roads, I use to check my pressures daily....only takes a few seconds you know.

It seems to be the standard here to have poorly maintained vehicles, I will most likely be killed by somebody elses wreck.

[Plus]

I don't think manufacturers require people to buy their own air compressors. Checking pressure regularly is another thing, but these days people just rely on their cars to go without any problems between required service intervals, thanks to Japanese.

[neverdie]

I don't think manufacturers require people to buy their own air compressors. Checking pressure regularly is another thing, but these days people just rely on their cars to go without any problems between required service intervals, thanks to Japanese.

Plus, I was NOT trying to suggest that tyre manufacturers require people to buy their own compressors, just explaining thats how I managed to bypass the circus at the gas station & it only cost a couple of hundred baht to do so.

You may like to re-read ur car manual, japenese or not most of them recommend certain checks be done more often than during the scheduled services, tyre pressures being one of them.

[luckyboy]

@ 30 PSI it feels FlaT > 32-33 is rideable ok.. but 35-38 is nicer. Depending on the load going upto 40 is reasonable, while anything above that is silly.. Btw. besides the recommended pressure your tyre will also have Max. pressure written on the side.. Usually it says 50psi.. so in that case anything below 40psi shouldn't hurt .

Very true, 30psi is riding on very flat, poor handling, only after 34 or so then feel better especially at low revs so this experience vs the recommended sticker by the door jamb has actually prove it wrong or atleast by a big difference.

[BSJ]

With good tyre brands you can stretch your check to monthly, but no longer. And over inflating is bl00dy stupid! As your driving the pressure is building up anyway. Do ya wanta risk a blowout at 120kph? If it's a front tyre it can be scary, I know from experience!

[tomartoh]

Is it possible that the Thais see a correlation between tyre size and air pressure?

In a car i never have problems about how much air goes in a tyre. On two occasions recently i have had new sets of tyres fitted on cars and the mechanics have put in as per manufacturers specs. However , with a pickup i find they just go to about 50lb. Do you think that the mechs think a bigger tyre need more air in it [which is does] but that more air means need for more pressure.

As a coincidence i was sat waiting for the car at a car cleaners this afternoon, when a vigo preerunner came in. The tyres were so over inflated i even pointed them out to the gf as i was so surprised. They were perfectly round, even the contact with the road. A band of uneven wear could be seen quite plainly. What would theu be like in an emergency stop from high speed????

I have been caught out in the past looking for fuel stations with air pumps, so i now always carry a little compressor, about 300/400baht, plus jack and wheel brace. Jump leads have also come in handy a few times.

[dave_boo]

Is it possible that the Thais see a correlation between tyre size and air pressure?

In a car i never have problems about how much air goes in a tyre. On two occasions recently i have had new sets of tyres fitted on cars and the mechanics have put in as per manufacturers specs. However , with a pickup i find they just go to about 50lb. Do you think that the mechs think a bigger tyre need more air in it [which is does] but that more air means need for more pressure.

As a coincidence i was sat waiting for the car at a car cleaners this afternoon, when a vigo preerunner came in. The tyres were so over inflated i even pointed them out to the gf as i was so surprised. They were perfectly round, even the contact with the road. A band of uneven wear could be seen quite plainly. What would theu be like in an emergency stop from high speed????

I have been caught out in the past looking for fuel stations with air pumps, so i now always carry a little compressor, about 300/400baht, plus jack and wheel brace. Jump leads have also come in handy a few times.

It could be possible that they think they understand some relationship....but than they don't understand that it's Pounds per Square Inch. As in, when you have 32 psi in a truck tyre or a motorcycle tyre, the pressure will be the same. There's obviously going to be more air in the truck tyre since there's more surface for the air to push against!

[denboy]

Is it possible that the Thais see a correlation between tyre size and air pressure?

In a car i never have problems about how much air goes in a tyre. On two occasions recently i have had new sets of tyres fitted on cars and the mechanics have put in as per manufacturers specs. However , with a pickup i find they just go to about 50lb. Do you think that the mechs think a bigger tyre need more air in it [which is does] but that more air means need for more pressure.

As a coincidence i was sat waiting for the car at a car cleaners this afternoon, when a vigo preerunner came in. The tyres were so over inflated i even pointed them out to the gf as i was so surprised. They were perfectly round, even the contact with the road. A band of uneven wear could be seen quite plainly. What would theu be like in an emergency stop from high speed????

I have been caught out in the past looking for fuel stations with air pumps, so i now always carry a little compressor, about 300/400baht, plus jack and wheel brace. Jump leads have also come in handy a few times.

Best chuckle all week. It's really a no brainer. Tyre manufacuters spend millions on research on wear loads etc,

The trye presure recomended on the car door pillar or in the handbook for that brand?size of tyre is the absolute correct one.

Having spent 50 plus years involved in saving money on fleet tyres, I have been proved correct it is essentail for safety and money saving to have the correct tyre/load pressure.

Tyres should be checked and inflated at cold at the ambeint temp in the part of the world you happen to be in.

A very tiring subject to boot.

[Lickey]

I used to work for a large haulage contractor in the UK, servicing tri-axle trailers with super singles [tyres] on, the PSI was normally set at 125, and 130 PSI for the center axle, as recommended by Michelin, the only way we could get a correct reading/pressure was by jacking up the axle when testing brgs and adjusting brakes, The noted pressure difference was as much as 20PSI,

With a 32psi tyre it would mean about 3/5 psi difference when loaded,

Cheers, Lickey..

[Plus]

Tyres should be checked and inflated at cold at the ambeint temp

Usually it's done at a gas station after driving for a while and the tires are hot. That's one of the reasons why they put a couple of extra psi.

Not everyone inflates to 40psi, btw. Only older types pickup drives and mechanics.