Tire pressure

[Kruzenvax]

Manual specifies 210-220 kPa (for all models). WHen mine cam from the dealer all 4 had about 250 kpA. So what's the right pressure?

Thanks

Edited March 3, 2008 by Kruzenvax

[The Fly]

The manufacturer specifies tyre pressures primarily for ride comfort. It's usually recommended to inflate tyre pressure by 2-4psi above the mft's specification, with the result being better fuel economy due to decreased rolling resistance and (marginally) better handling depending on the additional pressure used due to decreased tyre wall flex.

Eg, on my WRX is use 37psi front and 35psi rear, as opposed to Subaru's recommendation of 32/33psi but my priorities are performance, comfort and fuel consumption in that order.

We've had our K for less than a month, so when the fuel consumption normalises I'll try incremental pressure increases for comparisons before deciding on what to leave it at.

Decide what your priorities are and inflate your tyres accordingly.

[Taka]

All 4 in 38psi. Drop it for off road adventure, but if you ever been to ANY defensive driving course you will know.

Sports car is different, and when I go to race track, I measure the tyre temperature and match it with the tyre pressure. That is another thread on its own

[Kruzenvax]

Thanks guys.

So, against 32 recommended psi's I have 36 and 38. Guess I'll be doing that instead of 32. Now need to inflate them back

Taka, what about the defense driving course - e.g. how is related to tire pressure if you don't mind?

Thanks

Edited March 3, 2008 by Kruzenvax

[Taka]

I was told my the defensive driving course (whose company started with an M....). I am not promoting them now since Kevin (whom I have known for a few years) is holding similar driving course. At least he is doing at lot of stunt courses

Having said that, it is common knowledge being pass on in any driving course I have been to.

The recommanded psi is aimed for comfort. But for safety you should get the tyres up to 36 psi for city and 40psi for highway. The reason being that even the modern technology of our tyres, the side wall is still relatively weak. Strong side wall tyres (the one more hardcore then sports, say R spec *semi slick tyres) will have disadvantage of road noise. New compound and thread now make it much stronger than ever before, but it is still not a substitute of good old fashion air power. The increase pressure will in fact flatten the rubber in contact with the ground. Hence, there is more rubber on the road.

If you want observe it more closely. Spray a patch of water in your street outside (Government forbid it in Vic so you use your bath water to do that). Have the car with underinflated tyres (say 25psi). You will see the side of the tyres will imprint more water and the tract of water will show you that, after your Kluger went over the paddle of water. If you overinflate (say 50 psi), you will see more imprint in the middle. Yes it is very subjective still, but that is the theory.

The reason of why they recommend 40psi on the highway? Well during high speed crusing, the tyre will heat up no matter what. The pressure will increase at the same time, to the same level despite the different amount of air you have in your tyre (so they said it will roughly be at 44psi while crusing). The amount of heat you generate is somehow in relation (although may not be in portion) to the amount of air inside of the tyre. So more air inside, the cooler the tyre will be. Logical since more air to absorb heat.

I use that theory in my track driving as well. So after every session I went back to the pits. My wife and i will measure the tyre surface temperature with a laser gun. If it is too low (for my tyre it will be 65 degree for best grip), then I will lower the pressure to get more heat to the tyre. The converse is also true.

Sorry that it is a long post but I am sure I can keep going on here.

Also wheel alignment it also important but I am sure it is a different topic all together.

[Kruzenvax]

Thanks Taka,

That's a very useful info.

I have 36 psi now.

Alex

I was told my the defensive driving course (whose company started with an M....). I am not promoting them now since Kevin (whom I have known for a few years) is holding similar driving course. At least he is doing at lot of stunt courses

Having said that, it is common knowledge being pass on in any driving course I have been to.

The recommanded psi is aimed for comfort. But for safety you should get the tyres up to 36 psi for city and 40psi for highway. The reason being that even the modern technology of our tyres, the side wall is still relatively weak. Strong side wall tyres (the one more hardcore then sports, say R spec *semi slick tyres) will have disadvantage of road noise. New compound and thread now make it much stronger than ever before, but it is still not a substitute of good old fashion air power. The increase pressure will in fact flatten the rubber in contact with the ground. Hence, there is more rubber on the road.

If you want observe it more closely. Spray a patch of water in your street outside (Government forbid it in Vic so you use your bath water to do that). Have the car with underinflated tyres (say 25psi). You will see the side of the tyres will imprint more water and the tract of water will show you that, after your Kluger went over the paddle of water. If you overinflate (say 50 psi), you will see more imprint in the middle. Yes it is very subjective still, but that is the theory.

The reason of why they recommend 40psi on the highway? Well during high speed crusing, the tyre will heat up no matter what. The pressure will increase at the same time, to the same level despite the different amount of air you have in your tyre (so they said it will roughly be at 44psi while crusing). The amount of heat you generate is somehow in relation (although may not be in portion) to the amount of air inside of the tyre. So more air inside, the cooler the tyre will be. Logical since more air to absorb heat.

I use that theory in my track driving as well. So after every session I went back to the pits. My wife and i will measure the tyre surface temperature with a laser gun. If it is too low (for my tyre it will be 65 degree for best grip), then I will lower the pressure to get more heat to the tyre. The converse is also true.

Sorry that it is a long post but I am sure I can keep going on here.

Also wheel alignment it also important but I am sure it is a different topic all together.

[mrbishi]

Thanks guys, good thread.

Ill be upping our pressure next visit to the petrol station.

[Scott_C]

You know, my mechanic always inflates my tyres to higher levels than I wouldve thought reasonable. And he said much the same things as Taka.

So, thanks Taka!

[kluger200711]

The amount of heat you generate is somehow in relation (although may not be in portion) to the amount of air inside of the tyre. So more air inside, the cooler the tyre will be. Logical since more air to absorb heat.

I don't think it is because air absorbing heat. Instead with more air inside tyre is more ridged thus less distortion while rolling, therefore less heat generated.

[Taka]

I don't think it is because air absorbing heat. Instead with more air inside tyre is more ridged thus less distortion while rolling, therefore less heat generated.

That is the reason I keep forgeting too. I forgot we have high profile tyres . But the casing is much stronger and can get rid of heat more, so it can tolerate lower pressure but I really don't want to risk it. Have a cushion or something to get myself comfortable.

Holiday season coming up, if anyone going away (like us), should do an once-over (eye ball all fluid levels and check tyres for puncture) before setting off, since there will be a queue at tyre shops just before Easter. And Victorians have a long weekend coming up too.

Edited March 5, 2008 by Taka

[PC XT]

I was told my the defensive driving course (whose company started with an M....). I am not promoting them now since Kevin (whom I have known for a few years) is holding similar driving course. At least he is doing at lot of stunt courses

Having said that, it is common knowledge being pass on in any driving course I have been to.

The recommended psi is aimed for comfort. But for safety you should get the tyres up to 36 psi for city and 40psi for highway. The reason being that even the modern technology of our tyres, the side wall is still relatively weak. Strong side wall tyres (the one more hardcore then sports, say R spec *semi slick tyres) will have disadvantage of road noise. New compound and thread now make it much stronger than ever before, but it is still not a substitute of good old fashion air power. The increase pressure will in fact flatten the rubber in contact with the ground. Hence, there is more rubber on the road.

If you want observe it more closely. Spray a patch of water in your street outside (Government forbid it in Vic so you use your bath water to do that). Have the car with underinflated tyres (say 25psi). You will see the side of the tyres will imprint more water and the tract of water will show you that, after your Kluger went over the paddle of water. If you overinflate (say 50 psi), you will see more imprint in the middle. Yes it is very subjective still, but that is the theory.

The reason of why they recommend 40psi on the highway? Well during high speed crusing, the tyre will heat up no matter what. The pressure will increase at the same time, to the same level despite the different amount of air you have in your tyre (so they said it will roughly be at 44psi while crusing). The amount of heat you generate is somehow in relation (although may not be in portion) to the amount of air inside of the tyre. So more air inside, the cooler the tyre will be. Logical since more air to absorb heat.

I use that theory in my track driving as well. So after every session I went back to the pits. My wife and i will measure the tyre surface temperature with a laser gun. If it is too low (for my tyre it will be 65 degree for best grip), then I will lower the pressure to get more heat to the tyre. The converse is also true.

Sorry that it is a long post but I am sure I can keep going on here.

Also wheel alignment it also important but I am sure it is a different topic all together.

Done a couple of courses and track days, Higher is better I put 38-40 in because the wife will never check them and they can only loose air over time! Thats my theory anyway + you can corner more aggressively and hopefully not roll it like Wheels did

[Hiro]

Manual specifies 210-220 kPa (for all models). WHen mine cam from the dealer all 4 had about 250 kpA. So what's the right pressure?

Thanks

The reason that tyre pressures are higher than recommended when you get the car from the dealer is that the manufacturer over-inflates the tyres so that they don't flat-spot during transportation and display at the showroom (which is why it is recommended you also over-inflate your tyres if you're going away for a long holiday overseas, so the tyres aren't flat-spotted when you get back, which leads to serious wheel shudder)

[mrk]

sory to bring up the old thread. i have a kx-r (17" rims anyway) and been driving it for 2 weeks now. yesterday i decided to check the tyre pressure and i was shocked to find out all 4 of them are at 48psi. i didnt deflate them yet cos i been driving them with that pressure for 2 weeks now and i found them to be quite comfortable to drive with. only occasionally a bit too hard when the road is terribly uneven. issit safe to be inflated that high?

[PC XT]

sory to bring up the old thread. i have a kx-r (17" rims anyway) and been driving it for 2 weeks now. yesterday i decided to check the tyre pressure and i was shocked to find out all 4 of them are at 48psi. i didnt deflate them yet cos i been driving them with that pressure for 2 weeks now and i found them to be quite comfortable to drive with. only occasionally a bit too hard when the road is terribly uneven. issit safe to be inflated that high?

Prados are set to 50PSI from Japan :)

[mrk]

sory to bring up the old thread. i have a kx-r (17" rims anyway) and been driving it for 2 weeks now. yesterday i decided to check the tyre pressure and i was shocked to find out all 4 of them are at 48psi. i didnt deflate them yet cos i been driving them with that pressure for 2 weeks now and i found them to be quite comfortable to drive with. only occasionally a bit too hard when the road is terribly uneven. issit safe to be inflated that high?

Prados are set to 50PSI from Japan :)

so does this mean its ok to be set at 48 psi here???? thank u

[Taka]

I think the best is to get it reset to around 38-40psi. I drive around town in this pressure. 42psi for highway trips.

[Colonel]

so does this mean its ok to be set at 48 psi here???? thank u

Depends on the tyre but I'd guess you shouldn't inflate any more than 40psi. If you over inflate too much you will get great fuel economy but you will wear out the middle of your tyre and you will have less grip as the outsides of the tyre won't have as good contact with the road, just as if it's under inflated the middle of the tyre won't have as good road contact and you will wear out the outsides of the tyre. As others have said, keep it inflated about 10% over for city driving and 15% over for highway. If you really want great fuel economy at the cost of tyre wear and safety try for 120psi (or untill it looks like the tyrers are about to jump off the rims), however you may kill yourself or others..

Edited January 21, 2009 by Colonel

[KevO]

toyota has put 38psi when i got it serviced but the recommended psi was 34 (zre corolla)

[Colonel]

toyota has put 38psi when i got it serviced but the recommended psi was 34 (zre corolla)

The fuel efficiency difference between 30psi and 38psi is definately noticable. I usually inflate mine to a bit over 35. I know when my tyrers need air 'cause I notice the milage going down.

[RICE RACING]

I should check my kuntz, have not looked at them in 10,000km lol

[KevO]

checking kuntz ? lols

Edited January 22, 2009 by BlackKnight

[kevnbec]

How about for offroad driving....does anyone know the recommended minimum pressure? We took to the beach the other day and dropped the tyre pressure from 38psi to 20psi. This seemed to be okay and we got down the beach and back up a fairly steep sandy hill track. However it did make me wonder at the time how low the tyres can be.

[PC XT]

How about for offroad driving....does anyone know the recommended minimum pressure? We took to the beach the other day and dropped the tyre pressure from 38psi to 20psi. This seemed to be okay and we got down the beach and back up a fairly steep sandy hill track. However it did make me wonder at the time how low the tyres can be.

I used 20PSI in ours two weeks ago and it gave a great feeling!

This is a real photo no editing, I'm at the rear of the car not the front!!

Edited January 29, 2009 by PC XT

[57fritz]

An interesting topic - one not really appreciated as to how important it can be. I've been a emergency services driving instructor for 18 yrs, both road (including high speed) & 4WD.

On road - normal tyres (ie: not low profile under 60 series) a good compromise is 35psi all round. This is called the KISS principle and makes it easy to remember, especially for the other / better halves on the rare occasion they do check the tyres. The other suggestion is that you either buy a good quality pressure gauge or use the electronic versions found at many servos now. Preferably use try to use the same machine for consistency. I use 35 psi all round in my KX-R and have 30K on the speedo with good even wear. I did the same in my old X-trail and was getting 70K out of a set. As someone else said, wheel alignment is also critical. Low profile tyres - 40 or 42 psi all round but you don't want it feeling like a skate board when you drive it, if it does its over inflated so drop the pressure a little.

Off-road - depends on where you are driving. You can buy after market tyre deflators that are pre-set at 18 psi for rocks and sand. Any lower and you risk the chance of the tyre coming off the rim. If you have to drive on road with such low pressure, slow speed until the first servo and pump them up.

[PaulG]

An even easier number to remember is 250kPa. And as an added bonus, it's metric, a system we converted to in the 70's. <_<