whats the proper tire pressure???

[Darth Vader]

Re: whats the proper tire pressure???

my front is 250 kpa and rear 280kpa.recommended by bmw sticker on car door.are they ok ??

when hot they go up to 270kpa and 300 kpa.

my front 225/40/18 and rear 255/35/18

safe or not ?

 

[phil]

Re: whats the proper tire pressure???

totally disagree about the under inflation. Except maybe with a remould or retreaded tyre.

why wouldnt you want to increase your grip on public roads? For braking sake at least. And you contradicted yourself saying it's better in the rain, yet you have less grip.

I just cant see any logic inflating to 40psi. The amount of times aone has 4 full size adults and a boot full of luggage is what, once in 5 yeras?

 

[centurion]

Re: whats the proper tire pressure???

totally disagree about the under inflation. Except maybe with a remould or retreaded tyre.

why wouldnt you want to increase your grip on public roads? For braking sake at least. And you contradicted yourself saying it's better in the rain, yet you have less grip.

I just cant see any logic inflating to 40psi. The amount of times aone has 4 full size adults and a boot full of luggage is what, once in 5 yeras?

High inflation: contact area reduced.

it has less grip in dry, but more aquaplaning resistance in the wet.

 

[centurion]

Re: whats the proper tire pressure???

my front is 250 kpa and rear 280kpa.recommended by bmw sticker on car door.are they ok ??

when hot they go up to 270kpa and 300 kpa.

my front 225/40/18 and rear 255/35/18

safe or not ?

darth, the pressures indicated is at 24C normal air 50% humidity.

If you fill your tyres at 24C normal air (early morning) you are in compliance. However since we have often 90% humidity I suggest that you fill 10-20kpa less. Because humidity makes big expansion in heat. Increase 10% per 10C increase in filling temp.

If you fill nitrogen dry, you should fill at hot pressure - 10kpa thereabouts estimate. Coz nitrogen expands little, and is dry.

 

[Darth Vader]

Re: whats the proper tire pressure???

darth, the pressures indicated is at 24C normal air 50% humidity.

If you fill your tyres at 24C normal air (early morning) you are in compliance. However since we have often 90% humidity I suggest that you fill 10-20kpa less. Because humidity makes big expansion in heat. Increase 10% per 10C increase in filling temp.

If you fill nitrogen dry, you should fill at hot pressure - 10kpa thereabouts estimate. Coz nitrogen expands little, and is dry.

ok thanks for the info.
that means 230kpa front and 260kpa rear ??
no wonder my tires sound noisy.
later i go adjust.

 

[centurion]

Re: whats the proper tire pressure???

ok thanks for the info.
that means 230kpa front and 260kpa rear ??
no wonder my tires sound noisy.
later i go adjust.

roughly, about right. still you will not be optimal at low temp, but as you drive it gets higher so most of your trip you're OK.

Nitrogen is better only if you go to track, when you will have such high tyre temp that your whole car balance will go out of whack.

For street, no need so extreme lah ...c'mon.

 

[acupunch]

Re: whats the proper tire pressure???

Max recommended pressure for full load of people and luggage is still safe. Without those loads you can go slightly higher even. I know people personally that go high side to 44 psi and ever have a problem or uneven wear logging thousands of miles on some pretty bad road too. I go to 40 with no problems. It is true grip is reduced somewhat, but I've never needed a lot of grip on public roads. I like the mileage I get from it. Better in the rain too.

I agree with acupunch that there is no fixed rule and depends on a range of factors. Pressure in itself within the limits stated by manufacturer (tire and car) is fine. You're more likely to blow a tire up from under inflation since you're putting more heat into the tire from continuous sidewall deformation and increase in patch friction.

thanks, Shaun. now I knew I'm not alone that had tried 40psi.

 

[T6]

Re: whats the proper tire pressure???

I wld NOT trade grip for mileage. The point abt getting good tyres is not abt getting good mileage. To me it is all abot improving handling, maximising grip. If want good mileage, might as well juz get cheap tyrs and change them often.

 

[SHAMELESS]

Re: whats the proper tire pressure???

I wld trade grip for mileage anytime. The point abt getting good tyres is not abt getting good mileage. To me it is all abot improving handling, maximising grip. If want good mileage, might as well juz get cheap tyrs and change them often.

hahahahaaaaa....damn true....well said andy...............

 

[Terry]

Re: whats the proper tire pressure???

of course..grip is number one.... mileage wont differ so much...at most pay 5 bucks more when pumping petrol... grip can cost u your life...

 

[Shaun]

Re: whats the proper tire pressure???

Surely you guys realize that everyone, including yourself, trades grip for many reasons. From packaging, to noise, weight, impractical replacement intervals, narrow operating windows, comfort, cost, etc.

It isn't the last few hundredths in grip that will save your life. It is safe sensible driving that will. If you really needed all the grip you could possible get, your wheels and tires would be very different, so would your car. Your existing inflation pressures would probably be different too, even if nothing else changed.

 

[SHAMELESS]

Re: whats the proper tire pressure???

Surely you guys realize that everyone, including yourself, trades grip for many reasons. From packaging, to noise, weight, impractical replacement intervals, narrow operating windows, comfort, cost, etc.

It isn't the last few hundredths in grip that will save your life. It is safe sensible driving that will. If you really needed all the grip you could possible get, your wheels and tires would be very different, so would your car. Your existing inflation pressures would probably be different too, even if nothing else changed.

shaun - your analogy very funny leh.....of cos its safe driving lah that will safe lives...but we talking abt grip mah rite??? not driving style.... theres so many variants here that can save lives.....

cheers...

 

[Shaun]

Re: whats the proper tire pressure???

Yes point being that within broad limits of partical grip levels, knowledge of what the limits are and driving accordingly (sensibly) will be a much bigger factor in determining safeness. We all choose to be at different points within the upper and lower limits of practical grip. It's all compromise for one reason or another. Look at grip spread between the most and least grippy street legal vehicles, and also at which kinds are involved most often in the big fatal crashes.

cheers and peace

 

[PerverTT]

Re: whats the proper tire pressure???

Surely you guys realize that everyone, including yourself, trades grip for many reasons.

Totally agree with that sentiment, Shaun. Grip is important but it's not everything to me. I will happily sacrifice a little bit of grip in my front tyres (higher pressures > smaller contact patch) in return for sharper steering, made possible by better slip angles. You might even say that sharper steering adds to primary safety as it will help you avoid a prang in the first place.

 

[TripleM]

Re: whats the proper tire pressure???

Terry,
U hv changed rims n tires like many many bloody times and u r still asking this basic question....haiz..

Ok, u shud ask urself if u carry passengers alot or not....coz some say u pick up quite a few at SarLau....kekeke

 

[TripleM]

Re: whats the proper tire pressure???

In view of rising fuel cost, recent climate change talk in Bali.....I increase my tire pressure by a couple of PSI than normal for street driving....U think I m joking?

 

[T6]

Re: whats the proper tire pressure???

I think at the end, we juz wanna know what is an appropriate pressure for Singapore roads given a certain tyre size etc.

 

[Jadis]

Re: whats the proper tire pressure???

I used to pump 225kpa (front 225/18and 255 kpa (rear 255/18BMW recommend 220 front and 250 rear. but PML put 230 and 260 for me when sent in for servicing.

 

[Shaun]

Re: whats the proper tire pressure???

Totally agree with that sentiment, Shaun. Grip is important but it's not everything to me. I will happily sacrifice a little bit of grip in my front tyres (higher pressures > smaller contact patch) in return for sharper steering, made possible by better slip angles. You might even say that sharper steering adds to primary safety as it will help you avoid a prang in the first place.

Hahahh you make a good point and are now breaking the surface of tire dynamics! (Inflation pressure to cornering stiffness (N/rad, G/deg) relation) You must be quite an enthusiast or possibly auto industry involved in some way.

 

[phil]

Re: whats the proper tire pressure???

I really cant beleive what i am reading

higher pressure will not give sharper steering, it will give lighter steering, but not sharper. Plus, higher pressure equals less grip equals less steering control. It also equals less braking ease of skid and understeer in wet weather.

And Achu, you seriously think you are the only one on the planet with large diameter wheels dont you!!