Tyre pressure too high?

[krypto Avid PP Poster! Find all posts View Profile Close krypto]

Hi Krypto

I am not on my ride. Interstate by air.
Will push up the pressure again on return.

Running below 30psi cold on a highway is asking for trouble you mentioned. Is it applicable only for the Prado?

My previous ride was the XC90 with pressure set 220 to 270 kPa..... which in this case is equivalent to 32 to 39psi.

Just wondering why the has that 210kPa setting sticker at the side door.

I think it has been explained pretty well in the previous posts. It doesn't just apply to Prados, manufacturers recommend tyre pressures based primarily on comfort. I haven't checked on the Prado but you will see most cars have a different recommended tyre pressure for highway driving but it is still on the low side.

The best way to understand it better is to go on a driver course or have a play on a race track or skid pan.

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

Lots of different reasons for higher & lower tyre pressures.
I hope everyone does not go and over inflate their tyres for the best handling and braking.
Although a 40psi front tyre are supported better in the centre and will require more braking effort to lock it up, the rear is lifting as the front is loading, I hope your braking str8 as over inflate it can help get the rear loose too.
Don't forget tyres are designed to work best at their designed operating temps, high pressure = much cooler tyre.
A too cold tyre especially in the middle of winter could see you sliding all over the place in the wet.
Naturally traction may not be as good in the dry either.
Manufacturers take tis into account on their placard, it's not just comfort.

[brogers Advanced Member Find all posts View Profile Close brogers]

Lots of different reasons for higher & lower tyre pressures.
I hope everyone does not go and over inflate their tyres for the best handling and braking.
Although a 40psi front tyre are supported better in the centre and will require more braking effort to lock it up, the rear is lifting as the front is loading, I hope your braking str8 as over inflate it can help get the rear loose too.
Don't forget tyres are designed to work best at their designed operating temps, high pressure = much cooler tyre.
A too cold tyre especially in the middle of winter could see you sliding all over the place in the wet.
Naturally traction may not be as good in the dry either.
Manufacturers take tis into account on their placard, it's not just comfort.

some excellent points thankyou.

For what it'sworth, I saw this info on the Bridgestone site the otehr day, and whilst it doesn't explain everything about tyre pressures, it may add something to the information being shared..perhaps?

Tyre pressure tips

Contrary to popular belief, tyre pressure is not determined by the type of tyre or its size but
upon your vehicle's load and driving application i.e. speed
To find out what your car's tyre pressure should be, consult the manufacturers tyre placard usually found inside the driver's door sill, glove box, fuel filler cap or under the bonnet.
The placard also displays the manufacturers recommended tyre sizes.
Tyre pressures should be checked when the tyre is 'cold', as pressure increases as the tyre becomes 'hot'.
Take the "cold" reading and check them against the recommended tyre pressures from your placard.
Heavy loads or towing puts an extra strain on your tyres. So if your vehicle is fully loaded with passengers and luggage, the general rule is to add 28kpa (4PSI or 4lbs).
At high speed, (defined as driving at 120km/h for over one hour), your tyres will wear out twice as fast as when you drive at 70-80 km/h. If your tyres are under-inflated by twenty per cent tyre life can be reduced by thirty per cent. The rule here is to add 28Kpa (4PSI) from your Minimum Compliance Plate Pressure. Don't inflate your tyres above 40 psi or 280 kPa. When the tyres get hot from driving, the pressure will increase even more.

Believe it or not, checking your tyre pressure can have a big impact on our environment. An under-inflated tyre creates more rolling resistance and therefore more fuel consumption. By keeping your tyres inflated to their proper levels, you can help maximise your car's fuel economy and minimise its impact on our environment.
http://www.bridgestone.com.au/tyres/.../pressure.aspx

[Prone Member Find all posts View Profile Close Prone]

Just wondering why the has that 210kPa setting sticker at the side door.

Why a placard pressure of 210kPa? My placard and manual says 200kPa which converts to 29PSI (I am old!)

It would seem that the placard pressure is based on the tyre manufacturers max load and max pressure rating as shown below.

Check the sidewall of the tyre it will have a max load at a maximum pressure somewhere. For the AT20 265/65R17 it is 1120kg at 51psi, for a Cooper LT265/70R17 it would be 1550Kg at 80PSI. If the tyre is supporting less load it will need a lower pressure.

Lets say the TD 150 Prado weighs in at 2330Kg (from Toyota web page specs). If the weight is distributed equally (an assumption) over the 4 wheels that's 582 kg per wheel. So using the tyre manufacturers ratings that would give a pressure requirement of (582/1120)*51 = 26.5PSI for an empty car. Add 240KG of people and luggage etc changes it to 642kg per wheel then the calculation becomes (642/1120)*51 = 29.23PSI

For the LT265/70-17 Cooper ST as above on this car it would be (650/1450)*80 = 33.13PSI

Note that LT construction tyres need a higher pressure than Passenger construction for the same load.

My old 95 series prado had a placard pressure of 26PSI. It was also about 300 kg lighter. So using the above formula for DUNLOP Grandtrek TG35 - 265/70R16 which were also 1120Kg at 51PSI
(567/1120)*51 = 25.82PSI, close to 26PSI.

On sealed roads I run my tyres 4 to 10 PSI higher than the placard pressure depending on load, speed and temperature rise. Dirt, rock or sand roads/tracks are a whole different subject.

In the above calculations I have assumed that the pressure to load rating of the tyre is linear, this may not be the case but it will suffice for the general idea.

Cheers
Prone

[krypto Avid PP Poster! Find all posts View Profile Close krypto]

Why a placard pressure of 210kPa? My placard and manual says 200kPa which converts to 29PSI (I am old!)

It would seem that the placard pressure is based on the tyre manufacturers max load and max pressure rating as shown below.

Check the sidewall of the tyre it will have a max load at a maximum pressure somewhere. For the AT20 265/65R17 it is 1120kg at 51psi, for a Cooper LT265/70R17 it would be 1550Kg at 80PSI. If the tyre is supporting less load it will need a lower pressure.

Lets say the TD 150 Prado weighs in at 2330Kg (from Toyota web page specs). If the weight is distributed equally (an assumption) over the 4 wheels that's 582 kg per wheel. So using the tyre manufacturers ratings that would give a pressure requirement of (582/1120)*51 = 26.5PSI for an empty car. Add 240KG of people and luggage etc changes it to 642kg per wheel then the calculation becomes (642/1120)*51 = 29.23PSI

For the LT265/70-17 Cooper ST as above on this car it would be (650/1450)*80 = 33.13PSI

Note that LT construction tyres need a higher pressure than Passenger construction for the same load.

My old 95 series prado had a placard pressure of 26PSI. It was also about 300 kg lighter. So using the above formula for DUNLOP Grandtrek TG35 - 265/70R16 which were also 1120Kg at 51PSI
(567/1120)*51 = 25.82PSI, close to 26PSI.

On sealed roads I run my tyres 4 to 10 PSI higher than the placard pressure depending on load, speed and temperature rise. Dirt, rock or sand roads/tracks are a whole different subject.

In the above calculations I have assumed that the pressure to load rating of the tyre is linear, this may not be the case but it will suffice for the general idea.

Cheers
Prone

Thanks, always wondered how the recommended pressures were calculated, pretty simple really.

Supports the earlier discussion as matching load carrying capacity to tyre pressure is very different to setting up tyres for performance and handling.

[KAKADAZ Avid PP Poster! Find all posts View Profile Close KAKADAZ]

I was told by a coopers expert last week to lower the pressures on my AT3's so I went down from 40psi to 34psi and its such nicer to drive. 34psi still feels solid on the road without any Wollow etc but just irons out the small bumps etc in the road....very happy.

[Richoson Avid PP Poster! Find all posts View Profile Close Richoson]

I have run 36 in my MT ATZ's and have a great ride and even tyre wear.

See ya on the tracks, Richo.

[Bear63 Senior Member Find all posts View Profile Close Bear63]

I was told by a coopers expert last week to lower the pressures on my AT3's so I went down from 40psi to 34psi and its such nicer to drive. 34psi still feels solid on the road without any Wollow etc but just irons out the small bumps etc in the road....very happy.

Was his name Rob? I have been dealing with tyres since 1985 , and Coopers for 18 years of that ( i know showing my age) and 34psi may ride nice but they will start to wear unevenly on the shoulders on the front so you will need to cross rotate them more often at that low pressure

[krypto Avid PP Poster! Find all posts View Profile Close krypto]

I think tyre manufacturers want you to have the most comfortable ride possible and I'm sure they don't mind if you buy new tyres sooner. Maybe I'm just cynical but I'm sure you get better high speed handling and better breaking with higher pressure.

I think you've nailed it, tyre companies need to sell tyres. After having tried different pressures on a wet and dry skip pan I'm pretty clear on what works. I've also measured how hot my tyres get at different pressures and there is no way I'd drive a tyre fast on the highway at 30psi.

[KAKADAZ Avid PP Poster! Find all posts View Profile Close KAKADAZ]

Was his name Rob? I have been dealing with tyres since 1985 , and Coopers for 18 years of that ( i know showing my age) and 34psi may ride nice but they will start to wear unevenly on the shoulders on the front so you will need to cross rotate them more often at that low pressure

No not the same guy mate this ones a member of LCOOL forum he's a coopers guru and said if you want even wear and your coopers to last longer lower the pressures to around 34psi. He said alot of coopers issues come from over inflated tyres.

[gxllouie Member Find all posts View Profile Close gxllouie]

No not the same guy mate this ones a member of LCOOL forum he's a coopers guru and said if you want even wear and your coopers to last longer lower the pressures to around 34psi. He said alot of coopers issues come from over inflated tyres.

Mate I can't comment on coopers specifically, but my stock dunlops at 40psi wore out on the edges first @ 105000kms. If I had to of run them at 34, the edges would have been shot so much earlier! And that was with 10000km rotations.

Louie

[Ozpat Advanced Member Find all posts View Profile Close Ozpat]

Mate I can't comment on coopers specifically, but my stock dunlops at 40psi wore out on the edges first @ 105000kms. If I had to of run them at 34, the edges would have been shot so much earlier! And that was with 10000km rotations.

Louie

105000kms on dunlops? I'll assume you've got a zero too many in there. I ran my dunlops @ 34psi on the bitumen and around 20psi on sand and offroad (80%/20%) throughout their 60 000km life with similar rotations and they wore perfectly even on all 5 tyres in my 120.

Cheers, Jim

[gxllouie Member Find all posts View Profile Close gxllouie]

105000kms on dunlops? I'll assume you've got a zero too many in there. I ran my dunlops @ 34psi on the bitumen and around 20psi on sand and offroad (80%/20%) throughout their 60 000km life with similar rotations and they wore perfectly even on all 5 tyres in my 120.

Cheers, Jim

No - 105000kms. Still wore on the edges at 40psi.

Louie

[Anth120playdo Banned Find all posts View Profile Close Anth120playdo]

No - 105000kms. Still wore on the edges at 40psi.

Louie

You corner too fast! Slow down a bit!
LOL.......

Varying pressures is for sure the go.
34 sounds should be a good bitumen light load pressure.

Hey nobody is wrong. We just have different results from everyone's personal experience from 29 to at least 40psi

20 years ago 28-32 was the norm.
Cars were driven at excessive speeds with no issues.
We always put 40psi in the front of the cop cars as clearly it will help keep the centre of the tyre down for better braking traction at the front. That is what they needed. After a pursuit, new Tyres and brakes often also.

It is common in service these days to see Tyres worn in the centers due only to over inflation.

[Prone Member Find all posts View Profile Close Prone]

121504Km out of the OEM Grandtreks tyres on my old 95. But there were seven in the rotation, 2 extras. Included 2 crossings of Gunbarrel, multiple Oodnadatta track and Dalhousie Springs area, Fraser island and quite a few other "proper" non sealed type roads. If it was muddy I didn't even try, no contest. No flats for first 70K, more flats as they wore down. Ran them at 30 to 36 on road, less off road depending on need. Second set were OK at 60K when I sold the car. I think the at20's on the 150 may wear a bit quicker though, seem a bit softer.

Prone