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Split/Different Front and Rear Cold Tire Pressures



 
 
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  #1  
Old August 18th 20, 05:26 PM posted to rec.autos.tech
Chris K-Man
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Posts: 17
Default Split/Different Front and Rear Cold Tire Pressures

Split Cold Tire Pressures: Front-to-Rear

I understand the technical reasons for why some car makers specify different cold tire pressures for the front and rear axles of certain models. My question concerns those vehicles (except for the obvious: large SUVs and work vans) for which different pressures are specified, vs vehicles for which a single cold pressure is recommended all around(all four wheels):

IE: Makes and models with less of a Front/Rear GAWR(Gross Axle Weight Rating ie: less than 55/45) - Audi, BMW, Mercedes, Subaru, etc., might specify up to a 5psi difference for the Front vs Rear axle pressures, where as makes with a significantly higher Front/Rear weight split(60/40) - Chevrolet, Ford, Honda, Hyundai, Toyota, etc., recommend a single pressure
value for front and rear Axle - in particular front-wheel drive models.


Typical late-model European sports sedan or wagon recommended cold tire pressures: F/R: 32/36psi

Typical late-model domestic or import front-wheel drive sedan or wagon cold pressures: F/R: 30 to 36psi, all tires.


My theory: The former are built for a more discriminating, enthusiast driving demographic whom will pay more attention to such things as different front/rear axle tire pressures, while the latter are built for the blue-collar masses, whose main priority is economical transportation in reasonably well equipped, reliably built vehicles, and live a busy lifestyle where it is easier to remember one PSI number - a compromise I'm sure - to set all of their tires to.

What's your feeling behind this difference?
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  #2  
Old August 18th 20, 05:40 PM posted to rec.autos.tech
Wade Garrett
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Posts: 26
Default Split/Different Front and Rear Cold Tire Pressures

On 8/18/20 12:26 PM, Chris K-Man wrote:
> Split Cold Tire Pressures: Front-to-Rear
>
> I understand the technical reasons for why some car makers specify different cold tire pressures for the front and rear axles of certain models. My question concerns those vehicles (except for the obvious: large SUVs and work vans) for which different pressures are specified, vs vehicles for which a single cold pressure is recommended all around(all four wheels):
>
> IE: Makes and models with less of a Front/Rear GAWR(Gross Axle Weight Rating ie: less than 55/45) - Audi, BMW, Mercedes, Subaru, etc., might specify up to a 5psi difference for the Front vs Rear axle pressures, where as makes with a significantly higher Front/Rear weight split(60/40) - Chevrolet, Ford, Honda, Hyundai, Toyota, etc., recommend a single pressure
> value for front and rear Axle - in particular front-wheel drive models.
>
>
> Typical late-model European sports sedan or wagon recommended cold tire pressures: F/R: 32/36psi
>
> Typical late-model domestic or import front-wheel drive sedan or wagon cold pressures: F/R: 30 to 36psi, all tires.
>
>
> My theory: The former are built for a more discriminating, enthusiast driving demographic whom will pay more attention to such things as different front/rear axle tire pressures, while the latter are built for the blue-collar masses, whose main priority is economical transportation in reasonably well equipped, reliably built vehicles, and live a busy lifestyle where it is easier to remember one PSI number - a compromise I'm sure - to set all of their tires to.
>
> What's your feeling behind this difference?
>

Ya' got way too much time on your hands, dude ;-)

--
Why is it that the people who want more government control over your
life are the same ones who want you to be disarmed?
  #3  
Old August 19th 20, 12:02 AM posted to rec.autos.tech
AMuzi
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Posts: 488
Default Split/Different Front and Rear Cold Tire Pressures

On 8/18/2020 11:26 AM, Chris K-Man wrote:
> Split Cold Tire Pressures: Front-to-Rear
>
> I understand the technical reasons for why some car makers specify different cold tire pressures for the front and rear axles of certain models. My question concerns those vehicles (except for the obvious: large SUVs and work vans) for which different pressures are specified, vs vehicles for which a single cold pressure is recommended all around(all four wheels):
>
> IE: Makes and models with less of a Front/Rear GAWR(Gross Axle Weight Rating ie: less than 55/45) - Audi, BMW, Mercedes, Subaru, etc., might specify up to a 5psi difference for the Front vs Rear axle pressures, where as makes with a significantly higher Front/Rear weight split(60/40) - Chevrolet, Ford, Honda, Hyundai, Toyota, etc., recommend a single pressure
> value for front and rear Axle - in particular front-wheel drive models.
>
>
> Typical late-model European sports sedan or wagon recommended cold tire pressures: F/R: 32/36psi
>
> Typical late-model domestic or import front-wheel drive sedan or wagon cold pressures: F/R: 30 to 36psi, all tires.
>
>
> My theory: The former are built for a more discriminating, enthusiast driving demographic whom will pay more attention to such things as different front/rear axle tire pressures, while the latter are built for the blue-collar masses, whose main priority is economical transportation in reasonably well equipped, reliably built vehicles, and live a busy lifestyle where it is easier to remember one PSI number - a compromise I'm sure - to set all of their tires to.
>
> What's your feeling behind this difference?
>



Feeling?? Engineers actually know something about this.

Try running a Corvair with same F/R pressure some time. Just
don't try cornering!

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971


  #4  
Old August 19th 20, 12:11 AM posted to rec.autos.tech
Heron[_2_]
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Posts: 22
Default Split/Different Front and Rear Cold Tire Pressures

On 8/18/2020 6:02 PM, AMuzi wrote:
> On 8/18/2020 11:26 AM, Chris K-Man wrote:
>> Split Cold Tire Pressures: Front-to-Rear
>>
>> I understand the technical reasons for why some car makers specify
>> different cold tire pressures for the front and rear axles of certain
>> models. My question concerns those vehicles (except for the obvious:
>> large SUVs and work vans) for which different pressures are specified,
>> vs vehicles for which a single cold pressure is recommended all
>> around(all four wheels):
>>
>> IE: Makes and models with less of a Front/Rear GAWR(Gross Axle Weight
>> Rating ie: less than 55/45) - Audi, BMW, Mercedes, Subaru, etc., might
>> specify up to a 5psi difference for the Front vs Rear axle pressures,
>> where as makes with a significantly higher Front/Rear weight
>> split(60/40) - Chevrolet, Ford, Honda, Hyundai, Toyota, etc.,
>> recommend a single pressure
>> value for front and rear Axle - in particular front-wheel drive models.
>>
>>
>> Typical late-model European sports sedan or wagon recommended cold
>> tire pressures: F/R: 32/36psi
>>
>> Typical late-model domestic or import front-wheel drive sedan or wagon
>> cold pressures: F/R: 30 to 36psi, all tires.
>>
>>
>> My theory: The former are built for a more discriminating, enthusiast
>> driving demographic whom will pay more attention to such things as
>> different front/rear axle tire pressures, while the latter are built
>> for the blue-collar masses, whose main priority is economical
>> transportation in reasonably well equipped, reliably built vehicles,
>> and live a busy lifestyle where it is easier to remember one PSI
>> number - a compromise I'm sure - to set all of their tires to.
>>
>> What's your feeling behind this difference?

>
>
> Feeling?? Engineers actually know something about this.
>
> Try running a Corvair with same F/R pressure some time. Just don't try
> cornering!


Don't try cornering in a swing axle Corvair, period.
  #5  
Old August 19th 20, 12:43 AM posted to rec.autos.tech
[email protected]
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Posts: 539
Default Split/Different Front and Rear Cold Tire Pressures

AMuzi:

Corvair

The Corvair had a Front/Rear weight difference that
definitely warranted the big difference between
recommended front and rear cold tire pressures.

The cars I'm talking about are somewhere in between
that extreme, and the other: rear- and all-wheel drive
sports sedans with almost no(less than 55/45) front-rear
weight bias. The last time I checked, a typical BMW
F/R weight split is like 51/49%. Yet recommended
front/rear pressures differ by 5psi.

My Honda Accord, for example, is F/R: 54/46% axle
weight split. Some 'econoboxes' venture toward 60/40,
yet for the Accord and those cars, a single pressure
figure, for all tires, is specified on the door frame placard.
  #8  
Old August 19th 20, 05:46 AM posted to rec.autos.tech
Xeno
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Posts: 363
Default Split/Different Front and Rear Cold Tire Pressures

On 19/8/20 1:42 pm, Xeno wrote:
> On 19/8/20 9:43 am, wrote:
>> AMuzi:
>>
>> Corvair
>>
>> The Corvair had a Front/Rear weight difference that
>> definitely warranted the big difference between
>> recommended front and rear cold tire pressures.
>>
>> The cars I'm talking about are somewhere in between
>> that extreme, and the other: rear- and all-wheel drive
>> sports sedans with almost no(less than 55/45) front-rear
>> weight bias.Â* The last time I checked, a typical BMW
>> F/R weight split is like 51/49%. Yet recommended
>> front/rear pressures differ by 5psi.
>>
>> My Honda Accord, for example, is F/R: 54/46% axle
>> weight split.Â* Some 'econoboxes' venture toward 60/40,
>> yet for the Accord and those cars, a single pressure
>> figure, for all tires, is specified on the door frame placard.
>>

> Varying the tyre pressure will vary the slip angles at which the tyres
> run. The *specification* of that variation, ie. different pressure F &
> R, will ensure the car runs understeer rather than oversteer.
> Manufacturers design cars to oversteer and, depending on the suspension
> design, tyre pressure variation is the way to ensure it.
>

Make that; "Manufacturers design cars to *understeer*".

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)
  #9  
Old August 19th 20, 06:32 AM posted to rec.autos.tech
Xeno
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Posts: 363
Default Split/Different Front and Rear Cold Tire Pressures

On 19/8/20 10:23 am, AMuzi wrote:
> On 8/18/2020 6:43 PM, wrote:
>> AMuzi:
>>
>> Corvair
>>
>> The Corvair had a Front/Rear weight difference that
>> definitely warranted the big difference between
>> recommended front and rear cold tire pressures.
>>
>> The cars I'm talking about are somewhere in between
>> that extreme, and the other: rear- and all-wheel drive
>> sports sedans with almost no(less than 55/45) front-rear
>> weight bias.Â* The last time I checked, a typical BMW
>> F/R weight split is like 51/49%. Yet recommended
>> front/rear pressures differ by 5psi.
>>
>> My Honda Accord, for example, is F/R: 54/46% axle
>> weight split.Â* Some 'econoboxes' venture toward 60/40,
>> yet for the Accord and those cars, a single pressure
>> figure, for all tires, is specified on the door frame placard.
>>

>
> And all those have different suspension designs, rates, tire sizes,
> front end geometry, body roll or lack thereof and so on.
>
> You're isolating one very small aspect of 'auto handling' which is a
> very large area.
>

Yep, way too complex an issue to be isolated to one specific aspect. You
need to look at the car as an entity - and that would, of necessity, be
from an engineering perspective.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)
  #10  
Old August 20th 20, 10:24 AM posted to rec.autos.tech
[email protected]
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Posts: 539
Default Split/Different Front and Rear Cold Tire Pressures

Xeno:

My particular mid-size front-wheel drive specifies 32psi, front and rear.
It already has 'light'(easy) steering due to its wide, 50-series low profile
tires.

So for a while, I took it upon myself to experiment with adding 2psi to
the heavier axle(the engine) and removing 1-2psi from the lighter rear
axle. So I had a set up of 34front, 31rear.

While the back end seemed more planted, the steering actually became
more 'dartier' than ever on the highway, and I found I had to make more
corrections thn ever to stay in a lane!

During the third week, I reset all tires back to 32psi cold, and the car
calmed down, and actually drive as intended. I'm actually running
33psi cold all around now, because the weather here is starting to
get cooler, and handling is still fine.

So for my specific car, a 56/44 split weight front wheel driver, using the
same front/rear pressure - as specified - actually works!

Can BMW and Audi do different front/back pressures simoly because
their models' axle weights are closer to 50/50?
 




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